Radius arm front suspensions; Hopping?

[Greg]

Has anyone else noticed how certain radius arm suspensions, when combined with sticky tires and a healthy engine, tend to hop under throttle? This video isn't the first time I have noticed this, but thought I'd post this here as an example.

[YOUTUBE]DdHikqmuLjo[/YOUTUBE]


That Bronco's front suspension seems practically useless, the front tires are jumping all over while the rear tires are doing 90% of the work, to the point of smoking and pulling the front tires off the ground as it climbs. At least the rear seems planted!


There was a yellow YJ on Constrictor a few years ago that had the same issue. It would start hopping so bad that forward progress was immediately halted. He really had to get on the throttle and use momentum to make any forward progress, it did not work well at all. (My apologies to the owner for throwing him under the bus, if he's on here or sees this.)

Any ideas on what's causing this? Is it just the way a radius arms work, as far as planting the tires? Is the tire is hooking up, then breaking loose when the axle rotates, then rocks back and forth in the mounts?

Has anyone seen a radius arm suspension that really hooked up with sticky tires and a lot of throttle?

 

[LT.]

I wonder if the radius arm mounts on the frame have enough give to aide in the wheel hop. Or maybe it is in the C mounts on the axle. They are just bushings as well.

LT.

 

[Greg]

I wonder if the radius arm mounts on the frame have enough give to aide in the wheel hop. Or maybe it is in the C mounts on the axle. They are just bushings as well.

LT.

I think the axle is rotating in the C mounts, creating wheel-hop much like leaf springs do in a high powered muscle car. The axle binds to a point under extreme traction where it wraps, then lets go, loosing all traction.

I also wondered how much the angle of the radius arm mattered, I could see steeper arms fighting traction, but honestly I don't think that is the issue.

 

[Panos]

i am curious about what causes this as well. my new buggy build i was planning on using a hybrid fj80 radius arm type set up. i guess i can always change it if it end up being as useless as the one in the video

 

[RockMonkey]

I'd look more at the shocks than the radius arms. Cody's unibuggy didn't do that, did it Cody? The few times I've had my Chero-thing out it didn't do anything resembling that.

 

[bull7467]

I think what happens is the "triangle" that is formed by link suspension is relative to your wheel hop. The further back that point A gets from B+C change where the weight distrubution is carried. In effect the longer the arm, the further back from the weight in the front end is carried. Also withh rock monkeys point What does he have in the front that is pushing point B+C apart? Does he have the weight of a dana 60 and aftermarket bumper pulling down or is it stock 44 without a bumper....... at least that what is in my head. Correct me if I am wrong.

 

[Gravy]

That's israels jeep: he is running cage radius arms front and rear with stiff coils and stiff poly "c" bushings. It isn't balanced. I love his jeep though. Imagine those arms with a short upper and long lower at a steep angle and when you compare the convergance of the links with the instant center you get a huge antisquat # in the rear. And a high anti dive # up front. Lower lift and some more balanced suspension can make up for that though. Look how well carl's bronco buggy works with cage radius arms up front, low lift height and a balanced suspension and sticky baja claws. As well as rock monkeys. Both have nearly flat angles on the radius arms so the antidive isn't so high. You could help it with a center limit strap too. Sure a 3 link will flex better but there is something to be said about a balanced and predictable suspension. Carl's comp rig isn't the most flexy on the planet but I've yet to see a more preditable + simpler suspension setup on a comp rig just watch the tip over challenge footage (there's something to be said about driver skill and knowing your rig that I certianly don't have that comes with seat time too).

 

[ID Bronco]

I have not had that issue with my Bronco but I don't run stickys

 

[Herzog]

I had a radius arm on my full body 89 XJ back in the day and don't recall experiencing anything like this, for what it's worth. But the radius arm style I was using was different than that of the bronco arms. Same concept though.

Another thing to consider is if they are running some kind of "wristed" arm on one side. Could torque be building up in the housing and letting go at the other end?

 

[I Lean]

The biggest things are length and angle of the radius arm, like has been mentioned already. As well as loose/worn out bushings at the axle....

Marc Bryson's XJ with a super-short radius arm hopped REALLY badly.

 

[jsudar]

My cousin had a 3.5" lift on an early bronco with stock length radius arms and no drop brackets and it hopped pretty badly in the front. He broke both passenger side ball joints (D44) trying to climb Dump Bump because it hopped so much. That was with old BFG muds, not stickies.

 

[ID Bronco]

My cousin had a 3.5" lift on an early bronco with stock length radius arms and no drop brackets and it hopped pretty badly in the front. He broke both passenger side ball joints (D44) trying to climb Dump Bump because it hopped so much. That was with old BFG muds, not stickies.

Crazy, I have a 3.5" lift, same set up, stock arms, no drop bracket and no hop. I wonder what the differnce is.

 

[jcruiser70]

Crazy, I have a 3.5" lift, same set up, stock arms, no drop bracket and no hop. I wonder what the differnce is.

I think the problem may have been in his right shoe

 

[Floydargue]

winch?

Would sucking the front end down a little more with a winch help at all? If the springs are more compressed, it may be less able to hop like that. But maybe not. I think the guys talking about the health of the bushings up front are probably preaching the most truth.

 

[jsudar]

I think the problem may have been in his right shoe

Maybe so, but it made for an interesting afternoon.

Didn't we see like 14 more people break and somebody almost lose their head to a flying jeep driveline?

 

[jcruiser70]

Maybe so, but it made for an interesting afternoon.

Didn't we see like 14 more people break and somebody almost lose their head to a flying jeep driveline?

Yeah, something like that, it was good times.