I know what bump steer is. I have 30yrs as a MB technician.
I mean when the mirror isn't perpendicular , the reading could have a fault.
Thats why I preferre to , like you said , mount the laser to the hub and read the result on your garage door.
Terry's starting point is to span a string exact in the middle under the car, front to back.
Find the middle position of the steeringbox's rotation ? (said right? ) . Position the steeringwheel at the "normal driving position" , center .
Lock the steeringwheel so it holds its position during regulation at the front wheels .
Regulate and check toe , caster and camber as often as needed so all measurements are whitin specs.
Thats for normal wheelalighment.
When this has been done properly , then its time to attack bumpsteer.
When the car sits on his own feet/tires , measure center wheel to top of wheelwell. Keep that figure in mind.
Remove tire and spring and bring center of hub back to that distance to the wheelwell.
Thats your starting point.
Mount the laser to the hub and move the hub up and down, as it would during normal road condition .
Now you can see how much bump steer you have and see what happens when you shimm your tie rods.
Sorry for my bad english explanation. Old dude from across the big pont who learned english on his own .
Terry , correct me if I am wrong.
