Quote:
Originally Posted by rowsdower
Why is a smaller diameter bad? The gearing would be slightly shorter, the odometer would creep up a bit faster, the speedo would read higher than actual speed, and the car would be lower than it is currently by 1/2 of the decrease in diameter. None of these seem like dealbreakers considering these would only be driven on the street to get to the track and back. But is there another reason why this should be avoided?
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You are correct on all of the above. Many people run a slightly smaller diameter for a gearing advantage for autocross. I personally don't like doing this though, especially if your street tires will be stock diameter. I do track days so that I can learn car control on my daily driver so that I can safely and confidently do tail out antics on back road intersections and such. I think the car will behave quite differently though with a tire that is 1.5" smaller in diameter. And if you learn car control with a 23.5" tire, does that directly translate into having car control with a 25" tire......I guess I am not positive?
Either way your car will not explode with a 23.5" tire on it for track days, but that seems like a little too much gearing advantage in my opinion. Maybe others with experience running that small of a tire on track can chime in.
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Edit: The 23.5" tire I am referencing is the 205/40R17. Rereading your post it looks like you are wanting to run the 215/45R17. That tire makes much more sense and is what I would suggest for your 7.5" wheels. You also said it is cheaper, so win win.