i recently bought a "new" truck after someone rearended my last f150 and totalled it (they were gion about 50 mph). anyways, the dealership put a 5 inch trailmaster lift and 315x75x16 m/t's. it still has a lot of pep to it but it i still am considering changing the gears. is it worth puttin 4.10s for the extra power? will it make my gas mileage better or worse?
btw, its a 1999 f150, 5.4L, 4x4.

 

just made a sig...now you can see my truck

edit-how do you make the picture show up?

edit2- nevermind...lol...figured it out

 

Yes I definately recommend regearing it. For 35's I'd recommend a minimum of 4.10's. If you do alot of highway driving I'd probably stick with the 4.10's. If you do any offroad I'd opt for 4.56's.

The in town gas mileage will get better with the new gears because the motor doesn't have to work as hard to get them pigs moving. Highway mileage may increase or decrease, hard to say. It should get better because the motor isn't working as hard, then again it may get worse because the rpms increase slightly. Either way it isnt' gonna be that much of a difference. The intown mileage should increase quite a bit.

Nice truck btw.

 

thanks alot for the help!!!

 

Keep an eye on your torque converter too, they dont really seem to be very happy about turning larger tires.......

 

OK well.... Someone with true experence here.... I've been running 315's for the last 3 1/2 years. Put over 75,000 miles on my truck so far.... HArd miles too.

NO PROBLEMS with stock 3.55's and a 5.4.....I even flat tow my explorer and use to flat tow B2's when I had them.


Here are some pictures to check out

 

i would recomend 4.56 gears for 35" tires to get the RPM back to within 100rpm of stock, good luck

 

I think its always a good idea to re-gear whn you get large tires 35 and up.

 

I second that. while its possible to drive with lower gearing, its harder on your drivetrain and less fuel efficient.

 

it hink you mean higher gearing, it would be lower numbers because it has less teeth on the ring and pinion (3.55ex), but higher gearing lower gears have more teeth on the ring and pinion to get the gearing lower(4.56ex) FYI