Originally Posted by FTAP
I have 16" tires and I'd like to upgrade to a larger wheel and tire.
2009 Silverado 2500 pickups came with either 245/75R16, 265/75R16, or optional 265/70R17 tires. If your wheels are 16" diameter instead of 17", and you want bigger wheels, then I would go with 18" diameter wheels.
Then be certain the wheels are wide enough and strong enough to handle the max weight of the tire. For example LT275/65R18E tires require 18" wheels at least 7.5" wide and not more than 9.5" wide. The are rated for 3,305 pounds weight capacity @ 80 PSI. So be certain the new wheels are rated for at least that much weight and PSI.
That takes care of the wheels. Next is tires. If you don't want to change the performance of your truck, then you want the new tires to have close to the same tire revolutions per mile (revs/mile) as the old tires. When going from 16" wheels to 18" wheels, that means reducing the aspect ratio (middle number of the tire size) as the wheel diameter goes up.
In your case, I'll assume your OEM tire size is LT265/75R16E, which has 657 revs/mile. So the replacement tire for 18" wheels would be size LT265/65R18E which has 659 revs/mile. Insignificant difference in tire diameter means insignificant change in power and performance of the drivetrain. IOW, you effective axle ratio doesn't change, so your speedo, odo, and tripmeter are all unchanged. No difference in the power and torque going to the ground to drag your trailer.
Now the problem with the LT265R18E. Very few manufacturers produce that size. The only one I find with a quick search is BFGoodrich AllTerrain. Several other brands make that size but in P-series instead of LT. So if you want a different LT tire than the AllTerrain, then you have to go to a more available size = LT265/70R18E.
Note the aspect ratio went from 65 to 70, which means a taller tire with fewer revs/mile. With that size you can add General, Goodyear, and Toyo to the available manufacturers. But revs/mile dropped from 659 to 637, or 3.3% difference. That means 3.3% change in the effective axle ratio, as well as 3.3% change in the speedo error unless you have the speedo calibrated to match the new tires. Because of the change in axle ratio, your engine RPM at the same corrected speed will be 3.3% lower. IOW, if you now cruise at 2,000 RPM, you'll be cruising at only 1,934 RPM with the taller tires. Depending on the HP and torque curves of your engine, you'll probably have less power and torque delivered to the ground at the lower RPM.
If you're wanting the image of taller tires and are willing to sacrifice performance to get it, then you can go to even taller tires than LT265/70R18. Or else you can plan on spending several thousand dollars to change the ring and pinion gears in the front and rear differentials to offset the change in revs/mile of the really-tall tires.