tire help for a 2012 GMC 2500HD Sierra

zacker · November 25, 2015

Hey guys, im wondering, what is the biggest tire (width wise) I can get away with on a bone stock 2012 GMC Sierra 2500 HD?

Its got LT265 / 60R20's on it now.

Would like it to look a bit more beefy... I would also like to be able to possibly use a spacer to get them to stick out more.

I really don't want to install a lift kit because its a work truck (company owned) so I don't want to put too much $$$ into something I don't really own. Its not leased, we bought it outright in 2012 for my boss as his company vehicle but, he just bought himself a new Jeep so we traded in my 2010 F150 and I took over this GMC because its a lot nicer than the Ford and I was always a GM guy anyways! lol

Thanks!

Blue2500CC · November 26, 2015

From what I have found, the largest that will fit on our trucks is a 295/55/20, possibly a 305/55/20. You may need to crank the t-bars a little depending on your truck. Easily done. Just need a socket and a jack.

I have been hoping someone would come out with a 275/60/20, though it isn't much different in size than stock. The 285/55/20 is a little smaller diameter, but a little wider. The 295 is about the same diameter (just a little larger from what I recall), same with the 305.

Good luck and let us know what you go with!

Big Whiskey · November 27, 2015

275/65/20 and 305/55/20 are both pretty common on trucks like yours, with a few cranks on the torsion bars. 295/55/20 and 275/60/20 should both fit without any trouble at all.

zacker · November 30, 2015

Thanks guys. the "265" part of the tire size is the height correct? so the bigger the number, the taller the tire. so a 295/55/20 is taller and wider than a 275/60/20 ?

Cranking up the T Bar, will that hurt the alignment any and how bad of a ride will it have afterwards?

What about wheel spacers, what size can I get away with if I use my stock tires and not crank the t bars? My guess is that if I use too large a spacer, the stock tires will rub on the fender when I turn?

thanks again guys!

zacker · November 30, 2015

From what I have found, the largest that will fit on our trucks is a 295/55/20, possibly a 305/55/20. You may need to crank the t-bars a little depending on your truck. Easily done. Just need a socket and a jack.

how do you turn em up? I saw a video awhile back that made it look kind of complicated with out a lift and an air gun. is it something doable on my back in the drive way with a regular hand ratchet or breaker bar? My compressor died and I haven't replaced it yet! lol

Big Whiskey · December 3, 2015

Thanks guys. the "265" part of the tire size is the height correct? so the bigger the number, the taller the tire. so a 295/55/20 is taller and wider than a 275/60/20 ?

Cranking up the T Bar, will that hurt the alignment any and how bad of a ride will it have afterwards?

What about wheel spacers, what size can I get away with if I use my stock tires and not crank the t bars? My guess is that if I use too large a spacer, the stock tires will rub on the fender when I turn?

thanks again guys!

Actually, the first number in a metric tire size is the width of the tire in millimeters. The second number is called the aspect ratio, which translates into the height of the sidewall. The aspect ratio helps to determine the tire's height because it's expressed as a percentage of the tire's width. Let's take a 305/55/20 tire vs a 275/65/20 for example. Most would think that the 305 tire is taller, but in this case, it's not. It's only wider. The 305/55/20 tire is 305mm wide (or 12.1 inches), and the sidewall height is 55% (because the second number is 55) of the width...so that means the sidewall is 167.75mm tall. To determine the overall height of that 305/55/20 tire....you double the sidewall height (which comes to 335.5mm) and convert that number to inches (which comes to 13.2") and then add that number to the rim size (20)...so that tire is 33.2" tall and 12.1" wide. Now for the 275/65/20....the width is 275mm (or 10.8 inches)...and the sidewall height (65% of 275) is 178.75mm. So now we double the sidewall height and convert it to inches (178.75 x 2 = 357.5mm....which equals 14.1 inches)...and add that to the rim size (14.1 + 20 = 34.1). So a 275/65/20 tire is 34.1" tall and 10.8" wide.

Edit: And to answer your question about cranking the torsion bars...you don't need a lift or air tools. Just block the back tires...jack up the front end to take some weight off (and use jack stands for safety)...grab a good 3/4" drive ratchet or breaker bar (and socket, but I can't remember what size at the moment) and start cranking (you'll actually be tightening the bolt). Just be sure to keep track of how many turns you're going. I usually use the frame cross-member as a reference point for 1/4, 1/2, 3/4 turns, etc. I'd start with 4-5 turns (same number on both sides)...let it down, drive it around the block so it settles, and evaluate from there. If you stay under 2.5" of lift, your ride shouldn't suffer too much.

zacker · December 3, 2015

wow... who'd-a thunk it.. lol I always thought that the "60" or the "50" were the width.. like say if a car had a set of "N-50's" on the back or "60's" on it... it meant they were fat tires. lol

So why do they make it so complicated instead of making it easier by stating tire height x rim by tire width like on ATV tires ... like my trike, the back tires are 22 - 8 x 11... ( 22" tall x 8" rim x 11" wide.) lol

Big Whiskey · December 3, 2015

wow... who'd-a thunk it.. lol I always thought that the "60" or the "50" were the width.. like say if a car had a set of "N-50's" on the back or "60's" on it... it meant they were fat tires. lol

So why do they make it so complicated instead of making it easier by stating tire height x rim by tire width like on ATV tires ... like my trike, the back tires are 22 - 8 x 11... ( 22" tall x 8" rim x 11" wide.) lol

Haha yeah I know. I've always been a tire nut, so I have a good understanding of the sizes...but it can be quite difficult for many to understand...and rightfully so. My buddies are always calling or texting me with tire questions, haha. Many tire companies still offer traditional sizes, like 33x12.50x20, but there's a lot more options in the metric sizes.

zacker · December 3, 2015

yeah that was my next question... what happened to the old sizes like 33's, 36's, 38's, 44's...? lol

Big Whiskey · December 4, 2015

yeah that was my next question... what happened to the old sizes like 33's, 36's, 38's, 44's...? lol

Oh, they're still out there, but the metric sizes are much more common these days. I think the draw of the metric sizes is that many of them tend to run a bit narrow for their height (when compared to something like an old school 33x12.50). The more narrow tread width helps them clear the fenders easier, allows the use of stock rims, and helps them have better road manners than a wide tire.

BTW, you could also look at a 295/60/20 tire. That's like a 34" x 11.5" Those would probably fit with stock rims and a few turns on the bars. And you could probably even run a 33x12.50x20 if you wanted to. You might need to trim a bit of plastic though.

zacker · December 4, 2015

BTW, you could also look at a 295/60/20 tire. That's like a 34" x 11.5" Those would probably fit with stock rims and a few turns on the bars. And you could probably even run a 33x12.50x20 if you wanted to. You might need to trim a bit of plastic though.

That would be cool... lol thanks!

Blue2500CC · December 15, 2015

Glad BW answered the t-bar question. TY BW!!

I haven't really come across anything stating a 34" tire will fit with the stock rims (or aftermarket rims) without some form of trimming.

If you do get a larger set to fit please post up!!!

Good luck!

zacker · December 16, 2015

Glad BW answered the t-bar question. TY BW!!

I haven't really come across anything stating a 34" tire will fit with the stock rims (or aftermarket rims) without some form of trimming.

If you do get a larger set to fit please post up!!!

Good luck!

will do!