by Jim "Ack" Cambron
Bump steer is when the steering wheel is yanked out of your hands when you hit a bump while driving at speed.
In a stock suspension setup, the draglink is set so that both ends are positioned at the center of suspension travel when the truck is at rest on flat pavement. This means that,at rest, the axle end of the draglink is at the center of the arc of motion created by suspension travel. In normal driving when you hit a bump, the draglink moves up and down with just a tiny bit of side-to-side motion since the draglink ends is moving in an arc rather than a straight line.
When you add a suspension lift, you lower the axle end of the draglink changing the geometry described above. When you hit a bump, instead of the draglink just moving up and down with very little side to side motion it also moves left or right - so much so that the motion is transmitted to the steering wheel as noticible (if not violent) rotation. Thus the phrase "bumpsteer".
The only true cure is to figure a way to either raise the axle end of the draglink through an over the top (OTT) steering system or by installing a drop pittman arm at the steering gearbox end of the draglink. Each method has it's advantage and disadvantage.
In My Humble Opinion, Z-Bar/Z-link draglinks and all their variations are a waste of time in curing bumpsteer. They DO help keep your draglink from tangling up with your springs but that's about all that they do. I have seen numerous homade Z-links get pretzelized on the trail leaving the drive and his truck stranded, so if you go that route, make SURE that it is strongly built!
Here are some graphics that I created that describes the effect of bumpsteer:
Bumpsteer illustrated using a Z-Link.Notice how the pittman arm turns as the suspension is compressed. The more the pitman arm moves, the more violent the bumpsteer is at the steering wheel.
Bumpsteer eliminated using a High-Steer or Over The Top (OTT) system.Note that the pittman arm barely turns thus transmitting hardly any bumpsteer motion to the steering wheel.
I used Photoshop Elements to animate the above graphics. This program allowed me to reposition all moving components without actually changing their physical dimesions which illustrates the true motion of the suspension components.
In an Ideal world, the pittman arm end should be exactly at the same height as the tierod end of the draglink (draglink is parallel to the ground) when the suspension is at rest.