I recently upgraded from the stock 17" wheels to 20"s and its my understanding that this may cause some problems if I dont get the computer reprogrammed. I went to Summit Racing and they told me that the miles on my truck will add up quicker and inaccurately, the speedometer will be off and my shift points are likely wrong... My truck is new and Im freaking out. They suggested the Ford Recalibration Unit. Its only $100 but Im curious if anyone has installed it or used it. Does it work and how diffucult is installation? Thanks for the help

 

See Here. For $100, I'd rather save some more for a custom engine tune that also can change the tire size for you.

What size tires do you have now vs. stock?

 

My truck had 265/55/17 continentals and I upgraded to 275/55/20. I think its about 3 inches bigger in diameter.

 

When you refer to a custom tune do you mean a dyno? Im a novice at this stuff and I just want to make sure I dont do any long term damage for a short term thrill. Nor do I want my miles to add up incorrectly

 

There's about 3.5" difference in those tires. Your odometer, however, will actually put on miles more SLOWLY than with the smaller tires (bigger tires=less rotation to travel the same distance). Likewise, your speedometer will read low (slower) for any given speed.

 

That's over 10% larger. I highly recommend getting the tire size updated. I would think that any Ford dealer can change that for under $50 as long as it is to another stock size. In this case, using the stock 4wd 18" tire size would be close enough.

By custom tune, i mean a custom engine PCM, liek the XCAL, etc. The tire size can also be programming into that performance tune.

 

I agree.

 

I called 3 Ford dealers and none of them can recalibrate to 20" wheels which surprises me becuae they are 20" OEM Ford wheels. Anyway, 18" is the highest they have the ability to do. I think I may install an Edge tuner but I think its a bit costly. Summit Racing has them for $440... But if that what i have to do to get my truck right and make sure Im not causing future problems then its a worthwhile $440. I just hope the Edge Tuner is as nice as I keep hearing and I hope I get some performance out of it.

 

The size of the wheel doesn't matter. It's the height of the tire. In other words, the callibration would be the same for a 33 inch tall tire on a 17 inch wheel as a 33 inch tall tire on a 24 inch wheel.

 

Ok i got ya now. Either way, my total wheel diameter is appx 3 inches bigger now than it was factory so i have to do something. Unless someone convinces me otherwise Im probbaly going to try the Egde Tuner

 

Check with Troyer performance on the tuner. I believe they offer discounts for F150online members and his tunes are great.

 

I went with 275/60/20 my speedometer was way off from the stock 17's. I bought the micro max tuner off of Ebay(200.00). Best investment I ever made for my truck. Shift points were horrible even before I upgraded my wheels. Anyway I am dead on with my speedometer. I had to manually enter in the tire sizes little by little until I got it right 32.25 inches. Just by changing tire size in the tuner it automatically changes shift points also. I found a neighborhood speed calculator unit around the corner from me. Kept driving through at about 50 mph till I got it right. Shift points are perfect now. Great investment, Scott