Feverzero

I have a 1987 Mustang GT and I am trying to change my gear ratio to a 373. My tire size is 24540R18. How do you calculate that?

Turbo4banger

Are you putting 3.73 gears in the rear?

What are you trying to calculate?

Feverzero

I'm going from the stock gears in my mustang, I want 3.73 and I have 18" rims

nitrous_bob

that has nothing to do with it.

you buy 3.73 gears and have them installed. are you trying to figure what speedo gear you need to correct the speedo ?

what trans and what year ?

fordboy5.0

its the 23 tooth speedo gear for the 373s thats what u should need

Feverzero

even if i have a 140mph tac?

Feverzero

140mph speedo

badlx87

mph on the speedo doesn't matter, any gear that's not what your stock gear is will make your speedo read wrong. Even if your stock gear is, lets say a 3.08, jumpin up to just a 3.27 will throw your speedo off.

89GTnoob

Some things to think about also that I didn't pay attention to until recently: if you don't change your speedo gear then those extra MPH turn into extra miles on your odometer and add extra miles on your trip counter. lol I thought I was getting 18 mpg with mods and 4.10s

nitrous_bob

23t is incorrect for every mustang and the 23t is NOT a ford part it will not last very long. it's from a jeep

again... what year trans, and what trans.

nvm... just read here... aod cars are 8t , and '91 or '92 and newer t5 are also 8t

aod cars CANNOT change out the drive gear, only the driven... t5's require the case to be disassembled to replace the drive

the driven takes 5 minutes though


http://www.ddperformance.com/PDF/SpeedoChart.pdf