today i was finally able to up my tire size on my 05 FX4 to 275/70/R18 after doing so i went to the dealer to have a second key made and have the new tire size coded in at the same time. well the took the truck back and put it on the computer and about 15 mins later guy comes up and says that the tires are not within the allowed range (not sure if the range is set on the truck or the computer) and after a few more mins of him messing with it i decided to have it set as close as he could get it. so my question is how do i force the new size to stick

 

What was the stock tire size ?? 275/70/18 sounds really close to stock to me...

 

I've heard that dealerships can only program the sizes that were available standard. Maybe someone knows more on this than I.

 

Stock size is probably 275/65-18 which is less than a 4% difference.

The dealership can only program sizes that were offered new. The stock size is probably the closest they can get.

If it's important for you to have the speedometer be as correct as possible, you'll need to buy a programmer. I'd recommend one anyway, it really makes a noticeable difference.

 

yep...an Edge programmer would correct this and help your truck out like Flash said !!

 

thanks i ordered and edge cs last night looking forward to getting it in