If you want it to be like a Caterham:
Determine the ratios and tire od of a Caterham with a similar or same powerplant.
http://en.wikipedia.org/wiki/Caterham_7_CSR245-40-15 rear tire
245 / 25.4 x .40 x 2 + 15 = 22.71" od
6 spd: 2.69/201/1.59/1.32/1.13/1.0 with 3.38 diff
or
5 spd 3.36/1.81/1.26/1.00/0.82 with 3.92 diff
Calculate mph for each gear at one rpm:
RPM x Tire OD / 336 x diff ratio x gear ratio = mph for that gear
i.e., 22.71 x 5000 / 336 x 3.92 x 3.36 = 113550 / 4425.5232 = 25.65 mph in first
22.71 x 5000 / 336 x 3.92 x 1 = 113550 / 13.17.12 = 86.21 mph in 4th
Take your proposed tire OD:
i.e., 205 50 15 = 23.07" od
Your proposed t5 ratios
i.e., 3.75 first, 1.0 4th
rpm x tire od / mph x gear ratio x 336 = diff
5000 x 23.07 / 25.65 x 3.75 x 336 = 115350 / 32319 = 3.569:1 diff to match first
5000 x 23.07 / 86.21 x 1 x 336 = 115350 / 28966.56 = 3.98:1 diff to match 4th.
Do this for each gear, add all the diff ratios up, then divide by the number of gears to determine the closest average ratio to match, then look at what is available.
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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS
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