If you're not sure what gear ratio your car has, it's probably because the sticker with that information is long gone. Or, if you just bought a used car, the previous owner may have removed it. Fortunately, there are a few ways to figure out your gear ratio without too much trouble.
The easiest way is to simply look up your car's make, model and year online and find the factory gear ratios. However, this won't work if your car has been modified or if the previous owner changed the gears.
Another way is to jack up one of the rear wheels and spin it while counting how many times the driveshaft turns. Then, count how many times the wheel turns. The first number is your drive (ring) gear ratio and the second number is your axle (pinion) gear ratio. For example, if the driveshaft turns 3 1/2 times for every one turn of the wheel, then you have a 3.50:1 drive ratio. To get your final gear ratio, divide the ring gear by the pinion gear like this: 3.50/1 = 3.50 finalgearratio . This method only works on cars with live axles