A big tire upgrade can make a massive difference in both aesthetics and performance. Larger tires are one of the most popular modifications done to off-road trucks since it’s the quickest way to get a more aggressive look, increase the ride height, and improve traction and capability on and off-road. So, what are your big tire options on the GMC Sierra? 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’re not prepared to do any trimming and cutting while running stock suspension then you’ll be limited to a 32.5-inch tire. Depending on the tire brand, mold, and aggressive lug patterns, of course. On the upside, there are many other alternatives you can explore.
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 Sierra owners have tried with great success.
GMC Sierra 33-inch tires and no lift – Options
When looking at 2014 to the current Sierra shape, the maximum tire size you can go is 32.5”
This can be in any of the below configurations:
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 |
Spend some time on any truck internet forum and you’ll be surprised to see how many 4WD truck owners enquire about fitting bigger than a 33” tire on a stock suspension. I’m not sure about the percentage of guys that actually end up running bigger than 33s on stock suspension is another story altogether, since the amount of cutting and trimming without a leveling kit is plain ridiculous. Many eventually opt for a small 2“ leveling kit to allow better clearance inside the wheel arches and increased clearance from the UCA (Upper Control Arms).
On the other hand, a 2” suspension upgrade combined with an aftermarket UCA will solve most body clearance issues associated with fitting 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 for 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.
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 the extra trimming.
A 33” tire can be in the form of any of the following sizes depending on if you intend to go 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 manufacturers limit you with the wheel arch clearance. This is what severely restricts you from fitting wider tires like fat aggressive 33” or bigger 35-inch tires.
What needs to be trimmed to run 33s?
You will need to do some light trimming to the plastic behind the front valence which 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 is 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. The 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 increase the wheel size 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, but 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. Also, make sure to check those CV angles.
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 unsprung weight of the truck. The quickest way to increase fuel consumption is by increasing unsprung 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 on 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 a 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://wheelsasap.com/gmc-at4-oversized-tire-trimming-guide/
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, UCAs, or leveling kit and you really want to fit 33” tires, you’ll need to do cutting, rolling, and more trimming of wheel wells. You’ll be limited to the biggest 32-inch or a small 33-inch tire. A leveling 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 more negative offset aftermarket wheels, it would improve UCA clearance and backspace with no need to do any other mods.