Front bump steer

There is plenty of information about bump steer to be found on the internet. Basically bump steer is when the toe alignment changes during bump, ie when the suspension compress.

Here is an article explaining how to correct bump steer on Caterhams. 

There are lots of different techniques to measure bump steer. I used a construction laser level which projects a line when you point it on a surface.

I jacked up the car, removed the wheels and disconnected the link to the dampers on the lower a-arm making it possible to raise (bump) the wheels by hand.

Then I put my laser level firmly on brake disc with one hand and pointed the laser to it to the wall in front of the car. When I raised the wheel with my other hand and watched how the line moved on the concrete floor. With zero bump steer the line should not move sideways. To  be more accurate you can reverse the level and look backwards. The movement (if any) should be the same backwards as forwards.

There are many other ways to measure bump steer. One is explained in the article above, another one of the more clever ways I've seen is by using a mirror to remove the camber-gain effect.

You adjust bump steer by adding or removing spacers under the steering rack. It turned out that I had quite a lot bump steer on the front right and I ended up by removing one big 4mm spacer. For me it was a bit of a pain to undo the steering rack clamps because the dampers is making it hard to access the hex bolts from above, but eventually I got it apart.

If you change the steering rack height, you have to reset the toe alignment! I aim for zero degrees front toe. Some say a bit of toe out won't hurt and will give the car better turn in.

Note to self: Never undo the rod-end-to-upright nut! It's a real pain to get back!