The measurements you’ve made seems to be normal. Although I did not measured it myself I’ve got a VX220 related document that shows the same results. The verdict is to change the angle of the steering arm by installing an adjustable steering arm. I can sent you the document via PM if you like.
At least it can be clearly seen why it is absolutely important to adjust the front toe only at the right ride height.
To achieve this a suitable weight has to be put on the driver and/or passenger seat.
On Seloc someone posted an interesting comment concernig the bumpsteer that has been designed by Lotus into the front suspension:
Reading the November 2018 issue of Octane, in the article about the genesis of the Elise, I found this comment very interesting:
“Once installed and out on the
road, I’m more aware of the sounds of moving
suspension parts than I was in the Elise, and the gentle,
almost old-911-like writhing of the steering wheel
over bumps and cambers is more obvious.
Dave Minter explains what’s going on. ‘The Elise had
too much grip at the front originally,’ he says of the
prototypes, 'and in the wet it could spin suddenly.We
had to fit an anti-roll bar and make the front wheels
toe-out over bumps, to add understeer and have some
chance of the rear gripping. That’s why the steering
writhes. It’s very “un-engineering” but we had to do it.”
So as always when it comes to suspension design, Lotus did things for a good reason. It generally wonders me that many people think they could do it better than Lotus int the first place. You need to fully understand why Lotus did it and than to be sure you can live without it or even do it better.
It would have been an easy task to design the front suspension with much reduced or even elininated bump steer.
Very interesting, thanks for sharing. Did you find a plot of the original bumpsteer graph somewhere? I have never seen one, only the one for the rear wheels.
Somewhere on the net I found a comment about the bumpsteer curve of the S1 having a strange shape on full droop that causes damage to the track rods when hitting a bump (like driving over curbs with the inside wheel). The shape of your plot does reflect that fact so could well be the right one.
Another aspect that could be taken from your curve is that you really should setup your car with the full 150kg of weight in the seats. If you are driving alone the toe will not change a lot as the graph is nearly vertical in that area giving a slight toe in. I did setup my car with only the weight of half a passenger but I think I will use a ‘full passenger weight’ when setting up the car the next time.
How did you measure the bump steer on your car? I thought of using a mirror fixed to the hub and a laser pointer.
Can you share a picture of the ‘reduced bumpsteer arm’ and how did you setup it?
There are no original graphs for the S1, the only graph that was ever circulated was the one that was issued with the Lotus motorsport kit for the rear but this was not only lower but also had different rate springs and dampers. It needs to be used on any other setup with caution and at the end of the day it is very personal.
If you are going to play I would suggest you do it in isolation and not when changing several other settings at the same time which may easily blind any effect.
After recently getting my geo done, the garage passed comment that the angle of my toe-link kit seemed quite steep compared to the wishbone angle, as if I had too many washers in.
Thinking about rigging up something to check it, but the graph is for 110mm whereas my car is +10mm. The shape/slope of the graph depends on shims, but I’m thinking the actually geometry should be the same (since you’re moving the wishbones through the same arc); does this look right? The dots are targets by the way - expecting toe-in to increase at the same rate and minimal toe changes in droop.