My Thoughts on Rock Crawler Suspension

The post below contains a lot of definitions and some explanations of what is going on with suspension whether it be a road car, drag car, off road car, or rock crawler, the physics are the same, but may need different applications.

Right now I am working on my rock crawler, so in this post I will address some of those applications. It's been my experience that without enough anti-squat, the rear suspension will unload and loose traction, adversely with too much anti-squat, the rear suspension will drive under itself and bind. To adjust the amount of anti-squat, I put several holes for the upper links to bolt to. This allows you to fine tune your suspension. Non rock crawling applications, road cars, stock cars, and drag cars, will have several holes in the upper and lower link mounts on the chassis as well as the axle, to allow even more adjustment. This however, is not feasible on a rock crawler as the extra brackets hanging down would constantly get hung up. Another thing to consider with link placement is that as the suspension articulates the instant center will move, you can get a differing IC left and right which will cause the dropping tire to jack the chassis and not push the chassis over the rock.

Then there is bump steer. On a four link this is where the axle no longer remains perpendicular to the chassis, but begins to steer as the axle is compressed on one side and extended on the other. When you have four link front and rear, the effect is greatly exaggerated. Under chassis roll conditions, the front and rear axles steer together much like steering a skate board, so as you initiate a turn, and as the chassis rolls, it encounters gross over steer. While rock crawling this will cause crab walk. To reduce bump steer you need longer lower arms with less angle, say 5 to 10 degrees from the axle angled up to the chassis. I generally have the lower links as long as possible, but one drawback would be that the longer the links are, the more they can get in the way when setting up for an obstacle. There are trade-offs for almost everything.

With the roll center I like to keep it from moving around when the suspension cycles. Therefore I like to use a uniball, or large spherical bearing mounted to an "A" type upper link to keep it from moving as the axle articulates.

I don't like too much anti-dive with the front suspension as this will cause hop under power, and braking.

With all this in mind, I am working on an experimental torque arm suspension for the rear of AR-MOG-GEDDON that utilizes a large spherical bearing at the front of the torque arm and an "A" arm in the rear for lateral location. My goal is a constant instant center and predictable roll center