Interesting Offroad Behavior

[SpaceEVDriver]

We went for a short camping trip in the nearby forest where there are a lot of great 4x4 / jeep trails with rocky sections. No photos because (luckily) everyone was in the Lightning.

On the way up one road, there was enough cross-axle terrain that we were on three wheels multiple times. There was a lot of loose, fist-sized limestone rocks. The truck mostly did great in Normal mode with the rear differential locked and 1PD engaged. Still on the factory Hankooks.

On the way down that same section, however, we experienced something unexpected. Every time we had a front wheel off the ground, it would spin... Backwards!

A couple of times it shot a bunch of rocks out in front of the truck.

That's why I said luckily everybody was inside the truck. None of my passengers are experienced spotters so I didn't ask anyone to get out and spot. They very well could have been injured by the flying rocks. The trajectory and fact that no rocks were spun up into the underbody make it clear the free wheel was spinning backwards.

I wish I had video of it.

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[HOTAS]

When an open differential is used in the front of a vehicle and one wheel is lifted off the ground, turning (driving) that wheel will cause the other front wheel to spin in the opposite direction. This is a normal characteristic of an open differential, which allows the wheels to rotate at different speeds when turning or when one wheel encounters less resistance. It doesn't indicate a problem with the differential itself, but rather how it functions.
Applying some light brake pressure will help stop it, and some traction control systems will do the same.
Im thinking ’off-road‘ mode may have helped eliminate it too.
Ford describes it….

• OFF-ROAD: Optimizes accelerator, traction and stability control settings for enhanced off-road performance

Sometimes that backward turning wheel will get enough traction to kick you back down the hill.
In a traditional 4x4 system where the front and rear axles are connected, it will bind the whole system and flip a jeep Sideways and cause it to roll over. Hardcore Jeepers often prefer a front locker over a rear locker.

 

[Firn]

We went for a short camping trip in the nearby forest where there are a lot of great 4x4 / jeep trails with rocky sections. No photos because (luckily) everyone was in the Lightning.

On the way up one road, there was enough cross-axle terrain that we were on three wheels multiple times. There was a lot of loose, fist-sized limestone rocks. The truck mostly did great in Normal mode with the rear differential locked and 1PD engaged. Still on the factory Hankooks.

On the way down that same section, however, we experienced something unexpected. Every time we had a front wheel off the ground, it would spin... Backwards!

A couple of times it shot a bunch of rocks out in front of the truck.

That's why I said luckily everybody was inside the truck. None of my passengers are experienced spotters so I didn't ask anyone to get out and spot. They very well could have been injured by the flying rocks. The trajectory and fact that no rocks were spun up into the underbody make it clear the free wheel was spinning backwards.

I wish I had video of it.

Hmm, never thought about it. But with regen and an open diff it makes sense.

 

[SpaceEVDriver]

We went back and got some video.
I've experienced slow backward rotation with an open diff, but this feels like it's something more.

Going up.

Coming down.

 

[Heliian]

Did you try off road mode?

 

[SpaceEVDriver]

Did you try off road mode?

No. I dislike driving with 1PD turned off. So I didn’t think to try offroad mode. I suspect it has some added brake-control on the open differential.

 

[SpaceEVDriver]

When an open differential is used in the front of a vehicle and one wheel is lifted off the ground, turning (driving) that wheel will cause the other front wheel to spin in the opposite direction. This is a normal characteristic of an open differential, which allows the wheels to rotate at different speeds when turning or when one wheel encounters less resistance. It doesn't indicate a problem with the differential itself, but rather how it functions.
Applying some light brake pressure will help stop it, and some traction control systems will do the same.
Im thinking ’off-road‘ mode may have helped eliminate it too.
Ford describes it….

• OFF-ROAD: Optimizes accelerator, traction and stability control settings for enhanced off-road performance

Sometimes that backward turning wheel will get enough traction to kick you back down the hill.
In a traditional 4x4 system where the front and rear axles are connected, it will bind the whole system and flip a jeep Sideways and cause it to roll over. Hardcore Jeepers often prefer a front locker over a rear locker.

I think this explanation is mostly correct. I’ve also experienced a similar behavior when trying to stop on an icy surface. I think there’s some extra engagement from the traction control+regen.

 

[B177y]

Could the 1pd braking actually be applying reverse torque? If the driver side wheel with grip is "braking" from 1pd, the passenger side wheel spins backward without grip?

 

[SpaceEVDriver]

Could the 1pd braking actually be applying reverse torque? If the driver side wheel with grip is "braking" from 1pd, the passenger side wheel spins backward without grip?

I think that’s part of it, yes.

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