I can't believe I'm having such a hard time with this but,...I own a 2010 GMC Sierra 1500. It's an SLT and came with P275/55R20's. I would like to get different rims and tires for a few reasons:
1)in my opinion, Goodyear tires are junk, junk, JUNK
2)I do like the 20' wheels but I feel like the low profile tires are just plain horrible in snow(I live in Wisconsin).
3)I'd like to install a leveling kit -no lift-(so of course I need some nice tread to give it a nice stance.

Any help would be appreciated because right now I don't even know if I should go with 17" or 18" wheels.
A big worry I have is: how big of tires can I go without having to re-gear and/or dealing with my speedometer being off.

my stock wheel/tire diameter: 31.9
LT275/70R18: 33.2
LT275/70R17: 32.2
I would hate to ruin the incredible ride of the truck but I should be able to find a middle ground????

 

The 17's with those LT's wont hardly throw off your speedometer or affect gear ratio. Maybe just 1 mph. Thats what I went with on my 4x4 Burban.

 

As long as you maintain the same tire diameter as stock, you can go almost any size wheel tire combo as long as the brake assembly still fits. Use a Tire Size Calculator and try a few different sizes to see how they compare. There's quite a few on the web, but here's one you can try...

Tire Size Calculator - Compare Tire Sizes

If you tried a 275/65/18 your diameter would be 32.07, a little closer. The 17" size you quoted is pretty close too.

Keep in mind that changing your tire size can also affect your ABS brakes and traction control as well as your speedometer. Keeping below 1% difference is best.

 

Thanks guys! I do like the idea of 18's better than 17's. I think I also want LT265's or LT275's at the most. I had a '04 Silverado with LT285/70R17's with Nitto Terra Grapplers.
The truck looked really good but mileage went way down and it didn't get around very good AT ALL in the snow...or mud. I wonder if that was tire size or the Nitto's?? I guess I'm not much of a fan of those Terra Grapplers either. Probably nothing but BFGoodrich's for this guy.

 

Ill swap you my stock 17's with P265/70/17 Goodyear AT/S with less than 6000 miles off of my 2011 Sierra with you.

 

Thanks but no thanks. I've kinda got my mind set on a few different aftermarket choices and I really don't like Goodyear tires.
I appreciate the offer though.

 

Me neither... I refer to them as Good For A Year.