After researching here I've decided to pull the trigger on a 2" AS spacer and a set of BF Goodrich AT in 285/70/17 on stock rims. I pull a trailer that is really heavy on the tongue which is why I only went with the 2" lift and 32.7" tires. My question is, how far off will the speedometer and odometer be at highway speeds after going to the bigger tires? Can it be corrected?
I'm driving an 04 FX4, 5.4, 3.73 gears. stock tires are 255/70/17 General Americraps. Thanks

 

It can be fixed, best way is with the edge programmer there or something like it. I have a fixed box from Ford Motorsport that goes underneath for 100 bucks, I haven't installed because my speedo isn't off much, like 3 mph @70. You, ya, it will be more, but a little, like 5mph. It'll work out good if you get a programmer, but these are the ways I know. Others will be more accurate in their experiences as they'll have done things with the newer trucks, mines a 2000 and I started with 265/70/17's to 285/70/17's.

 

Your stock tires/replacement are the same sizes as mine, and my speedo is off 3 mph at 60mph. (BFGoodrich's website has a calculator) Granted, the higher the speed the more the error, so really you dont need to worry about it unless you are on the highway.

 

i was gonna say the same thing...

 

5% larger, so your speedometer and odometer will read 5% less than what you actualy travel. So, 60mph indicated, you are going 63mph. @ 80, you are really going 84mph. When your odemeter say you drove 300 miles, you actually drove 315.

 

I went to the Goodrich Site and couldnt find any Calculator? Can you provide the Link? Thanks..
Nevermind, I found a great Calculator under Discount Tires after doing a Search for "Tire Calculator"...