How do you figure out gear ratios??

[Trunks]

i have always wondered, how do you figure out gear ratios? like the best ones and stuff, i know it is math BS like if one gear was this long ________ and the gear ratio was 2:1 then the next gear would be ____ but i dont see how that goes for cars, could someone explain how to figure gear ratios and how to find the best ones...

[imported_admin]

What's the purpose of the calculation? What's your goal? Deciding which rear gears to put in or deciding on a new custom transmission where you select the ratios?

In the transmission, the ratio states how many times the crank turns for one turn of the driveshaft. I.e. if first gear is 3.2 and second is 2.6 then in first your driveshaft will spin 0.31 times for every crank revolution (i.e. it takes 3.2 crank revolutions to spin the driveshaft once) and in second your driveshaft will spin 0.38 times for every crank revolution.

In the rear, the ratio states how many times the driveshaft has to turn in order to turn the wheels once. For example, on a 3.23:1 rear end, one revolution of your driveshaft will turn your wheels 0.31 times (i.e. your driveshaft has to turn 3.23 times to turn the wheels once) whereas with a 3.73 rear end one revolution of your driveshaft will turn your wheels 0.27 times.

If you're deciding on a rear, 3.42 is usually safest for V6 F-Bodies. It might be different for third gen owners but I doubt it...

Moving to Drivetrain...

[Slow-N-ugly]

The formula for ratio is drive divided by driven, I think or it may be backward. This will give you your gear ratio.

I think what you are asking is how do you figure optimum gear ratio for performance, say the 1/4?

To find the best one is a very vague question. As Stefan pointed out you can change gear ratios in your transmission, or your rear end, and we wont even get into tire circumference for the sake of simplicity.

Road racers change out gears so they can be fast or slow in certain parts of the track, without having to shift.

Lets stick with the quarter, you want to cross the finish line in the lowest transmission gear you can, while still being in rpms that provide peak hp and or torque depending on your motor.

You can play with the gearing, to not have to shift into fourth and hold third a little longer for E.T., or shift to fourth a little sooner and try to get there with MPH.


Your rear end gear, is more for adjusting top speed. If you go with a low gear you wont top out as fast, but you will get there quicker and vise-versa if you have a tall gear. I believe gearing is limited by weight, a lighter car can get away with lower gears, while a heavier car needs a slightly taller gear.

Ever heard of a granny gear? the ratio is low to provide torque, which gives you off the line acceleration.
I knew a guy who ran a S-6 in an old Vega, his 1sr gear was so low it shifted to 2nd after one rotation of the back tires.

Did we help ya any?