because the same weight transfer under torque that lifts the front left is causing the right rear to dig a hole?
Let's see if this works
- Thread starter mrblaine
- Start date
because the same weight transfer under torque that lifts the front left is causing the right rear to dig a hole?
Don’t know about that, but the rear passenger spring sagging over time is a very real thing.
OP
Yes and in our world, those exist at almost every obstacle from the folks that drive down the middle of the trail which almost is never the line. Now that you know what to look for, a line may be able to be picked to steer the rear tires to a better spot.
Thank you for posting this. Wish we had more wheeling talk/tips here.
I know a local spot where I can test this, and maybe get a video.
Does the front driveshaft spin in the same direction as the rear?
Thinking about street car drag racing. The driveshaft tries to spin the rear axle, lifting the right wheel and dropping the left. This is why open diffs almost always spin the right tire.
This torque is transferred through the engine mounts trying to rotate the front frame the other way. This is why drag cars lift the left front wheel first when the body is flexy and suspension isn't adjusted to counter it.
Just an illustration of the forces at work, even on flat ground.
Thinking about street car drag racing. The driveshaft tries to spin the rear axle, lifting the right wheel and dropping the left. This is why open diffs almost always spin the right tire.
This torque is transferred through the engine mounts trying to rotate the front frame the other way. This is why drag cars lift the left front wheel first when the body is flexy and suspension isn't adjusted to counter it.
Just an illustration of the forces at work, even on flat ground.
On either case available in a TJ they do.
I understand the forces at play causing the twist. I'm at a loss as to why the steering angle has anything to do with it, but I've both seen it in the OP video as well as experienced it firsthand.
OP
Is it as simple as that? As in, if you removed the rear driveshaft, would the chassis still torque over the same driving the front?
I first noticed it due to our type of wheeling very often puts the side of the right side tire while it is fully turned left against the flat face of a rock on an obstacle. That tire will not move but the left front will keep climbing as long as you have the balls to stay in it. If you give it just a tiny bit of right turn, the left will drop and the tire will barely move. I started watching for it both as a spotter and while driving and once you recognize what is happening, with a bit of practice you get to where you just drive through it with tiny bit of turn to drop it and then back into it. I got so good at it, folks don't even see it happen until the rig behind has a left front tire 5 feet in the air.
If the front is locked, maybe, but I would be kinda surprised if one front tire could get enough grip to provide the resistance necessary.
But yeah if the front driveshaft spins the same then it'll do the same under torque: lift the passenger's tire and drop the driver's, while the engine is trying to rotate the frame the other way.
I feel like steering plays a role, too. Have you noticed the same behavior in rigs with full hydro steering? Our drag link angle has some vertical push/pull.
Is this really about drive shaft torque though? I was under the impression this was more about steering geometry and trac bar, like lifting the left front tire accelerating from a stop while turning left on flat ground. Front drive shaft doesn't come into play in 2wd, but the left front will lift when right side is under more load.
Agree with the directions, I just think if the front is light enough to lift, there won't be enough traction to produce the torque necessary to lift...
That's an interesting thought. There's definitely some moments created by the distances between the track bar frame end and steering box, as well as the track bar axle end vs knuckle end of the drag link.
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Suspension joint friction could be part of it too, where a little steering wiggle helps unstick things and lets it cycle.
Also, as @mrblaine described, "the side of the right side tire while it is fully turned left against the flat face of a rock." The back side of that tire is going up so friction is trying to push that tire down, which will act to lift the left side tire. Turing right will release the back side and engage the front, lifting the right tire and dropping the left.
There are so many forces involved it's tough to determine the dominate ones. I've noticed similar behavior in my r/c crawler, where it strongly prefers climbing to the right than the left. One way it's stable, the other it tries to lift and roll.
OP
I would strongly urge everyone to stop focusing on the why of it and just understand that it does happen, it is very predictable, and when you encounter it, play with it and the steering wheel to see how to very easily mitigate the issue. When you figure it out and understand how to deal with it, it is a thing of beauty.
I need to try it again to remember which side it was but I was climbing the steps in the sidewalk up to my front porch a couple months ago and found the same with approaching from one side vs the other. I may have trouble reproducing the full scale behavior though because my RC has portals so the driveshafts spin the other way and tend to load up the left rear tire instead of the right, but the track bar and drag link are oriented the same as a TJ (other than being crossover steering which I dont think should change anything here).
Now I kinda want to convert to straight axles so the habits I learn from the RC will translate better.
OP
Think about how much fun it would be with a reverse rotation transfer case.