How To Tow-Charge a Rivian—Uh, Maybe Just Don't Do It

Regenerative braking is one of the neatest features on electric vehicles. By running the motor backwards (in essence), it becomes a generator that puts electricity back into the battery while providing a braking force. It doesn't matter how the vehicle got moving in the first place - under its own power, rolling down a hill, or otherwise - it works. Clever folks put 2 and 2 together and realized that it should also work if the EV is being flat towed with its regenerative braking engaged. We tried it on our long-term 2022 Rivian R1T and while it does work, it's dangerous and we don't recommend it.

The Concept

While tow charging has technically been possible since the first EV with regenerative brakes hit the road, it didn't enter the popular consciousness until it was featured in the Apple TV documentary "Long Way Up," in which a prototype Rivian R1T support vehicle was flat tow-charged by a big rig (flat towing means all four of the towed vehicle's wheels are on the ground, like you see when an RV tows a smaller vehicle). Since then, it's been bandied about as a potential emergency fix for stranded EVs too low on battery to reach a charger or wall socket, but few have actually tried it.

The Setup

To make sure it really is feasible, we spoke to the experts before giving it a go . Engineers at Rivian, Lucid, and Ford each confirmed it works, and even offered different tips on how to get the best result, all of which we tested. They also gave us some parameters to start with. First, the stranded EV can't be completely dead as it needs to be able to go into drive and apply the regenerative brakes. Second, you need the right equipment, including a sufficiently robust tow vehicle and straps rated for a heavy EV.

Our long-term R1T weighs 7,165 pounds without the driver in it, so we needed a tow rig up to the challenge. We chose our long-term 2023 Toyota Tundra TRD Pro as the tow vehicle thanks to its 11,175-pound max tow rating and torquey 3.4-liter twin-turbo V-6 hybrid powertrain with 437 hp and 583 lb-ft. Connecting the two vehicles would be done with an ARB tow strap rated at 17,500 pounds, a trailer hitch mounted D-ring shackle rated for 9,500 pounds, and a separate D-ring shackle rated for 8,800 pounds connected to the R1T's standard front recovery hooks.

The Risks

Anyone who's ever pulled a vehicle out of a ditch (or even seen it done) can see how this could be dangerous. Ideally, you're never pulling a vehicle with a recovery strap more than a few dozen feet, just enough to get it unstuck. For this test, we'd need to travel several miles tethered together. Any miscommunication between the drivers could end up with the R1T rear-ending the Tundra. Turning too tight or allowing any slack in the tow rope could risk damaging the vehicles and the equipment if it got caught under the moving wheels. We'd also be putting a lot of strain on the equipment, which isn't really meant for long-distance towing under constant load, which is why we used gear with a significant safety margin. We also used walkie talkies to keep the drivers in constant contact in case anything went wrong.

How To

In theory, once the trucks were strapped together, all we needed to do is put both in drive and have the Tundra drag the Rivian down the road with the regenerative braking engaged until it generated enough power to get to a charger. In practice, it was far more difficult.

The biggest issue is the Rivian's "hold" feature, which automatically applies the brakes when the truck is stopped and your foot is off the accelerator. It's designed to keep the truck from accidentally rolling away, and it's handy driving around town sitting at traffic lights all day. For this process, it was a major pain in the ass.

As it turns out, hold grabs the brakes hard enough the Tundra was unable to move the R1T. In one attempt, the Toyota even started doing a burnout. In order to get the R1T moving, the driver had to very gently step on the accelerator right before the Tundra began pulling, just enough to get the brakes to release but not so much as to run into the other truck.

That's not all. Because regenerative braking loses its effectiveness at low speeds, the R1T blends regenerative and mechanical braking at low speeds, so in order to prevent the Rivian from reapplying its mechanical brakes and dragging both trucks to a stop, the driver had to keep their foot gently on the accelerator until the pair got above 10 mph. Below that, it's a delicate dance of giving it enough power to keep the brakes off but not so much it out-accelerates the Tundra, causing the strap to go slack and potentially get caught under the wheels, causing catastrophic damage. Allow the R1T to drop below 5 mph and its brakes will lock up and drag both trucks to a stop.

Unlike most other vehicles with a hold function, the Rivian's can't be directly turned off. As such, the best workaround we found was putting the R1T in neutral and allowing the Tundra to pull it up to 10 mph before engaging drive and the regenerative brakes. We later learned of another workaround, which is to put the truck into Off-Road Rock Crawl mode, which disables the hold function. Just make sure you manually set the ride height to "high" rather than Rock Crawl's default "highest," which limits top speed to 20 mph.

We also tried changing the regenerative braking from "high" to "normal," but found it didn't make much difference as the setting mostly seems to control how quickly the regenerative braking ramps up when you release the accelerator, not the maximum regenerative braking force.

The Results

Over the course of six individual tests and 8.0 miles of driving, we increased the Rivian's battery from 15 percent state of charge to 26 percent and gained 51 miles of indicated range. That's an average of 6.4 miles of range gained per mile of towing, not a bad result at all.

The experts had suggested that the faster we went, the more energy the EV would capture, but we didn't find that to be the case. By 35 mph, the braking portion of the Rivian's power and braking meter was maxxed out and a subsequent test at 25 mph over the same distance generated roughly the same amount of power according to the truck's onboard charging telemetry.

We also didn't observe any difference between "normal" regenerative braking and "high." With the driver's foot completely off the accelerator, maximum regenerative braking was engaged either way and there was no difference in the amount of power being generated.

The Other Truck

While we eventually perfected the procedure, it was by no means easy on the Tundra. With the R1T applying full regenerative braking, the Tundra was working hard to accelerate. We tried rear-wheel drive and four-wheel drive, tow mode, and even four-wheel drive low, and it made little difference. With the Tundra at full throttle the pair of trucks still struggled to reach 40 mph and couldn't go much beyond that.

As you can imagine, this was wildly inefficient. We reset the Tundra's onboard fuel economy meter before testing and after it showed we'd averaged just 1.9 mpg. We'd burned a little more than 4 gallons of gas to go 8 miles and add 51 miles to the R1T.

Charging Rate and Drag Force

Taking two 2-mile tow-charging stretches as an example, a 25-mph pull added 6.7 kWh of energy, while a 35-mph one added 6.3 kWh. Those pencil out to charging rates of nearly 84 and 110 kW. Because the Tundra essentially "hit a wall" at 40 mph, we can deduce that it had reached its maximum pulling force. This can be calculated by multiplying peak torque (583 lb-ft) x gear ratio x final drive ratio and dividing by the tire radius. That works out to just under 7,000 pounds in first gear, dropping to about 4,650 in second and 3,350 in fourth. Note that these numbers have nothing to do with rated towing capacity, as a truck should seldom require peak force simply to get a wheeled trailer moving.

What About Reverse?

The experts we consulted ahead of this test also had an even riskier idea. One suggested we'd get the maximum regenerative braking effect by putting the Rivian in reverse and towing it forward with full regenerative braking engaged. If that sounds dangerous and ill-advised, that's because it is, but we tried it anyway in the name of science.

As with drive, the hold function is active in reverse and doesn't release until the Rivian driver applies the accelerator. This meant the trucks effectively ended up in a low speed tug of war, with the Rivian trying gently to pull the Toyota backwards and the Tundra overpowering it. As you can imagine, this put even more strain on the Tundra and made it exceedingly difficult to get the pair moving quickly enough to deactivate the Rivian's hold feature and mechanical brakes.

To be entirely thorough, we also tried our workaround of starting the Rivian in neutral and letting the Tundra tow the pair up to speed, but this time it didn't work. The R1T, it turns out, will only shift into reverse at speeds up to 4 mph, so the driver had to time the shift very carefully. 4 mph is slow enough the hold feature would begin automatically applying the mechanical brakes, which made it nearly impossible for the tow vehicle to keep gaining speed and release them.

In addition to being the most dangerous method of tow charging we attempted, we also saw no indication it was generating any more power than using drive. We really don't recommend this method.

The Recommendation

Our advice is simple: don't do this. If at all possible, find an electrical outlet of any kind within your remaining driving range and beg to use it. It'll take longer, but it'll be much, much safer and easier.

If you have no other choice, use Rock Crawl mode or start the Rivian in neutral before shifting to drive in order to bypass the hold feature. Use cell phones or walkie talkies to maintain contact between the drivers of the two vehicles, coordinate your stops and starts. Go slow, and only tow charge as far as is absolutely necessary to get enough range to get the Rivian to a real charger.

MotorTrend's 2022 Rivian R1T Launch Edition

More On Our Long-Term 2022 Rivian R1T

• The Start of Something Remarkable
• Using the R1T as a Farm Truck
• The Net-Zero Camping Trip (That Almost Wasn't)
• Our Long-Term Rivian R1T Has a Secret Software Mode
• The Difference Between an R1S and an R1T
• Rivian's Phone as Key Feature Needs Work
• Winter Storms Tire Out Our Electric Pickup
• All The New Features Rivian Added To Our Truck Since We Got It
• We Charged An E-Bike With Our Rivian R1T While Driving - Then Hit The Trail
• How Fast Is A Rivian R1T?

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T

Long-Term 2022 Rivian R1T