checking Gear ratio

Now i cant remember, i think if you jack up the rear and spin the tire and count how many times the driveshaft spins to make a complete rotation of the tire, or the other way around adn that how you get the rear gear ratio?

Yep, count the number of rotations of the drive shaft.

Yep, the numbers of times the driveshaft spins in one rotation of the tire is the correct way of finding out your gears.

sweet, cause i got rid of my rear with the 4:11 posi in it and i picked this one up n the guy says he thinks there are gears in it but hes not sure so i wanted to check...

well the driveshaft spun twice in one rotation of the tire...What gears would that be?? something don't seem right here...stock pony wheels are on the car also i know that can matter....

The size of the tires or wheels make no difference. One revolution is one revolution. You need to turn both wheels exactly one turn in the same direction, or the differential gears will throw your drive shaft and pinion count off.

i cant spin em both in the same direction its not a posi

Well I can, and until you figure out how to turn both axles exactly one turn. you do not stand a chance of guessing at the gear ratio. Couldn't you have looked inside and read the tooth count by now? Don't you have any friends that will help you turn both wheels at the same time and count the drive shaft.

well the driveshaft spun twice in one rotation of the tire...What gears would that be?? something don't seem right here...stock pony wheels are on the car also i know that can matter....

you can turn the drive shaft. count the turns until the tire makes one rev

ill have someone give me a hand later when its not so cold out and check again

You can turn the driveshaft and pinion but if both axles don't turn the exact same one turn your estimate will be off. It is possible to turn the pinion and observe one axle turning, and the other axle may not turn at all, or it may turn in the opposite direction.

ok now that sounds about right..ima try that whenever it stops raining...according to the news that'll be thursday

If you have a differential, you can hold one wheel totally still while the other wheel is spun one full rotation. This will spin the drive shaft half the distance it needs to spin to tell you the ratio. Next hold the other wheel still and spin the previously still wheel one full rotation. How ever many times the driveshaft has turned is you gear ratio.

ive never heard of that being done before....but if its true then on the first wheel the driveshaft spun twice on the other it spun 2 more times...so thats 4 times total for 1 tire rotation on each side, whats the gear ratio?

Drive the car in 4th gear(if its a manual) going 60mph, let me know what RPM you are at and I can tell you what ratio you are.

Drive the car in 4th gear(if its a manual) going 60mph, let me know what RPM you are at and I can tell you what ratio you are.That work on every car?

That work on every car?

Yes, as far as I know. If not, pretty darn close.

I also need to know how tall the back tires are. Should be 26" for a Mustang.

ok ill do that as soon as the weather lets up here ill go out and let you know....thanx

ive never heard of that being done before....but if its true then on the first wheel the driveshaft spun twice on the other it spun 2 more times...so thats 4 times total for 1 tire rotation on each side, whats the gear ratio?
Are you sure that the drive shaft is spinning 2 full rotations from a full rotation of each wheel? e If the first wheel spins the drive shaft 2 and a fraction ,and the second wheel spins it 2 exactly they are probably 4.11's alittle less than 2 full rotations of the shaft from one tire and 2 full rotations from the other would probably be 3.73's.

just pull the cover off if you really what to know! if not you hold one wheel and spin the other one turn and count drive shaft revolutions car in neutral if its 4.11:1 thats 1 tire rotation to 4.11 drive shaft revolutions

At 60 mph im at about 3000 rpm in 4th gear...

rpm x tire diameter
Gear ratio x 336


You have 3.73ish :D I am going off of a 26 diameter tire.

Math does not lie!

i believe the stock tire size is about 26in dia. thats pretty cool though.

Have you seen this gear ratio calculator?:wink:

http://www.cargister.com/calculator-gear