Should I Be Using Competition Tires?
[BSD] I'll give you four examples of people I know. Maybe you can relate. I'll start with me, my buddy Steve and my buddy Richard. Steve, Richard and I (us/we) are all professionals with colage degrees (:-) who got into doing driving schools all about the same time. We all had lowly Mustangs that were stock or near stock. Richard was on a pretty tight budget and I chose not to spend much money on my car. I just wanted to drive as opposed to build. I actually drove on stock tires for the first 1.5 years. I probably did 10 events on stock tires. Fortunately, Mustangs can swap tires from front to back or side to side (depending on tire) and I was able to make them last pretty well. I would keep rotating my best tire to the right front and my worst to the left rear.
My buddy Steve is just frugal. He won't spend money unless he has to. He had a 1986 Mustang (two tone: grey on grey) and it was a rev back as far as engine management goes (it was CFI as opposed to MAF - which is sequential fuel injection.) Richard did a bunch of autocrosses and driving schools, but really only afforded race tires. The day I got my race tires for the first time I dropped my lap times 3 seconds per lap. Richard, Steve and I all did about the same lap times, give or take a second or parts of one (with equal stock cars and race tires).
In our big group of Mustang owners and drivers, there isn't one other of them who can turn the same lap times we did with stock engines and suspensions and they have major engine upgrades, very modified suspensions, etc. Driving skill from bad to good can make up 5 or 10 seconds a lap (ok, from very bad to very good). Engine and suspension mods make up much less than that.
My final example is a guy who bought a Porsche TT who was a student of mine. He had huge wheels fitted under there with slicks on it. He also had the suspension lowered and stiffened up by a serious Porsche shop. When he took me out on the course, it was as if he had never even been told to try and maintain momentum in turns. Further, he would leap off the gas right in the middle of a turn and I thought for sure we were going around. Fortunately, his car was better than the mistakes he made and we lived. Although he did tire squealing turns and passed almost everyone, his driving was terrible.
Driving is more of an art form or like playing a musical instrument than it is buying the best equipment. Ever heard a Pianist say, you know, I'd be much better if I had a <insert top of line piano here>? It doesn't work that way.
Moral of the (long) story: In my opinion, you will learn more about driving if you leave the car alone. You will probably become a better driver if you drive the same car (unmodified) event after event.
One last note. The NSX is easy to go fast in. However, it is hard to go very fast in. Keep it stock until you can go very fast.
[KS] My first suggestion would be not to use track tires for your first few (three to five) track events. Why?
- Without any track experience, you won't be using ANY tires to their performance limits.
- You'll be spending your time getting a feel for driving your car on the track, learning the track, learning the rules (for passing and so forth) under which the event is conducted, etc. So the fewer new and different things you throw into the mix, the easier time you'll have.
- Starting out with your car in a stock configuration will give you a baseline so that once you get some track experience, you will be better able to judge the impact that any particular upgrade you make will have on your performance.
- Any of the Z-rated street tires you mentioned (including the Yoko A-022H, the Dunlop SP9000, etc) will give you very good performance on the track. Yes, track tires will give you ultimately quicker lap times, but these street tires are all good enough to perform well on the track. In fact, many experienced track drivers still use street tires. (Including me, in my case the A-022H.)
- Using street tires will be less expensive, because they wear so much less. You won't go through a set of street tires in a track weekend. In most track events, you'll drive maybe 150 miles on the track over the course of the weekend. Even though this might be the equivalent in tire wear of perhaps four times that mileage on the street,
it's still only a relatively small portion of the life of the tire, whereas track tires will wear much more quickly
What Are People's Experience With Various Track Tires?
[DH] I get one event out of a set of R1 rear tires. This is defined as:
- 60-90 Minutes of track time on Saturday, same on Sunday
- Really pushing the car very, very hard
- Toe/camber settings set to 1992 stock settings
- Tires have less than 25% of tread left after the event.(very often the tires are worn down to a complete slick)
- I also drive up to the event on the R1 tires, and back.(usually 180+ miles round trip).
I also have a friend who has a set of R1 last what seems like forever. He only uses them at the track, but it seemed like he got 7+ events out of them. Wayne's R1s on his 944 turbo also last a long time, so I guess it is the camber/toe settings that thrash the tires.
[99/1/18] BFG R1 - very good tire in the dry. Not a lot of warning. Used to be my tire of choice, as well as tire of choice of about 6 other people that I go to the track with.
[HS] The "groove of doom" on the BFG R1 tires is well described. The construction of the tire includes a "hinge". Incorrect inflation causes the tread to bend and groove at the hinge point.
And BFG recommends tire pressures be set cold and not adjusted after they get hot! This was really news to a lot of people. It is still possible to adjust pressure up and down, but it needs to be done relatively. Start at 30 cold, goes to 34 hot. An adjustmet to 32 is really a setting of 28.
[BSD] A base point is 28 front, 30 rear. I use the stock size R1s on 15/16s and that is what I use. I have also found that for this size R1, there is not a big difference in grip from say 24 - 30 front and 26 to 34 rear. The pressures I give are cold.
[BH] Compromises, compromises...I use 275/40-17 R1s (3.6% larger diameter than stock) for rear track tires and 225/50-16s up front. The car will not win any drag races with those rear tires. Acceleration is easily slower than stock, but *lap times* are quicker than with the narrower tires because the extra grip of the larger tires allows me to carry more speed *throughout* the track. Would I love a 275/35-17 R1, you bet, but they don't make one.
[BMC] I ended up going with Hoosier R3S02's, but I'm running 17" Forgelines all around. So I went with 245-40-17 up front and 275-40-17 in the rear.
The fronts rub on the inside of the fender wells, even after pounding on them with various sized sledge hammers. But this only happens when you get close to full lock. Dave Davis claims to have solved this by changing his caster, but I think that's not the way to go. Anyway, if your racing with these, who cares if they rub? You never (or rarely) actually get to full lock in a race situation anyway.
The same theory applies to the fact that your TCS will not work with this setup -- who cares? It should be off anyway. I don't know if the 335's will fit in the rear fender wells, but there's a lot of room back there, so I would think so. I went with the 275's because I didn't want to overpower the fronts with 335's, causing the handling to tend more toward understeer.
[DS] I'm using the stock 91-93 rims. Two reasons. I Autocross in a "stock" class and therefore am required to use stock size rims. I want keep the gearing as low as possible. I do also use this car at the track and have no complaints with this set up.
I use BFG R1's in a 225/50ZR15 in front, and a 245/45ZR16 in rear. The only problem is that the TCS, HAS to be turned off. This size combination means you can't go anywhere period. The TCS cuts the engine so you can't pull away from a stop (well hardly). This of course is no problem on the track/AX course (where I want it off), but for close events I drive there on my R1's.
Handling has been great, apart from a little turn in understeer (due to an alignment problem) and a little oversteer (due to a right foot).
[EBK] Excellent dry track tire, worthless in the rain, tread life is nil (have gone through a complete set on a 3-day event)
[CMI - 99/4/15] I was running R1's on stock 15/16'" wheels before and thought they were very good...but they don't hold a candle to the Hoosier tires. In case any missed my earlier post, I had to go with a 205/45 16 front size as they don't come in the stock 215/45 16 stock size but I did use the stock 245/40 17 rear stock size.
[BJ]In the Ford Racing Mustang Challenge race series (3,400lb cars) we ran 38-42psi hot pressures. In the FXMD Time Attack NSX (265/330) we ran slightly less at about 36-38psi hot. I wouldn't classify this as a 'true slick' and would run hot pressures similar to street/R-compound tires rather than the lower pressures used in real racing slicks. I think the combination of a narrow stock tire 205/225 and the excessive rear toe-in was a big factor in DH's poor tire wear. The R1 has more grip than most R-compound tires, gives little audible sound or warning in its 'feel', and has a more abrupt break-away than other R-compound tires. The first 3 laps are the tire's sweet spot then level off in performance and last for a 60lap+ race and even other test days without falling off too much. Too low of pressure especially on a heavy car can cause the tire to crack and break at the sidewall. I would not suggest running these tires on the street or in the wet, and I would ALWAYS check tire pressures when hot. <p> <p> Hoosier S02
[EBK] The best dry track tire, dangerous in the rain (don't go out unless you've checked the validation of your car's insurance), Tread life is even worst than the R1's if that's possible.
[WSC] Well folks, just got back from a Trackspeed driving school/racer's challenge cup at Sebring's Long Course. The combination of my new Hoosier slicks and my current suspension, brake combo package is AWESOME (at least that's what NSX club member TJWright said). In a nutshell:
Hoosier 245/45/17F, 275/35/18R on Forgeline wheels......$2600
Brembo 4 piston calipers, 13.5" cross-drilled rotors.......$8000
Eibach springs, Koni adjustable shocks, Dali anti-roll bars......$4000
Passing FIVE cars on the back straight AND a C5 coming out of turn 17 onto the front straight with a passenger witness......PRICELESS.
I had no problems with the front tire/wheel combo after making modifications to the fender liner. Tire temperature across rear tread suggests that 2 degrees negative camber probably too much. In my estimation, these tires worth 2-3 sec./lap, maybe more on the 3.8 mile 17 turn course.
[DH - 99/1/18] Everyone I know who used to use R1 has switched to Hoosier. Great tire, tire life is less than the R1. So you probably have to trailer the rims/tires to the track.
[DH - 99/2/16] I run the 17/18 inch Hoosiers. Depending on temp of track and air temp, I run around 28/30 cold when the air temp is hot(80+ degrees). At Laguna last week, air temp was 50-60, I ran around 31/34. I use the infrared gun and try to make sure the middle of the tire isn't overly hot compared to the outsides, or overly cold compared to the outsides. I also beat the shit of the tires in sweeper turns, which also heats them up more than if you are driving more sanely. Not sure if this is the correct temps, but it works for me.
Hoosier Tire Break-in Procedure
Proper break-in will not affect initial performance but will increase the competitive life of the tire. The procedure can be broken down into phases.
1st phase: The initial run
2nd phase: The length of the time the tire is allowed to "cure"
The initial run
The first laps for the tire are critical for setting up the durability and competitive life. The first session should consist of 10-15 minutes of running. The early part of the session should be run at an easy pace, with the speed gradually increased until the end of the session. The final lap should be run at the fastest possible speed. The intent is to achieve maximum tire temp on the last lap. At this point the car should be brought in and the tires allowed to cool at a normal rate. Optimally, the tires should be removed or have the car jacked up during this cooling.
During this process, the inflation pressure should be 3-5 psi higher than you would normally use. The best progression would have the driver taking 4-7 laps to accomplish this break-in. Each lap should be approximately 7-10 seconds a lap faster than the previous lap. The goal is to have the tire temp as high as possible on the last lap without "shocking" the tire during the warm up laps. In essence, no wheelspin, late braking, or sliding. The last lap should be at, or very close, the maximum possible.
After completing the above, the length of time the tire is allowed to set is possibly more important. The barest minimum for this process to be beneficial is 24 hours. (Not "the next day"). Any less than this is a waste of time. The best situation would allow a week before using the tire again.
Proper tire management is a difficult process. To accomplish this almost always requires a second set of wheels. The payoff is greatly increased competitive tire life.
Tire Pressure recommendations
Hoosier Tire typically require higher pressures than other brands. Reference the following chart for suggested pressures:
|Vehicle Weight||Recommended Pressure|
|1800-2200 lbs||39-42 psi||31-36 psi|
|2200-2600 lbs||40-43 psi||32-37 psi|
|2600-3000 lbs||42-46 psi||32-37 psi|
|Over 3000 lbs||43-48 psi||32-38 psi|
+ Higher pressures will improve the performance capability but will require a more sensitive feel to take advantage of the increase.
One characteristic of the tires is the tendency to "skate" initially (when inflation pressures are correct). It is important to resist lowering the pressure to attempt to eliminate this feeling. Dropping the pressure may improve the "feel" of the tire
however it will also lower the performance and increase the wear on the tire.
Tire temperature recommendations
For best performance the expected temperature range will vary from track to track. Generally, optimum traction will be generated when the pit lane temps show 180-200 degrees. Check with the tire technicians at the event for the recommendations for that particular track and car combination. Take advantage of the temperature checking station that will be set up during the practice session. Use of Hoosier technicians measurements eliminates variables in instruments and procedure which can influence the data.
Chassis setup recommendations
For optimum performance the tires will require around 3 degrees of camber. There will be a trade off im maximum performance to maximize wear. Generally 1/2 degrees less than optimum will result in the best compromise for wear and speed. Less than 2.5 degrees can result in excessive wear on the shoulder junction.
The tires should offer better performance with spring/shock rates higher than previous brands you may have run.
Things to consider
These tires are molded to their designed tread depth. They do not require shaving to be prepared for competition use. Shave the tire further will not improve performance. It is not recommended that they be altered in this manner.
Due to extremely light construction, the Hoosier tires have a much lower polar moment than other radial tires. This translates to a very low rotational mass, which is a good thing for performance applications. The down side to this feature is that the tires don't resist "spikes" in braking force as well as a heavier tire might. As a result, there is a tendency for drivers to "flatspot" a tire the first time really getting to the limit. Vehicles equipped with ABS will benefit from its use. If you do not use ABS it is recommended that you make an effort to minimize stabbing the brakes until you have some experience with the feel of the tire under hard braking.
The light construction also provides less protection from impact damage and punctures. Off course excursions or running over debris on the track will likely result in tire damage.
Tire tires are not directional, however the tread is asymmetrical in design. A new tire should be mounted with the two grooves on the inboard side. Once some wear has occurred it may be desirable to flip the tire on the wheel in order to even out the wear and maximize tire life.
Following the recommended break-in procedure will require a lot of planning to make it work. The benefits to doing it right include greatly increased tire life as well as more consistent performance and durability under stress. Please make an effort to educate your team on the importance of this. It can save you a lot of money.
The Hoosier D.O.T. Radial tires are extremely good in dry conditions, however they don't make very good wet weather tires. Having dedicated rain tires available will be necessary for your team to be properly prepared. Hoosier makes a D.O.T. approved bias-ply tire called a "Dirt Stocker" that has been proven to be far superior to any competitors tire as long as it is a steady "wet" condition. Check with your Hoosier representative for size availability.
R3S03 Racing Radial
Hoosier R3S03 is a DOT approved Road Racing Radial with sizes that will fit the OEM 16"/17" NSX wheels (a 205/45/16 for up front and a 245/40/17 rear).
[AT] These tires used to be the hot setup for most autocrossers in my area (Sacramento) because they were stickier than the BFG's and would last longer on most cars. They also didn't have to be shaved before being used to have them last longer. It seems that this year the hot setup are the Kuhmo's. Soon the BF-Goodrich will be coming out with a newer version of their R1's and they should be competitive as ever. Either way they all stick real well, however you haven't lived till you've driven on racing slicks. Talk about stick. You won't believe how much deeper and faster you can go into
corners and come out of them with racing slicks. Man those were the fun days. Good luck.
Hoosier vs. BFG-R1
[BH] I have just worn out my first set of Hoosier road race tires, and here are my impressions:
- I have used R1s on various cars including the NSX for four years, and I like the R1s a lot. And, in my opinion, to a large extent, tires are a personal thing. I have 225/50-16 front and 275/40-17 rear R1s and 245/45-16 / 275/40-17 Hoosiers. The Hoosiers are shorter but fatter than the R1s hence I could get 245/45-16s up front.
- My conclusion - don't buy the Hoosiers *unless* you want to pay more than R1s to go slightly ( 1-2 seconds out of a 1:40 lap time) faster than R1s, you want to be able to slide the car more, you live very close to the track, and you don't mind the fact that Hoosiers seem to wear at least twice as fast as R1s. Read on if you want more details.
- The Hoosiers are so sticky, they were picking up dead insects off my garage floor *before* I even mounted them on the car. I mean they are sticky when they are stone cold. The tread wear indicator on the sidewall states "0".
- They ran best at much higher pressures than the R1s. I generally use 30/33 lbs w/R1s. I ended up w/ 34/38 lbs w/ the Hoosiers. It took a little getting-used-to not having those stiff R1 sidewalls to lean on. I use 1 and 2 negative degrees of camber on the front and rear, respectively. I have Comptech's pro suspension package.
- In a half hour run session my best lap times were right after I heated up the tires, but then I had to be sure to cool them off because when they overheated, I ran *slower* lap times than I do on over heated R1s. Cooling off tires is easier said than done for me. I usually ended up sliding around even more. As you can probably guess, my lap times on the Hoosiers varied much more than I experience on the R1s.
- The Hoosiers have no tread after four 2.52 mile laps so forget it if there is any rain. My experience as well as most people I know are comfortable negotiating light/moderate rain on R1s with some tread left.
- You should really trailer your car to the track on the Hoosiers as fast as they wear. The R1s can stand drives to the track much, much better.
- I think the Hoosiers are more fun because you have to think about them more than the R1s. And they are easier to slide than R1s when they're hot. Of course that doesn't help you cool them off.
- The Hoosiers did not give me much of a warning before they broke loose, but that was fun too. It was much easier to correct and then initiate slides once they're heated up vs the R1s.
- You get what you pay for, but since I usually drive to the track, I will need to stay on the R1s. Maybe next year I will get a third set of wheels and mount Hoosiers on them after I get the short gears, R&P, headers...yea, right.
- I used to get a whole year ( about 12-15 track days ) out of a set of unshaved R1s on my, dare I say it, HKS Supra T. On the NSX, I got about ten 90 minute sessions out of unshaved R1 275/40-17 rears, and the 225/50-16 fronts still have about four sessions left.
- The rear Hoosiers lasted five 90 sessions and the fronts have maybe two sessions left. However the Hoosier people told me exactly what to expect- faster times and faster wear than R1s. Plus, I thought the Hoosiers were more fun than the R1s. I would use them *if* I trailered my car to the track. I also think my 90 mile r/t drive to/from the track took its toll on the Hoosiers much more so than the R1s. Street driving just wastes the soft Hoosier tread.
- I could see there was less tread on the Hoosier just by looking at them. The Hoosier is also lighter ( about 8 lbs per 275/40-17 ) than the R1 as you'd expect with less tread and narrower sidewalls.
- I spoke to Bruce at Hoosier (219-784-3152). I told him I really enjoyed the Hoosiers, and he agreed that my pressures and driving impressions were accurate. He said the only problem some NSX guy had was a result of running too low pressures. He also mentioned that heat cycling helps extend the tread life. For about $15/tire Tire Rack has some machine that heat cycles tires w/o scuffing them. Hoosier tested the Tire Rack heat cycled tires and found them to last about 20% longer. Otherwise you need to scuff them at the track which take two sets of wheels.
Once again, if I needed quick lap times I would use Hoosiers and trailer the car. Otherwise I would use Rs. Maybe at the next NSXPO we can work on a demo of different race tires. How many of us have two sets of wheels?
Toyo Proxies RA1
[EBK] I've preached about them before in the past but they are the best all around tire you can get. Very good dry track tire, very good rain tire, tread life is the best I've seen out of all race compounds (most tread depth in the rain groove 8/32). I drove to NSXPO '98 and back to Montreal (over 1,400 miles), did the 2 day track event at Mid-Ohio, and 2 more 3 day track events back home before my tires were gone. This is the reason I place the Toyo's in first above the 032Rs.
[EBK] Very good dry track tire, worthless in the rain, no tread life. This is the first race compound I ever used and found out the world of difference between street vs. tack tires (P.S. I believe those tires have been discontinued for a while now. There may be some still laying around but before buying, check the date to make sure they are not too old (an old tire can be dried out)
Also FWIW, out of five good drivers of various cars at various tracks, no one is re-ordering the Yok 032s. No one I met seems to like them. Everyone claims they are slower than R1s, although they wear longer. I know this contradicts what the NSXPO crowd thought so don't shoot the messenger. I am just reporting what five people think.
[BC] I've had the new Yokohama A032R "road racing" tires on my old '91 wheels for a few days of thrashing, here are my observations:
- They make a bit of high pitched noise, but it is barely audible above my supertrapp muffler, like everything else.
- They have great directional stability on the back roads and highways, which was a big surprise given the tread design, only tugging at the steering in places where my SP8000s would go wonky anyway.
- I'm glad I got 245/45s for the rear instead of 225/50s. The A032Rs flat sidewalls and sharp edges make for a clean fit on the narrow 8 inch wheels, yet the contact patch from the rear looks almost like a 255mm.
- They are super sticky, with that new sneaker feeling. When they are hot they are actually sticky to the touch. Pity those following behind you too closely, they'll get a storm of road debris thrown at them.
- Cornering is tenacious, definitely at a higher level than my wider SP8000s on the forgeline rims (a 5-10 mph advantage). However they seem a touch less stable during sharp maneuvers which I attribute to two factors: 1) my forgeline rims have 20mm wider tires all around and are offset to give a 30mm wider rear track on top of that. 2) the shorter sidewalls on the 17in dunlops are a bit stiffer than the 16in Yokos. But have no doubt that with these tires you will completely annihilate anyone "impudently" trying to follow you around a highway ramp.
- I set the rear tire pressure to 35psi initially, after 30 minutes of driving it went up to 43psi (44psi is the max rated), and the tire retained its heat for quite a while. Something to consider if you want to travel long distances with this tire.
- My overall impression is that the A032R is a great tire upgrade for occasional fair weather aggressive driving on the street if you still have the 91 style rims. And when mail ordered they are so cheap that it hardly matters that they will only last a few thousand miles.
- These tires might enable my car to significantly exceed 1g in a turn if I could get them in 16 and 17 inch sizes for my Forgelines. Maybe next year...
[EBK] Very good dry track tire, very good rain tire, tread life has improved drastically over the RSII's. This tire comes in 2nd place for me after the Toyo's.
What Tire Pressure Is Best For The Track?
[BSD] What is the goals of track use? Maximum grip is normally the goal for your tires at the track. Secondarily,
is maximum tread life.
Race tires (tires meant for track only use... usually with a tread wear rating of 60 or less) can attain excellent grip on the track. The design of these tires can vary a lot. An example race tire is the (infamous) Yokohama A008RS. These tires have a low tread wear rating but have excellent grip. The excellent grip they get causes the car's weight to transfer to the outside shoulder of the outer side tires. This extra weight can cause the tire to "roll over" or ride just on the shoulder. To compensate for this, higher than "normal" tire pressure is used. Cold pressures in the mid to upper 30's PSI is common.
Another common race tire is the BFG R1. This tire has a unique design with the outer sidewall extra stiff compared with other race tires. In fact, the outer sidewall is stiffer than the inner side wall. Because of this, the tire stays very square on the road, even when cornering. Because of this, super high tire pressuers are not required. Tire pressures in the upper 20's or lower 30's is common.
The real way to get the tire pressure on the track right is to use a pyrometer. This device can measure the tire temperatures in the inner edge, middle and outer edge (3 spots). If the middle temperature is higher than the others, then lowering the pressure is in order. If the middle temp is too low, then raising the pressure is in order.
In general, and not counting the BFG R1 race tire, higher pressure on the track compared to the street is normal. You get more grip but a harsher ride and less tire life.
[BH] In Carroll Smith's book, 'Drive to Win', he states that taking pyrometer readings across a *radial* tire is useless because of the radial construction. In addition, suspension and alignment settings, driving style, tire construction, and track temperature also influence tire temps. So what can we do to be sure we are maximizing our contact patches if we don't have an engineering degree?
Smith recommends watching tire wear to adjust tire pressures. The idea is that you don't want the tire to roll under in cornering (too low pressure), nor do you want to create a small contact patch in the middle of the tire (too much pressure).
I can add that Goodrich and Hoosier are more concerned with the tire pressures *after* a track session. Basically both tires are designed to work best in the 44 lb area. However, they did not want large ( more than 8 lb) pressure increases on the track vs cold. An under inflated tire will generate a lot of heat resulting in high pressures but poor performance. ( I do not know what the Yok people would like to see in the oem tires. )
Personally, at a track with high speed corners and straights like Road Atlanta, I find the oem 022 Yoks run/wear best with 30-32 lbs front and 34-36 lbs rear pressures. ( I run 32-34 front/35-37 rear with R1s, which is much higher than what others run, but that's what works for me). At Watkins Glen, I had to use slightly higher front pressures to reduce some understeer I was experiencing with the oem Yoks. Also, I have the stiff Comptech suspension, which seems to work best with slightly higher pressures than did the stock suspension. (I am also carrying more speed than I used to with the stock suspension so that probably has something to do with it.)
So, watch the lap times and look for even wear across the tire. Try to feel the how the car turns in and exits corners. If the front end is understeering and/or you are seeing wear beyond the outside of the tire's usable tread, add a couple lbs of pressure to the front tires. If the rear end is coming around to much, add some pressure to the rears. In general, I like to adjust the end of the car that I am not happy with, at the time.
When you arrive at the track, I believe you should start with higher pressures than you think you need and lower them accordingly. Pressures that are too low will chunk the Yoks - I know this from experience. Applying a little white shoe polish on the tire's top outside edge will help you see the wear better if you are having problems seeing the fresh wear on the track. It's tough to get an R1 to roll under, but there is always the 'groove of doom' as a result of under inflation. Hoosiers just plain overheat and start sliding if the presures are too low, and lap times start suffering immediately.
You can drive yourself nuts on this tire presure thing. The NSX is more sensitive to tire pressure changes than any other car I have owned. Two lbs makes a difference, but there is only so much you can accomplish with pressure changes. However, even if you are on the track, you can still get even tread wear and maximize the tire's life and contact patch.
[AWN] Here's something I wrote on the Porsche mailing list a few months ago when someone asked about optimum street pressures for Yokohama AVS Intermediates; maybe it'll help:
Inflation settings for the street is an interesting topic... MORE interesting, I think, than inflation settings for the track.
If you're racing, it's all pretty simple (in theory, at least)... You can find the right inflation pressures one of three ways:
- 1. Test a bunch of tire compounds until you find one that, on your particular car and on that particular day at that particular track, gets to its optimum temperature when inflated to somewhere around the middle of its recommended pressure range... Then fine-tune the pressures until you get the exact temperature profiles across the tire that you want.
- If you're running race radials and (as is currently fashionable) you don't believe that tire temperatures are meaningful, use whatever trendy method was recommended in the latest issue of Grassroots Motorsports.
- Take a walk over to the Goodyear truck and just ask them.
For street driving, on the other hand, you can't do any of that... And you probably don't even WANT to, since the sole criterion for track driving -- maximum lateral grip when hot -- is WAY down the list of important criteria for street driving... You're probably much more concerned with tread wear, tire noise, and precise "feel".
Don't tell me, by the way, that you don't care about tread life... My other (non-Porsche) car goes through a set of its OEM rear tires about every 5,000 miles, and even _I_ think that changing tires that often is a pain in the ass.
Anyway... The process I'd use to determine the "best" inflation pressures for non-OEM street tires would probably be something like this:
- Start with the factory-recommended cold pressures front and rear (and start EARLY... This will take most of a day).
- Drive ten miles or so, listening to the noise from the tires.
- Drive your favorite twisty stretch of road, paying attention to:
* How sharply the car turns in.
* How quickly the car "settles" into a turn.
* How easy it is to "flick" the car back and forth (as though through a slalom).
* How stable the car is in a straight line at high speed.
* How stable the car is under the brakes.
* How securely-planted it feels over bumps and washboard surfaces.
- Stop, measure the hot (well, "warm") tire pressures and write them dowm in a notebook, along with the results of your noise-and-handling evaluation.
- Drop the rear tire pressures by two pounds and repeat steps 2-4. Continue until EITHER:
a. the rear tires are at the same pressure as the fronts, or
b. you see an unmistakable negative trend in your handling evaluations.
If you've stopped because the rear tires are at the same pressure as the fronts, continue to step 6. Otherwise,
inflate the rears back up to the lowest pressure at which they still performed well, then continue to step 6.
- Repeat steps 2-4, dropping the FRONT tire pressures by two pounds per run, leaving the rears alone. Stop when:
a. the handling goes to hell, or
b. you've reached 3/4 of the factory-recommended front-tire pressure.
If you made it all the way to 3/4-pressure, continue to step 7. Otherwise, inflate the front tires back up to the lowest pressure at which they still performed well, then continue to step 7.
- Repeat steps 2-4, RAISING the presures in ALL FOUR tires two pounds per run, until you reach a point at which the performance degrades.
- Drop the presures in all four tires equally, back to the highest pressures at which they performed well.
- THIS IS IMPORTANT. Go home, park your car, put your car keys in an envelope, seal it, and write on the outside: "Check Tire Pressures".
- Go to sleep and let the tires cool down overnight. The next morning, check your tire pressures before you even start the car... That way, you'll know what cold pressures give you the best-performing hot pressures.
I don't remember, offhand, what pressures I finally settled on for the Yoko AVS Intermediates on my 914/6 -- the numbers are on a label taped to the tire-pressure gauge in the car's glovebox, and as you know, my 914's in storage -- but I can give you one interesting bit of data that shows how widely the optimum pressures can vary among tires:
The factory-recommended pressures for the special, NSX-only Yokohamas on my other car are 33 front, 40 rear. When a friend of mine who also owns an NSX switched to Pirelli P-Zeros, he found that they worked best at 32 psi ALL AROUND.
[AWN] If you adjust your HOT tire pressures and are happy with the results, wait for the tires to cool down at the end of the day then measure the COLD pressures that resulted from your adjustments. That way, you'll know what cold pressures to use next time in order to achieve the hot pressures you liked.
[BJ]A PROBE-type TIRE PYROMETER is just as important as a tire pressure gauge to determine ideal tire pressures, camber, and toe at the track. A general rule of thumb is you want a 20*F temperature spread with the inside of the tire 20*F hotter than the outside of the tire. Changing camber and raising/lowering your tire pressure will find an ideal and linear temperature spread that will increase the grip, performance, and longevity of your tires. For most street/R-compound tires, you don't want to see much higher than 210-220*F. Ideally 170-210*F is a good operating temperature for tires. Another general rule of thumb is most street and R-compound tires (including the BFG R1) generate the most grip at 36-38psi HOT. 30-33psi HOT can work for some R-compound tires on lightweight cars to increase the contact patch and generate more grip for a qualifying/time attack style event, but it will be harder to drive and the tires will 'squirm' more and not last a 30lap+ race. Another rule of thumb is for every 10*F ambient temperature, tire pressures increase 1psi. Example: If you set your tires at 33psi cold, on a 50*F day = 5psi increase to 38psi and on a 90*F day, there will be a 9psi increase to 42psi HOT. Target 36-40psi, use a pyrometer, and dial in your camber to maximize your tires pressures and performance.<p>