Biggest Tire You Can Fit On a Stock GMC Sierra – Fitment Guide

A decent tire and rim combo can make such a massive difference on looks and performance if done correctly. Big tire upgrades are one of the first and most popular modifications to off-road trucks since it’s the easiest way to get a more aggressive look, increase ride height, and improve traction on and off-road. So what are your big tire options on the GMC Sierra’s? Let’s find out!

The biggest tire you can fit on a 2014-current GMC Sierra 1500 running factory stock suspension and rims are a maximum of 32.6 inches.

If you are not prepared to do trimming and cutting and you are running stock suspension then you’ll be limited to a 32.5-inch tire, depending on the tire brand of course. The up side, there are many other alternatives you can try.

Let’s now look at exactly what is required to make the biggest 33-inch tires fit, as well as some of the most popular tire and suspension combinations guys have tried with 100% success.

GMC Sierra 33-inch tires and no lift – Options

When looking at 2014 to current Sierra shapes, the maximum tires size you can go is a 32.5”

This can be in the following forms:

17 Inch Tires on a Sierra GMC 1500

235/85R17= 32.7X9.3R17 (Trimming Required)
255/75R17= 32.1x10R17
275/70R17= 32.2×10.8R17
305/65R17= 32.6x12R17 (Light Trimming)

18 Inch Tires on a Sierra GMC 1500

255/70R18 =32.1x10R18
275/65R18 =32.1×10.8R18
305/60R18 =32.4x12R18

20 Inch Tires on a Sierra GMC 1500

265/60R20= 32.5×10.4R20
285/55R20= 32.3×11.2R20
305/50R20= 32x12R20
275/60R20= 33×10.8R20


Many truck owners want to know if it’s actually possible to run bigger than 33” tire on a stock suspension without issues. How many actually end up running bigger than 33’s on stock suspension is another story altogether, since the amount of cutting and trimming without a leveling kit is ridiculous. Many eventually opt for a small 2“ leveling kit to allow better clearance inside the wheel arches and increased clearance from the UCA.

On the other hand, a 2” suspension upgrade will resolve many UCA and body clearance issues associated with fitting a 33” or bigger tires while still running on the stock rims. The tire width and rim offset is actually the most important issue to be concerned about. Once you go than a 2” or 3” lift with a combination of aftermarket rims with a more negative offset things become a lot easier, but also a lot more expensive.

Read this if you want to find out what the biggest size tire is you can fit on a Colorado w/without a lift kit

So in summary, the absolute biggest tire you can squeeze in a stock GMC Sierra, without a 2” leveling kit, and no suspension upgrade would be a big 32.5” max, but it might require a bit of wheel well trimming, since there might still be some rub at full lock or in reverse. Again, the tire brand and tread pattern can mean the difference between clearance and having to do extra trimming.

A 33” tire can be in the form of any of the following sizes depending if you intend going off-road and want to keep all the practicality or you just want a more aesthetically pleasing “show truck” stance.

17” Wheel Size 
255/80R17= 33.1x10R17
285/75R17= 33.8×11.2R17
295/70R17= 33.3×11.6R17
305/70R17= 33.8x12R17
33X10.5R17 
33X12.5R17 
33X13R17 
33X13.5R17 
33X9.5R17 
  
18” Wheel Size 
275/70R18= 33.2×10.8R18
285/70R18= 33.7×11.2R18
295/65R18= 33.1×11.6R18
305/65R18= 33.6x12R18
325/60R18= 33.4×12.8R18
33X10.5R18 
33X11.5R18 
33X12.5R18 
33X13R18 
33X13.5R18 
  
20” Wheel Size 
275/60R20= 33×10.8R20
285/60R20= 33.5×11.2R20
295/60R20= 33.9X11.6R20
305/55R20= 33.2x12R20
33X11.5R20 
33X12R20 
33X12.5R20 
33X13.5R20 

Cutting up your Sierra

The problem with most IFS (Independent Front Suspension) setups is the clearance of the UCA (upper Control Arm) as well as wheel backspacing. The wheel aspect ratio isn’t the main issue. The GMC Sierra might be a large truck, however most manufactures limit you with the wheel arch clearance. This is what severely restricts you from fitting wider tires like a fat aggressive 33” or bigger 35 inch tires.

What needs to be trimmed to run 33’s?

You will need to do some light trimming to plastic behind the front valence and requires cutting approximately half of the front mud flap off. You will also need to completely remove the steel mud flap bracket.

The mud flaps will touch and the plastic fender insert will need some massaging or pulling back to allow the wheel to clear when at full lock. Unlike the 3rd Gen Tacoma you don’t have to worry about cab mount chops or crash bars as are the case with the new Ford Rangers.

Will a small leveling kit or wheel spacer help with 33” tires?

Usually when wheel spacers are mentioned, many will quickly give you their opinion and fob it off as a bad idea. Truth is they aren’t nearly as bad as people make them out to be. They definitely aren’t the fix all of suspension woes either, however they will offer improved backspacing, which allows for a slightly wider tire. It’s a very affordable way to improve the aesthetics and ride height of your GMC Sierra.

Wheel spacers have a similar effect to fitting wider tires or more negative offset wheels. Yes it might improve your backspacing somewhat, and even clear your UCA better, however you still need to take into consideration the clearance of the upper inside of the wheel arch at full articulation. You don’t want to go too wild with the spacers.

Installing a spacer kit above the front coil struts and springs is another affordable way to get extra wheel clearance. This does not improve off-road performance or load carrying ability, although it will increase your approach angle slightly since the body sits slighter higher. Fitting a leveling kit means you’re still bound to a 33” tire but there won’t be much need for wheel well modifications. If you really want to fit a bigger 33″ (33.9″) tire, and you have a 2″ leveling kit, you might need to do some minor trimming of the fender liner.

Big tires on a GMC Sierra and fuel economy

With any upgrade, comes a small tradeoff and a big tire upgrade is no exception. Fitting wider, heavier tires definitely comes at a price and since the tires are positioned below the suspension, they fall part of the unsprang weight of the truck. The quickest way to increase fuel consumption is by increasing unsprang weight. The heavier rolling mass of the tires has a direct impact on your fuel consumption, especially when pulling off.

So before you do the big tire upgrade make sure you understand the impact it could have on your fuel economy. Your truck might look more aesthetically pleasing and have a more aggressive stance, but it all comes at a price.

Also, depending how big you go, you’ll feel a drop in pull-off performance as well due to the heavier tires needing to be pulled along. It might not even be more than 4kg heavier per tire, however, this makes is big difference in torque transfer on the wheels and if you decide to go bigger than 33” then re-gearing of diffs should be a consideration since there will be more strain on diffs and other drivetrain components.

Resources

https://www.gm-trucks.com/forums/topic/240553-biggest-tire-upgrade-on-stock-rims-20%E2%80%99-sierra/

https://www.silveradosierra.com/wheels-tires/biggest-tires-with-stock-20-rims-t416857-40.html

Conclusion

So the takeaway here is, without a 2” or 3” suspension upgrade or leveling kit and you really want to fit 33” tires, you’ll need to do cutting and trimming of wheel wells. You’ll be limited to the biggest 32-inch, or a small 33 inch tire. A levelling kit will help with wheel clearance, however, the best option for your Sierra is to opt for a 3” suspension kit if you want to run wide 33” comfortably. If you can include a more negative offset aftermarket wheels, it would improve UCA clearance and backspacing with no need to do any other mods.

Jade C.

4-Wheel drives and off-road driving techniques has been my passion for over 20 years. Here we strive to provide the most accurate, up-to-date, information about the functionality, common faults and latest technology built into most 4 Wheel Drives.

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