Is Re-gearing worth it?

wnjj wrote:

06Fargo wrote:
Like I said not much experience with light duty trucks but I know there is something to gear reduction occurring closer to the wheels (rear axle) vs dropping gears in the trans - at least in heavy trucks - there is probably a mechanical law somewhere - alls I know if you hook up a high geared truck to a heavy set of trailers, you will be rowin' the stick all day in hilly terrain while the lower rear axle geared truck drives away...

Lower rear axle gearing has the very real effect of spacing the transmission gears closer. That's why there can be a performance difference.

I'll try to explain it here:

The axle gearing divides the wheel speed (relative to the driveline speed) the same amount in every transmission gear.

Let's say you lower the rear axle gearing by 10%. Every gear in the transmission will now have the wheels turning 10% slower than before (e.g. 30mph -> 27mph) and in a higher gear (70mph -> 63mph), etc.

You now have the same number of gears between 0 and 63mph as you used to have between 0 and 70mph. If you were to change the rear by 20% you now space the same gears to 56mph. This means you have better choices about what RPM to run the engine for any given hill/road speed and can make use of yet another gear for speeds above 56mph.

In essence lowering the rear gears acts a bit like adding a gear (or part of one) to the transmission. This is why it is less important with a 6-speed than a 4-speed.

Good post. I will add one thing. If you put short gears in your truck it won't make much difference in how fast you make it up a hill because you are not adding power. It will make some, but not much. The flatter the torque curve of your engine the less difference.