Robbie brought up this subject reminding me not to forget to tell you about bump steer. Well bump steer has a lot to do with the handling of your rig, it’s alignment, and is not adjustable. Bump steer is found on any axle on a rig that is a solid axle, that is both wheels are connected to a solid piece of steel running from one side of the rig to the other. Bump steer does not effect independent suspension. Bump steer cannot be corrected with add on steering stabilizers. They can help in the after effects of bump steer to a point.
Bump steer is caused when one wheel of an axle, say the right front, goes over a bump. The left front wheel in this case stays on smooth ground. The axle rises on the right side tilting the axle so that it is no longer parallel with the ground. This makes the imaginary center line of the axle tilt down and at a point out to the left of the vehicle intersect the ground. Now comes the ice cream cone effect as the rig will tend to steer around that imaginary point causing the front of the rig to steer left.
Now you the driver feel the left swing and correct the steering wheel to the right, but just about that time the wheel is now coming down off the bump. The net effect is a slight overcorrection. In an independent front suspension each wheel is free to negotiate bumps without effect to the other wheel.
Now, just when you think you have the rig straighted out the rear end hits the bump, but this time as the right rear goes over the bump the action of the right wheel rising and the left staying on smooth terrafirma causes the same ice cream cone effect but the rear of the rig swings to the left causing the nose to point to the right. Now steering correction is needed and the process starts all over again. Smaller diameter wheels and tires will react more to bump steer than larger tires. The reason is that that imaginary center line is higher off the ground and the tip of the ice cream cone will be further away from the rig creating a larger radius and less swing.
Bump steer will be more noticable when the shocks are weak as the rig tends to bounce more. And speaking of shocks, I consider them more of a safety item than a comfort item. The purpose of the shock is to stop rebound oscillation of the springs and keep the tires in contact with the ground on rough roads. But we will cover more on shocks in a future blog.
Now, a word on toe in and toe out. When going down a road straight the ideal is to have both front wheels rolling down the pavement parrallel to each other. In that position there is zero scuff and minimal tire wear and minimal drag. The later has more of an effect on fuel economy than we would like to believe. Ideally toe in is what we call a static angle. This means that when the rig is sitting still the front of the tires are closer together than the rear. As the rig moves pressure is exerted on the wheels and tries to open the front up as all the slack in each of the joints in the steering linkage is stressed. The faster you go the more pressure is exerted and the further they will open up.
However front wheel drive cars are just the opposite. They are set with static toe out. As the power is applied to the front wheels to pull the car along the wheels try to get out in front of the car and will toe in.
Excessive toe either in or out will cause the car to dart and have a directional control problem. Excessive toe in or out will wear tires as they are dragged across the pavement. If you run your hand across the tire tread from the inside out and then the other way and feel the edges of the tread like saw teeth, to can be suspected as a problem.
Well space is running pout so next week we will wrap this subject up and get onto something else. Happy camping, Brad.