On my '01 SuperDuty, you could re-set the "revolutions per mile" figure in the stock computer to correct the speedo/odo when running larger tires. I believe a 35" tire was the max the stock computer could compensate for.

Can the '04 F150 be re-set the same way?

I just want the speedo and odo back to accurate as I'm running 305/70R17's. I'm not up for buying a "tuner" solely for the recalibration ability.
Has anyone had the dealer make the change for them?

Thanks for any insight.

Bill

 

There is a limited range that can be reset. I replaced my 235/70r17 with 265/70r17. The dealer tried to reset with the tire size and the error message said "outside of range". They set it for the largest size tire that is built in and said that the speedometer would reflect a slower speed than I was actually going. By using a couple of different radar units and a GPS, I discovered that my actual speed is 1.6 mph slower than the speedometer reading. I measured the tire and noticed that even though it is labled 265/70r17 it is actually smaller than the published standard. Measure your tires, determine your "real" rpm, and they can probably get fairly close.

 

on my 04 lariate I have the 275's and with my GPS I was able to determine that my speedometer shows im actually going 1.8 mph faster than I really am at 70mph, so I can go up two sizes without changing the speedometer.

 

you can calculate the error in speed here http://www.discountpartcenter.com/tirecalc.html

 

wldwilliam, are you having any problems with rubbing with the 305's with just the leveling kit? and what is the backspacing on the 17 gordon racing rims

 

lewisbest,
I ever-so-slighlty trimmed the lower part of the inner fender liner and fender flare where the tires would rub on full-lock. I get no rubbing with normal street driving. I haven't had it out in the rough yet but I am fairly certain that there will be contact when the tires are turned and some rough terrain encountered. With that said, the 305s look great as it sits. I believe the B/S on the Gordon wheels is 4 1/8".

RandyH,
my stock tires were 275/65r18 which if I'm not mistaken, are a little taller than your 265/70r17. They should have been able to hook you up...unless maybe you have a 2WD or V6 or something that would not carry the same tire choices in it's computer...interesting

blitzen25bm,
cool calculator. thanks

I wonder if the tech only has a choice between tire sizes or if the actual rpm figure can be programmed. On the SD I had, I think 601 was the lowest rpm figure (largest tire) that was available.I think I'll give my service dept. a call tomorrow.

thanks guys

 

They can set it by tire size or rpm. Standard tire size definition on 265/70r17 is 31.7 or 657 rpm. This is outside the range on my 2wd XL with 3:73 rear. I don't remember the range available in the computer, but it was stored in the truck not the laptop. After it was set for the largest tire available and being told that I would actually be going about 4 MPH faster that the speedometer indicated I noticed that everyone was passing me. I checked my speed with a GPS and two different radar units and determined that I was actually going 1.6 MPH slower than the speedometer indicated. I measured my tires (Bridgestone Dueler AT REVO) and they are smaller than the published specs. Close enough.

 

RandyH,
Thanks for the info...good to hear they can change the rpm...hopefully they can go as low as 596 or so.
I think I'll take the GPS out this week end and do that test as well...