265/75/R16 to 245/75/R16

Hemling wrote:
My new Excursion is getting some front end work done, which led to some uneven wear of the tires it has on it. I would like to put the tires from my Suburban on my Excursion, but they are a little smaller (title). What will this do to my final drive ratio? I have a 4.10 rear.

If you have a 4:10 rear ratio, and if your ring and pinion is OEM stock, then that must mean you have a 5.4L gas engine in your Excursion. Which means that a shorter tire will help your small gas engine accelerate better, and make more use of the transmission's higher gears when pulling a load.

It also means that you may get slightly worse fuel economy. You would be going from your current 4.10 ratio to a 4.26 effective ratio, if you changed from stock 265 tires to your Suburban's 245 tires.

A 4.26 ratio is not that far off from the factory upgraded 4.30 ratio that was available as an option on V10 Excursions. The 4.30 was not offered on the 5.4L, even as an option, so prepare for the PCM and electronic transmission shift scheduling to be a bit miffed. It might be possible to have a dealer reprogram the info that the transmission logic relies upon via the PCM to account for the reduction in tire diameter... which would also help keep your VSS readings more accurate.

If you don't have a 5.4L, and your rear end is still stock, then you have a different ratio.

If you have wider wheels than the stock 7" rim width, then I would not advise mounting the 245s before checking with the tire manufacturer specs for the widest rims your particular 245s can be fitted to. I believe the widest rim my Suburban's 245 tires can be fitted to is 7", maybe 7.5". However, many aftermarket wheels are as wide as 8", 9" and 10", so if your Excursion has a set of those things, then you might want to double check the specs for your tires.