Bump Steer Measurements Again

Worked on this Last night and all of Today - 14 Hours in Total!! - It's a pain with the body on!

As before - time to break out the mirror, laser and graph paper:

Firstly I removed the spring and damper (and disconnecting the anti-roll bar). I then swapped some shims over on the top balljoint / wishbone to remove a bit of caster - this as you might expect made a mess of the bump steer effect.

To cut a very long story short - I moved the steering rack around in small increments (not easy with the body on and an accusump in the way) - moved the suspension through it's range and plotted the results. I then input these into the laptop to provide a record of the changes and try to figure out the next step:

I ended up with lots of results:

Conscious that Christmas was not that far way I settled on the best I could manage, repeated the exercise for the other side, then checked the first side. Here's an averaged set for both sides - (both sides were with a couple of minutes of each other):Despite my best efforts I could not reduce the effects to any less than this - nor could I achieve the ideal of some toe-in under bump). On my first graph when I first measured the bump steer - when i got confused with minutes and seconds! - I also got confused with toe-in and toe-out! - the slight toe-in under bump was in reality toe-out. All in all then not a good effort as it turns out. Ignoring the extremes of travel (where things tend to get excessive no matter what you do) the bump steer effects are generally less than 5 minutes - less than the 13 I had before!

Having adjusted the caster and rack height I nipped off down the local tyre centre to get the tracking re-set. On the way back I sought out some bumpy bits of road. I still noticed a slight effect on large bumps but it was much reduced from that previously not requiring any steering correction. On generally uneven / bumpy roads the car felt quite settled. Plotting graphs is one thing - it is how it feels when driving that is important. All in all a good improvement over the previous set up. The reduction in caster (2 x 1.0mm shims swapped) has reduced the steering effort a bit without affecting straight line stability.

I am now however - intrigued with the whole concept of steering geometry and bump steer. Over the winter I am going to see if it would be possible to eliminate it completely - probably not notice that much difference on the road - but that's not the point now!