Marc UrbanoVehicle and Driver
From the June 2022 issue of Vehicle and Driver.
Vehicle and Driver started testing the car’s acceleration in the 1950s, but it took us a decade to stop. That is, to measure the distance needed to stop. We initially tested the brakes at 80 mph, but in the early 1970s we settled on 70 mph. Back then, the average braking distance was about 200 feet, severe fading was common, and automakers had yet to implement anti-lock technology to optimize braking force at each contact point. Today’s hardware rarely fades into our standard six-stop routine. And last year, the average stopping distance fell to 168 feet, even as curb weight tested has increased by nearly 50% over the past five decades to nearly 4,400 pounds. Performance-oriented vehicles performed even better and typically clustered at 150 feet from 70 mph. To further challenge those cars’ solid brakes, we set off on three stops from 100 mph along with a 70 mph bogey. Kinetic energy expands with speed squared, so stopping from 100 mph will take more than twice as much energy as from 70, making this a challenging test that will create distances between results over several feet.
Let me stop you right there
Any brake test is a measurement to gauge how quickly the entire braking system reaches peak performance and stays there throughout the stopping time. A car with strong performance will stop from 100 mph in about twice as long as 70. But a number of factors influence the results. For example, a vehicle with aerodynamic lift will have less traction immediately upon a stop, while a vehicle with lift will benefit more from initial traction. As in all brake tests, tire grip is a major contributor to how quickly the vehicle can decelerate. In the 100 mph test, especially with all-season tyres, we occasionally noticed grip slipping away before any softening of the brake pedal. And then there’s how well the brakes radiate heat. Stopping the 6781-pound Ram 1500 TRX from 100 mph causes the brakes to gradually double its stopping distance from 70 mph. Fade doesn’t just affect full-size pickups — the brakes on the Acura TLX Type S and Cadillac CT5-V also wither from triple-digit speeds. We just recently started compiling data from 100 to 0 and now Porsche is topping that chart with 718 Cayman GT4 RStook just 242 feet (with an average of 1.38 g), compared with 132 feet from 70 mph (1.24 g).
Illustrated by SinelabVehicle and Driver
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