245/75/16 tires to 265/75/16

Wheel rim width is your biggest issue. As I remember the 265 requires a 7.5 inch rim width and the stock GM rimmis either 6.5 or 7 inch.

Yeah, overall height difference is about an inch as I recall. So about 1/2" difference in ride height. Unless you're already iffy, it's a non-issue.

The rim width is the issue. You can squeeze them onto 7" rims but putting them on 6.5" rims pinches them in too much, at least for my taste.

You are basically changing your final gear ratio. Your engine will either be working harder at lower RPMs, and/or need to downshift sooner and more frequent.

You are changing your final gear ratio by a little over 3%. When your speedo indicates 55mph, you'll actually be doing 57mph.

Good Year makes a 265/70/16 which is closer to the diameter of the 245/75/16. The problem is still putting a 265 on a wheel not designed for it. I had a Suburban with these tires on it and I would have to say there was a wondering feeling with that truck versus others I had driven with the OEM spec'ed tires.

The 265 is going to give up some wet/snow/ice traction versus the same 245 tire.

I had 265's on my K2500 Burb and my 2500HD. With the HD I always fought handling issues after going to our larger camper. It also wanted to wander while towing. I have no idea if it was the larger tires causing that or not.
With the diesel I doubt you'll notice a difference in power.

I don't know about wheel width, but height wise you won't have any issues. In fact I doubt you'll even notice it. I ran 265/75R16s on a little Xterra for years and it did fine with them. Better than fine offroad - I could get that thing about anywhere. I think they were just over 12% larger than the little stock size tires it came with.

ChooChooMan74 wrote:
You are basically changing your final gear ratio. Your engine will either be working harder at lower RPMs, and/or need to downshift sooner and more frequent.

Won't make hardly any difference.
With 3.73 gears, .67 final drive @60 mph it's only 58 rpms.

Depends on if you drive a 1500 or a 2500 ... if you go from 245 to 265 on a 1500, there may be a little catch on the front fender wells when you make deep turns - I just trimmed the well edges about an inch or so, and no problems.

Am not sure rims are an issue - but it's certainly doable ... My 2003 GMC 1500 came with 265's, my 2003 2500 came stock with 265's, and my 2015 2500HD came stock with 265's ...

I did that with our F250. The speedo read 2% fast with the 245's. With the 265's it's just about perfect comparing the speedo to GPS. Same with my Prius. Went from 215/45 R17's to 215/50 R17's and corrected the speedo. Most manufacturer's calibrate the speedo to read a little fast as it's illegal for it to read slower than actual speed. Better to err on the fast side.