While Rivian and other EV companies promote the benefits of quad-motor drivetrains, off-roaders prefer a simpler setup. Here's why.
The Rivian R1T and R1S Quads are some of the best vehicles on sale. With over 1,000 horsepower and plenty of clearance, the Rivians are comfortable running quarter-mile sprints as they are crawling up rocks. But while a quad-motor setup is perfect for all-around versatility, enthusiast off-roaders prefer a simpler solution.
First, to see how good the R1T is, watch TFLEV's rock crawling review here.
In it, host Roman Mica puts the R1T through its paces on a slippery rock pile near Lake Tahoe, California. I know it well, as I was standing about 50 feet away while Roman went up the hill. This was part of the first drive of the revised R1T and R1S Quads, which I wrote about here. But I want to use the video to dive into a nerdy off-road thing.
As you can see in the video, there's a decent amount of jerking over an obstacle only to have to lift off the throttle. You also hear tires slipping and, if you were there, you'd have smelled some hot rubber. This is all the result of the same fact: A four-motor EV powertrain is always going to have more wheel slip than you'd get in a vehicle with locking differentials.
For those that don't know, a locking differential (or "locker") is a component that ensures that two things spin at the same rate. So if your vehicle has a locking center differential, it means that the front and back tires will always split power evenly, regardless of what is going on. If you have a rear locker, that means you can lock the left and right rear wheels together.
This is different from an "open" differential, which is what you find on most cars. With an open diff, power flows via the path of least resistance. That can be a problem on tricky terrain, because if one wheel is slipping in the mud or raised in the air, it's going to get all of the power and, well, do nothing with it. That's why you'll see cars spinning their wheels in the dirt even as the opposing wheel has perfect traction.
A locker is how you solve that issue, and hard-core off-road products have locking center, front and rear differentials, which means you can guarantee that all four wheel will try to move the car forward over any terrain. The other way to achieve that is with four indepedent motors, which is what the Rivian R1T Quad and Mercedes G 580 With EQ Technology do.
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That gives you finer control, but with one key disadvantage: Slip. With a locker, the vehicles are mechanically linked, which means power is split before your wheels even slip. But when you have four separate motors controlled individually, you have to control power split using software. And the only way a wheel knows that it's in a slip condition is if it slips, which means the software has to let the wheel speed flare, detect it, then nab a brake or pull power. So you get a lot of spinning sounds and the car working things out in the background.
It can also be a bit counterintuitive. In a vehicle with lockers, if your wheels are spinning, you usually want to let off to regain traction. But in the R1T on the rock-crawling course, I found my right rear wheel spinning while the left rear wheel was stuck. So despite having 1,000-plus horsepower and a wheel that was already spinning, I was supposed to push the accelerator down harder. That was a stressful situation, because I was very aware that, if it found sufficient grip, the Quad could catapult me forward.
""There is just a slight sense that I would prefer a mechanical locker so that all four wheels are spinning all of the time," Mica says in the video. "You just feel like, at the end, you have more control."
Of course, the Quad did work its way up the hill. I saw journalists climb it dozens of times, and so long as they kept their foot in it, everyone got up easily. That's why this isn't a criticism of the R1T or R1S. In fact, for what Rivian is doing, Quad Motors make sense. They offer torque-vectoring capability on the road, helping Rivian deliver on its promise of offering an exceptional driving experience on- and off-road. Quad motors will get you through.
But for the hardcore crowd, the folks that don't care about on-road performance, lockers remain king. So when Scout launches its electric truck with front and rear lockers, I'm excited to see just how capable it is. My gut says it'll be more sure-footed off-road and a lot slower on the road, but we'll have to line up a comparison test to find out.
Contact the author: Mack.Hogan@insideevs.com.
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