Hey guys, here's my article taken from: https://motoiq.com/how-to-properly-select-and-size-tires-for-performance/
How to PROPERLY select and size TIRES for PERFORMANCE
by Billy Johnson
The most important part of your car is not the engine, suspension, or brakes. It’s the TIRES!!!* This is because your car can only perform as well as the capability of its tires. I’m often asked which tire is best and what size to buy.* In this article I discuss my methods for choosing and properly sizing the right tires. *I’m not into the “hella-flush” or “stance” scenes so this article is focused towards those who care about the PERFORMANCE of their car, whether on the street or on the track.
Pirelli had the best slogan for a tire company: “Power is nothing without control.” This is true for all forms of driving since it does not matter how much power you have if you can’t put it to the ground, it doesn’t matter how much you spend on a big brake kit if they easily lock up the tires, and your $7,000 coilovers can only deliver the performance that your tires are capable of. *It really does not matter how great and expensive your car is or how much money you’ve put into modifying it if you cheap out on tires; which is the only component on your car that actually touches the road.
I often see really nice cars with a ton of money thrown at it in power upgrades and ‘blingy’ wheels wearing an improperly sized tire or something that is obviously not up to the capabilities of the car.* Most people really do not understand the importance of their tires, not only from a performance standpoint but from a safety standpoint as well.* This includes the age of the tire.
In order to have a better ‘show’, keep costs down, and regulate competition, most racing series use a “spec” tire.* For those series that allow for more than one tire manufacturer, tire wars ensue and millions of dollars are spent in developing tires which often determine the success of a team or car.
In order to have a better ‘show’, keep costs down, and regulate competition, most racing series use a “spec” tire.* For those series that allow for more than one tire manufacturer, tire wars ensue and millions of dollars are spent in developing tires which often determine the success of a team or car.
Tires are consumable and expensive, but this should not be a justification for crippling the handling of your sports car, sports sedan, or minivan.* Whether you’re trying to break records and win races on the track or simply avoiding an accident on the street, choosing the right tire will often dictate the success of either.
There are 3 main steps that I follow when looking for tires: CHOOSE A TIRE CATEGORY, SIZE THE TIRE, and SELECT A TIRE.* SIZE & SELECT A WHEEL is my fourth and last step when also looking for new wheels.
STEP 1:* CHOOSE A TIRE CATEGORY
“What is the car being used for?”
Buying the right tires for your grocery-getting, baby-hauling daily driver in the northeast or Florida (where it rains most days of the week) is going to be a lot different than buying tires for your weekend toy in Southern California that never sees rain.* Determining the importance of dry, wet, snow performance, tire longevity, ride quality, and comfort should be the first step when looking for a tire.
Just like everything in life, choosing the best tire is often a compromise since it’s rare to find a tire that is really good in the rain, quiet and lasts a long time that can perform well in the dry and hold up to extensive track use.* Usually as you increase the dry capability of a tire, you start to suffer wet performance and comfort in terms of noise and ride quality.* However, in recent years a few manufacturers are starting to make tires that are very good in all categories.
TireRack.com is a great source of information for everything tire related.* They have numerous customer reviews, independent tests, and are a pleasure to do business with.* They break down tires into 5 main categories, while I added a 6th.* These 5 main categories are further broken down into sub-sections like “Ultra High Performance”, “High Performance”, “Performance”, “Touring”, etc…* I won’t go into detail since I usually pick tires from the top sub-section of every category.* I have arbitrarily listed some examples for each category below:
2020 update - I don't like what Tire Rack did to their categories so i'm sticking with their original categories below, and updating the list to add modern tires:
1.Winter/Snow:
Bridgestone Blizzak, Michelin Alpin, Continental ContiWinterContact, Pirelli Winter Snowcontol
2.All-Season:
Michelin Pilot Sport A/S 3, Continental ExtremeContact DWS, P Zero All-Season
3.Summer:
Michelin Pilot Super Sport & PS4S, Bridgestone Potenza RE070, Hankook R-S3, Dunlop ZII StarSpec, BFG Rival, Bridgestone RE-11, Pirelli P Zero Corsa System, Continental 5 & DW & SPORT
4.Streetable Track & Competition:
Michelin Pilot Sport Cup 2, Dunlop Sport Maxx Race 2*, Bridgestone RE-71R*, BF Goodrich G-Force Rival S/1.5*, Hankook Ventus TD, Hankook Ventus R-S4*, Continental ContiForceContact, Dunlop ZIII*, Falken Azenis RT660*, Firestone Firehawk Indy 500*, Yokohama AD08R*, Yokohama A052* (it's more accurately in this category)
5. D.O.T. –Approved Slick AND Modern 2019+ *R-Compound Tires:.*
Hoosier R7 & A7, BF Goodrich R1, Hankook Ventus Z214* -* Michelin Cup 2 R*, Pirelli Trofeo R*, Goodyear Eagle F1 SuperCar 3R** -* Nitto NT01, Toyo R888, Toyo R888R*, Yokohama A048,
6.Racing Slick:
Yokohama A005, Michelin, Hoosier, Pirelli
*Notice there is no “R-Compound” (“R” = Race Compound) tire definition in the above categories.* “R-comp” is not really well defined other than the vague description of “race-derived rubber” and as a middle ground between street tires and racing slicks.* This nomenclature is used for everything from the treaded NT01 and R888 to the slick A7, R7, and Ventus Z214.* I prefer Tire Rack’s separation of the treaded “R-comps” into the Streetable Track & Competition category while placing tires with only circumferential grooves (like the Hoosier R7 & BFG R1) into the “D.O.T.-approved Slick” category.**UPDATE: There is now a more prevalent use of "R-compound" tires from manufacturers like Michelin, Pirelli, and GoodYear that use motorsport "race" compounds in their "road" tires.* I moved the commonly used "R-comp" track tires like NT01 & R888 to the DOT-approved slick section along with adding the tit'e "R-comp".* Many of the high performance 'summer' street tires (like the AD08R and Indy 500) are more in lines with the Cup 2 and Dunlop Race 2 tire than they are a PS4S or Conti Sport tire.* I'm mostly considering the wet-weather performance in this re-categorization, but tire technology is getting better and blurring the lines between "summer" and "Streetable Track".
UPDATE for 2020:
The categories have changed and are fairly jumbled up now.* What use to be "Winter/Snow, All-Season, Performance Street, Streetable Track & Competition, DOT-approved Slick is now what you see below. Performance All-Season tires are now classified under the "Performance" category, so tires like the Pilot A/S 3 are now technically under category 3.
1.Winter/Snow (Studless Ice & Snow, Studded, Performance Winter):
Bridgestone Blizzak, Michelin Alpin, Continental ContiWinterContact, Pirelli Winter Snowcontol
2.Touring Tires (Grand Touring All-Season, Grand Touring Summer, Passenger All-Season):
Michelin Energy Saver, PremiumContact 6, Turanza ER30
3.Performance Tires (Extreme Performance Summer, Max Performance Summer, *UHP All-Season):
Michelin Pilot Super Sport & PS4S, Yokohama AD08R, Hankook R-S3, Dunlop ZII StarSpec, BFG Rival, Bridgestone RE-11, Pirelli P Zero Corsa System, Continental 5 & DW & DW SPORT, Bridgestone RE-71R*, BF Goodrich G-Force Rival S/1.5*, Hankook Ventus TD, Hankook Ventus R-S4*, Continental ContiForceContact, Dunlop ZIII*, Falken Azenis RT660*, Firestone Firehawk Indy 500*
Michelin Pilot Sport A/S 3, Continental ExtremeContact DWS, P Zero All-Season
4.Track & Competition (Racetrack & Autocross Only, Streetable Trak & Competition, Wet Racetrack & Autocross, Drag Racing):
Michelin Pilot Sport Cup 2, Dunlop Sport Maxx Race 2*, Michelin Cup 2 R*, Pirelli Trofeo R*, Goodyear Eagle F1 SuperCar 3R*, Hankook Ventus TD, Continental ContiForceContact, Nitto NT01, Toyo R888, Yokohama A048
5. All-Terrain Tires (On-/Off-Road All-Terrain, Off-Road Max Traction, On-/Off-Road Commercial Traction)
Mud-Terrain T/A KM2, Wrangler MT/R with Kevlar, Scorpion MTR, Open Country M/T
Here’s a Top Tip:*“Tires are the most important.* A narrower, but better (compound, construction, tread design, etc…) tire will,*to a point,*generally outperform a wider, inferior tire”.
STEP 2:* SIZE THE TIRE
When sizing a tire, there are a few important things to know:
1. *TIRE WIDTHS ARE USELESS.*
I’m referring to the first number in the tire size code such as the “275” in a 275/35-18 tire. This may sound crazy because other than the diameter of the wheel, this is usually the most important aspect of the tire for many people. But hear me out: Have you ever tried a different brand of tire just to realize it does not fit the same as the ones you took off, or not even fit under your fenders at all?* The reason for this is the tolerances tire manufactures have to follow when making a given tire size is substantial.* Brand X’s 275 can be as wide as Brand Y’s 305!* To make matters worse, there is no industry standard to establish how to measure tire tread widths.
Above are the "Specs" sheet for the Michelin Pilot Super Sport tire from TireRack.com. *Here we see the 255/35-19 Michelin Pilot Super Sport above is produced in two different widths (one bespoke version for BMW), while the*275/35-18 is offered in three different widths (one bespoke for BMW) and the 315/35-20 is offered in two different bespoke Ferrari-specific widths. I added the ideal wheel width range on the far right for each tire's specific tread width (highlighted in yellow). The red arrow indicates the widest version of each tire size.
Above are the "Specs" sheet for the Michelin Pilot Super Sport tire from TireRack.com. *Here we see the 255/35-19 Michelin Pilot Super Sport above is produced in two different widths (one bespoke version for BMW), while the*275/35-18 is offered in three different widths (one bespoke for BMW) and the 315/35-20 is offered in two different bespoke Ferrari-specific widths. I added the ideal wheel width range on the far right for each tire's specific tread width (highlighted in yellow). The red arrow indicates the widest version of each tire size.
Often tire manufacturers will have multiple offerings or bespoke versions*of the same size tire (as written on the sidewall). Due to the wide variance in tire construction, an auto manufacturer can specify not only the*tread compound, design, and many aspects of the composition of the tire, but the width as well for the specific needs of a certain car. This further illustrates how the written number isn't all that usefull.
Most people are too focused on the number on their sidewall rather than the true width of the tire, or what will give them the best performance.* I get it. Size matters for bragging rights just like the numbering on the side of a muscle car designating the car’s cubic displacement, or the chrome emblems on the side of a “hooptie” designating their wheel diameter.* But this article is about optimizing performance; not a “whose is bigger” bragging rights.* Instead we need to focus on the tire’s TREAD WIDTH.
2. *TREAD WIDTH **(THIS IS WHAT MATTERS):
TireRack.com*has come to the rescue by establishing a common measurement method to address this issue!!!* They literally measure every make, model and size of tire with the same test procedure using a 20” long tool with a 30-degree bend in it to measure the tread width of the tire to take account various tire shapes and radiuses.* This number, measured in inches, is what I view as the true width of the tread, not what is written on the side wall, since Tire Rack uses the same measurement procedures for all of the different brand tires they sell.
3. *SECTION WIDTH:
Is the measurement of the tire’s width from the inner sidewall to outer sidewall with the tire mounted on its industry assigned rim width at proper inflation pressures. While this is typically more consistent and representative of the nominal width, it*is not as important to me and is usually a bit wider than the tread width. A good rule of thumb to follow is that: for every 0.5” change in rim width, the tire’s section width will change by 0.2”.
4. *MEASURING RIM WIDTH:
Is the industry standard rim width for which the tire must be mounted to meet its dimensional targets.* AKA: the tire’s “Design rim width”. Without optimizing a tire’s performance, using this recommendation for rim width will be a quick and easy way to select your tire.
Here is a 285/35-20 Michelin Pilot Super Sport which has a 10.1" tread width (also available in a 10.5" tread width) mounted on a 20x10.5 wheel. This is a perfect tire-to-wheel sizing with a mild stretch, preloading the side wall just enough to improve steering response and performance.
Here is a 285/35-20 Michelin Pilot Super Sport which has a 10.1" tread width (also available in a 10.5" tread width) mounted on a 20x10.5 wheel. This is a perfect tire-to-wheel sizing with a mild stretch, preloading the side wall just enough to improve steering response and performance.
*Billy’s rule of thumb:
“For ideal handling:*when sizing a tire for a given wheel, I usually target a tire’s TREAD width to be as wide as the WHEEL width, or 0.5” narrower than the wheel width.”
From my personal experience working on and driving countless track days, time attacks, street cars and race cars, this typically optimizes the tire’s carcass for response and outright grip.* It also gives the sidewall a very slight ‘stretch’ or preload, which will improve the tire’s response and break-away characteristics.* OEM’s have to size tires to meet a ton of different targets like curb to wheel damage protection, cost, snow chain clearance (almost all cars have to take this into consideration) all which affects the decision on the size of the tire and is usually a compromise at the expense of peak performance.
Beauty is in the eye of the beholder and i'm not a huge fan of the 'hella-flush'*trend; but this 225/40-14 Toyo T1R has a tread width more than 3 inches narrower than this 14x11 wheel. Not only is the tire at risk of coming off the bead when cornering, the ride quality and overall grip is negatively affected from this extreme stretch and would benefit from a much wider tire.
Beauty is in the eye of the beholder and i'm not a huge fan of the 'hella-flush'*trend; but this 225/40-14 Toyo T1R has a tread width more than 3 inches narrower than this 14x11 wheel. Not only is the tire at risk of coming off the bead when cornering, the ride quality and overall grip is negatively affected from this extreme stretch and would benefit from a much wider tire.
If a tire is too narrow for a given wheel width, the sidewall becomes overly preloaded and the carcass can distort to have uneven pressure across the surface of the tire.* The preloaded sidewall also has greatly reduced flex and compliance, which would improve initial response, but it would ride poorly, be less forgiving over bumps, and the break-away characteristics would likely not be as predictable.
This 275/40-17 BFGoodrich g-Force KDW has a 10.8" tread width and is mounted on this relatively narrow 17x9 factory Firebird*wheel. *With a tread width nearly 2 inches wider then the rim width; this combination likely has a very vague and sloppy steering feel even if it increases peak grip over a properly sized 8.5" wide tire (245/40-17). *A better option would be to source a 17x11 wheel for this tire.
This 275/40-17 BFGoodrich g-Force KDW has a 10.8" tread width and is mounted on this relatively narrow 17x9 factory Firebird*wheel. *With a tread width nearly 2 inches wider then the rim width; this combination likely has a very vague and sloppy steering feel even if it increases peak grip over a properly sized 8.5" wide tire (245/40-17). *A better option would be to source a 17x11 wheel for this tire.
On the other hand, if a tire is too wide for a given wheel width, the sidewall ‘bulges”.* This usually results in sloppy handling characteristics, vague steering feel, excessive tread squirm, and the carcass of the tire can also distort and have uneven pressure across the surface of the tire.
….Okay, now with that education:* “What are the constraints?”
Constraints could be as simple as the size of your current wheels and specific outer diameter needed to maintain the accuracy of the speedometer, odometer, traction control, and ABS functionality.* Or it could be a little more in depth and limited by class specific rules (for competition) like maximum tire width, tread wear rating, or it can be very in depth with fitting the largest tire in the wheel well as possible.
1. Existing Wheels:*
If you are not purchasing new wheels and are simply looking for new tires, look up the TREAD width of your current tires on TireRack.com –*are they the same or 0.5” narrower than stock? If the tires are the OEM size, the tread width will probably be close to the rim width, and maybe even up to 0.5” wider.
For example: Let’s say your car has an 18x10” wheel and a Michelin Pilot Super Sport (PSS) tire on it from the factory.* It’s likely the PSS would be a 285/35-18 for this wheel which has a 10.2” tread width. Now following my generic rule of thumb, the best size tire would be a 275/35-18 that has a 9.6” tread width which will improve the tire’s response and grip, but this is relative to the same 275 tire on a narrower wheel.
In our example, the factory 285 is pretty good but isn’t optimal for our 10” wheel, and it could make even more grip and have better response on a 10.5” wheel. If you were to downsize the tire on the factory 10” wheel, you are optimizing the grip and response of a smaller tire, but that may be a slight net loss of grip for a slight improvement of response.* Depending on the situation, downsizing the tire could have slightly less, the same or slightly more grip.* You can go either way here, but depending on your needs, I would probably keep the factory 285 width UNLESS a better performing tire can be had in the 275 width (and tread width) range, then that would be a win-win over an inferior 285.* Remember the “Top Tip” earlier in the article?
2. Tire label width (Nominal width):
If you compete in time trials or wheel to wheel racing, but your class has a tire width limit of say, a 275.* By now you should know at least two things: 1) - The nominal sidewall*width is useless and 2) - The tire model (compound/construction) is more important than width. Given a rule constraint like a 275, there is not much to do other than look at the true tread widths of the various tires and (more importantly) find out which compound is truly better.
3. Wheel well room:
This can get very complex when increasing the width and diameter of the tire beyond what the factory has intended; but there are 3 main things to consider: Width, Diameter, and Volume/Total Tread Surface Area (TTSA).
-WIDTH:
The width of a tire usually does not influence the ABS or Traction Control, and the constraints here tend to be limitations with steering lock and the tire rubbing the inner chassis at full lock.* Optimizing the offsets and rim widths for the given amount of room is the goal here.
There are a few things to understand in regards to tire width.* A WIDER TIRE:
-Does NOT change the contact patch SIZE when the vehicle weight and tire pressure is the SAME.
-DOES change the contact patch SHAPE when the vehicle weight and tire pressure is the SAME.* The contact patch becomes wider and shorter (front to rear).
-(Typically) ALLOWS for LOWER PRESSURE which will then INCREASE the contact patch size (good).
-INCREASES the tires Total Tread Surface Area (TTSA), and makes it less prone to overheating and has a LONGER LIFE.
-Takes LONGER to WARM UP to its ideal operating range.* Usually not a problem on heavy cars.
-DIAMETER:
This has a huge influence on the ABS, Traction Control, speedometer, effective gear ratio, rotating mass, and much more. The easiest thing to do is to keep the diameter the same as the factory.* I wouldn’t recommend going above or below this diameter until you know more about how it is going to affect the rest of the systems on your car.
Increasing the Diameter also changes the contact patch SHAPE, making it longer (front to rear) and narrower (width) for a given vehicle weight and tire pressure. You can typically also lower tire pressures slightly to increase the contact patch SIZE due to a larger diameter tire.* Larger diameter tires generally help for longitudinal grip (drag racing) more than a wider tire.* There’s a reason drag racing tires have small diameter wheels, large sidewalls and very large outer diameter tires.
At one time,*18-inch wheels and anything smaller than a 40-series aspect ratio were considered 'blingy' and not for the performance-oriented; so*everyone ran 17" wheels or smaller. *You could say the same if you're older than I am for 15", 16" or 17" wheels. Now 18" wheels are the most popular size for performance tires on up to racing tires and manufacturers are increasing the overall wheel diameter of vehicles across the board to fit larger brakes for increasingly larger and heavier cars.
At one time,*18-inch wheels and anything smaller than a 40-series aspect ratio were considered 'blingy' and not for the performance-oriented; so*everyone ran 17" wheels or smaller. *You could say the same if you're older than I am for 15", 16" or 17" wheels. Now 18" wheels are the most popular size for performance tires on up to racing tires and manufacturers are increasing the overall wheel diameter of vehicles across the board to fit larger brakes for increasingly larger and heavier cars.
Keep in mind that*larger diameters also increases the tire's Total Tread Surface Area (TTSA) which can be advantageous. As far as sizing goes, this Ferrari 458 Speciale is arguably one of the best performance cars ever built and is equipped with massive*245/35-20 and 305/30-20 Michelin Pilot Sport Cup 2 tires that have*26.8" and 27.2" diameters respectively. Interestingly, the 300/650-18 and 320/710-18 racing slicks commonly used on GTE racecars have very similar outer diameters.
While slightly smaller brakes and either 18" or 19" wheels probably would have sufficed, Ferrari felt this direction of smaller sidewalls and larger diameter wheels were worth it and*it's hard to argue against it especially when amazing supercars from the 918/P1/LaF trio to the Aventador SV, McLaren 675LT and Ford GT have all gone in this direction. *Having driven the Speciale in bumpy pothole-riddled Toronto city streets, this package with its thin side wall heights*isn't as bad as you might think in the worst conditions*and is just brilliant on the racetrack.
-TOTAL TREAD SURFACE AREA (TTSA):
A tire's TTSA*is an important and often overlooked aspect that directly affects a tire’s performance. Bigger isn’t always better and there’s a point of diminishing returns (which probably won’t be an issue for most readers) where a larger and wider tire will not be any faster.* While a 245-width tire isn’t wide by today’s standards, Lotus Elise’s struggle to get heat into a 245 and tend to slip and slide on cold days due to their low weight and low center of gravity.* On the other hand, a heavy 3,800lb car on 275s can lay down a fast lap or two but cannot last a 20 minute session without overheating the tires and being seconds off pace.* All of this has to do with a tire’s TTSA, which is dictated by the tire’s overall diameter and width.
Remember that heavier cars need more TTSA/Volume from wider widths and increased diameters.
EXCEPTIONS:
There are always exceptions to every rule.* A car’s setup is like an inter-connected spider web where changing anything influences everything else.* Often one change will have a secondary effect that overshadows the primary change.
Because of this, it’s possible that running a tire a lot wider than the wheel width would improve the overall performance if it were on a heavy car, with a less than ideal alignment that is very heavy for the wheel width.* In this case, the increased VOLUME/TTSA of the tire, and tread width, would in fact improve the cornering ability of the car.
It’s important to understand the intended use of the car as well as the tire’s TTSA. You don’t want too much volume/TTSA (like the Elise example) if you are autocrossing, because you will never heat the tire up to its ideal operating range in time to make grip.* Likewise if you have a heavier car, increasing the volume/TTSA is key to making tire last longer in a session.
Tire compound and tread design also plays a big role here and while swapping to a more aggressive tire is the easiest way to make a car faster and last longer before overheating the tires; increasing the TTSA will make the tires last even longer, and even allow for a tire choice that is less of a compromise for daily driving.* Look at the following chart of various production cars and their weight-to-TTSA ratio:
Here we see various production cars and a few popular cars with commonly used track tire sizes sorted by Tire Loading (Total Tread Surface Area/vehicle weight)*from largest to smallest. Basically, how many square millimeters supports*each*pound of vehicle weight.
Here we see various production cars and a few popular cars with commonly used track tire sizes sorted by Tire Loading (Total Tread Surface Area/vehicle weight)*from largest to smallest. Basically, how many square millimeters supports*each*pound of vehicle weight.
This figure is calculated by adding the total front and rear Tread Surface Areas*(tire width x circumference) then dividing the Total Tread Surface Area (TTSA)*by the vehicle weight. The higher the mm per pound,*the more the load is distributed across the tires and the more resilient the tire will be to overheating.
STEP 3:* SELECT YOUR TIRE
“What tires fit your category and size?”
Now that you have determined what your tire is going to be used for and the respective tire category, and with the newfound knowledge of how to look at tires by their true size, it’s time to select a tire.* But with all of the different stats and criteria out there, what factors make a tire good?
Feel free to read the definitions below but I’ll save you some time with this sentence:
Due to the subjective or interpretive nature of these tests; other than speed ratings (which may not apply to most people) all of the other tire performance criteria is for the most part USELESS.
Load Index
-You can read Tire Rack’s Load Index Definition if you want, but it’s basically the load carrying capacity of the tire, which usually isn’t important unless you’re making hundreds of pounds of downforce, have a heavy car, and are driving on an oval.
Speed Ratings
-Click the link above for more detail, but I mainly focus on tires with W (168mph), “99Y” (186mph), and “(99Y)” (Parentheses = 186mph+) based on the application.* If you never go this fast (which you can’t do legally unless you’re on a racetrack, and even so, it’s rare to go this fast on track), then this probably does not matter.
Uniform Tire Quality Grade (UTQG)
-An arbitrary number originally developed to help consumers with a numerical value that represents the treadwear, traction, and temperature capabilities of the tire.* Since the Department Of Transportation (DOT) does not test the tires and it’s up to the tire manufacturer to come up with the value, tire manufacturers set these numbers based on how they perceive the customer will understand how the tire will perform, or to meet a random number/standard that a racing series might restrict, to have a softer faster tire as an advantage. Because of all of this, UTQG is USELESS.
Treadwear Ratings:
-A test based on a 7,200-mile test loop with routine tire pressure and rotation adjustments during it. A 100 rating should = the tread lasting the 7,200 miles, 200 rating = 2X that distance and so on.* Since a lot is left open for interpretation and the only decently comparable data is from one tire to another within the same brand, this is also somewhat useless.
Traction Grade:
-This is another useless test since it measures the deceleration g-forces of a locked tire across a WET road at 40mph. Other than seeing which tire will stop you the shortest distance with the tires locked; this is not relevant to cars with ABS or the braking ability of the tire under normal rack uses.
Temperature (Resistance) Grades:
-Indicates the amount of heat generated by what appears to be an under-inflated tire at 85mph.* Since this is also outside the scope of a properly maintained tire, I find it useless.
As tire technology gets better with each new design, often driven by what is learned in motorsports, tires are performing better in the dry and wet, are lasting longer, and are quieter than their predecessors.* Keep in mind those manufacturers who are winning in multi-tire racing series tend to offer the best products to their customers as well.
These advancements make it difficult to properly classify a tire or draw conclusions that tire A lasts longer than Tire B because it’s Treadwear Rating is higher, or it will have more grip and wear out quicker because its UTQG is lower. Remember, these numbers are useless?
So back to the decision of selecting the best tire; when looking at TireRack’s subcategories
(“Ultra High Performance”, “High Performance”, “Performance”…) I usually look in the highest category.* Price is usually a major factor in selecting a tire but since tires should be viewed as an INVESTMENT in terms of both performance and safety of your car, I rarely look below the second tier of subcategories.
When comparing tires within a category, the balancing of performance, comfort, and price begins.
TireRack’s rating table is going to be one of the best sources out there.* Using a scale of 1-10, each tire is rated in terms of dry grip, steering response, wet grip, hydroplane resistance, road noise, longevity, etc… *by consumer survey ratings which can be the average from hundreds of people.* Having tracked many tires, I personally feel these figures are fairly accurate when comparing across brands and have the most credibility, especially compared to the useless UTQG or Treadwear ratings of a tire. The individual customer reviews of the tire can also be somewhat insightful, but I tend to take them with a grain of salt and use them as a secondary factor to TireRack’s rating system.
The tread design is something to consider when looking for tires.* The design will usually reflect its performance in Tire Rack’s rating system, but in addition, looking at the outer shoulder, rain grooves and sipes will also give a vague idea of how they will perform.* For track use, large continuous outer tread blocks will deliver more grip and stability than smaller tread blocks which tend to tear off and chunk.* Larger tread blocks tend to be more prone to hydroplaning while tires with many, small tread blocks often perform better in rain and snow.
The tread design is something to consider when looking for tires.* The design will usually reflect its performance in Tire Rack’s rating system, but in addition, looking at the outer shoulder, rain grooves and sipes will also give a vague idea of how they will perform.* For track use, large continuous outer tread blocks will deliver more grip and stability than smaller tread blocks which tend to tear off and chunk.* Larger tread blocks tend to be more prone to hydroplaning while tires with many, small tread blocks often perform better in rain and snow.
As you start comparing different tires, it’s important to verify the TREAD WIDTH of each model, and if they run too narrow or wide, shop to see if a slightly different size would be more applicable.* If you are trying to break track records, further research would be beneficial but keep in mind that a review from a Lotus Elise owner on a set of tires probably won’t be as applicable on a heavy GTR or CTS-V, so try to find comments from someone with a car of similar weight and tire sizing.
I am not going to outright say buy this tire, or that tire sucks, but by now you have gained enough knowledge to make a more educated decision on your next set of tires with greater confidence that not only will the tires be more likely to fit, but will deliver the performance that you are looking for.
STEP 4:* CHOOSING A WHEEL
Wheels are an expensive investment that will affect the handling, performance, and yes, looks of your car; so it’s important to do your homework before dropping a lot of cash down.* This may sound backwards but since the tire is the most important part of your car, your wheel choice should be dictated by the tires you want to run.*
When I look to increase the diameter and width of a set of wheels on a car, I define the goal of the increase, whether it’s to increase tire width for cornering, or Total Tread Surface Area*(diameter and width) for prolonged track capability, or even simply for looks.* Based on the available room in the wheel well, I then look at the availability of the group of tires in the general size that I want to go to, which narrows down the ideal wheel size that I should run.
If you are limited by room in the wheel well or rules for a particular class, the tires should be your limiting and deciding factor.* Pick the best tire in the outer diameter and section width that will fit the room or rules, and then size the wheel accordingly.
This is the opposite from what almost everyone does.* Most people buy bigger wheels based on looks and offsets and then the tire tends to be a compromised afterthought to fit those wheels in the remaining room that’s available.* Since this article is about optimizing the performance of a car with tires, they should dictate what size wheel to run.* In many cases, the ideal tire may not be available in the size that properly fits your wheels.* If handling and performance is important to you, then your wheels will be sized accordingly.* If you view form > function, then this article probably isn’t for you anyway.
For a daily driver where maximizing outright grip or TTSA*may not be the top priority, choosing the widest tire possible may not be necessary at any expense of steering feel, fuel economy, and price.
* Remember the top tip?: *"A narrower high quality tire will often outperform a cheap wider tire".
A proper amount of time should be spent on researching or measuring the wheel offsets and clearances of your current wheels to determine how much larger and wider of a tire can fit.* Once the ideal tire is chosen, then you can select the diameter, width, and offset of your wheels. Staying the same or close to factory widths and offsets is a conservative way of making choosing a wheel much easier.
CONCLUSION
By now everyone should be an expert at*sizing and selecting*a tire, or at least possess*a greater education on how tires are sized and what aspects are important when choosing a tire.* By following the 3 main steps when looking for tires: *CHOOSE A TIRE CATEGORY, SIZE THE TIRE, and SELECT A TIRE, it’s hard to go wrong.
Disclaimer: The information above is a recommendation for OFF ROAD USE only. Please consult and follow your owner’s manual when sizing tires for street use, otherwise follow the above advice at your own risk.
SOURCES:
BillyJohnsonRacing
TireRack
If you enjoyed this*article and are interested in*improving*yourself as a driver, check out my articles:
DRIVER DEVELOPMENT: Car Control
DRIVER DEVELOPMENT: Learning Processes
How to PROPERLY select and size TIRES for PERFORMANCE
by Billy Johnson
The most important part of your car is not the engine, suspension, or brakes. It’s the TIRES!!!* This is because your car can only perform as well as the capability of its tires. I’m often asked which tire is best and what size to buy.* In this article I discuss my methods for choosing and properly sizing the right tires. *I’m not into the “hella-flush” or “stance” scenes so this article is focused towards those who care about the PERFORMANCE of their car, whether on the street or on the track.
Pirelli had the best slogan for a tire company: “Power is nothing without control.” This is true for all forms of driving since it does not matter how much power you have if you can’t put it to the ground, it doesn’t matter how much you spend on a big brake kit if they easily lock up the tires, and your $7,000 coilovers can only deliver the performance that your tires are capable of. *It really does not matter how great and expensive your car is or how much money you’ve put into modifying it if you cheap out on tires; which is the only component on your car that actually touches the road.
I often see really nice cars with a ton of money thrown at it in power upgrades and ‘blingy’ wheels wearing an improperly sized tire or something that is obviously not up to the capabilities of the car.* Most people really do not understand the importance of their tires, not only from a performance standpoint but from a safety standpoint as well.* This includes the age of the tire.
In order to have a better ‘show’, keep costs down, and regulate competition, most racing series use a “spec” tire.* For those series that allow for more than one tire manufacturer, tire wars ensue and millions of dollars are spent in developing tires which often determine the success of a team or car.
In order to have a better ‘show’, keep costs down, and regulate competition, most racing series use a “spec” tire.* For those series that allow for more than one tire manufacturer, tire wars ensue and millions of dollars are spent in developing tires which often determine the success of a team or car.
Tires are consumable and expensive, but this should not be a justification for crippling the handling of your sports car, sports sedan, or minivan.* Whether you’re trying to break records and win races on the track or simply avoiding an accident on the street, choosing the right tire will often dictate the success of either.
There are 3 main steps that I follow when looking for tires: CHOOSE A TIRE CATEGORY, SIZE THE TIRE, and SELECT A TIRE.* SIZE & SELECT A WHEEL is my fourth and last step when also looking for new wheels.
STEP 1:* CHOOSE A TIRE CATEGORY
“What is the car being used for?”
Buying the right tires for your grocery-getting, baby-hauling daily driver in the northeast or Florida (where it rains most days of the week) is going to be a lot different than buying tires for your weekend toy in Southern California that never sees rain.* Determining the importance of dry, wet, snow performance, tire longevity, ride quality, and comfort should be the first step when looking for a tire.
Just like everything in life, choosing the best tire is often a compromise since it’s rare to find a tire that is really good in the rain, quiet and lasts a long time that can perform well in the dry and hold up to extensive track use.* Usually as you increase the dry capability of a tire, you start to suffer wet performance and comfort in terms of noise and ride quality.* However, in recent years a few manufacturers are starting to make tires that are very good in all categories.
TireRack.com is a great source of information for everything tire related.* They have numerous customer reviews, independent tests, and are a pleasure to do business with.* They break down tires into 5 main categories, while I added a 6th.* These 5 main categories are further broken down into sub-sections like “Ultra High Performance”, “High Performance”, “Performance”, “Touring”, etc…* I won’t go into detail since I usually pick tires from the top sub-section of every category.* I have arbitrarily listed some examples for each category below:
2020 update - I don't like what Tire Rack did to their categories so i'm sticking with their original categories below, and updating the list to add modern tires:
1.Winter/Snow:
Bridgestone Blizzak, Michelin Alpin, Continental ContiWinterContact, Pirelli Winter Snowcontol
2.All-Season:
Michelin Pilot Sport A/S 3, Continental ExtremeContact DWS, P Zero All-Season
3.Summer:
Michelin Pilot Super Sport & PS4S, Bridgestone Potenza RE070, Hankook R-S3, Dunlop ZII StarSpec, BFG Rival, Bridgestone RE-11, Pirelli P Zero Corsa System, Continental 5 & DW & SPORT
4.Streetable Track & Competition:
Michelin Pilot Sport Cup 2, Dunlop Sport Maxx Race 2*, Bridgestone RE-71R*, BF Goodrich G-Force Rival S/1.5*, Hankook Ventus TD, Hankook Ventus R-S4*, Continental ContiForceContact, Dunlop ZIII*, Falken Azenis RT660*, Firestone Firehawk Indy 500*, Yokohama AD08R*, Yokohama A052* (it's more accurately in this category)
5. D.O.T. –Approved Slick AND Modern 2019+ *R-Compound Tires:.*
Hoosier R7 & A7, BF Goodrich R1, Hankook Ventus Z214* -* Michelin Cup 2 R*, Pirelli Trofeo R*, Goodyear Eagle F1 SuperCar 3R** -* Nitto NT01, Toyo R888, Toyo R888R*, Yokohama A048,
6.Racing Slick:
Yokohama A005, Michelin, Hoosier, Pirelli
*Notice there is no “R-Compound” (“R” = Race Compound) tire definition in the above categories.* “R-comp” is not really well defined other than the vague description of “race-derived rubber” and as a middle ground between street tires and racing slicks.* This nomenclature is used for everything from the treaded NT01 and R888 to the slick A7, R7, and Ventus Z214.* I prefer Tire Rack’s separation of the treaded “R-comps” into the Streetable Track & Competition category while placing tires with only circumferential grooves (like the Hoosier R7 & BFG R1) into the “D.O.T.-approved Slick” category.**UPDATE: There is now a more prevalent use of "R-compound" tires from manufacturers like Michelin, Pirelli, and GoodYear that use motorsport "race" compounds in their "road" tires.* I moved the commonly used "R-comp" track tires like NT01 & R888 to the DOT-approved slick section along with adding the tit'e "R-comp".* Many of the high performance 'summer' street tires (like the AD08R and Indy 500) are more in lines with the Cup 2 and Dunlop Race 2 tire than they are a PS4S or Conti Sport tire.* I'm mostly considering the wet-weather performance in this re-categorization, but tire technology is getting better and blurring the lines between "summer" and "Streetable Track".
UPDATE for 2020:
The categories have changed and are fairly jumbled up now.* What use to be "Winter/Snow, All-Season, Performance Street, Streetable Track & Competition, DOT-approved Slick is now what you see below. Performance All-Season tires are now classified under the "Performance" category, so tires like the Pilot A/S 3 are now technically under category 3.
1.Winter/Snow (Studless Ice & Snow, Studded, Performance Winter):
Bridgestone Blizzak, Michelin Alpin, Continental ContiWinterContact, Pirelli Winter Snowcontol
2.Touring Tires (Grand Touring All-Season, Grand Touring Summer, Passenger All-Season):
Michelin Energy Saver, PremiumContact 6, Turanza ER30
3.Performance Tires (Extreme Performance Summer, Max Performance Summer, *UHP All-Season):
Michelin Pilot Super Sport & PS4S, Yokohama AD08R, Hankook R-S3, Dunlop ZII StarSpec, BFG Rival, Bridgestone RE-11, Pirelli P Zero Corsa System, Continental 5 & DW & DW SPORT, Bridgestone RE-71R*, BF Goodrich G-Force Rival S/1.5*, Hankook Ventus TD, Hankook Ventus R-S4*, Continental ContiForceContact, Dunlop ZIII*, Falken Azenis RT660*, Firestone Firehawk Indy 500*
Michelin Pilot Sport A/S 3, Continental ExtremeContact DWS, P Zero All-Season
4.Track & Competition (Racetrack & Autocross Only, Streetable Trak & Competition, Wet Racetrack & Autocross, Drag Racing):
Michelin Pilot Sport Cup 2, Dunlop Sport Maxx Race 2*, Michelin Cup 2 R*, Pirelli Trofeo R*, Goodyear Eagle F1 SuperCar 3R*, Hankook Ventus TD, Continental ContiForceContact, Nitto NT01, Toyo R888, Yokohama A048
5. All-Terrain Tires (On-/Off-Road All-Terrain, Off-Road Max Traction, On-/Off-Road Commercial Traction)
Mud-Terrain T/A KM2, Wrangler MT/R with Kevlar, Scorpion MTR, Open Country M/T
Here’s a Top Tip:*“Tires are the most important.* A narrower, but better (compound, construction, tread design, etc…) tire will,*to a point,*generally outperform a wider, inferior tire”.
STEP 2:* SIZE THE TIRE
When sizing a tire, there are a few important things to know:
1. *TIRE WIDTHS ARE USELESS.*
I’m referring to the first number in the tire size code such as the “275” in a 275/35-18 tire. This may sound crazy because other than the diameter of the wheel, this is usually the most important aspect of the tire for many people. But hear me out: Have you ever tried a different brand of tire just to realize it does not fit the same as the ones you took off, or not even fit under your fenders at all?* The reason for this is the tolerances tire manufactures have to follow when making a given tire size is substantial.* Brand X’s 275 can be as wide as Brand Y’s 305!* To make matters worse, there is no industry standard to establish how to measure tire tread widths.
Above are the "Specs" sheet for the Michelin Pilot Super Sport tire from TireRack.com. *Here we see the 255/35-19 Michelin Pilot Super Sport above is produced in two different widths (one bespoke version for BMW), while the*275/35-18 is offered in three different widths (one bespoke for BMW) and the 315/35-20 is offered in two different bespoke Ferrari-specific widths. I added the ideal wheel width range on the far right for each tire's specific tread width (highlighted in yellow). The red arrow indicates the widest version of each tire size.
Above are the "Specs" sheet for the Michelin Pilot Super Sport tire from TireRack.com. *Here we see the 255/35-19 Michelin Pilot Super Sport above is produced in two different widths (one bespoke version for BMW), while the*275/35-18 is offered in three different widths (one bespoke for BMW) and the 315/35-20 is offered in two different bespoke Ferrari-specific widths. I added the ideal wheel width range on the far right for each tire's specific tread width (highlighted in yellow). The red arrow indicates the widest version of each tire size.
Often tire manufacturers will have multiple offerings or bespoke versions*of the same size tire (as written on the sidewall). Due to the wide variance in tire construction, an auto manufacturer can specify not only the*tread compound, design, and many aspects of the composition of the tire, but the width as well for the specific needs of a certain car. This further illustrates how the written number isn't all that usefull.
Most people are too focused on the number on their sidewall rather than the true width of the tire, or what will give them the best performance.* I get it. Size matters for bragging rights just like the numbering on the side of a muscle car designating the car’s cubic displacement, or the chrome emblems on the side of a “hooptie” designating their wheel diameter.* But this article is about optimizing performance; not a “whose is bigger” bragging rights.* Instead we need to focus on the tire’s TREAD WIDTH.
2. *TREAD WIDTH **(THIS IS WHAT MATTERS):
TireRack.com*has come to the rescue by establishing a common measurement method to address this issue!!!* They literally measure every make, model and size of tire with the same test procedure using a 20” long tool with a 30-degree bend in it to measure the tread width of the tire to take account various tire shapes and radiuses.* This number, measured in inches, is what I view as the true width of the tread, not what is written on the side wall, since Tire Rack uses the same measurement procedures for all of the different brand tires they sell.
3. *SECTION WIDTH:
Is the measurement of the tire’s width from the inner sidewall to outer sidewall with the tire mounted on its industry assigned rim width at proper inflation pressures. While this is typically more consistent and representative of the nominal width, it*is not as important to me and is usually a bit wider than the tread width. A good rule of thumb to follow is that: for every 0.5” change in rim width, the tire’s section width will change by 0.2”.
4. *MEASURING RIM WIDTH:
Is the industry standard rim width for which the tire must be mounted to meet its dimensional targets.* AKA: the tire’s “Design rim width”. Without optimizing a tire’s performance, using this recommendation for rim width will be a quick and easy way to select your tire.
Here is a 285/35-20 Michelin Pilot Super Sport which has a 10.1" tread width (also available in a 10.5" tread width) mounted on a 20x10.5 wheel. This is a perfect tire-to-wheel sizing with a mild stretch, preloading the side wall just enough to improve steering response and performance.
Here is a 285/35-20 Michelin Pilot Super Sport which has a 10.1" tread width (also available in a 10.5" tread width) mounted on a 20x10.5 wheel. This is a perfect tire-to-wheel sizing with a mild stretch, preloading the side wall just enough to improve steering response and performance.
*Billy’s rule of thumb:
“For ideal handling:*when sizing a tire for a given wheel, I usually target a tire’s TREAD width to be as wide as the WHEEL width, or 0.5” narrower than the wheel width.”
From my personal experience working on and driving countless track days, time attacks, street cars and race cars, this typically optimizes the tire’s carcass for response and outright grip.* It also gives the sidewall a very slight ‘stretch’ or preload, which will improve the tire’s response and break-away characteristics.* OEM’s have to size tires to meet a ton of different targets like curb to wheel damage protection, cost, snow chain clearance (almost all cars have to take this into consideration) all which affects the decision on the size of the tire and is usually a compromise at the expense of peak performance.
Beauty is in the eye of the beholder and i'm not a huge fan of the 'hella-flush'*trend; but this 225/40-14 Toyo T1R has a tread width more than 3 inches narrower than this 14x11 wheel. Not only is the tire at risk of coming off the bead when cornering, the ride quality and overall grip is negatively affected from this extreme stretch and would benefit from a much wider tire.
Beauty is in the eye of the beholder and i'm not a huge fan of the 'hella-flush'*trend; but this 225/40-14 Toyo T1R has a tread width more than 3 inches narrower than this 14x11 wheel. Not only is the tire at risk of coming off the bead when cornering, the ride quality and overall grip is negatively affected from this extreme stretch and would benefit from a much wider tire.
If a tire is too narrow for a given wheel width, the sidewall becomes overly preloaded and the carcass can distort to have uneven pressure across the surface of the tire.* The preloaded sidewall also has greatly reduced flex and compliance, which would improve initial response, but it would ride poorly, be less forgiving over bumps, and the break-away characteristics would likely not be as predictable.
This 275/40-17 BFGoodrich g-Force KDW has a 10.8" tread width and is mounted on this relatively narrow 17x9 factory Firebird*wheel. *With a tread width nearly 2 inches wider then the rim width; this combination likely has a very vague and sloppy steering feel even if it increases peak grip over a properly sized 8.5" wide tire (245/40-17). *A better option would be to source a 17x11 wheel for this tire.
This 275/40-17 BFGoodrich g-Force KDW has a 10.8" tread width and is mounted on this relatively narrow 17x9 factory Firebird*wheel. *With a tread width nearly 2 inches wider then the rim width; this combination likely has a very vague and sloppy steering feel even if it increases peak grip over a properly sized 8.5" wide tire (245/40-17). *A better option would be to source a 17x11 wheel for this tire.
On the other hand, if a tire is too wide for a given wheel width, the sidewall ‘bulges”.* This usually results in sloppy handling characteristics, vague steering feel, excessive tread squirm, and the carcass of the tire can also distort and have uneven pressure across the surface of the tire.
….Okay, now with that education:* “What are the constraints?”
Constraints could be as simple as the size of your current wheels and specific outer diameter needed to maintain the accuracy of the speedometer, odometer, traction control, and ABS functionality.* Or it could be a little more in depth and limited by class specific rules (for competition) like maximum tire width, tread wear rating, or it can be very in depth with fitting the largest tire in the wheel well as possible.
1. Existing Wheels:*
If you are not purchasing new wheels and are simply looking for new tires, look up the TREAD width of your current tires on TireRack.com –*are they the same or 0.5” narrower than stock? If the tires are the OEM size, the tread width will probably be close to the rim width, and maybe even up to 0.5” wider.
For example: Let’s say your car has an 18x10” wheel and a Michelin Pilot Super Sport (PSS) tire on it from the factory.* It’s likely the PSS would be a 285/35-18 for this wheel which has a 10.2” tread width. Now following my generic rule of thumb, the best size tire would be a 275/35-18 that has a 9.6” tread width which will improve the tire’s response and grip, but this is relative to the same 275 tire on a narrower wheel.
In our example, the factory 285 is pretty good but isn’t optimal for our 10” wheel, and it could make even more grip and have better response on a 10.5” wheel. If you were to downsize the tire on the factory 10” wheel, you are optimizing the grip and response of a smaller tire, but that may be a slight net loss of grip for a slight improvement of response.* Depending on the situation, downsizing the tire could have slightly less, the same or slightly more grip.* You can go either way here, but depending on your needs, I would probably keep the factory 285 width UNLESS a better performing tire can be had in the 275 width (and tread width) range, then that would be a win-win over an inferior 285.* Remember the “Top Tip” earlier in the article?
2. Tire label width (Nominal width):
If you compete in time trials or wheel to wheel racing, but your class has a tire width limit of say, a 275.* By now you should know at least two things: 1) - The nominal sidewall*width is useless and 2) - The tire model (compound/construction) is more important than width. Given a rule constraint like a 275, there is not much to do other than look at the true tread widths of the various tires and (more importantly) find out which compound is truly better.
3. Wheel well room:
This can get very complex when increasing the width and diameter of the tire beyond what the factory has intended; but there are 3 main things to consider: Width, Diameter, and Volume/Total Tread Surface Area (TTSA).
-WIDTH:
The width of a tire usually does not influence the ABS or Traction Control, and the constraints here tend to be limitations with steering lock and the tire rubbing the inner chassis at full lock.* Optimizing the offsets and rim widths for the given amount of room is the goal here.
There are a few things to understand in regards to tire width.* A WIDER TIRE:
-Does NOT change the contact patch SIZE when the vehicle weight and tire pressure is the SAME.
-DOES change the contact patch SHAPE when the vehicle weight and tire pressure is the SAME.* The contact patch becomes wider and shorter (front to rear).
-(Typically) ALLOWS for LOWER PRESSURE which will then INCREASE the contact patch size (good).
-INCREASES the tires Total Tread Surface Area (TTSA), and makes it less prone to overheating and has a LONGER LIFE.
-Takes LONGER to WARM UP to its ideal operating range.* Usually not a problem on heavy cars.
-DIAMETER:
This has a huge influence on the ABS, Traction Control, speedometer, effective gear ratio, rotating mass, and much more. The easiest thing to do is to keep the diameter the same as the factory.* I wouldn’t recommend going above or below this diameter until you know more about how it is going to affect the rest of the systems on your car.
Increasing the Diameter also changes the contact patch SHAPE, making it longer (front to rear) and narrower (width) for a given vehicle weight and tire pressure. You can typically also lower tire pressures slightly to increase the contact patch SIZE due to a larger diameter tire.* Larger diameter tires generally help for longitudinal grip (drag racing) more than a wider tire.* There’s a reason drag racing tires have small diameter wheels, large sidewalls and very large outer diameter tires.
At one time,*18-inch wheels and anything smaller than a 40-series aspect ratio were considered 'blingy' and not for the performance-oriented; so*everyone ran 17" wheels or smaller. *You could say the same if you're older than I am for 15", 16" or 17" wheels. Now 18" wheels are the most popular size for performance tires on up to racing tires and manufacturers are increasing the overall wheel diameter of vehicles across the board to fit larger brakes for increasingly larger and heavier cars.
At one time,*18-inch wheels and anything smaller than a 40-series aspect ratio were considered 'blingy' and not for the performance-oriented; so*everyone ran 17" wheels or smaller. *You could say the same if you're older than I am for 15", 16" or 17" wheels. Now 18" wheels are the most popular size for performance tires on up to racing tires and manufacturers are increasing the overall wheel diameter of vehicles across the board to fit larger brakes for increasingly larger and heavier cars.
Keep in mind that*larger diameters also increases the tire's Total Tread Surface Area (TTSA) which can be advantageous. As far as sizing goes, this Ferrari 458 Speciale is arguably one of the best performance cars ever built and is equipped with massive*245/35-20 and 305/30-20 Michelin Pilot Sport Cup 2 tires that have*26.8" and 27.2" diameters respectively. Interestingly, the 300/650-18 and 320/710-18 racing slicks commonly used on GTE racecars have very similar outer diameters.
While slightly smaller brakes and either 18" or 19" wheels probably would have sufficed, Ferrari felt this direction of smaller sidewalls and larger diameter wheels were worth it and*it's hard to argue against it especially when amazing supercars from the 918/P1/LaF trio to the Aventador SV, McLaren 675LT and Ford GT have all gone in this direction. *Having driven the Speciale in bumpy pothole-riddled Toronto city streets, this package with its thin side wall heights*isn't as bad as you might think in the worst conditions*and is just brilliant on the racetrack.
-TOTAL TREAD SURFACE AREA (TTSA):
A tire's TTSA*is an important and often overlooked aspect that directly affects a tire’s performance. Bigger isn’t always better and there’s a point of diminishing returns (which probably won’t be an issue for most readers) where a larger and wider tire will not be any faster.* While a 245-width tire isn’t wide by today’s standards, Lotus Elise’s struggle to get heat into a 245 and tend to slip and slide on cold days due to their low weight and low center of gravity.* On the other hand, a heavy 3,800lb car on 275s can lay down a fast lap or two but cannot last a 20 minute session without overheating the tires and being seconds off pace.* All of this has to do with a tire’s TTSA, which is dictated by the tire’s overall diameter and width.
Remember that heavier cars need more TTSA/Volume from wider widths and increased diameters.
EXCEPTIONS:
There are always exceptions to every rule.* A car’s setup is like an inter-connected spider web where changing anything influences everything else.* Often one change will have a secondary effect that overshadows the primary change.
Because of this, it’s possible that running a tire a lot wider than the wheel width would improve the overall performance if it were on a heavy car, with a less than ideal alignment that is very heavy for the wheel width.* In this case, the increased VOLUME/TTSA of the tire, and tread width, would in fact improve the cornering ability of the car.
It’s important to understand the intended use of the car as well as the tire’s TTSA. You don’t want too much volume/TTSA (like the Elise example) if you are autocrossing, because you will never heat the tire up to its ideal operating range in time to make grip.* Likewise if you have a heavier car, increasing the volume/TTSA is key to making tire last longer in a session.
Tire compound and tread design also plays a big role here and while swapping to a more aggressive tire is the easiest way to make a car faster and last longer before overheating the tires; increasing the TTSA will make the tires last even longer, and even allow for a tire choice that is less of a compromise for daily driving.* Look at the following chart of various production cars and their weight-to-TTSA ratio:
Here we see various production cars and a few popular cars with commonly used track tire sizes sorted by Tire Loading (Total Tread Surface Area/vehicle weight)*from largest to smallest. Basically, how many square millimeters supports*each*pound of vehicle weight.
Here we see various production cars and a few popular cars with commonly used track tire sizes sorted by Tire Loading (Total Tread Surface Area/vehicle weight)*from largest to smallest. Basically, how many square millimeters supports*each*pound of vehicle weight.
This figure is calculated by adding the total front and rear Tread Surface Areas*(tire width x circumference) then dividing the Total Tread Surface Area (TTSA)*by the vehicle weight. The higher the mm per pound,*the more the load is distributed across the tires and the more resilient the tire will be to overheating.
STEP 3:* SELECT YOUR TIRE
“What tires fit your category and size?”
Now that you have determined what your tire is going to be used for and the respective tire category, and with the newfound knowledge of how to look at tires by their true size, it’s time to select a tire.* But with all of the different stats and criteria out there, what factors make a tire good?
Feel free to read the definitions below but I’ll save you some time with this sentence:
Due to the subjective or interpretive nature of these tests; other than speed ratings (which may not apply to most people) all of the other tire performance criteria is for the most part USELESS.
Load Index
-You can read Tire Rack’s Load Index Definition if you want, but it’s basically the load carrying capacity of the tire, which usually isn’t important unless you’re making hundreds of pounds of downforce, have a heavy car, and are driving on an oval.
Speed Ratings
-Click the link above for more detail, but I mainly focus on tires with W (168mph), “99Y” (186mph), and “(99Y)” (Parentheses = 186mph+) based on the application.* If you never go this fast (which you can’t do legally unless you’re on a racetrack, and even so, it’s rare to go this fast on track), then this probably does not matter.
Uniform Tire Quality Grade (UTQG)
-An arbitrary number originally developed to help consumers with a numerical value that represents the treadwear, traction, and temperature capabilities of the tire.* Since the Department Of Transportation (DOT) does not test the tires and it’s up to the tire manufacturer to come up with the value, tire manufacturers set these numbers based on how they perceive the customer will understand how the tire will perform, or to meet a random number/standard that a racing series might restrict, to have a softer faster tire as an advantage. Because of all of this, UTQG is USELESS.
Treadwear Ratings:
-A test based on a 7,200-mile test loop with routine tire pressure and rotation adjustments during it. A 100 rating should = the tread lasting the 7,200 miles, 200 rating = 2X that distance and so on.* Since a lot is left open for interpretation and the only decently comparable data is from one tire to another within the same brand, this is also somewhat useless.
Traction Grade:
-This is another useless test since it measures the deceleration g-forces of a locked tire across a WET road at 40mph. Other than seeing which tire will stop you the shortest distance with the tires locked; this is not relevant to cars with ABS or the braking ability of the tire under normal rack uses.
Temperature (Resistance) Grades:
-Indicates the amount of heat generated by what appears to be an under-inflated tire at 85mph.* Since this is also outside the scope of a properly maintained tire, I find it useless.
As tire technology gets better with each new design, often driven by what is learned in motorsports, tires are performing better in the dry and wet, are lasting longer, and are quieter than their predecessors.* Keep in mind those manufacturers who are winning in multi-tire racing series tend to offer the best products to their customers as well.
These advancements make it difficult to properly classify a tire or draw conclusions that tire A lasts longer than Tire B because it’s Treadwear Rating is higher, or it will have more grip and wear out quicker because its UTQG is lower. Remember, these numbers are useless?
So back to the decision of selecting the best tire; when looking at TireRack’s subcategories
(“Ultra High Performance”, “High Performance”, “Performance”…) I usually look in the highest category.* Price is usually a major factor in selecting a tire but since tires should be viewed as an INVESTMENT in terms of both performance and safety of your car, I rarely look below the second tier of subcategories.
When comparing tires within a category, the balancing of performance, comfort, and price begins.
TireRack’s rating table is going to be one of the best sources out there.* Using a scale of 1-10, each tire is rated in terms of dry grip, steering response, wet grip, hydroplane resistance, road noise, longevity, etc… *by consumer survey ratings which can be the average from hundreds of people.* Having tracked many tires, I personally feel these figures are fairly accurate when comparing across brands and have the most credibility, especially compared to the useless UTQG or Treadwear ratings of a tire. The individual customer reviews of the tire can also be somewhat insightful, but I tend to take them with a grain of salt and use them as a secondary factor to TireRack’s rating system.
The tread design is something to consider when looking for tires.* The design will usually reflect its performance in Tire Rack’s rating system, but in addition, looking at the outer shoulder, rain grooves and sipes will also give a vague idea of how they will perform.* For track use, large continuous outer tread blocks will deliver more grip and stability than smaller tread blocks which tend to tear off and chunk.* Larger tread blocks tend to be more prone to hydroplaning while tires with many, small tread blocks often perform better in rain and snow.
The tread design is something to consider when looking for tires.* The design will usually reflect its performance in Tire Rack’s rating system, but in addition, looking at the outer shoulder, rain grooves and sipes will also give a vague idea of how they will perform.* For track use, large continuous outer tread blocks will deliver more grip and stability than smaller tread blocks which tend to tear off and chunk.* Larger tread blocks tend to be more prone to hydroplaning while tires with many, small tread blocks often perform better in rain and snow.
As you start comparing different tires, it’s important to verify the TREAD WIDTH of each model, and if they run too narrow or wide, shop to see if a slightly different size would be more applicable.* If you are trying to break track records, further research would be beneficial but keep in mind that a review from a Lotus Elise owner on a set of tires probably won’t be as applicable on a heavy GTR or CTS-V, so try to find comments from someone with a car of similar weight and tire sizing.
I am not going to outright say buy this tire, or that tire sucks, but by now you have gained enough knowledge to make a more educated decision on your next set of tires with greater confidence that not only will the tires be more likely to fit, but will deliver the performance that you are looking for.
STEP 4:* CHOOSING A WHEEL
Wheels are an expensive investment that will affect the handling, performance, and yes, looks of your car; so it’s important to do your homework before dropping a lot of cash down.* This may sound backwards but since the tire is the most important part of your car, your wheel choice should be dictated by the tires you want to run.*
When I look to increase the diameter and width of a set of wheels on a car, I define the goal of the increase, whether it’s to increase tire width for cornering, or Total Tread Surface Area*(diameter and width) for prolonged track capability, or even simply for looks.* Based on the available room in the wheel well, I then look at the availability of the group of tires in the general size that I want to go to, which narrows down the ideal wheel size that I should run.
If you are limited by room in the wheel well or rules for a particular class, the tires should be your limiting and deciding factor.* Pick the best tire in the outer diameter and section width that will fit the room or rules, and then size the wheel accordingly.
This is the opposite from what almost everyone does.* Most people buy bigger wheels based on looks and offsets and then the tire tends to be a compromised afterthought to fit those wheels in the remaining room that’s available.* Since this article is about optimizing the performance of a car with tires, they should dictate what size wheel to run.* In many cases, the ideal tire may not be available in the size that properly fits your wheels.* If handling and performance is important to you, then your wheels will be sized accordingly.* If you view form > function, then this article probably isn’t for you anyway.
For a daily driver where maximizing outright grip or TTSA*may not be the top priority, choosing the widest tire possible may not be necessary at any expense of steering feel, fuel economy, and price.
* Remember the top tip?: *"A narrower high quality tire will often outperform a cheap wider tire".
A proper amount of time should be spent on researching or measuring the wheel offsets and clearances of your current wheels to determine how much larger and wider of a tire can fit.* Once the ideal tire is chosen, then you can select the diameter, width, and offset of your wheels. Staying the same or close to factory widths and offsets is a conservative way of making choosing a wheel much easier.
CONCLUSION
By now everyone should be an expert at*sizing and selecting*a tire, or at least possess*a greater education on how tires are sized and what aspects are important when choosing a tire.* By following the 3 main steps when looking for tires: *CHOOSE A TIRE CATEGORY, SIZE THE TIRE, and SELECT A TIRE, it’s hard to go wrong.
Disclaimer: The information above is a recommendation for OFF ROAD USE only. Please consult and follow your owner’s manual when sizing tires for street use, otherwise follow the above advice at your own risk.
SOURCES:
BillyJohnsonRacing
TireRack
If you enjoyed this*article and are interested in*improving*yourself as a driver, check out my articles:
DRIVER DEVELOPMENT: Car Control
DRIVER DEVELOPMENT: Learning Processes
