rear axle ratios

[92F350CC]

so what are the ups and downs of having say, a 3.55:1 verses a 4.10:1 rear axle. Basically, the 3.55 gets better economy on account of the driveline not having to rotate as fast to turn the wheels, resulting in lower RPMs, and a 4.10 will tow better and accelerate better, right? I can't quite see how the drivline having to turn more times would make it accelerate better.

EDIT: btw, my 92 has the 4.10 L/S in it and it'll throw me back against the seat.

 

[adrianspeeder]

Yup you got it. Higher numbered ratio "deeper" gears have higher off the line grunt, but rev the wee out of a motor at high speed.

Adrianspeeder

 

[PackRat]

I can't quite see how the drivline having to turn more times would make it accelerate better.

In the simplest terms, the rear axle ratio is how much the torque output is multiplied. For example, if you are making 100 ft/lbs torque, then a 3.55 ratio would be 355 ft/lbs, and a 4.11 would be 411 ft/lbs. The lower ratio axle has about 15% more torque. In theory, 15% better acceleration. There is a small trade off, in momentum, getting the driveline up to speed.

That is one reason why the 5 and 6-speed tranny's are so popular. You get to keep the low gears, that multiply your torque, and one or more overdrive gears, that compensate for a lower rear axle ratio.


Somebody correct me if I'm wrong here. I haven't had enough beer to be quiet, yet.

 

[Travis91]

from what i know. if you have a ford 4x4 you will have a 4.11 gear in the rear and 4.10 in the front.

 

[RLDSL]

I've got 4.10 rear in mine. I was thinking about maybe going to 3.70 for better mileage, but when towing my 8000lb 5er it runs in 4th most all the time and I can't pull 5th gear unless going over 70-75 mph on flat with a tailwind or downhill, I'll have to wait and see how it pulls with the new turbo on it, but if it doesn't want to pull 5th, I may go the other way and drop to a 4.30. I don't use it as a daily driver anyway, it's only used for pulling so I might actually gain a little fuel mileage that way It would make parking a little easier on the clutch foot.

--------Robert

 

[Russ]

Easiest way to understand axle radio's is to look a a 5sp. bicycle. When the chain is on the larger sprockets(tall gear like a 4.10) it is easier to pedal, but you have to turn the crank more to move. IF you use the small sprockets(short gear like a 3.55) you travel further with the same crank rotations but it will be harder pedal.