Tire sizes

Air Biscuit · February 22, 2004

I want to upgrade from 245s to 265s. I know the dealer can update the computer for the new size but when I went to ask about it, the service rep said that I probably won't need it. (The guy wasn't being a goof - said he wasn't sure - and asked me to check with the foreman I'm ready to switch.)

One thing he said made me go hmmmm...He said the dealer is now fitting 20" wheels on trucks out the door and as far as he knew, they weren't doing any computer recalibrations. Could this be true? Is the 20" wheel and tire combo similar to a 245 or, more likely, 265 setup?

Just curious.

Wingnut · February 22, 2004

The 20" part has nothing to do with your speedo....It's only the diameter of the rim. What matters is the diameter of the tire.

What size tires do you have now, and what size are you going to?

Air Biscuit · February 23, 2004

I'm just going to a 265. Should be no problem. I was just wondering if GM has changed the computer settings to incorporate the fact that they (effectively) now sell trucks with 20" wheels because until now, my understanding was that it used to be fairly limited (max 265/75r16). (i.e. the guys with 285s can't get reprogrammed unless they go to a performance chip).

Again, just curious.

Wingnut · February 23, 2004

265 is the width of the tire, not how tall it is. The second number is how tall it is, in relation to the width. The third number is the diameter of the rim.

The rim diameter is meaningless when it comes to computer calibration.