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Bill Verburg Bill Verburg is offline
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Join Date: Dec 2000
Posts: 23,335
Originally Posted by T77911S View Post
I was just looking at the "gearing" change by going to a smaller wheel as far as acceleration.
Originally Posted by GaryR View Post
it's the OD of the tire, not the wheel, look at that for comparison..
They both factor is but in somewhat different ways

just for comparison here 2 implementations of BS SO-4 tires in slightly different sizes

the front is 235/40 compared to 245/35 on the same wheel, the the tires weight the same but the inertial cost of the 245 is less because the mass distribution is in aggregate closer to the axis of rotation, there is no gearing cost here. the 245 would have a +4.3lb-ft axle gain available for acceleration rather than rotating the tires

In back 285/35 compared to 285/30, the 30 is both lighter and shorter than the 35, here there is an inertial cost to the 35 of ~11.5lb-ft for the axle, this is a maximum cost at max acceleration and less at more leisurely accelerations and an additional gearing cost that is always there of ~13lb-ft

Here the total benefit of the 245/35 & 285/30 at max accel is ~29lb-ft
Bill Verburg
'76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone)
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