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How much does the weight of your wheel and tires play on braking and accelerating?

Joined
1 April 2002
Messages
756
Location
Alameda, CA, USA
I am just curious if anyone have any research on how much affect on handling, braking and accelerating is affected by the weight of different tire and wheel combinations. For my everyday wheelset, I am running Volk AV3 in 17x8 and 18x10 with S-02 tires 215/40/17 and 275/35/18. I know the weight of the rear wheel with tire is a porky 55 pounds. I forgot about the fronts but if you compared the size and weight of this wheelset to my stock 15x6.5 and 16x8 wheels, how much performance am I actually losing or gaining? Thanks for your comments.
 
Bob Butler's analysis shows that, with a weight reduction of 100 pounds, the 0-60 and 1/4 mile times of a stock '91 are each reduced by 0.16 second.

He has also shown that the effect on acceleration of each pound in wheels is 1.5 pounds of sprung (body) weight, and the effect of each pound in tires is 2.0 pounds of sprung weight.

The stock wheel/tire for a '91 NSX weighs 32 pounds front, and 44 pounds rear.

We can use these numbers to calculate the effect of various wheels and tires.

For example, let's say you have a wheel/tire combo that weighs 11 pounds more than stock in the rear, and 14 pounds more than stock in the front. That means that the wheels and tires weigh 50 pounds more than stock. Depending on how much of the weight increase is due to the tires and how much is due to the wheels, the effect of that 50 pounds on acceleration is the same as 75 to 100 pounds in body weight. Interpolating the acceleration numbers above, that would increase 0-60 and 1/4 mile times between 0.12 and 0.16 second.
 
Bob's numbers are always telling. I know when I upgraded my Lexus to 18x8.5 from 15x6.5, it felt as if I had lost first gear, and I was a little nervous the first time I stopped hard, as the 2 ton beast just did not want to slow down all that quickly. Now that I am use to it, it is not so bad, but braking is still noticeably different. But DAMN, she sure looks better!!

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Gary Yates
1995 Red/Tan
1992 White/Black
2002 Red and White Cooper S
 
Originally posted by nsxtasy:


and the effect of each pound in tires is 2.0 pounds of sprung weight.

B]


Do you think they sell light weight tires?
biggrin.gif
 
Weight is the enemy. But as Ken and Bob mentioned, unsprung weight (i.e. wheels and tires) is the supreme enemy.

A 50 lb reduction of unsprung weight is much more valuable than sprung weight reduction.

You also have the rotational mass of heavy tires and wheels do deal with.

-Jim

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1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html

[This message has been edited by Jimbo (edited 25 November 2002).]
 
This may seem like a dumb question, but what exactly is the advantage of larger wheels then? I understand that most people think gigantic wheels look better, and I suppose there's a bit of a handling improvement, but is it really worth the added weight?
 
Besides apearence a plus 1 or 2 wheel size increase requires that the tire aspect ratio change to allow similar rolling diameter.In simple terms the tire sidewall decreases in height-ie lower profile.To a point this lower profile will reduce the effects of side wall flex;the tire is more responsive to stearing input and squirms less under hard cornering.Some tires like bridgstone also have stiff sidewalls.Of course you hope your car has the performance susp to utilize lower profile tires.The downside on a street car is a harsher ride over rough pavement.
 
That's right Doc...and in many cases there's no advantage in going to larger wheels. In many cases, it's a disadvantage.

Most of the people desirous of large wheels do so because of cosmetic reasons and not performance.

-Jim

------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html
 
Originally posted by docjohn:
decreases in height-ie lower profile.To a point this lower profile will reduce the effects of side wall flex;the tire is more responsive to stearing input and squirms less under hard cornering.Some tires like bridgstone also have stiff sidewalls.Of course you hope your car has the performance susp to utilize lower profile tires.The downside on a street car is a harsher ride over rough pavement.

Another downside to low profile tires is the lack of warning. Since the sidewalls are much stiffer, there is little give before breaking loose.
 
One more downside is that, with the shorter sidewall, it's a lot easier to damage a wheel when you hit potholes and ruts in the road.
 
Originally posted by Smoothaccel:
Do you think they sell light weight tires?
biggrin.gif

Actually, one of the selling points of the Hoosiers is their very light weight, as they are only fiberglass belts, instead of steel, and the thinner tread (or actually slick) thickness. Also, many people have run Toyos and Pirellis because of their supposed lighter carcass weight.

------------------
Gary Yates
1995 Red/Tan
1992 White/Black
2002 Red and White Cooper S
 
Wider wheels/tires also improve braking distance via two factor: wider surface area while braking and a better colling effect (having bigger surface area, it can more efficently dissipate the heat energy than a narrower tire),
 
Originally posted by ncdogdoc:
I know when I upgraded my Lexus to 18x8.5 from 15x6.5, it felt as if I had lost first gear, and I was a little nervous the first time I stopped hard, as the 2 ton beast just did not want to slow down all that quickly.

Gary,

Yes, the weight disadvantage is magnified further during braking. I have not done the calculations for braking, but because the vehicle can decelerate faster than it can accelerate, the 1.5-2.0 weight factor would be larger during braking. The 1.5-2.0 numbers Ken quoted from me above were calculated for an NSX accelerating.

I thought the NSXPO time trial results were interesting with the stock 15-16" (boat anchor) folks doing very well with sticky rubber.

Bob
 
Originally posted by gheba_nsx:
Wider wheels/tires also improve braking distance via two factor: wider surface area while braking and a better colling effect (having bigger surface area, it can more efficently dissipate the heat energy than a narrower tire),

Wider wheels and tires do NOT have a bigger contact patch (surface area in contact with the road). The size of the contact patch is a function of the weight of the car and the pressure in the tires. The size of the four contact patches for a 3000 pound car with 30 psi in the tires will be 100 square inches regardless of whether it's sitting on tires that are 345 mm wide or 185 mm wide. The size of the contact patch will be the same, although the shape will be different. This is illustrated on the Tire Rack website.

Bob has already addressed the question of why wider and heavier wheels and tires may actually be worse for braking.
 
Originally posted by nsxtasy:
Wider wheels and tires do NOT have a bigger contact patch (surface area in contact with the road).

I don't think gheba_nsx said the wider tires had a larger contact patch, he said they have a wider contact patch (i.e. different shape), and that the tire as a whole has more surface area.

[This message has been edited by Lud (edited 26 November 2002).]
 
Originally posted by 1BADNSX:
I thought the NSXPO time trial results were interesting with the stock 15-16" (boat anchor) folks doing very well with sticky rubber.

Not that the time trial very terribly scientific, and not to take anything away from anyone's times, but since you brought it up... All the guys on stock wheels in the top half of the time trial results were locals with considerable prior experience at that track. All the first-timers at MSR who were in the top half of the time trial results were on larger aftermarket wheels.
wink.gif
 
Lud, exactely my point. The wider contact offer more friction between the tire and the ground. The other benefit of cooling down faster is also to be taken in consideration: a cool tire brakes about 15-20% better than a hot one.
 
I spoke to a Formula Ford guy about the wide tire relation to the contact patch. . .ah, nevermind. Anyway, I think putting a light weight 15" and 16" wheel and tire package on '91-93 would make for a very well performing track car. Say a Volk TE-37 with some Hoho's (that's Hoosiers in local track talk).

I will say this though about wider tires. . .they will provide improved cornering speeds compared with a thinner tire. That I think we can agree on.

[This message has been edited by Ponyboy (edited 26 November 2002).]
 
Originally posted by gheba_nsx:
...The other benefit of cooling down faster is also to be taken in consideration: a cool tire brakes about 15-20% better than a hot one.

Gotta disagree with you there. Sticky tires don't stop or turn until they get hot. Sure, they can get too hot and semi-liquefy but that's rare on anything but qualifiers and cooling differences due to contact patch shape seems a most unlikely factor at any rate.
 
IMO, I think us weekend warriors shouldn't worry much about the weight of the wheels and tires so much. It's quite insignificant unless your wheels alone are like 40lbs each or something.

For me, these are the rules I go by:

1. Learn to drive the car at the limit in stock form.
2. Beef up the suspension and use sticky tyres. Learn how to drive the car with the new mods.
3. Change to a well balanced big brake kit (front and rear). Again, learn to drive the car with the mods.
4. Lastly, explore options for hp gain.

YMMV

The Don
 
Originally posted by nsxtasy:
Wider wheels and tires do NOT have a bigger contact patch (surface area in contact with the road). The size of the contact patch is a function of the weight of the car and the pressure in the tires. The size of the four contact patches for a 3000 pound car with 30 psi in the tires will be 100 square inches regardless of whether it's sitting on tires that are 345 mm wide or 185 mm wide. The size of the contact patch will be the same, although the shape will be different. B]


I hate to argue with Ken (usually a losing proposition).
wink.gif
But I believe the mistake being made here is that we are looking at contact patches when the car is static. Under dynamic loading (on the track)the contact patch of the tires can vary quite a bit as loads are transferred to and from specific tires. Why else would our favorite driver (P.D. Cunningham) use such wide tires on his race car? After all, it's much lighter than our street cars. I believe the answer is that under dynamic loads wider tires indeed give more friction and a larger contact patch.

S.L.
 
Originally posted by gheba_nsx:
sjs,

here are some lecture about wide tires and improved braking:
http://www.vdat.de/prg17e.htm
http://www.datsuns.com/Tech/tech_tires-2.htm


Well, the first is a nice article about a scientific experiment which for the most part merely proves what we’ve already know for many years, but I didn’t notice any reference to the better cooling qualities of wider tires. In other words a good article but I don’t see anything to support your assertion.

The second is not so much an article as an individual doing his best to explain a few things about braking, and as it says at the end “*While Mark is no tire company engineer, he is a degreed and licensed mechanical engineer, so is probably as qualified as anyone to answer the posed question.“ I’d disagree that a mechanical engineer is inherently qualified on this subject. As even he states, things are more complex than they seem, so applied knowledge from other areas has limitations. But yes, as I said in my prior post there are extreme cases where the rubber gets too hot but beyond that I think his reasoning is flawed if he attributes the braking benefits of wider tires to better “cooling” due to their greater surface area. For example, he seems to completely ignore the added mass and therefore heat absorption capacity of the larger tire. Seems a pretty big omission for an engineer.
smile.gif
I put the word “cooling” in quotes earlier because someone might argue that I’m splitting hairs here since it sounds like I’m saying that the heat is spread out over a greater area and therefore lower at any given point. But there is a big difference between the ability to absorb heat and the tendency to shed it.

So to summarize, wider tires certainly will cool faster than narrow ones, no argument there. The question is whether over heated tires play a significant role in braking limitations, and then whether the added cooling provided by the increased surface area of wider tires can make a significant difference in that situation. I’m not even an engineer, but I’d guess that the answer to the first is “rarely”, and to the second “probably not”.
 
Originally posted by V12NSX:
I hate to argue with Ken (usually a losing proposition).
wink.gif
But I believe the mistake being made here is that we are looking at contact patches when the car is static. Under dynamic loading (on the track)the contact patch of the tires can vary quite a bit as loads are transferred to and from specific tires. Why else would our favorite driver (P.D. Cunningham) use such wide tires on his race car? After all, it's much lighter than our street cars. I believe the answer is that under dynamic loads wider tires indeed give more friction and a larger contact patch.

Sorry, but that's not right.

What happens in dynamic situations is that the weight is shifting - from front to rear during acceleration, from side to side during cornering - but that only increases the size of the contact patch at one end/side of the car while decreasing it at the other end/side, with the total area remaining constant. Somewhat similarly, the car can, in dynamic situations, get "heavier" or "lighter" (vertical g forces more or less than the normal 1.0 of gravity) which does indeed change the total size of the contact patch - however, those forces operating on the car will be the same regardless of whether the tires are wide or narrow, so the total contact patch size will be the same.

The reason race cars use wider tires is because the shape of the contact patch changes - wider from side to side while narrower from front to back - even though the size remains the same.

I have discussed this with John Rastetter, the leading technical tire expect at the Tire Rack, and he noted that it was indeed true that the size of the contact patch is the same. In fact, they have actually measured the size of the contact patch for wide tires and narrow tires on the same car, and found that the size was exactly the same, within the accuracy of their measurements (around 1-2 percent).
 
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