Auto Cross tire recomendation
actually it does take a while to get a autocross tire up to temp... and the wider it is the longer it takes. thats why our UTA FSAE car ran the narrower hoosier on a 13in rim... we couldn't get the wider tires up to temp fast enough to be quick in all the runs. this is from extensive tire testing in state of the art labs, simulation data , and 20 years of autocross experience 
i know the situation is different... open wheel versus closed wheel, but the fact of the matter is, physics says it doesn't matter how wide the tire is, if the coefficient of friction is equal given two different width tires, your frictional force will be the same (i.e. same torque to the ground). however, common sense tells us that if you can overcome the shear force the rubber has (i.e. leave black marks everywhere), then a wider tire can benefit you by distrubuting the load, thus more grip from less spin.
so thinking logically, if you go to a skinnier tire, and get it up to operating temp quicker, your runs should be more consistent, with more grip due to having a better coefficient of friction (generally tires friction coefficient increases with temperature until it reaches to high of temps, and begins to fall off again.).
i would be interested in see tire temp comparisons of two driver and single driver cars... as well as temp comparisons of 285 tires and say a 255 or 265 tire... (maybe even a 275 if thats all hoosier makes).
additionally at smaller regional events the time between runs can be very short, whereas events like here in DFW, you have to wait a long time before runs, totally killing your tire temps. nationals is obviously that way as well... two driver cars get a huge advantage of tire temps.
warr, you very well could be right about the wider tire getting up to temp quickly on the evo. i'm just posing this logic to see if anyone has actually tried the narrower tire with success, and actually done some data logging of tire temps to go with it.
i know the situation is different... open wheel versus closed wheel, but the fact of the matter is, physics says it doesn't matter how wide the tire is, if the coefficient of friction is equal given two different width tires, your frictional force will be the same (i.e. same torque to the ground). however, common sense tells us that if you can overcome the shear force the rubber has (i.e. leave black marks everywhere), then a wider tire can benefit you by distrubuting the load, thus more grip from less spin. so thinking logically, if you go to a skinnier tire, and get it up to operating temp quicker, your runs should be more consistent, with more grip due to having a better coefficient of friction (generally tires friction coefficient increases with temperature until it reaches to high of temps, and begins to fall off again.).
i would be interested in see tire temp comparisons of two driver and single driver cars... as well as temp comparisons of 285 tires and say a 255 or 265 tire... (maybe even a 275 if thats all hoosier makes).
additionally at smaller regional events the time between runs can be very short, whereas events like here in DFW, you have to wait a long time before runs, totally killing your tire temps. nationals is obviously that way as well... two driver cars get a huge advantage of tire temps.
warr, you very well could be right about the wider tire getting up to temp quickly on the evo. i'm just posing this logic to see if anyone has actually tried the narrower tire with success, and actually done some data logging of tire temps to go with it.
Speaking of which, you going to comp in a couple of weeks?
For a 3000 lb evo, it's less of deal. But I have definitely had trouble getting heat into 245 falkens on a 30 degree day.
d
I know of people running 275s kumho v710s on 17x8 rims and they do fine and the tires last long, but i'd personally run a wider rim.
Another point...This is also running on the stock suspension
Another point...This is also running on the stock suspension
Last edited by el producto; Apr 23, 2007 at 08:59 PM.
They only do that, because they're in A-Stock and are limited to stock-sized rims. Anyone who is allowed to run a larger rim would do so with a tire that big.
I'm also in the market for new autocross wheels and tires. How much difference per autocross run on a 60 second course do you guys think there is between a 245 or 255/17 and a 285/18 set up, assuming comparable tires and 9.5 inch rims for both (like V710s)?
Our local events (DC Region) are in a big lot with lots of high speed sections -- basically a nationals style course every event.
Our local events (DC Region) are in a big lot with lots of high speed sections -- basically a nationals style course every event.
nope i retired from FSAE... after trying to be the team captain under the iron fist rule of dr. woods, we got into so many fights it just wasn't worth it. i guess the saying, you can't teach an old dog new tricks is applicable because hes still trying to win the 2000 FSAE detroit competition and it is 2007 now.
oh, and i spent so much time working on the car i got in quite a bit of trouble at my job for missing time, and i was doing awful in my graduate classes...
the alternative was to start my own thing which i did, so now i get paid to work on cars instead of spending 80 hours a week working on the race car for free, in addition to my 40 hour/week job.
i have seen the 07 uta car though... it is a "safe" car unlike what we did last year (where just about every part was different except the carbon wheels... and even those used lighter fasteners to hold the two piece wheels together). in fact, it is very similiar to the 05 car that has won the last two years in a row at SCCA solo2 nationals.
nope i retired from FSAE... after trying to be the team captain under the iron fist rule of dr. woods, we got into so many fights it just wasn't worth it. i guess the saying, you can't teach an old dog new tricks is applicable because hes still trying to win the 2000 FSAE detroit competition and it is 2007 now.
oh, and i spent so much time working on the car i got in quite a bit of trouble at my job for missing time, and i was doing awful in my graduate classes...
d
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