Spy Photos Point to a Major Suspension Upgrade on GMC’s New Pickup

A prototype of the next-generation GMC Sierra 1500 AT4 has been spotted during road testing in the U.S., and new spy photos reveal one of the truck’s most notable technical updates: a switch to larger off-road tires.

The test vehicle is fitted with 20-inch wheels, but instead of the current model’s standard 275/60R20 tires, it’s running 275/65R20 rubber. Based on visual cues, the tires appear to be Hankook Dynapro AT2 Xtreme. Thanks to the taller sidewalls, overall tire diameter has increased from roughly 33 inches to about 34 inches.

Until now, GM’s full-size pickups have effectively been limited to 33-inch tires because of suspension design and clearance constraints. Owners who wanted larger tires typically had to turn to aftermarket modifications. The latest images suggest that this limitation may be addressed at the factory on the next-generation model.

A larger tire diameter could give the Sierra AT4 more ground clearance, improved approach and departure angles, and a more aggressive stance. It would also help the truck better match competitors that already offer oversized tires on their off-road-oriented trims.