2020 GMC Sierra 1500 Lift and Tire Fitment with Mud Flaps Issue
I have a GMC Sierra 1500 Crew Cab and I’m installing a Rough Country 3.5” lift (shocks/struts) along with their forged upper control arms. I’m also upgrading tires and I’m seeing conflicting fitment info. I don’t want to remove the mud flaps. Can I run 285/65R20 with this lift and keep the mud flaps without rubbing? If not, is 275/65R20 the safer option? What are the common rubbing points or checks I should do with this setup?
You’re on the right track with the Rough Country 3.5” lift and forged upper control arms—they’re designed to work together and keep your suspension geometry in check. Regarding tire size, 285/65R20 is borderline with this lift if you want to keep the factory mud flaps. You’ll likely experience some rubbing on the mud flaps or inner fender liners under full lock or compression. The safer bet is 275/65R20, which provides good clearance and less chance of rubbing without trimming or removing mud flaps.
Top recommendations
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275/65R20 Tires – Best balance of size and clearance with 3.5” lift and mud flaps intact. Cost: $1,000-$1,400 for a set of 4. Install difficulty: DIY-friendly if you have tire mounting tools or pro shop.
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Rough Country Forged Upper Control Arms – Essential to maintain proper caster and reduce bump steer with this lift height. Cost: ~$400-$500. Install difficulty: Moderate, requires ball joint press and alignment after.
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Check and Trim Mud Flaps if Needed – Some slight trimming of lower mud flap edges may be required for 285 tires, but this voids mud flap warranty and can reduce splash protection. Cost: minimal. Install difficulty: DIY.
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Wheel Backspacing Check – If running aftermarket wheels, confirm backspacing is compatible to avoid rubbing on control arms or inner fender. Cost: varies. Install difficulty: DIY with calipers.
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Alignment After Installation – Required to ensure proper handling and tire wear after lift and control arm installation. Cost: $100-$150. Install difficulty: Pro recommended.
Compatibility & prerequisites
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Confirm your Sierra 1500 is 4WD or 2WD, as lift kits and control arms differ slightly.
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Verify factory mud flap mounting points and clearance with 285 vs 275 tires before finalizing.
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Check wheel backspacing and offset if using aftermarket wheels; OEM wheels usually fit fine.
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Expect to do a full alignment after lift and control arm install.
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Larger tires may affect speedometer accuracy; recalibration may be needed.
Realistic expectations & tradeoffs
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285/65R20 tires will give a more aggressive look and slightly better off-road traction but may rub mud flaps or inner fenders on full lock or compression.
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275/65R20 tires are less aggressive but safer for daily driving with mud flaps and no trimming.
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Lift and larger tires will slightly reduce fuel economy and may increase road noise.
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Ride quality may get a bit firmer with upgraded shocks and larger tires.
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Mud flap trimming reduces splash protection and may void warranty.
A few questions
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Are you running OEM wheels or aftermarket? What’s the wheel offset/backspacing?
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Is your Sierra 1500 4WD or 2WD?
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How aggressive do you want your tire look vs daily drivability?
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Are you willing to trim mud flaps if necessary?
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Do you plan to recalibrate your speedometer after tire upgrade?
Bottom line: For your 2020 Sierra 1500 Crew Cab with Rough Country 3.5” lift and forged upper control arms, 275/65R20 tires are the safer, less problematic choice if you want to keep mud flaps stock. 285/65R20 is possible but expect rubbing on mud flaps or liners unless you trim or modify. Always check wheel specs and do a proper alignment after install.