I'd like to know what the effects will be if I swap my ring and pinion from 4.10 to 3.73, or 3.55. My truck is an 96 F-250 HD with 4.10 gears, 460 EFI, 4WD. Thanks for all the answers that come back.

 

IMO keep the 4.10s. I've got 3.55s (but a 351w though) and while it cruises nice on the freeway, getting going from a dead stop with a load leaves something to be desired. What are you planning on doing with the truck?

 

A little better fuel milage but a little less towing power.

 

Mostly around town, and highway, but also some boat pulling. Thanks for your answer. That's exactly what I needed to know. I was wondering if I could stretch my gas mileage without losing too much performance.

 

Changing gearing is one of the biggest performance differences you can make. I had 4.10s in my truck when I bought it. I swapped to 3.55s when I did my SAS because thats what the D44 had in it. I absolutely hate it. Its gutless as all hell and doesnt get any better mileage.

 

I ran 3.55 gears for about 10 years in a '95 F-150, 351W, E4OD, ~32" tires, so pretty close to your set up but you've got a bigger engine and I had a lighter truck. But I drove that truck with a 1200 lb camper in the bed, towing a 3500 lb Jeep. 75 mph freeways, Colorado mountains. The performance was definitely down from when it had the stock tires, but it was acceptable to me. I ran it in 3rd gear on hills and didn't plan on winning many drag races. So I don't think you'd lose too much performance.

HOWEVER, my advice would be don't do it. It'll cost about $2000 to change gears in both axles. If your mileage skyrockets from 10 to 11 mpg (and I wouldn't bet on that much), you'll save less than $400 / year (assuming 10,000 miles / year, $4/gal gas). Run your own numbers, but for at best a 5 year payback I wouldn't do it.

Of course if you need to replace gears for any other reason, or if you can do it yourself for a lot less money, or if you can find axles with the right gears cheap and in good shape, or if your gears were way off and you were looking at going from 6.32s to 3.08s (exagerating for effect), maybe it would be worth it. But generally gears are an expensive way to get a little gain.