I know we discussed this earlier but is more contingency $$ from Toyo not an option? I think that may make up for a tire that doesn't last as long. Of course, it would have to be a considerable amount more with our much larger fields and award some money to people in the back (not just top 5) in order to hold true to our equal, low cost, racing mantra.

Also, not trying to stir the pot, but will NASA let us change tires?

Chris

Nitto is owned by Toyo and the NT01 shares many of its charteristics (ie contstruction & compound) with the R888 and RA-1. From what I am told however it more like an R888 with revised tread than the RA-1. However I am not sure how much use in small 225/50 R15 type sizes the tire has had.

Chris wrote:


NASA is not going to want us to change tires for the sake of changing tires. However if we can present fair data on tire life and the associated operational cost impact NASA National will gladly listen.

That is why I want all of you to track the heat cycle (1 heat cycle = 1 session) usage of the R888. I have data going back to 2002 loging RA-1 heat cycles so we can use that as baseline to compare too.

Also on care and feeding of the tire.

Hot pressures seem to work best in 40 psi range. 38 psi may work too, but 40 seems reasonable. So cold pressures should start around 31-33 psi.

The also seem to work best new out of the box. Again limit sliding as excessive sliding will cause the tire to fall off badly during the session and they will not recover that session.

The tires might work a tiny bit better with a little less camber, but that has not been tried just yet. Maybe next time out.

Joe,

Each contact patch has to support roughly 650 pounds. The question is...How does the contact patch support that weight? My guess is that the 205 will support the weight in a way that more uniformly distributes that 650# in dynamic conditions than the 225 and that will allow the 205 to wear more uniformly and therefore last longer than the 225.

Try this if you have a chance. Run a session at 44 psi hot and take your temp profiles. Now drop your pressures five pounds and check the temps again. The profile should now tell you that you need more camber. You can see why if you draw a picture of the tire.

Draw a quadrilateral with two parallel lines one centered over the other 4.9 (225*0.55/25.4) inches apart. The bottom one seven inches long and the top one 8.9 (225/25.4) inches long.

That's about what the tire looks like when mounted on the rim. As the car loads the 8.9 inch long line (tread), it will move off center of the 7 inch line (rim). This will cause the outer sidewall to decamber the tire. The inner sidewall will try to stand up (go more vertical) which would also decamber the tire. We even see that with a 205 on a seven inch rim, but work around that dynamic with static camber and tire pressure. You should now consider that the top line in the example above is really an arc or complex curve, depending on the air pressure. Ever seen wear patterns that look like a wave?

This is all just a guess at this point, but it is based on data that I’ve collected while supporting my SM clients and by analyzing my own data. I rely on you and all the other 944 guys, to test for me until I can get out there.

Will this class grow faster if the tires give us faster lap times or longer life? I effectively burned through one set of 3/32 R888s in one double national weekend. That’s over $600. I won’t run another SM race until we have another tire.

Karl,
So far our wear patterns have not been an issue. There was some concern back in the fall of 2008, but testing at a range of pressures leads us to believe the wear across the tread of the tire is decent. Granted it may not be perfect, but it is not a source of problems.

Now the 7" wheel might be a little narrow for a 225, but that just means to me that we may not be seeing all the gains over a 205 you would expect to see. Still the 944 is heavier than a SM car and by you own data you show that you get more wear on a heavier SM car. I have no reason to believe we would not see even greater wear on an even heavier car. So no I don't thing 205 are perfect for our cars. 205 may be a better match for 7 wheel, but I think the 225s are better match for the car weight. The ideal wheel for the 944 is probably the 8" wheel, but supplies of those are limited in cheap form so that is why we spec'ed only the 7's. History has shown the 225 RA-1 is works fine on these cars even with 7" wheels and also remember we are not seeing problematic wear patterns with the R888.

The wear out for the R888 is when the rubber gets old and hard and no longer sticks. This heat cycle effect is the issue.