[Tom]

I have a Z/28 with a 410 rear ratio the tire size stock is 27.4 in dia I'm going to a 29,5 in dia tire how will this alter my gear ratio? I used to know this stuff but can't remember the math.

[patgizz]

will be like goin to a 3.80 gear and speedo will read 60mph when you're really going 65

[Tom]

thanks now here's part two I will be using a 700R4 tranny which will change every thing,with a 350+060 TPI engine I am hoping to be still street efficient.the first gear as I understand is around 306:1 which will be like using 488s and final drive is .70 which is like running somwhere around 323s as close as I can figure so with larger dia tires the top end should be higher and scince the TPI is limited to around 5000rpms it should make a major difference if I can get the tires in the wheelwells. any thoughts

[Rex Tribble]

Hi Tom,
I believe the formula you are looking for would be;

Tire radius X desired RPM over 168 X desired MPH

[igotachevyor2]

here is a couple o links of math calculators this should tell you what you needcalc 2

[Scotty]

Tom ,these are some formulas for you to
play with: MPH = RPM x Tire Dia divided by
Gear ratio x 336, RPM = MPH x GR x 336
divide by Tire dia, Tire Dia = MPH x GR
x 336 divide by RPM. Don't forget to get
your speedo re calibrated, just to keep the
local sherrif happy.