Different sized winter tires

[Fordnatic]

I live in Anchorage, where it is common to run studs in the winter. I found a good deal on some Ranger steelies with studded tires (4 for $100). They are sized 235 75 15, while my originals are 255 70 16 on my wife's 99 Ex. The tire size calculator says this is going from 30.06 diameter to 28.88, a difference of 3.92%. I can live with the speedo being off (calc says 2.45 MPH at 60). My question is....will this be OK with the computer and running of the engine? I have and Xcal 2 for my F150 and I can adjust the rev's per mile on it. It will read codes on the Ex, but I don't think I can adjust parameters on the Ex as long as it has tunes for my F150. Thanks for any knowledge.

 

[askingxforxit]

you can buy a programmer or take it to the dealer and have them reprogram your ex for the different size tires.

 

[Gator Jeff]

The only hard and fast rule about tire sizes is to make sure all four are the same size on a 4WD/AWD vehicle. There's a member here who just killed a transfer case because of mismatched tires.

A computer flash will keep everything accurate, but the smaller diameter, especially that slight difference will do nothing.

That does sound like your found a great deal, too.

 

[Explorer#2]

My X came with 235/75/15 as stock so I dont think its going to cause a problem

 

[brianjwilson]

The only possible problem would be if you have larger rotors on your 99 than the previous years did.

 

[Fordnatic]

I wondered about the rotors, but I could always try before I buy for that. And I knew about the reprogramming at the dealer, but don't want to have to do that twice per year. Seems the consensus is that just under 4% smaller diameter won't bother the computer too much.

The main reason I was concerned was because when I got my Xcal and tunes for the F150 from Troyer Perf, that seemed to be a big factor and you are supposed to change the revs/mile anytime you change tires. Even the same size tires from different manufacturers are supposed to be different enough to matter, you're supposed to go to the manufacturer and get the revs/mile for that specific tire. Maybe that's more a factor for the custom tunes.

 

[WhiteLimited]

No...The rotors are the same size for the 95-01s explorers...as far as i know.

I have stock 16" Limited wheels with 255/55 16s for summer and i ran 31x10.50 on 15" steelies studds last year...This year will be 235/75 15 it wont make a differance except the speedo being off a very little...

welcome! another local guy!