Currently I have stock 20's with 3.55ls, I'm plannin on adding a leveling kit and 35's on stock wheels. How bad do I need to regear? Thanks for any input.

 

Depends on if you want old ladies driving tractor-trailers to beat you off the line. I wouldn't say that you HAVE to, but it's probably a good idea. If you've got a 4.6L with 3.55s then you really should, but there's nothing saying you can't run that setup with 35s. I believe there's a few people on here doing that without any issues. Big tires just put a lot of stress on your tranny and, well, just about your whole drivetrain. I've got a 4.6L with 3.55s and I noticed that when I put my 33s on, the truck seemed really unhappy. Luckily I've got my new 4.56s sitting right in front of me and they'll be going in the truck on Wednesday.

If you've got the money, it would be well worth it to regear.

 

I drove my truck with 35's and 3;55 gears for a year, Then put 4;56's. Halfway home from the shop I had to get out to make sure I was driving my truck!!!!

 

hey guys, what are the bad parts of running your truck with bigger tires and not regearing? ive got a 99 f150 2wd, i put 285-75-16 on it with the stock 3.55LS gears. I did notice the power change, but what will that do to my tranny and other parts? Thanks for the info.

 

I had 35's on my truck with a 3.73 and had to leave the OD off untill I hit 50mph so it did'nt feel like a 6cyl. Also in town mileage was terrible.

 

It really depends a lot on how you drive the truck. If you accelerate heavily everywhere then you will be putting more stress on your tranny and engine. If you take it easy you will probably never have any problems. Chances are, you will never have any problems just because you went up one tire size. If you live in hilly terrain you should be careful with your OD (if you have it) and/or towing. I live in south Florida where there are no hills, but if I get on a hill on a highway, the truck kicks in and out of gears like it has no idea what it should be doing. You run the risk of overheating the transmission if this happens. You shouldn't have any trouble on 33s as long as you're careful, but regearing is definitely worth the money in my opinion.

 

alright thanks for the info. when should i keep my overdrive off?

 

I do have the 5.4 if that makes a difference. So 33's I should be ok, but 35's I should regear to 4.56's?

 

As a general rule of thumb, OD should be turned off during city driving less than 55mph. You should also keep it off when towing or in hilly terrain. DEFINITELY keep it off if you're offroad.

Having a 5.4 WILL make a difference. With 33s I wouldn't bother regearing unless you are doing it for performance reasons. If you do decide to get 35s and regear then it's totally up to you what gears you get. If you want better highway fuel economy then go with 4.10s. If you want more low end grunt for off road use and better acceleration get 4.56s. Personally, I would go with 4.56s because because IMO a truck on 35s that hauls *** is better than a truck on 35s that get 17mpg. I think I have seen that you can get 4.30s from somewhere, which would be a good compromise. What gears you should get really depends on what kind of driving you do.

 

so what your saying is that i should always have overdrive turned off unless im driving faster than 55? I always thought it got you better in town mileage.

 

This is what I have always been told. However, I just went and read up on it a bit and I saw a number of different suggestions on OD use. All of them said to turn it off in hilly terrain or while towing. The general consensus was to turn it off in stop and go driving, which is what I mean when I said city driving. Just about everything I read did say to turn the OD back on at over 40mph, where I said 55.
You'd probably be best to wander up to the Transmissions forum as they have threads on this all the time.

 

You can get 4.30s for the rear but not the front. So if you have a 4x2 you are ok and if you have a 4x4 you are out of luck.