2021 Chevy Tahoe Suspension Deep Dive | Explaining the IRS you should be happy about

Dan Edmunds
·11 min read

For years, the Chevrolet Tahoe had something in common with the Ford Mustang: both were the last holdouts in their respective segments to employ solid rear axles long after it became obvious that independent rear suspension would make them better. Ford’s development team finally blessed the 2015 Mustang with IRS when the current generation debuted, but as noted in Autoblog's 2021 Chevrolet Tahoe/Suburban review, GM's full-size SUVs have finally joined the IRS club as well.

For the Mustang, it’s about handling: lateral stability, quick transitions, and the ability to put power down hard out of corners that might not be racetrack smooth. The change to IRS was transformative, and the Mustang leaped from worst to first in my personal pony car rankings.

In the case of the Tahoe, the dynamic benefits amount to improved ride comfort and a newfound ability to carve through lumpy corners without having the rear end flince sideways over sharp bumps. But there’s much more. The absence of a bulky axle bounding belowdecks means the rear floor can be lower, which means significant Tahoe shortcomings have been wiped away. There are now 9.9 inches of added third-row legroom, 20.9 cubic feet more cargo volume behind the second row and 10.2 cubic feet more behind the third row.

Those are massive space increases, and the effects are even more impressive in person than they are on paper. But the spec sheets don’t lay out exactly what they’d done. So I got my hands on a new 2021 Chevrolet Tahoe Z71 4x4, dusted off the multi-color arrows and did what I do best. Here’s what I found after I pulled off the wheels.

Right out of the gate, we can see what looks like the upper half of a double-wishbone front suspension. But the scene is dominated by something else: front air springs. Front air springs have never before appeared on a Tahoe. Also, if there are front air springs, you can bet money that *spoiler alert* we’ll see rear ones later on, too.

On the Z71, these come as part of the optional Off-Road Capability package. We’d be seeing coil springs if the Off-Road Capability option wasn’t present on this Z71. We’d also be seeing coils if this was any other trim level -- except for the top-level High Country, which can also be equipped with air suspension if you opt for the High Country Deluxe package.

This lower view confirms that this is, in fact, a double wishbone suspension. The upper wishbone (yellow arrow) and steering knuckle (green) are made of aluminum, while the lower wishbone (red) is made of steel.

The air spring envelops the damper (white) to the point where we can barely see it. Coil-over isn’t the right descriptor here, so I’ve taken to calling this a bag-over configuration.

The angled orientation (yellow) of the upper wishbone indicates a generous amount of anti-dive geometry, while the rearward-biased upper ball joint (green) tips the steering axis back to provide a decent amount of front caster.

The attached linkage and suspension position sensor (red) are quite long, which makes sense when you consider the resolution needed to accurately manage the 4-inch difference between Entry Height (2 inches below standard height,) and Maximum Ground Clearance mode (2 inches above standard height.)

There’s a tangle of plumbing at the top-mount of the front air spring. The air injection piping is fairly well hidden, but we can clearly see the control wire (yellow) that goes down the center of the damper shaft to adjust the damping.

These are MagneRide magnetorheological (I amaze myself every time I spell that right) continuously adjustable dampers that can be added in addition to the air springs, which operate backwards from other types in that the valving is fixed and the fluid is variable. The very viscosity of the damper fluid itself can be altered by the degree to which a magnetic coil built into the housing is energized.

GM tells me this is a fourth-generation MR system, with accelerometer-based feedback control supplementing the position sensors at the corners, as well as reduced internal friction and a new control algorithm with a comfort bias. It pays off, too, because this Z71 delivers an uncommonly smooth ride without feeling the least bit floaty. It can also smother the impact of big dips taken a bit too fast without bottoming out. It’s hard to tell how much credit should go to the air springs, but the combination certainly works.

I find the lower wishbone’s construction to be a bit curious. Ostensibly, it’s a V-shaped weldment, with a slender bolt-on brace (yellow) that makes it technically OK to call it an A-arm. Additional stiffness is added by the way in which the tie-bar mounting of the damper (green) also bridges and connects the two branches of the Vee.

Interestingly, the stabilizer bar link feeds in off to the side (red), which stands in contrast to the change we recently saw in the new 2021 Ford F-150. Ford engineers made a point of abandoning this arrangement in favor of a direct mount to the knuckle so the arm wouldn’t be subject to twist-loading from stabilizer bar inputs.

On the other hand, Ford doesn’t offer adjustments where the F-150’s lower wishbone bolts to the frame, but Chevrolet clearly does here on the Tahoe

By now you’re probably used to seeing hard steering stops that are set up so the lower wishbone and knuckle come into contact before the steering rack binds. Here we can see how Chevrolet does it, and we’re in luck because there are clear witness marks left behind from prior contact.

The Tahoe’s front stabilizer bar routing (yellow) is pretty straightforward. The linkage (green) is short and stiff, too, and we can clearly see where it attaches to the lower wishbone.

From here we can eyeball the relevant motion ratios, although the perspective isn’t the best in this view. Still, the spring and damper share a mounting that looks to be about 60% of the way out from the inner pivot, while the stabilizer bar sits a bit farther out at something like two-thirds or 67% motion efficiency with respect to wheel movement.

The Tahoe’s front brakes feature four-piston fixed calipers (yellow) with an open-window design that makes pad changes a breeze after you remove two pins (green). The rotors are ventilated, but I appreciate the extra-long studs with smooth-turned ends (red) that make it easy to lift a wheel into place without fear of damaging the threads.

This overall rear view of the Tahoe/Suburban’s new and long-overdue independent rear suspension shows that this is most definitely not a double wishbone rear suspension like the Toyota Sequoia and Nissan Armada, nor is it a pure multilink as used in the Ford Expedition. It’s clearly something else. We’ll have to get in closer to figure out what they’ve come up with.

As expected after seeing the front, the rear end of this Z71 is supported by an air spring (yellow). The outgoing generation of Tahoe/Suburban had rear air leveling, but that system served a load-assist function that supplemented coil springs. Here the air spring is a full-fledged replacement.

Other than that, there’s little to see up here except a single upper lateral link (green). There’s not much up here that could intrude into the passenger compartment.

Now things are starting to come into focus. There’s a substantial trailing arm (green), and a toe-control link (yellow).

OK, I’m calling it. This looks like the Control Blade suspension that I’ve seen underneath many of the better-handling compact sedans. The GM engineer I talked with said they use the term four-link, but that name tells us very little about what is going on. Whatever you call it, I like this suspension type because it clearly divides the responsibility of the various links and their bushings, which makes everything easier to tune and optimize -- not to mention explain.

The trailing arm (yellow) bolts to the aluminum knuckle (green) in two places, which means it alone is responsible for locating the wheel in the fore-aft direction, as well as controlling acceleration and braking torque. The upper lateral link we saw before controls the camber angle, while the toe link keeps the wheel pointed straight ahead and provides a means of static tow adjustment via an eccentric cam (red) at its inner end.

But for this to work, there needs to be one more link we can’t yet see.

Here it is, the lower lateral link (yellow). Now we have accounted for everything necessary to locate the wheel in 3D space.

It’s worth noting that this lower lateral link is much longer than the upper one (red), which means this suspension will develop a useful amount of negative camber gain. As the outside wheel compresses in corners, the upper link will swing in a tighter arc and pull the top of the knuckle inward. Don’t worry if it doesn’t look that way now; the suspension is unweighted at full droop.

This view shows that the trailing arm is quite long, with a pivot point (green) that is positioned quite far forward. This reduces the amount of wheelbase change that might otherwise occur if the trailing arm were shorter, and that improves the feeling of stability, particularly if the suspension strikes a mid-corner bump.

The Tahoe’s rear stabilizer bar is a textbook example because of its very simple U-shape and unobstructed mounting. It’s clear to see how the opposite-phase suspension deflection that occurs when the body rolls will cause it to twist and resist that roll motion. In-phase wheel motions, on the other hand, cause the bar to pivot in its bushings without developing any resistance.

You may have wondered about that stray bolt in the trailing arm. That’s where our stabilizer bar (yellow) and its drop link (green) attach to the moving elements of the suspension.

The stabilizer bar’s motion ratio may not be what you think it is. The trailing arm mounts to the knuckle in two places, so the arm’s effective length reaches all the way to the hub. Comparing both to the forward pivot point, the stabilizer bar’s mounting efficiency is about 70% relative to wheel motion.

That long forward trailing arm we saw earlier is partnered with a long lower lateral link, which is so long that it nearly meets its partner in the middle (yellow). Eccentrics are provided for camber adjustment.

We can also finally see the damper (green). It’s another bag-over setup and, even though we can’t quite see it, the MagneRide control wire comes down from the top just as we saw up front.

The lower link shoulders nearly all of the cornering load, so its connection to the knuckle is a rigid mono-ball (yellow). That helps handling, but it doesn’t harm ride comfort because of the clear division of labor inherent in this suspension type. It’s the job of the forward trailing arm bushings to absorb for-aft impacts, not the lateral links.

I know it looks like 60% here, but in real life without photo distortion the shared motion ratio of the spring/damper assembly is more like 67%.

The Tahoe’s rear brakes are ventilated discs with a single-piston sliding caliper that has an added electronic parking brake actuator.

There’s no denying that 82 pounds is heavy for a single tire/wheel assembly. But, then again, it’s not that bad when you consider that these are 33-inch tall tires mounted on 20-by-9 inch wheels. For the record, the tire size is 275/60R20. If these were LT-designated tires I’m almost certain we would be seeing a much higher scale reading.

I have to hand it to them. The Tahoe’s new independent rear suspension really works, and its more compact design has opened up a ton of third-row legroom and cargo space. For an SUV, that alone would have been reason enough to do it. But the ride is undeniably smooth, and there’s a noticeable improvement in poise and control, too. The air suspension and MagneRide dampers are no doubt playing a part here, but I think that a standard Tahoe without those premium upgrades would benefit, too. After all, this type of independent rear suspension is known for its ability to allow development engineers to clearly separate comfort tuning elements from handling ones.

Like pre-2015 Mustangs, I was never a fan of the previous Tahoe generations because of the numerous negative traits attributed to GM's stubborn reliance on a solid rear axle. Now that it has finally made the switch to IRS, the 2021 Chevrolet Tahoe is a full-size SUV that I respect a lot more than I ever did before.

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