GM’s Big SUVs Can Stop Shorter Than a Mazda 3
When a vehicle enters a new generation, we expect to see improvement. Usually the car has more power, performs better, and is more efficient despite being bigger and heavier. We appreciate the steady gains. But we can’t plan a parade every time a car shaves a couple of seconds off its zero-to-60 mph time. Sometimes, though, the improvements are significant enough that they do seem worthy of special attention. The case of the shrinking braking distance of General Motors’ big SUVs is a perfect example.
Since the mid-nineties, we’ve tested 50 members of GM’s large SUV family, which includes the Escalade, Suburban, Tahoe, and Yukon. In 1999, we recorded a 248-foot stop from 70 mph in a Tahoe. That’s public menace territory by today’s standards. We even recorded an over-200-foot result in a 2016 Cadillac Escalade. As of mid-December 2020, we’ve tested six members of the newest generation of that family (we doubled up on Escalade and Tahoe). They’re larger and heavier than the trucks that came before, but all of them stopped in 184 feet or less. The best of the bunch, a 2021 Suburban High Country, only needed 166 feet of runway to do the job. That’s better than all kinds of smaller, nimbler cars, including a Mazda 3 we recently tested, and it’s only six feet off the mark set by an Audi RS6 Avant.
We’d usually attribute this kind of thing almost entirely to the tires, but even the Tahoe Z71 with its off-road-oriented tires is among the best-braking Tahoes we’ve ever tested, and the tires on the five other vehicles have similar specs and ratings to those worn by worse-performing Escalades, Suburbans, Tahoes, and Yukons in the past. The caveat here is that both the old tires and the new ones are built by the tire manufacturers to GM’s own performance specs in a process that’s mostly hidden from the public eye, so it’s possible they’ve hit on a winning compound-and-tread combination that’s doesn’t translate to changed performance ratings but does contribute to better braking.
Gallery: Toyota Celica Supra MkI Photos (Road & Track)
GM, for its part, says the better stopping distances are related to improvements in a variety of systems. Tweaks to the tires are part of the story. Plus, this new generation of trucks finally has an independent rear suspension. The ones we tested had the optional magnetorheological adaptive dampers, also freshly tuned for the new generation. Our braking test measures the distance from when our foot activates a trigger on the brake pedal until the vehicle comes to rest, and GM also credits its eBoost brake-by-wire system for some of the improvement, as it reacts more quickly to quick stabs of the brakes. However, that new braking system in the latest SUVs also now estimates the brake temperatures, and during our routine of six stops from 70 mph it flashed a warning to the driver that the brakes are getting too hot and then set a check-engine light before the end of our test. Interestingly, while the full-size pickup trucks on which these SUVs are based have also improved their stopping distances over time, the improvement is only about a third of the impressive gains of the utilities.
Also noteworthy is that this dramatic gain in longitudinal grip has occurred with almost no improvement in lateral grip. Indeed, the current generation has even taken a step backward in that regard, from the high 0.7-g range in the previous generation to the mid-0.7s today. And, at a piddling 0.63 g, the latest Tahoe Z71 musters less cornering grip than decades-older models.
While we’d prefer a vehicle with exemplary braking and cornering abilities, shortening stopping distances by even a few feet can make a big difference in an emergency, and that the new generation’s results are clustered at the top of a long list of data shows that the gains aren’t a fluke. The difference between the 248-foot stop we recorded 21 years ago—or even the 200-foot stops we’ve recorded more recently—and the best 166-foot stop is huge. And that the feat was achieved by the accumulated effect of several different tire and chassis improvements is proof that we don’t need to wait for a breakthrough on the order of autonomous driving or the three-point seat belt to feel safer in our cars.