The GL has a unibody frame — rare among full-size SUVs — and its four-wheel-independent air suspension swaps traditional coil springs for inflatable air bladders. Ride height can be varied to enhance high-speed stability or offroad ground clearance. An optional adaptive suspension constantly adjusts ride stiffness as conditions require, with Sport and Comfort modes that yield, respectively, stiffer or softer response. There's also an Auto mode that calibrates the settings somewhere between those two based on conditions. Both the GL550 and GL320 I drove had the system, and I'll attest that Sport mode resists body roll marginally better than Comfort, but the differences are slight.

More consequential are the GL550's 21-inch alloy wheels and sporty P295/40R21 tires, which combine with unusually precise steering to make curvy roads a bit of fun. There's still enough power assist at lower speeds for tight parking-lot maneuvers, though at times I found lumpy pockets of resistance while navigating our downtown parking garage. That's a noticeable difference from the steering wheel's confident, planted feeling on the highway.

Naturally, fun comes at a price. The GL550's advanced suspension can't make up for the brittle ride quality of its thin 40-series tires. You'll hear and feel every highway expansion joint, and potholes and speed bumps become a jarring, noisy experience. Most annoying was the abundance of suspension reverberation I felt around Chicago's roughed-up streets: No matter what setting I had the suspension on, major bumps sent palpable motions through the entire chassis for a half-second or more.

On smoother roads — that's you, Governator State — the ride feels more agreeable. Tire noise is still noticeable, but wind noise is minimal and the engine is nearly silent. The GL320's 20-inchers and P275/50R20s yield better ride comfort still, though the GL450, which has 18-inch wheels and P265/60R18 tires, is probably the most forgiving of the three.

At 39.7 feet, the GL's turning circle is competitive with its peers.