7" wheels are stock size, cheap and common for these cars. As such 15x7 is the stock wheel size.

225 were selected as it is a good size for the car and the 7" wheel. Orignal stock size on the 944 was 215/60 R15. Turbo cars used 205/55 and 225/50 on 16" wheels. The 225/50 give us a good rubber patch on the stock wheel and a 1" shorter overall diameter for slightly improved gearing.


205/50's could be run, but at 2600lbs we are 400lbs heavier than a Miata which also runs that size. With a 7" wheel we can run the 225 with ease so why not. I can't see a 205 wearing and better than a 225 for our cars.

Joe,

Thanks again for the information. You have been wonderful about sharing your knowledge, and I'm sure I'm not the only one who has benefitted. I'm still learning the 944 and have not driven one since I sold mine in 1991.

I can only share my eight years of experience with the SMs which may or may NOT cross over to the 944. We ran 205/60 and 195/60 R14s on 5.5 and 6 inch stock rims in addition to the 205/50 R15s on the aftermarket 7" rims. The 205s on R15s wore/wear better by far.

Small correction. The 1600 SM is the lightest and comes in at 2300 or 2325 with driver. The 99 SM comes in at 2450 or 2475 with driver. Both run the 205/50 R15. All the fastest SMs still wear to the cord at either the inner or outer edge. I believe a better wheel in SM would be a 15x8 (assuming they stay with the Toyo RA1)but you just can't find those in the price range of the 15x7.

Weight does not always mean more wear or more heat in the tire. I supported both a 99 and 1600 at a NASA race earlier this year. They finished first and second in all three races (swapping position and finishing spots) and the 99's tire temps were always lower than the 1600s.

Give the 205/50 a try. You might find you like the acceleration (lighter tire with smaller diameter) and wear better. I have tons sitting around, so I'll use them to sort out our 944. If they don't work well I'll be the first to let everyone know.

205 divided by 25.4 = 8.07 inches
225 divided by 25.4 = 8.86 inches

I have a set of 205/50/15 RA1s mounted on 15x7 cookies and the tire does fit better on the rim. I tracked this setup on my 1988 944 before and I liked them a lot. I could tell there was less unsprung weight as acceleration seemed a little better but I did get caught up in between gears in certain turns that I normally would have just stayed in 3rd.

Everything has its advantages and disadvantages but since the rules are set to run 225/50/15, I am sure they are not going to change that.

If the long term cost is lower without a big performance sacrifice almost everyone is onboard. If you get lower costs and performance gains, everyone is onboard.

The question is...Which tire gives the best compromise? I have no idea with the 944, but I did want to plant the seed.

According to my tire guy, the R888 comes new at 6/32nds at the following prices:

225/50 R15 = $148 (22 pounds)
225/45 R15 = $145 (20 pounds)
205/50 R15 = $131 (20 pounds)

Add $15 per tire for shaving.

Though the compound is supposed to be the same as the RA1, the R888 seems to wear faster.

Joe,

You've done such a good job with this so far. The more 944 Spec grows the more tires will get shaved. You might consider a page from pro racing for any "Big" event. If you decide to stay with the R888 or select any tire that can be raced effectively at full tread depth, you can mandate that the tires start the weekend (first Q session) at full tread depth. Great way to even the field and keep the costs down.

It was common to shave the RA-1. The reason for this was to reduce the break in time from 12 heat cycles full tread 8/32 to about 6 if shaved to 4/32. There is no evidence to support shaving on the tires in our class. In fact those that have shaved the tires have bee quite UNHAPPY with results. The tires have infact been slower. As such run them full tread and be done with it. Our tire guy is recommending to NOT shave them. While it was common on the RA-1 it just does not seem to work for the R888 at the club racing level.

As for putting limits on tires at each event this does not make much sense since most tires will last multiple events and knowing the history of a set of tires before they come to an event is not feasible. Also I have yet to see anyone trying to use new tires to gain an advantage.

Here's more data points.
Rick brought his R888's over to AIM tires at Thunderhill to ask them about the pattern on the tire about the second quarter when counting from the outside. It's the dark area, left hand side of the center of the tire in the picture.



The AIM guys said the tires were under inflated. It's dark because it doesn't touch the dusty ground.
Rick was inflating the R888's as he would a RA-1 about 32psi cold and aim for about 38 hot.
The spec e30 guys are running R888's also and going thru the same learning process.
The reason I mention spec 30 is because their fast guys and our fast guys run comparable times.
The AIM guy said the fastest e30 time on R888's was with 40psi COLD!
Rick tried it at 40 cold and said it has probably less grip than a RA-1 for one or two laps but after that they perform just as well as a good condition shaved RA-1.
For Rick to say they perform as well as a good condition shaved RA-1 is a big deal because Rick never had a good thing to say about the R888's.
Aubie was testing with a white paint marker on the side of his R888's and even at 38 cold it was rubbing paint off the raised triangle indicator so perhaps 40 cold is the right thing for these tires.
Just a FYI of our experience.