Gear ratios, I need help

[Vizior]

Ok, I'll be the first to admit it... I'm ignorant about a lot of car related things.

Can someone explain to me or point me in the direction of an explaination about what exactly gear ratios represent?

From what I've gathered through search and whatnot the higher the ratio, then the quicker the acceleration.

I'm looking at a Toyota Tacoma(one that I will actually buy and pay for, unlike the cavalier, although parental help will not be objected to!), and I was wondering about it.

It says that on the 5-speeds the final axle ratio is 4.10, while on the 6-speeds and the automatics it is 3.73. Is this the same as gear ratios?

I've seen people write 4:10... I assume that's the same as 4.10.

How do the ratios affect torque?

I'm sure I'll end up adding more questions, but thanks in advance for any help you can give me in understanding.

 

[05 Roush]

You should be more concerned with the final ratio moreso than the rear-end gear ratio. The higher the final ratio, the higher the RPM will be at a particular wheel speed, and thus MPH.

Final ratios are affected by wheel size, rear-end ratio, and tranmission gear ratios. If you go with larger wheels, this essentially lowers your final ratio. If you raise the rear differential gear ratio to a higher number, you are raising your overal final ratio.

So, raising your final ratio either using smaller diameter wheels or high gear ratios means more HP/TQ at lower MPH, but mileage may suffer, and so will your top speed. To calculate torque from engine speed, use this formula:

HP = (TQ*5250)/RPM

Also, here are some useful formulas for calculating final driveline ratios:

drive wheel torque (DWT) = Engine Torque x Gear ration x Rear gear ratio x driveline loss multiplier

Example:

Engine torque = 400 ft-lb
First gear ration = 2.6
Rear diff ratio = 3.55
DL Loss multiplier = .85 (or 15% driveline loss)

DWT = 400 x 2.6 x 3.55 x .85 =3138 ft-lbs

This, however, gives us true torque at the center of real wheels. You'd then have to divide by the rolling radius to get thrust.

Here's a good site you can use to see how gear changes affect your HP/TQ:

http://www.freewebs.com/soslo/formulas.htm