Generally speaking, there are two ways to measure the power output of a vehicle. You can list ratings at the engine crankshaft, or at the wheels. Since pretty much forever, automakers have presented vehicle power – both horsepower and torque – as measured from the engine. However, some modern electric vehicle companies use torque ratings at the wheel because it's a much larger number, and large numbers look better on paper, right?
That's what we have with the GMC Hummer EV. A big stink was made about the off-roader having an estimated 11,500 pound-feet of torque which sounds absolutely incredible. However, that rating is at the wheel, where such measurements aren't typically used. GMC admitted as much in its Hummer EV debut announcement, and today the automaker went even further by telling us the gear ratios for the front and rear axles.
For reasons unknown, GMC still won't list an official torque rating at the engine (or in the case, combined motor rating at the shaft), but some simple math gets us a pretty good estimate and surprise, it's not as bonkers as you've been led to believe. We were getting ready to attack our own whiteboard with equations, but we happily yield to the mathematical mind of Jason Fenske at Engineering Explained, as seen in the video at the top of the article.
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GMC listed the Hummer EV's front gear ratio at 13.3:1, and the rear ratio at 10.5:1. We'll leave all the specific number crunching to the video, but with GMC's estimated wheel torque of 11,500 lb-ft and the assumption that the Hummer EV's three electric motors have the same output, we arrive at a combined torque rating at the shaft of around 1,000 lb-ft, or 1,356 Newton-meters.
Make no mistake, that's still a mountain of twist and with the nature of electric motors, it's available as soon as you touch the throttle. However, it's not some supernatural amount of power as the wheel measurement suggests. It actually matches up with heavy-duty diesel pickups from Ram, Ford, even GMC's own Sierra HD with 910 lb-ft from its 6.6-liter Duramax engine.
Why do electric brands seem so keen on quoting wheel torque? Torque from the shaft of an engine or electric motor is multiplied through gear ratios, thus creating a much larger and more fantastic number to grab attention, as previously mentioned. It's still an accurate power measurement, but it is very different from what buyers are used to seeing. That makes it frustrating for many people, as it very much feels like a bait-and-switch move by automakers.
The frustration is made worse when automakers offer figures for torque at the wheel, but horsepower at the shaft. As we know, horsepower ratings are lower at the wheel because of parasitic power loss – it's not transmitted to the wheels in the same manner as torque. Nobody wants to brag about a smaller number, but choosing to rate torque and horsepower in different locations creates an apples-to-oranges comparison that's confusing at best, disingenuous at worst. It's something GMC is certainly guilty of with the Hummer EV, as its estimated 1,000 hp is quoted not at the wheel, but the shaft.
At least now we have a clearer picture of the Hummer EV's output in context with other vehicles. Why we couldn't have this from the beginning is a mystery, because 1,000 lb-ft of torque is nothing to sneeze at.
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October 22, 2020 at 06:23AM
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GMC Hummer EV Really Makes The Same Torque As A Heavy-Duty Pickup - Motor1
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