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The 215's sidewall is actually at an inward angle, whereas the 225 isn't. This can be seen on my Viggen. My 215 street tyres look small and narrow for the wheel (the tread patch is thinner than the wheel width) compared to my 225 race tyres which have a completely verticle sidewall.
As far as your statement. You are correct, however we've found in autocross applications that using a wider tyre on the same sized wheel, actually, helps ('94 Nissan Sentra SE-R is the guinea pig). I know this sounds completely out of left field, but hear me out. A stock SE-R uses 195/60/14 tyres on a 5.5" wheel. Unfortunately in running a stock class, we dealt with the typical understeer associated with a FWD/Front Engined vehicle, and were not allowed a great deal of alignment adjustablility given the suspension geometry of the car (and the inability to use shims as per the rulebook :-( ). The front 195's were clearly not enough tyre. We found that the 205's were slightly better, but on a whim tried 225's. The amount of excess tread patch rolled over the edges slightly and, in a way, simulated a sidewall. Other than looking completely ridiculous, they performed very well. What feel was lost at initial turn in was more than made up for in mid corner grip. With higher tyre pressures and stiff sidewalls a lot, but not all, of the sidewall roll problem is curbed. We found that when using the smaller diameter tyre that the cornering force would consistantly cause the tire to roll off of the contact patch and wear on the sidewall, and unfortunately the only way to prevent this is to raise the tyre pressures; but one can only raise the tyre pressures so far. By switching to a wider tyre on the wheel, the tyre roll, which is inevitable in hard cornering, rolled onto the additional contact patch compound, that is curved to the sides, instead of the sidewalls (which as we all know are not made to stick to pavement). You also have to remember that we are dealing with Hoosier race tyres which are extremely light weight tyres; therefore unsprung weight was not nearly as much as an issue as lateral grip.
I understand that this is merely gibberish and rambling as far as a street application is concerned, but fun to yip about on a cloudy day when nothing better can be discussed.
Cheers,
Brian.
posted by 65.106.25...
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