manual gear ratios?

Question

What exactly do the gear ratio's mean? For example: I/II/III gear, 4.35/2.50/1.66:1 gear ratio...?

In English, please? :-) thanks

Also, what is the final drive ratio?

Answer 1

OK you have two sets of cogs in the car. 1) Gear Box 2) Differential

If your car is front wheel drive the diff is in the gear box.

Final drive ratio is the ratio of the diff. 4.55:1 is considered a low ratio and 2.75 is considered high.

Low ratio gets you off the line in a hurry but not much top speed. High ratio is high top speed but slow to get there.

Lets say first gear is 4:1 or 4. Diff (or final drive) ratio is 3. you multipy the two together to get the overall ratio. In our example here, the engine will spin 12 times for every one time the drive wheels turn.

If second gear was 2.5 then the engine will spin 7.5 times for every turn of hte drive wheels.

4th gear is usually 1:1 which means in our example the engine will turn 3 times for every one turn of the drive wheels.

5th gear is usually somewhere about 0.8 so the engine will turn 2.4 times for one turn of the wheels.

Make sense?

Answer 2

Think of it as torque multiplication or revolution reduction. If your engine were to drive your tires directly, it would not have enough power or if it did, you would go too fast. Final drive is the axle gearing and is usually between 2.5 and 4.0 to one. Top gears are closer to 1 to 1 because speed is more important than power and lower gears are usually 4 or 3 to one more for power (torque) than speed. For an interesting explanation of torque and horsepower visit this page at my website:
http://www.geocities.com/seabulls69/HPandTorque.html