2010 GMC Terrain: Suspension Walkaround
February 26, 2010
No, our 2010 GMC Terrain does not have a flat tire. The rear wheel is off to facilitate yet another episode of everyone's favorite semi-regular tech feature (work with me, here), the Suspension Walkaround.
*cricket noises interspersed with a smattering of polite golf applause*
Anyway, our new 2010 GMC Terrain is an all-new crossover SUV, which is more or less code for a unibody chassis with front-wheel drive architecture and car-like suspension bits. This exercise is a two-for-one deal because pretty much everything we'll see in the coming photos applies equally to its stablemate, the Chevrolet Equinox.
The basic layout found up front is standard front-drive stuff. A coil-over MacPherson strut (yellow) is paired with a one-piece, L-shaped lower control arm (white).
Here's another view of the L-shaped lower control arm (white) and it's single, riveted-on ball joint (yellow). The main knuckle (aka hub carrier or upright) is a nice-looking piece of aluminum. If you're trying to keep the price down and you want to get the most bang for your unsprung weight buck, an aluminum knuckle is a good choice.
This close-up shows behind-the-axle mounting of the steering (yellow) that almost all front-drive layouts must use because of the position of the transverse-mounted engine and transmission. A slender aluminum stabilizer bar link (white) connects directly to the strut housing for a motion ratio that's more or less 1-to-1.
The rearmost lower control arm pivot bushing (yellow) is the one that takes up the brunt of the longitudinal tire impact forces. The L-shape of the arm redirects fore-aft shocks and turns them through 90 degrees to produce left-right motion in this bushing. The large-diameter aluminum housing seen here indicates that GM is serious about taking the bite out of potholes.
Here's a close-up of the steering rack (white) and the stabilizer bar (yellow) and their cross-car routing between the firewall and the engine.
Front braking duties are handled by single-piston floating calipers and ventilated rotors. The circled label indicates these were made by Mando, a South-Korean parts maker that works closely, but not exclusively, with Hyundai. They've had US plants staffed by US workers for a few years.
GM knows motorsports, of course, and I keep seeing these elongated racing-inspired wheel studs on their recent products. I like them because it's much easier to start the wheel nuts without fear of cross-threading.
As you can clearly see, the wheels that bolt up to those studs are 18x7-inch aluminum alloy castings with a 46 mm offset. The tires on our Terrain are P235/55R18 (99T) Michelin Latitude Tour all-season rubber. Mounted together, each assembly weighs about 51.5 pounds.
At the rear we find a multilink suspension with a trailing arm (green) and three lateral links. If this were a Ford, I'd be tempted to call it Control Blade rear suspension. But it's not, so I won't. Besides, the trailing arm is indented and has rolled edges, so it isn't really as flexible as Ford's control blade. It's also differs in that the trailing arm bolts to an aluminum knuckle (yellow) rather than having the whole thing be one piece.
The main lateral link (green) carries the spring and shock absorber, and the shorter toe-link (yellow) defines the amount of dynamic toe-in (or bump steer) that is generated as the tire moves up and down. The upper camber link (white) holds the wheel at the desired camber angle. And of course we get another look at the trailing arm (orange).
Once more, from below: main lateral link (green); toe-link (yellow); camber link (white); and trailing arm (orange). The camber link has an eccentric built into its inner pivot for camber adjustment.
Here's my standard motion ratio shot. The stabilizer bar looks to be about 0.35:1, the spring is a hare over 0.5:1 and the shock looks to be set at 0.85:1-ish. I reserve the right to make no comments at all about that, er, bump stop and its location within the coil spring.
Let's try to move on, shall we? The stabilizer bar's small motion ratio means the diameter of the bar itself (yellow) needs to be larger to generate the required amount of roll resistance. It bends down at the end in an unconventional (but effective) way in order to keep the length of the unique reinforced plastic link (white) to a workable minimum.
Although the pieces are smaller, the rear brakes are similar to those in front: single-piston sliding calipers (made by Mando) squeeze ventilated rotors. The deep rotor profile indicates that a drum parking brake resides within the rotor's "hat" section.
The gaping hole in the rear hubs (white) indicates that our Terrain is strictly a front-wheel drive machine. The splines within indicate that this part is nevertheless shared between FWD and AWD versions of this vehicle. Home DIY mechanics will like these rear rotors because the minimum thickness at which they become boat-anchors is cast right onto them. No need for a shop manual to look that one up. And in so doing GM reveals that they're in fact a metric company on the engineering side (no surprise, really). No inches are found here.
Dan Edmunds, Director of Vehicle Testing @ 1,993 miles