Hey, I have a 2003 F250 with the 5.4l and 3.73 gears. I am going to be putting on a lift soon and have a great deal on some 38" tires. How bad would it be to drive with those gears temporarily?(tempoararily means less than 6 months) Also, from an RPM calculator I see that 4.56 would be about equal but I drive mostly city so would 4.88s be better? Let me know what you guys are running.

Yes, I know I will not have much power with such large tires and towing will be even worse but this is what I bought the truck for.

 

With the 5.4 it will be a dog. Assuming you have the equivelant of a 31" tire on it now, the corrected gear ratio for 38's would be 4.59 in which case you'd probably want 4.88's. I would regear, you're trucks transmission will thank you.

 

I wasnt asking if I should re-gear or not, I know for sure that I have to re-gear but would the truck be ok for a short amount of time?

 

If it were me and my truck, No, I wouldn't run it. It's just too much stress for the tranny IMO

 

Assuming you had 31 inch tires and went to 38 inch tires, you reduced your effective gearing from 3.73 to 3.04. The problem is the transmission. With 3.04 effective gearing you are creating a lot more stress inside the transmission to move the truck down the road. Once up to speed, the transmission isn't turning as fast. Tranny fluid isn't circulating as fast. This leads to a lack of lubrication and a buildup of heat. Not good for an automatic. For a very short term it will work, but you're taking an expensive risk.

If you have a manual transmission, go for it. It'll be OK for a while.

You will need a 4.56 gear ratio just to return your truck to the stock (3.73) effective ratio. I would take the recommendation on the 4.88 gears, it will help get the big tires rolling a lot easier.

 

I have to say, I am impressed with all of the replies above.
Many times this question is asked, we see too many guys eager to say "yeah go ahead and do it", or "I run 3.73's and 40 inch tires and the truck pulls them just fine".
The guys that will tell you to do it, have never driven a truck with and without gears to compenstate for larger tires. The ones that have never driven a heavy truck with big tires and the right gears will say it is alright, and you will hurt the truck. The ones that really know, will tell you to wait until you can do it right. Many guys that lift and then drive around for a while, then get around to changing gears ask themselves, "what was i thinking, driving around with those gears?"
Best bet is to simply wait until you can do it all. If you can get a good deal on tires now, buy them. Nothing says that you have to bolt them on yet.
Your truck will thank you. If you dont believe it, take a 38 inch tire and take your stock tire, and roll the little one up and down your street on time as fast as you can, stopping it as fast as you can ever 50 feet or so. then do it with a 38. This will give you a real appreciation for what your truck has to do every day. Lol.
How about this. Install gears first, and drive it with 4.56's or 4.88's and little tires. You will not believe the acceleration you gain, even with the little engine.
For 38 inch tires and the 5.4L, I kinda like the 4.88's over the 4.56's.

 

Wow, good advice. You could have some fun by putting on the 4.88 gears first.

 

Wow, I knew there was a reason I starting going to this forum. Thanks for all the input and I will just wait until I can get all of it at once.

Thanks

 

Great Post! When I sold my first SD (f350 6"rcd 4.88 banks powerpack plus some extras and 38's) I thought about parting it out and selling the bits one at a time.

That brought about thoughts of a powerpack propelled 4.88 V10 turning 32 or 33's/ Sweet! but bad for the highway.

Anyways... be nice to your truck, get gears first. It's funner that way!