Largest tire that fits a 2018 3500 duramax

xRogrimx · October 19, 2017

My brother in law ordered a new 2018 duramax 3500 ltz and wanted me to ask what is the largest tire you can fit on this truck stock. He does have a leveling kit to install on it. He has a set of 305/70/18 And I told him no way.

SierraHD17 · October 19, 2017

I cranked my stock keys as high as they would go more or less on my 2017 2500HD. With the stock 20's I have a 295/60/R20 and I have well over an inch between the inner fender and the tire with the wheels cranked...... he will be pushing it with a tire that's 0.8" taller than mine but it should still fit.

For a "levelling kit" all he really needs is shock extensions lol.

Edited October 19, 2017 by SierraHD17

SMiller · October 20, 2017

They will rub at full wheel lock but I would run them no stress.

GMC4Zee · October 20, 2017

I am thinking the same only just going wider. 285-55-20's. almost same height as stock. should I be okay with these? I have stock suspension.

SMiller · October 21, 2017

On 10/20/2017 at 4:36 PM, GMC4Zee said:

I am thinking the same only just going wider. 285-55-20's. almost same height as stock. should I be okay with these? I have stock suspension.

Those tires are to small, at least go 285/60/20's.

CRApex · October 22, 2017

3 hours ago, SMiller said:

Those tires are to small, at least go 285/60/20's.

I went with 305/55/20 on mine. No rub stock and wider tire looks much better.

Big Whiskey · October 22, 2017

On 10/19/2017 at 6:08 PM, xRogrimx said:

My brother in law ordered a new 2018 duramax 3500 ltz and wanted me to ask what is the largest tire you can fit on this truck stock. He does have a leveling kit to install on it. He has a set of 305/70/18 And I told him no way.

With a level, 305/70/18 might be possible, with some trimming. "No way" is probably over-reacting a bit, but they won't fit easily. That being said, lots of guys are running 295/70/18, 285/75/18, and 305/65/18 without any trouble at all on trucks like that with a level. There are also guys running 35x12.50x18 BFG's (which tend to run a bit small) with leveling kits and no problems. If he already has the tires, then I'd do whatever it takes to make them fit.....which probably won't be much more than installing the leveling kit and trimming the carpet liner.

On 10/20/2017 at 3:36 PM, GMC4Zee said:

I am thinking the same only just going wider. 285-55-20's. almost same height as stock. should I be okay with these? I have stock suspension.

Yes, those will clear on a stock truck without any problems at all......but they'll look too small in my opinion. Something like a 305/55/20, 275/65/20, or 295/60/20 would look much better.

gearheadesw · October 22, 2017

Running 325 65 18 BFG ko regulars on my 2016 GMC 2500, cranked bars, shock extensions, no rubbing, I take the 1000 lbs 4 wheeler in the bed, into the sand tails flexing and with weight in the back, still no rubbing. That a short 35 x 13.50, only measures 34.25 inches mounted on the truck, though. I am running an aftermarket wheel, 18x9 with +18 offset, like 5.7 inches of backspacing, so that helps. The 305 70 18 is narrower, and just a touch taller, if he wants it, he can do it, will need to massage the fenders and bumper, my Backstop front bumper helps here also...

GMC4Zee · October 23, 2017

Will 305-55-20 fit on the stock rims? I think rims are 8.5" wide.

SMiller · October 23, 2017

7 hours ago, GMC4Zee said:

Will 305-55-20 fit on the stock rims? I think rims are 8.5" wide.

All day, TONS of GM HD trucks running this tire.

EZTundra77 · December 31, 2018

On 10/23/2017 at 5:53 PM, SMiller said:

All day, TONS of GM HD trucks running this tire.

So I have a '17 3500 HD. Currently bone stock except the lower valence removed. I would like to run 295/70/18 MT Baja MTZ P3. I dont want to bump up to 305 since my rims are only 8" wide. Also, 305 and larger are load E2 and I want to stick with E1 for towing. So for 295/70/18, I am assuming i need a level/shock extensions. Anything else? Minor trimming would be ok.

gearheadesw · January 1, 2019

You may be able to run the 295 70 18's on stock wheels with the stock torsion bar keys cranked way up, and shock extenders.... My trucks heavy at 8,300lbs, lots of tools, bumper and winch, etc... I always rub when others don't, with the same set up.

I'm running 285 75 18's, just about the same as the 295 70 18, a little taller, aftermarket keys, shock ext. and 18x9 wheels with +12 offset. It's the wheel offset that had me rubbing.

SierraHD17 · January 1, 2019

A 295/70/18 is functionally the same diameter as the 295/60/20 I have on my 17. With stock offset i have miles of room with the bars cranked up... wouldn't doubt they would still clear fine with the truck stock either.

EZTundra77 · January 1, 2019

14 minutes ago, SierraHD17 said:

A 295/70/18 is functionally the same diameter as the 295/60/20 I have on my 17. With stock offset i have miles of room with the bars cranked up... wouldn't doubt they would still clear fine with the truck stock either.

Is there something not stock about you truck aside from the cranked bars?

SierraHD17 · January 1, 2019

Nope. Well there is lots of things done to the truck but that's the only thing done to it affecting ride height. Stock front end with the bars cranked via the factory keys. I probably sit a lot higher than a lot you guys do, I dunno. I loaded an engine from a 2017 L5P truck into mine and he had a 6" lift and at least 35's. He might have been 4" taller than mine including the rear.. it kind of pissed him off lol.

Edited January 1, 2019 by SierraHD17