How to Determine Final Drive Gear Ratio Without a Code

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In this video, we're going to use this 2002 Suburban to show you how you can find your final drive or axle gear ratio. You can see I'm opening up the cover on the rear axle. While I'm doing that, I'll talk a little about axle ratio.

Axle ratio is basically the number of turns that your drive shaft turns to each turn of your wheel. We know on this Suburban, or we find out, that the axle ratio is 3.73 to 1. That means that the drive shaft turns 3.73 times to each turn of the wheels. If you think about riding an old bicycle, your ratio is the number of times you turn the pedals to the number of times that the wheel goes around on the bike. The lower gear ratios, which are actually the higher number, lower gear first gear, you would say pedal four turns to one turn of the wheel. It's easier to pedal, but the wheel does not turn as fast. Higher gears are the lower ratios. Say you turn one turn of the pedals to one turn of the wheels. You're pedaling harder, but you're also going faster.

As you see as we open up, on the ring gear two numbers are stamped: 41 and 11. We go to the computer, put in the calculator 41 divided by 11 is 3.727272 which is 3.73. It's basically the 41 and the 11. The 41 is the number of teeth that are on that larger ring gear. The 11 is the number of teeth that are on the smaller pinion gear. This is can be important if you do things like towing. Towing you generally want to have a higher ratio. You want to have more turns to the drive shaft than to the wheels. If you want a vehicle that does better on the highway, you'll want a lower ratio. There are other ways to find out your ratio. On later cars they have a sticker in the glove box that has 3 digit codes. You can go online, for example, code GU8 is usually an axle ratio code and you can find out that way. You can also do this. This also works for older 60s-70s vehicles if you want to find out your rear axle ratio.

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