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Old 07-22-2012, 08:59 PM   #1
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Default Semi SLick tyre pressure...

A quick question, I have a friend just stated running an LS1 mx5 on track days etc.

He has been running his semi slick R888's at 40-42 psi cold and has basically heat cycled them out after two track days of maybe 6 x 20 minute sessions per day.

I had a feeling the pressure was a bit high (but don't really know) and would like someones input who has experience with semi slicks to advise...

Also, if that is all they last, I can't afford to go that way...I know from road racing motorcycles that slicks out perform "production" based road tyres in almost every category, cost, wear rate, longevity and grip levels EXCEPT for in the wet (obviousley)....Is this true of cars?

Because that being the case I would just go to slicks on spare wheels for track days and leave the Toyo T1r (or equivalent) road tyres/wheels to dribble around on, on the few wet days....

So a reference tyre pressure for the common Hoosier slick that you guys run would also be appreciated...
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Old 07-22-2012, 10:04 PM   #2
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40-42 psi is pretty high for the track. Autocrossing that may be fine (although still fairly high) because runs are short, but on the track you can get like an 8 psi increase between cold and fully hot.
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Old 07-22-2012, 10:42 PM   #3
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I run around 35psi hot on 275 hoosier R6's. Car slicks will cost more and wear faster than high performance road tires. If you aren't trying to be on the cutting edge of competition, a high performance road tire (like RS-3, Star Spec, R1R, etc...) is usually a better bet.
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Old 07-22-2012, 10:42 PM   #4
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Try 36-38 HOT.
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Old 07-23-2012, 10:41 AM   #5
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40-42 cold means roughly 50psi HOT, they must been killed from the center being way too hot. Pyrometer data ? If not your friend should buy one, one of the best investment IMO.

R888 on let say 2300 stock miata should run in 36-38psi HOT like other said. Manufacturer give you those kind of advice or Google is your friend. It cost one set to learn...
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Old 07-23-2012, 10:45 AM   #6
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Quote:
Originally Posted by Handy Man View Post
I run around 35psi hot on 275 hoosier R6's. Car slicks will cost more and wear faster than high performance road tires. If you aren't trying to be on the cutting edge of competition, a high performance road tire (like RS-3, Star Spec, R1R, etc...) is usually a better bet.
This is right. I run 275 A6 and R6 and start them at 31-32psi cold. One thing tho, you need some aero to be able to warm the R6 up and I miss some because they run just below the 180-190F that Hoosier say is optimal temp.

RS3 and star spec are the way to go for dry and longevity, R1R for wet but they do go quickly on the dry IMO.
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Old 07-23-2012, 11:42 AM   #7
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When I ran R888 in the dry I needed to stay below 26psi hot, above that they became greasy and times went through the roof.
I have friends that can run them at 30psi but it depends a lot on dampers and driving style.
This is all on 205/50-15, dimensions with other load ratings etc can of course have different truths.

Heck, I only use 30psi cold when i use them as wet tires, and then they are steaming when I come in (at least lukewarm).
But my low speed compression is too high, which creates all sorts of interesting effects.
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Old 07-23-2012, 05:55 PM   #8
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It's going to be hard top nail down optimum tire pressures for the R888's They are all over the map from what I have seen. I have seen 2 cars set up the same exact way with one (mine) running 38psi hot and another 50psi hot. Both had even tire wear. I spoke to Ron at AIM tire about this and he got into a long explanation about tire construction. Bottom line is the R888's have a great tread compound and lousy carcass construction. Because of this tire pressures are all over the place with similar cars.
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