For those who wish to discuss "Bump Steer and Front Suspension" related topics with a more suitable topic tittle I have taken the liberty of starting this thread to help people move on from the thread drift on "another topic"
I also take the liberty of quoting PJB's informative post on the subject to get things started.
Originally Posted By PJB
As has been said before; MMC are working on a solution to the M3W front suspension & steering concerns. It is of course true that there is a lot of bump/roll steer for all the obvious reasons already stated, the steering & suspension geometry was designed by MMC and was and still is their responsibility, as is right and proper. The initial design of springs and dampers were designed and developed and funded by SUPLEX UK Ltd. The first cars that went as demonstrators had SUPLEX springs and dampers and generally had good write-ups for ride and handling. These units had an integral rebound spring to restrict droop of the inner wheel on cornering thus increasing roll stiffness AND a rising spring rate in bump achieved with a spring assister on the damper rod. The damper characteristics were also tuned to this set up. Due to the unexpected success of the M3W production volumes were significantly increased and SUPLEX were unable to ramp up production quick enough and so mass production was given to SPAX. The current SPAX units have none of the sophistication of the initial SUPLEX units resulting in the bump/roll steer being far more noticeable. Also the SPAX cars ride higher making to bump/roll steer effect even worse. The SUPLEX units did restrict the bump/roll steer as there was no droop on the inner wheel so no steer effect there, and also the bump travel was limited with the rising rate to also minimise the steer effect. SUPLEX have no design input in the steering geometry as that is being worked on by MMC. So although Kevin Rivette has come up with a spring/damper solution is it as sophisticated as the SUPLEX design, I do not know. SUPLEX UK are part of the solution to this concern and are of course working with MMC. I hope that this helps - PJB (Contract - Consultant Engineer and Test Driver for SUPLEX UK).
PS Both BMW and Mercedes are introducing rebound springs into their dampers to limit roll and thus reduce antirollbar stiffness to improve single wheel bump responses.
I moved my request to this thread as I think it would be a good visual starting point early in the tread. I continually read about the earlier Suplex and later Spax front suspension on the forum and was hoping someone could post a comparison picture or two showing the difference(s), if there is any to see.
It looks to me as if Morgan are working on a mod, which involves raising the height of the steering arm on the upright, which is more or less the same as putting a spacer in, it would be nice if that cured it, but that doesn't take account of the fact that the steering rack ball joint and the suspension pick up points are different lengths, so they are all going up and down in a different arc to each other. This basic problem has to be rectified first, then the tie rods issues can be dealt with. There is also the fact that the King Pin Inclination does not bisect the tyre, nor even come close, not vital, but it all helps.
That is with my limited knowledge, there are one two others here who actually understand the varying relationships that all the different parts of the suspension and steering system have with each other, change one item and it changes everything else.
Interesting photo comparison. While I guess it's better to have the steering arm parallel to the lower arm, one can see it's considerably shorter than it from the picture of the car with Spax suspension where the inner joint is angled.
However, it's nearer the upper arm and I imagine this is shorter than the lower one in any event. Moving the ball joint up would reduce the bump steer in that case. I would though wonder whether a spacer would create a weak point.
The other point is, what is (or are) the spring rates? A car with a stiffer front will exhibit less bump steer, even with identical suspension design.
I have spent some time, as others have looking at this “bump steer” problem and having seen the “fix kit” (online) available in the US and having seen the Williams’ spacers (in the flesh), that fit under the ball joint, raising it by around 1” 5/16, I feel the fix is easier than we might think.
I am no expert on suspension geometry, but I have been involved in building a prototype (which became a production) 3 wheeler. I think that the problem, ie. “Bump steer” is caused by the increase in length of the coil over unit. This has messed up the ride height and in doing so has changed the angle of the track rods. I would not be happy to fit a spacer into the system, without first seeing the maths, or a finite element analysis, proving that it is up to the job, as the forces exerted on it would be massive and as the spacer will be acting as a lever magnifying this force.
I would, however, be happy to replace the SPAX dampers with others of the correct length, remembering that the springing and damping differences will change the ride and body role, but not the bump steer. So a good adjustable damper with the correct rated spring would be the best cure in my opinion.
I am sure that if Morgan decides to change from the SPAX unit back to SUPLEX, or another manufacturer to cure the problem and it works, my dampers may well mysteriously stop working and have to be replaced on the warranty.
Is it possible to get the SUPLEX unit measured to compare it to the SPAX one, so we can look into “off the shelf” alternatives?
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