how can i tell?

[dstrbd1]

recently i did an axle swap on my car and put the rear axle from a z28 on there. it's suppose to have 3.42's/lsd, but i'm starting to wonder if i didn't maybe get 3.73's instead. the main reason i think this is because a former member of the board had installed 3.73's and said his speedo was 25mph off, and that's where mine is now. i know there is a formula where you can figure out from rpm, tire diameter, mph, and another number what gears you have, but i can't remember what it is. anybody have any clues?

[DominusEtDeusNatus]

mph = (rpm x tire diameter) / (gear ratio x 336)

rpm = (mph x gear ratio x 336) / tire daimeter

gear ratio = (rpm x tire diameter) / (mph x 336)

tire diameter = (mph x gear ratio x 336) / rpm

Be happy you have 3.73s.

[DominusEtDeusNatus]

Oh yeah, make sure you know how to use the gear ratio number. It's overall.

[dstrbd1]

now i'm all confused. according to those formulas, i have 33.7" diameter tires. when i measure them, i come up with 26". that changes the gear ratio quite a bit. if i go with 33.7", i have 3.73's. if i go with 26" i have 3.08's. what did i mess up here?

[DominusEtDeusNatus]

<blockquote>quote:</font><hr>Originally posted by Dom:
Oh yeah, make sure you know how to use the gear ratio number. It's overall.<hr></blockquote>

[Only4U]

dude i'm sorry, that really sucks. so someone screwed you over and put the 3.08's in there and you thought you had the 3.73's? sorry bro.

[dstrbd1]

got a little help from backfire, reworked the numbers i was putting in, used a couple different formulas for verification, and i do have 3.73's. not bad considering i thought i was getting 3.42's, and my mileage really isn't that horrible. i still get between 20 and 25 mpg. now to get on the track and see what i can do there.