I have an 03 F150 4x4. This truck has a 5.4 with 3.31 gears, auto tranny, and 235 75R 16 tires. I have nasty steely wheels that came OEM with the truck. I am looking to fill the gaps between my tires and wheel wells.

A local tire shop suggesting running 265 75R 16's to fill the gap. This looks like it will put me pretty much at "normal" stock tire size for the truck. This is what I am wanting, but I am a little concerned about performance loss with the taller tire size and the already high gear ratio that I have. Should I be concerned??

After this upgrade I want to buy a tuner of some kind to adjust the speedo and correct everything else that goes along with tire size changes. Any suggestions??

Brian

 

Should you be concerned?? I would be with the 3.31 gears...

I have 3.55 gears and my truck had the little 235's originally and I went to 265/75/16's and I could tell a difference in performance coming out of the parking lot..

I had to get the speedo/odo re calibrated too. That helped a lot, because it made the trans shift at the proper time again... On my truck, it was a simple swap of VSS gears, but your '03 is all done in the computer, so you will have to reprogram..

I also did a simple K&N drop in and a 3" cat back exhaust about that time (over 6 years ago) and that really helped in the 'seat O the pants' meter..

I do tow a #5000 TT and does fine with it, even with the taller tires. I don't think it would do as well with 3.31 gears however...

If you were to get some 3.73 gears and the 265's or even 285's, it would be about the same 'effective' gear ratio you have now with the 3.31 and 235's...

You could also go ahead and get some 4.10's for probably the same $$ as it would be for the 3.73's.... I've thought about 4.10's for my application, but I'm satisfied with what I've got for now... It's been working fine for me for over 100,000 miles, so why mess with it!!

Mitch

 

Regearing a 4x4 ain't cheap.

 

I do not tow much. The most I throw at the truck is a load of firewood or my ATV.

I understand about what you are saying about swapping in new gears, but from the estimates that i got that will be about 7 or 8 hundred an axle.

 

itll be around 1K to regear a 4wd but id recomend it if youre going to go with a bigger tire. go with 4.10s. itll be the same price and youll be happier in the long run.

 

You're at a big disadvantage with those 3.31's if you want to go to a taller tire.... The stock tire is something like 29" tall, while the 265's are just a shade under 32". (The 265's will look much better however!! )

As an example, here are some rpm figures for you to ponder..

With the 3.31's and your 29" tires, you are pulling around 2300 rpms in third going 60 mph. In OD, you are at around 1600 rpms.

With the 3.31's and 32" tires, you would be pulling around 2100 rpms in third going 60 mph. In OD, you are at around 1400 rpms.

That 200 rpm difference won't make a whole lot of difference at 60 mph, but you will really feel it when starting from a stop, or accelerating on the on ramp... You will also notice a bit of a 'bog' at every shift as the TC locks up, before your engine has time to settle in and gain some rpms...

With the 5.4, you could get away with it, but it'll be different from what it is like now!

Good luck! Too bad whoever ordered it originally, didn't pop for the gear upgrade... I think it was only a couple hundred buck option for either the 3.55's or even 3.73's from the factory....

Mitch

 

I bought it off the lot like this. I did it to myself. This is an odd ball truck though. It has the 9.75 and towing package, but 3.31's.

Thanks for the input guys.

Brian

 

I've got an '02 w/ the 5.4 and 3.31s in a non-posi 9.75 diff, and the tow package. I purchased the truck used and the dealership put 265-75-16s on it before it was put out on the lot. I greatly appreciated this since they look awesome, were brand new, and were the tires I would have chosen to put on it if I had bought them myself. However, it does feel like it could use at least 3.73s, and the speedo if off at least 5 mph (at least according to a state trooper a couple of weekends ago ). I have purchased a brand new OEM posi for it but I may not install it until I can afford to do the gears as well to hopefully decrease labor costs.