Why The Tesla Cybertruck Struggling Up A Steep Snowy Hill Isn’t Anything To Be Ashamed Of

Tesla and its vehicles are a polarizing topic in the automotive world. The company has its die hard fans that will go to the mat over even the slightest issue, and they believe that Tesla can do no wrong. On the other side, there are those that can see mistakes and flaws in Tesla’s vehicles and shout them from the rooftops. Thus, when video hit the Internet showing a Tesla Cybertruck attempting and failing to climb a snowy slope, the rage machine on both sides kicked into overdrive. Today, we’re going to dive in and examine what was really going on.

The videos were posted to Instagram by one Matt Chambers, who noted that it was actually a video shot by a friend of his who helped with the recovery. The Cybertruck is branded as an “RC”, or “Release Candidate” model, with stickers on the side denoting that it’s an engineering prototype. We see the truck attempting to climb a steep slope near a pine forest at the Corral Hollow OHV Trail, with a Christmas tree loaded in the bed. It helplessly spins its wheels and makes little forward progress, and is eventually pulled back on to a flat trail by a Ford.

Ultimately, from what we’re told about the incident, and what we can see ourselves, there are a number of factors at play behind the Cybertruck getting stranded in this situation. Let’s tick them off one by one.

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A post shared by Matt Chambers (@mchambers_22)

The first thing to reckon with is the slope. Video and photos are often a poor indication of just how steep a slope is, but there are certain context clues that tell us that the truck is contending with a fairly decent incline. If you look at the people in the background of the shot, you can get an idea of the angle of the terrain. It’s not an impassable slope, by any means, but steeper inclines do rob a vehicle of grip.

Steep Slopes Are Hard To Climb, Especially If Traction Is Low

This is fairly obvious, but let’s get into it; it’s all about friction and that friend of ours from physics, the normal force. (What follows is a heavily simplified explanation; for a deeper one, dive into some beginner’s physics and engineering courses).

The more friction between a tire and a surface, the more power you can put down to move in the direction you want to go. The amount of friction available can be determined by an equation where the friction force equals the coefficient of friction multiplied by the normal force. Ultimately, the coefficient of friction is determined by the surfaces involved – in this case, rubber and snow – and is affected by things like wetness, surface contact, and so on. If the coefficient is zero, there is no friction at all between the two surfaces in question. Higher coefficients are indicative of more available grip. Rubber on asphalt in the dry can have a coefficient around 0.7 in typical cases. Obviously, in the case of rubber on ice, which is much slipperier, the coefficient can be as low as 0.15.

However, the coefficient only tells half the story. You can have a good coefficient of friction, but if the normal force is low, you won’t have much friction, and thus grip, anyway. For our cases, the normal force is always perpendicular to the surface on which a vehicle rests. It’s the equal and opposite force to that of the car’s mass being pulled down by gravity. As the gravity pulls the car towards the ground, the ground exerts an equal and opposite force in return. This is what stops your car falling through to the center of the Earth.

The problem is that on a slope, gravity keeps pulling straight down, but the normal force remains perpendicular to the slope. What this means is that the normal force ends up equal to only a fraction of the gravitational force, and the steeper the slope, the smaller that fraction is. Effectively, the component of the gravitational force that is perpendicular to the slope generates the normal force, which helps with grip, while the rest is tugging the vehicle down the hill.

[Ed Note: Just as important as the drop in normal force (and thus friction) is the fact that the force due to gravity — which is giant given the vehicle’s girth — has a significant component pulling the truck down the slope (m*g*sin of the angle). This means that tractive forces pushing the truck uphill will have to overcome that plus the other opposing forces that would exist on a flat grade like rolling resistance, bearing resistance, etc. -DT]. 

The Tires Clearly Weren’t Ideal

With the physics out of the way, we should move on to the specifics of the situation. It’s plainly apparent that the Cybertruck doesn’t have the right tires for the situation. It looks to be wearing a relatively tame set of all seasons which are never going to be the best kit for snow, dirt, and mud.

Beyond their lack of aggressive tread, all seasons generally use rubber compounds that aren’t super grippy in low temperatures, either. When things get really cold, the rubber tends to become harder and less compliant, so it can’t mold to a surface as effectively and generates less grip. Winter tires are specifically designed to remain more supple in lower temperatures to avoid this.

My Autopian colleague Pete performed some Google magic and discovered this forum post, which shows the tire above is almost certainly a Goodyear Wrangler Territory MT, as previously seen on Cybertrucks in the wild. It’s an all-season, all-terrain tire. In other words, it’s a jack of all trades, but a master of none.

Here’s an example of a Goodyear Wrangler Territory (left). More aggressive tread designs such as the Dunlop Grandtrek SJ6 (center), Falken Wildpeak AT3W, or one of Goodyear’s more heavily lugged Wrangler models would have helped the Cybertruck – or any other truck – find more grip on that snowy slope. Production Cybertrucks are to be shod with the Pirelli Scorpion ATR, which is known for good performance in snow.

Along with the impact of tire choice, we can further speculate that tire pressure played a role. Dropping tire pressures is a simple way to get more grip, particularly in softer surfaces. As tire pressure goes down, the contact patch on the tire increases in size. This is because as a greater surface area of tire is required to support the vehicle’s weight with less air pressure in the tire. You want more rubber in contact with the ground trying to find some purchase and something to grab on to, to help pull the car along. By airing down the tires, you spread the vehicle’s weight over a greater area of rubber, and increase the chance of the tires gripping and moving the car, rather than simply slipping and spinning. A great example is the way that tank tracks take this to the extreme, creating excellent grip by spreading a vehicle’s weight across a long, wide tread.

In snow, airing down for a larger contact patch can be particularly helpful. It tends to help the tire “float” over a wider patch of snow because the tire’s load is spread over a greater area. This is desirable compared to seeing a higher-inflated tire punch through and sink into the slush. It’s very similar to how things work when sand driving.

[Ed Note: I haven’t had a tun of success airing down in the snow, though admittedly I haven’t done it a ton. -DT]. 

The Prototype Traction Control System Likely Needs A Few Updates

We can also see the Cybertruck, which is all-wheel-drive, is failing to put its power down. It’s spinning wheels both front and rear. According to the posts, this was in part due to a software issue which disabled the ability of the rear brakes to act as a locking differential. We don’t know exactly what drivetrain configuration this pre-release version of the Cybertruck had, but let’s explore the topic of why this can cause problems offroad.

Vehicles with open differentials face a common problem when tackling difficult terrain. An open differential transmits torque equally to both wheels. This becomes a problem when one wheel is on a slippery surface or dangling in the air without contact to the ground. This is because the further limitation of the open differential is that it can only deliver as much torque as the wheel with the least grip can take. Thus, if one wheel is spinning freely and putting down virtually no torque to the ground, the other wheel will get the same tiny amount of torque, and the car will go nowhere.

In the case of the Cybertruck seen here, it appears it may be suffering this problem. Some off-roaders get around this flaw by using the brakes. Hitting the brakes creates some resistance for a wheel dangling in the air, allowing it to accept more torque. This higher torque can be transferred to both wheels, hopefully providing some forward motion. Some modern vehicles use computer systems as a sort of “faux-locker” to selectively brake the wheels independently to generate this effect and allow forward motion. For example, the wheel spinning freely can have its brake engaged to create some resistance, allowing the differential to send more torque to both wheels. It’s not as good as a real locking differential, but it can sometimes make enough difference to get your vehicle out of a tight spot. In this case, though, reports from the ground are that a software issue disabled this feature on the Cybertruck.

It’s worth noting, though, that production Cybertrucks may not be victim to the same circumstance. As reported by Drew Baglino, Tesla’s SVP of Powertrain and Energy, production dual-motor Cybertrucks come with differential locks front and rear. A locked differential effectively allows 100% of torque to be transferred to a single wheel on an axle. It doesn’t matter if one wheel loses grip or has no contact with the ground; full torque can be sent to the other wheel to provide propulsion. In the case of the tri-motor Cybertruck, there is only a front differential lock. However, that’s because each rear wheel gets its own independent motor, and thus there is no need for a rear differential at all.

Front diff locker for tri, front & rear locker for dual.

— Drew Baglino (@baglino) December 1, 2023

Locking diffs would have probably been a great boon in this case. Combined with the prodigious low-down torque available from the truck’s electric motors, it may have had more luck crawling up the slippery slope without needlessly spinning its wheels.

Of course, it bears noting that we don’t have all the information. It’s possible that this slope is steeper than it looks, and slipperier than it looks, and that it may have been difficult for even a better-equipped Cybertruck to get up without issue. What would really fill us in is if we had footage of another truck in the same conditions doing a better job. Regardless, there’s still plenty that could have improved the Cybertruck’s chances, as discussed.

Just to be clear… this is a Super Duty and NOT advertising. Glad a @Ford owner was there to help. https://t.co/Rr78EY9k2T

— Jim Farley (@jimfarley98) December 13, 2023

Hilariously, this pre-production truck had one more flaw that complicated everything. It had zero recovery points fitted, and thus had to be recovered via a tow rope wrapped around the suspension. This is not ideal, and suggests the team involved with testing the truck had not properly prepared perfectly. If anything, you’d expect a prototype to have recovery gear available at all times given the higher likelihood of something breaking or failing.

Overall, the video doesn’t mean the Cybertruck is awful off-road. To avoid a similar situation yourself, make sure you’ve got snow tires, and that they’re appropriately inflated to optimize the conditions. Remember that going up a steep slope cuts your grip, and consider if you can safely find a way to make it up a lower grade instead. Engage diff locks if you have them, or any traction control or faux-locker aids that your truck might come with. And, if all else fails, make sure you’ve got the right recovery gear to make towing your truck out easy. Happy wheeling out there!