When it comes to upgrading your truck’s performance and appearance, few things make a bigger visual and functional impact than swapping out the tires. If you’re the proud owner of a GMC Sierra 1500 AT4, you might be wondering: What are the biggest tires I can run on my stock setup without rubbing, trimming, or adding a lift kit? In this guide, we’ll explore everything you need to know about fitting the biggest tires on stock GMC Sierra 1500 AT4 and how to do it safely and smartly.
Whether you’re gearing up for off-roading adventures, want a more aggressive stance, or simply love the rugged aesthetic, this article will help you understand your options when it comes to tire upgrades—without compromising performance or voiding your warranty.
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Understanding the Stock GMC Sierra 1500 AT4 Setup
Before diving into the biggest tires that can fit, it’s essential to understand the baseline from which you’re working.
The GMC Sierra 1500 AT4 is already a rugged, off-road-oriented version of the Sierra. It comes standard with:
- A 2-inch factory suspension lift
- Off-road-tuned Rancho monotube shocks
- 18″ or 20″ wheels (depending on the package)
- 275/65R18 or 275/60R20 Goodyear Wrangler DuraTrac tires
Because of the factory lift and upgraded shocks, the AT4 has slightly better tire clearance than other stock Sierra models. However, there are still limits to how big you can go without rubbing on components like the inner fender wells, control arms, or the wheel wells during full turns or compression.
What Are the Biggest Tires On Stock GMC Sierra 1500 AT4?
H2: The Biggest Tires On Stock GMC Sierra 1500 AT4 — Safe Sizes Without Trimming or Rubbing
Now let’s get to the core of the question: What are the biggest tires you can install on your stock GMC Sierra 1500 AT4 without modifications?
After extensive community testing, manufacturer specs, and expert off-road consultation, here’s what we know:
✅ Safest Maximum Size:
- 33-inch tires (i.e., 285/65R18 or 285/60R20)
These are generally the largest size that can be mounted on a stock AT4 without rubbing, cutting, or trimming. They offer a beefier look, improved traction, and more sidewall for off-roading—without pushing limits.
⚠️ Aggressive But Riskier Fit:
- 34-inch tires (e.g., 295/65R18 or 295/60R20)
Some owners have fit these successfully, but minor rubbing during full turn or under suspension flex is common. Often, mud flaps or fender liners need trimming.
❌ Not Recommended Without Modification:
- 35-inch tires (e.g., 315/60R20 or 325/60R18)
While the AT4 has a 2-inch lift, 35s typically require at least a small leveling kit or aggressive trimming to avoid rubbing—especially during turning or off-road articulation.
Key Factors That Influence Tire Fitment
Fitting the biggest tires on your GMC Sierra 1500 AT4 isn’t just about the tire size; it’s also influenced by several other factors:
1. Wheel Offset
- Factory AT4 wheels typically have a neutral to positive offset. Switching to aftermarket wheels with a more negative offset can push the wheels outward, increasing clearance between the upper control arm—but may cause rubbing on the fenders or bumper.
2. Tread Type
- Aggressive mud-terrain (M/T) or all-terrain (A/T) tires often have wider and chunkier sidewalls, which take up more space than highway-terrain (H/T) tires, even at the same nominal size.
3. Suspension Travel
- The more your truck articulates, the more likely your tires are to rub under compression. Even a 33” tire might cause issues during off-road flexing depending on your driving style.
4. Tire Width
- A 285/70R18 might be taller than a 305/60R18, but the 305 will be wider, potentially causing rubbing against the control arms or fender liners. Width is just as important as diameter when determining max fit.
Pros and Cons of Bigger Tires on Your Sierra 1500 AT4
If you’re considering running the biggest tires on stock GMC Sierra 1500 AT4, here are some benefits and trade-offs to keep in mind:
✅ Pros
- Improved off-road capability: Larger tires provide better traction and ground clearance.
- Aggressive stance: Visually transforms your Sierra into a more commanding, powerful truck.
- Softer ride off-road: Bigger tires with more sidewall flex better over rocks, dirt, and rough terrain.
❌ Cons
- Reduced fuel efficiency: Larger tires are heavier and create more rolling resistance.
- Speedometer inaccuracy: Upsizing tires will throw off speedometer and odometer readings unless recalibrated.
- Potential warranty issues: Some dealerships may push back on warranty work if they believe tire modifications caused the issue.
- Increased strain on suspension and brakes: Heavier tires may wear out components faster.
Tire Brands and Options for Bigger Tires
Once you’ve decided to go big, it’s time to choose the right tire. Here are some popular tire choices in the 33” to 34” range that are known to fit the Sierra 1500 AT4:
All-Terrain Options:
- BFGoodrich All-Terrain T/A KO2 – Durable, quiet, great all-around performer
- Goodyear Wrangler Duratrac – Comes stock, aggressive sidewall, good snow performance
- Toyo Open Country A/T III – Excellent off-road grip with highway comfort
Mud-Terrain Options:
- Nitto Ridge Grappler – Hybrid tire with aggressive tread but low noise
- Falken Wildpeak M/T – Rugged off-road performance with decent street manners
- General Grabber X3 – Affordable and durable option for deep terrain
Recalibrating After Installing Bigger Tires
If you upsize your tires, it’s highly recommended to recalibrate your truck’s systems. Here’s why:
- Speedometer Correction: Larger tires rotate fewer times per mile, causing your speedometer to under-report actual speed.
- Transmission Shift Points: Incorrect speed readings can affect when your transmission shifts.
- ABS and Stability Systems: These systems rely on accurate wheel speed readings to function properly.
Most recalibrations can be done with a handheld tuner or by visiting a tire shop or dealership that offers reprogramming services.
Tips Before You Buy Bigger Tires
Before making the investment in the biggest tires on stock GMC Sierra 1500 AT4, consider the following:
- Test fit tires if possible – Some tire shops allow test fits to ensure clearance.
- Read online forums and groups – Communities like GM-Trucks.com or Reddit’s r/GMT400 are filled with real-world advice.
- Measure actual clearance – Even 0.5 inches can make a big difference.
- Double-check your wheel specs – Wider aftermarket wheels can affect your results.
Conclusion: Is Bigger Always Better?
Bigger tires on a stock GMC Sierra 1500 AT4 can give you the aggressive look and off-road edge you’re after—but it’s essential to understand your truck’s limits. Most owners find that 33-inch tires (such as 285/65R18 or 285/60R20) offer the best balance between size, performance, and ease of installation without any trimming or suspension work.
If you push it to 34 inches, be prepared to do some minor modifications, and anything beyond that typically requires a leveling or lift kit. Make sure to recalibrate your speedometer and consider how the changes might impact ride quality, handling, and fuel economy.
By choosing the right size and brand, you’ll not only enhance your truck’s look but also boost its capability—turning your Sierra AT4 into a true off-road champion.
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