Craig's Track Tire Talk - 1997

This article reviews some R-compound tires generally available right now. This isn't a "tire test." The opinions expressed in this article are based on conversations with owners, dealers, and manufacturer's representatives and a lot of reading. Your experiences will be different. For instance, I was in the market for tires for competition (Solo I and II). Thus, I placed the most importance on performance. This is different from tires I would choose for driver education weekends (DEW). Long time readers will know that I don't believe R-compound tires are necessary for the "E" part of a DEW. Then again, I think Mont-Tremblant's short course is a better (and smoother) pedagogical tool than the long course. For a DEW, speed is not important (these are not timed events), but handling and tread wear are.

First, a word about tread wear ratings:

Moulded onto the sidewall of every tire is a tread wear rating. These ratings aren't perfect, but they give a rough indication of tread life. My interpretation of the readings (which isn't the same as the official one) is as follows:
> 300 This is the last set of tires you'll ever have to buy for this car. ZZzzzzz.
250-300 You will want to replace these tires due to old age, not wear.
150-250 High-performance street. If they could only last another event . . .
100-150 Ultra-High-performance. Another season of tread life would have been nice.
<100 R-compound race tires. Tires and rims are a significant cost of vehicle operation

Although manufacturers don't like to say this, there is a pretty much direct correlation between handling and tread life. It may be no longer technically true, but the relationship still holds when comparing tires of the same type. Yes, there have been improvements in tread compounding - an "all-season high-performance tire" would have been an oxymoron a few years ago. However that technology has given improvements across the board . . . an ultra-high-performance street tire like the Bridgestone S-02 offers unbelievable performance.

What is a track tire?

I've arbitrarily divided the tire market into four segments. I'm only looking at tires in the last segment.

Street performance tires

These are codewords for "Good tread life" which are codewords for "Hard compound" which means "Less performance" - still very good, though. These are tires that probably won't see a track event. They usually have excellent wet-weather performance (unlike some R-compound tires). Some are even all-season now. Tread wear ratings generally greater than 250. Example: Toyo Proxes U-1.

High-performance street tires

Driver education events can be done in almost any tire, except a brand-new one. Once students are comfortable driving by themselves, though, a common complaint is the search for better tires. Just keep in mind the general rule that the higher the performance, the higher the cost and the lower the tread life. Careful selection can yield a tire with excellent handling characteristics, but with lower limits and much longer life than more expensive tires. Make sure the tires are well scrubbed in before use on the track or you may chunk (ugh!) the tires. Tread wear ratings 150-250. Example: Yokohama AVS Intermediate.

Ultra high-performance street tires

This is the expensive part of the tire market. The tires are very expensive, and they don't last very long. They all handle very well and are the ultimate overall tires. Did I mention these things are expensive? Fun, though. Tread wear ratings 100-150. Example: Bridgestone S-02.

R-compound "street" tires (Track tires)

R-compound tires arose when racing sanctioning organizations decided that some classes of racing must run on "street tires," usually defined as DOT approved. Certain tire manufacturers saw a window of opportunity, giving racers tires that were the same as a "usual" street tire, but moulded with very soft rubber for great traction (and short tread life). After a while, the competition heated up, and now R-compound tires bear little relation to their street brethren other than the name on the sidewall. R-compound tires are designed specifically for the track. They grip. They have stiff sidewalls. They may even cost less than high-end street tires. With a good alignment, they are the most cost-effective performance upgrade you can make to your car. (Think about that for a second.)

Do I need Track tires?

Do you feel the need to go faster in corners, brake harder, and spend more money?

You do? Well, then do you do one or more of the following?

- drive on a track three or more times weekends annually

- Solo II/autocross

- Solo I/time trials

If the answer is again yes, then you probably want to consider R-compound tires. If any answer is no (including the "spend more money" part), then you may want to reconsider. If all the answers are no, then you don't need track tires!

If your car is heavily modified, why bother with R-compound tires? Go straight to out-and-out racing slicks. R-compound tires were designed to meet a specific rule in certain classes of racing - namely to use DOT-approved street tires. If you don't have that restriction, slicks may be a viable alternative.

Hint: A second set of tires usually involves a second set of rims. Heavy-duty steel wheels of the type used by the stock car crowd are much less expensive than alloy wheels, though heavier. Almost any size and offset are available. Used rims are also an option, but should be carefully inspected. If the brake and body clearances are there, smaller diameter rims (15" instead of 16", for example) are usually cheaper (smaller diameter tires are cheaper, too).

What size do I get?

Quite often the best bet is to stick with the manufacturer's original or optional sizes. OEM rims are quite often available used to save money. For extensive track use, the optional sizes are probably better. If the car's suspension has been extensively modified, sizing is often more of a question of what is available and can fit. Remember that wider tires need more horsepower. Having too much tire for a given application is possible.

A speed tip that may, or may not, work for you: Given that you're going to be using these tires just on the track, why worry about speedometer readings, ride, ground clearance, or fuel economy? Go with a lower profile tire on the same diameter rim, instead of +0 or +1. For example, on my 924S:
Type (Comp T/A R1) Size Diameter Tread Width
+0 size: 205/60 x 15 24.6" 6.8"
+1 size: 205/55 x 16 24.8" 7.3"
lower profile: 205/50 x 15 23.0" 7.3"

(Stock size is 195/65 x 15. Unmodified suspension and fenders restrict tire width to 205.)

Conventional wisdom (and the factory option) is to go with the +1 size, giving about the same overall diameter, but on a larger rim. This is true if you need to worry about speedometer readings, rides, ground clearance, fuel economy, etc. This makes the sidewall shorter (by 0.4" in this example), thus stiffer, thus better handling.

The lower profile, however, also makes the sidewall shorter (by 0.8"), and stiffer. It also lowers the car by that amount, lowering the centre of gravity and getting all the good things that come with that without buying new springs.

Finally, the lower profile tire gives the same effect as a numerically higher final-drive ratio (greater acceleration, lower fuel economy). Given the stock ratio is 3.889:1; the 205/50's give an implied final drive of 4.159:1. Cruising at 100 km/hr will take a 230 additional rpm (a 7 km/hr error), but this isn't important on the track. What is important is the car will pull just a little bit harder coming out of corners.

So, almost an inch drop, better handling, faster acceleration compounded with the higher absolute grip of the R-compound adds up to cheap track performance improvement. Do NOT use this combination on the street, though. Reducing ride height without increasing spring rate will cause bottoming out on bumps, which may damage expensive components. (One 944 owner had his oil pan ripped out by an errant rock, for instance.) Like any performance improvement, there are tradeoffs.

One can carry this even further on the 924S and use 225/45 x 15 tires (only available from Hoosier). These have a 22.8" ride height an 8.2" tread width, but will stick out beyond the fenders and would work best with wider rims, possibly with a custom offset.

Do tires need heat-cycling?

BFG Team T/A tests show heat cycling gives 50% greater track tread life than untreated R1's. Both untreated and heat-cycled had equal lap times, with the heat cycled being more consistent. Different tires will have different results.

What is heat-cycling?

The idea is to bring the tire up to operating temperature gently the first time the tire is used, heat the tire through, and then cool it gradually. First, increase cold pressure 4-6 psi. Then, there are two methods; I don't know which is best. One is to drive 150 continuous highway kilometres. The other is to drive about ten minutes on the track with the objectives of bringing the tire up to operating temperature gently and heating the tire completely - not low lap times. Then take the tires off the car, drop the pressure 4 psi below normal, and store in a clean, cool, dry place away from the sun (24 hr. minimum, 48 hr. recommended). Force-cooling should not be used.

Do I need to shave my tires?

If you are racing, yes. Even after a good initial heat-cycling, unshaved tires will eventually be slower than shaved tires, and can be damaged by early over-enthusiastic use. R-compound tires moulded to full tread depth must be shaved before use. However, most R-compound tires are made with special moulds and do not need to be shaved to function. Shaving still offers an immediate performance benefit, but most owners prefer to take advantage of the additional tread life, albeit at lower g's. Care must be taken to avoid chunking and/or the development of undesirable tread patterns if the tire is not shaved. (This was so common in one earlier tire that it attained the acronym EGOD - Evil Groove o' Doom.)

Shaved tires are not rain tires.

How long will the tires last?

Not long enough. Wheelspin, of course, affects tire life. A well setup car will be kind on tires; as will a smooth, mature driver. I'm neither smooth nor mature, so I really can't say. I can be very hard on tires. I have heard of very few people getting more than ten weekends out of a set of R-compounds, with quite a few replacing tires annually.

What pressure should I run?

Er, today's answer is: 36. Why? That's my car number. Seriously, though, no magic formula exists to answer this question. The reason is that the main factor affecting what pressure is optimal for you is your driving style. The driver has the greatest effect on pressure. Other factors are tire type, cold inflation pressure, hot pressure, tire temperatures/wear, and lap times. Your tire dealer can give you a good start. A complete discussion of this topic rates a separate (and probably quite controversial) article.

What brand should I buy?

All of the tires listed here are excellent, and I've talked to or corresponded with satisfied owners of all the tires. None of these tires is "bad." Each tire has its advantages and disadvantages. The Yokohama, Toyo, and B.F.G. are about the same price for most sizes, with the Hoosier around 20% more. Some sizes do have a very large price difference, so check. Usually, the more you spend, the faster you go, the faster the tires wear . . . but with this group you can't really go wrong. The main contenders are (in rough order of increasing performance):

Yokohama A032R

This is a tire with a radical tread pattern, brand new late last year. The tire promises great tread wear for a R-compound tire. Tread wear rating 60-80, depending on size. Yokohama claims they designed the tire for "track and driving school participants," which is a good description. Racing will probably not be this tire's strength. A very deep (for a R-compound) 8/32" tread is used, but they do not require shaving. The tread pattern is supposed to minimize wear and chunking, and have good rain performance. The only magazine test I've seen (Grassroots Motorsports) shows the tire is slower than Kumho Victoracers by a don't-bother-racing-with-these margin. (Two tests were run on Improved Touring racers. In both cases the Kumho's were shaved, with the A032R shaved in one test and unshaved in the other.) Limit behaviour of the tire tends to oversteer (at least when new).

Toyo Proxes RA/1

This is a very common and very successful tire on the local autocross courses, where it enjoys an extensive contingency program thanks to Toyo and Talon Tire. It carries a relatively full tread depth, so care must be taken with initial use. Tread life is surprisingly good for a R-compound. It isn't clear yet whether this tire or the Yoke has greater tread wear. Outright performance probably isn't as strong as the Hoosier or the T/A, but competitive. A great all-around tire. No vices.

B.F. Goodrich Comp T/A R1

The Comp T/A is the current favourite racer's tire, for good reason. It has grip, stability, and good breakaway characteristics. They probably won't last as long as the Yoke or the Toyo, but this tire is on winning production cars everywhere. BFG has contingency programs in many forms of racing, and it shows. The most interesting feature of tire for dual-purpose street/track cars is the T/A's unique asymmetrical construction that introduces a "pseudo-negative-camber-effect" to the suspension. What this is supposed to do is give the suspension the effect of having more negative camber than the actual suspension setting. Let's take an example, again my 924S. Front camber settings:
Stock camber settings: 0 degrees, +/- 1 degree
Street/track compromise: 3/4 of a degree negative
Track setting: 1 and 1/4 degree negative
Autocross: 2 degrees negative

(These settings are from magazine articles in Excellence and European Car.)

If the settings are left at stock, street tire wear will be great. At the track the car will plow (understeer). With a regular R-compound, the car will plow. With R1's, the car will understeer less, because of the camber effect of the tires. Now let's set the suspension to 3/4 degree negative. Handling is improved. Street tire wear goes up. At the track, the car understeers less . . . and with the R1's, the handling is even better, because the effective camber is getting closer to the "optimal" 1 and 1/4 degree. Also benefitting from the T/A's is the autocrosser, who is probably limited by rules to stock specifications. Two degrees is desired, but all the car can be set to is 1 degree negative (0 +/- 1). Here the T/A's help to make up the difference.

That is why R1's work better for many, but not all, street/track cars. On an ideal track car, the tire's camber effect wouldn't be necessary (and perhaps even unwelcome). Suspension settings are always a compromise, and using R1's lessens the effect of making the camber compromise.

There are other peculiarities due the T/A's radical construction - BFG actually has a 20-page guide on how to use the tire that is a must read for T/A owners.

Buying hint: BFG changed the T/A between 1996 and 1997. Newer stock has rectangular tread depth indicators instead of the usual round ones. The main difference in the tire is a wider centre tread. The previous centre tread was prone to excessive "chisel" wear in some situations.

Hoosier A3S02/R3S02 Radial

These tires are serious track-only tires, introduced a couple of years ago. Tread is virtually nonexistent. They are often called "cheater slicks." The tread wear rating is zero. (Hoosier never bothered running the DOT test on these tires.) Unlike the tires above, Hoosier uses fiberglass instead of steel in construction. This results in a very light, very stiff tire that works best with a modified suspension, but may make the tire more susceptible to flat-spotting. According to Hoosier, the tire works best with high inflation pressures and wide rims, and likes negative camber. It runs up front in all the classes of competition in which it is allowed. Two tread compounds are available, autocross (A3S02) and road-racing (R3S02). The autocross compound is incredibly soft and isn't really suitable for anything else. Even with the road-race version, tread life of these tires is minimal, but the grip . . . wow. The reduction in unsprung weight . . . wow. Price . . . about 20% more than R1's . . . but if your car is setup for them . . . wow.

Other Brands?

Bridgestone

Bridgestone does not currently import R-compound tires into Canada. The late, lamented RE71R was a favourite. They are concentrating their competition tire program on Firestone and Indy racing.

Goodyear Eagle GS-CS

This is Goodyear's R-compound tire. I have no idea what it is like, and I have never seen the tire. Rumour has it the tire is great, but the cost makes other brands much more attractive. Goodyear makes the vast majority of racing slicks seen in North America. (In the grassroots, Hoosier is the only other competitor.)

Hoosier Autocrosser/Street TD

These were Hoosier's first DOT-rated tires, bias-ply with lightweight fiberglass construction. Bias-ply's have totally different handling characteristics than radials. As with the Hoosier radial, two tread compounds are available: ultra-soft Autocrosser and the road-racer Street-TD.

Kumho Victoracer V700

This is the new hot up-and-coming tire in the U.S., highly rated in Grassroots Motorsports tests. Not currently available in Canada.

Pirelli P-Zero C

Pirelli introduced R-compound tires into Canada last year. However, I didn't consider them as their prices are now $60-$100 a tire more than the T/A.

So, what tires should I buy?

As the old saying goes . . . "Speed costs money. How fast do you want to go?"

The Yokohama's are too new for the jury to be in on them, but promise to be a long-wearing tire. The Toyo's are very good tires at a decent price in most sizes (except 17"). The BFG's may be better for you, but they wear faster. The Hoosier's may be faster still, but cost still more and wear still faster. BFG has the widest selection of tire sizes, and Hoosier carries some unique ultra-low-profile tires.

For a driver education weekend, though, how fast do you really need to go? I have tried many types of tires at DEW's. I think I've had the most fun with well-worn (over half) high-performance street tires like the Bridgestone RE-71 and Yokohama AVS. Of course, one can't deny the higher limits to the car, and thus the driver, of R-compound rubber.

On the 924S example I've been using, 205/50 x 15's all around would work well with the stock 15 x 6 rims, keeping costs down. A set of '86-up stock 944 rims (15 x 7) would make two sets of rims (15 x 6 front, 15 x 7 rear, like the factory sport option). As for tires, T/A's would probably work best, with equal tire pressures front and rear to start.

For my Solo car (which isn't a Porsche), I bought a set of A032R's for use as street/rain tires, and Hoosier Street TD's for dry pavement. Now if only the space between the pedals and the seat would drive better . . .

Acknowledgments and References

Thanks to the many drivers to whom I have persistently bugged about tires; to those who have volunteered their opinions, primarily over the Internet; and to Howard Korzenstein of Talon Tires for reviewing this article.

For more information, I found an excellent in-depth tire article entitled "Big Stick - Secrets of DOT Racing Tire Performance," by Mike Kaemer, in Grassroots Motorsports, Sept/Oct. 1996. If you're interested in Comp T/A's, Team T/A distributes the paper "Care and Feeding of BFG R1's," by Jim Fogarty.

 

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