GM designed the 3500 Duramax’s front IFS suspension with slight adjustability via torsion bars. This facilitates fitting larger tires with minimal scrubbing during full turn or compression. Yet, be cautious since adjusting torsion bars alters IFS suspension geometry, affecting CV joint angles, upper & lower ball joints, and tie rods.
With that being said, let’s see what the max tire size you can fit on a stock 3500.
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Biggest Tire on Stock 3500 Duramax [Without a Lift or Levelling Kit]
Adjusting torsion bars for larger tires reduces suspension travel. A 2-inch adjustment brings the Upper Control Arm near front bump stops, limiting downward travel. While accommodating a 35-inch tire is possible, it results in a firmer, bouncier ride and may require fender plastic trimming to prevent scrubbing at full lock.
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18-Inch Tires on a CHEV 3500 Duramax & GMC 3500
Many 3500 Duramax owners fit 295/65R18 tires on stock wheels and suspension without issues. These tires are about 33.1”, within factory specifications.
I prefer the look of a 34-inch tire with a higher sidewall aspect ratio. A 2-inch suspension or front leveling kit should maintain acceptable CV angles without requiring a diff drop, enhancing the appearance and ride quality.
Alternatively, consider a wider 305/55/20, approximately 33.2”. Ensure a 20×9 wheel with a +12 offset to clear UCA’s effectively.
20 Inch Tires on a CHEV & 3500 Duramax
Certain 2020 model trucks are sold factory stock with 34-inch tires, which equates to 275/65R20 to be specific, or 34.1 inches to be exact. You can easily go one jump up and fit a 285/55/20 or even 285/60/20 on factory stock suspension, however, the latter will look much better and not like the stock ’20s.
Opting for 20-inch rims purely for looks is fine, but for off-road capability and versatility, they might not be ideal. They limit sidewall flexibility and deflate less for sand driving, offering a stiffer ride and pricier tires.
However, if you are dead-set on 20” wheels then you’ll need to do the following to make them fit properly:
- Fit a +20 offset rim
- Adjust front and rear psi (60F and 80R)
- 6 Full turns on the OEM torsion bar keys.
- Cut a small 3″x3″ piece of the inner fender on the passenger side front to prevent rubbing over speed bumps, and potholes.
Biggest Tire on Stock 3500 Duramax [With a Lift Or Levelling Kit]
With a level, 305/70/18 is possible, with some trimming. That equates to 34.8” in metric values. Unfortunately, it won’t be a straight fit and finish, since you’ll need to still do some minor trimming on the inside fender liners and guards where rubbing occurs.
Many DURAMAX owners have reported running 295/70/18 (34.3”), 285/75/18 (34.8”), and 305/65/18 (33.6”) without any hassles on the DURAMAX with a small 2-3” level. There are also guys running 35×12.50×18 BFGs with leveling kits and no problems.
Big Tires on A 3500 DURAMAX (Fuel Economy)
With any upgrade, comes a small tradeoff and a big tire upgrade is no exception. Fitting wider, heavier tires comes at a price and since the tires are positioned below the suspension, they form 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 effect on your fuel consumption, especially when pulling off.
Your truck might look more aesthetically pleasing and have a more aggressive stance, but it will be thirstier, so be prepared to visit the pumps more regularly.
- Depending on how big you go, you’ll feel a drop in low-down torque which affects the pull-off performance as well.
- The weight difference in the tires might only be a few kg heavier per tire
- Weight makes a big difference in torque transfer on the wheels, and if you decide to go bigger than 3” then re-gearing of diffs should be a consideration.
- There will be more strain on diffs and other drivetrain components.
Difference between a 33″ and 35” Tire
Below you can see the physical differences between a 33 and 35-inch tire.
So the takeaway here is, without a 2” or 3” suspension upgrade or leveling kit on your 3500 Duramax you’re limited to bigger-sized 33” tires. You will need to do cutting and trimming of wheel wells if you decide to go bigger 34” on stock suspension on the stock rim.
- A leveling kit will help with wheel clearance and some suspension travel, however, the best option for your 3500 is to opt for a 2-3” suspension kit if you want to run wide 34-35” comfortably.
- If you can include +12 offset aftermarket wheels, it would improve UCA clearance and backspacing with no need to do any major trimming.
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