Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Missing in action - bump steer!

Had new upgraded wishbones fitted at the factory yesterday 26.4.13

Driving back to Stratford upon avon I suddenly realised something was missing - Bump steer!!

Well lets say its very noticeably better/almost gone!

The tracking had to be re-done at the same time so this too could well have added to the overall "fix"

The four new wishbones are of much thicker tubing - and I guess - not being an engineer, that the whole of the front steering /stabilty is now much stiffer/firmer.

Anyway hope this helps - and I would recommend this upgrade to M3W owners.

New cars are all now fitted with the upgrade BTW

And yes I was charged £70 for the labour -but overall a happy chappy

Oh, the price has gone up a tenner, since I had mine done in mid December!

Sadly my bump steer did not improve, slightly worse if anything.

Any chance you could post a picture of the new control arms in-situ? I suspect the improvements are a combination of new length bias between the top and bottom arms and, possibly, a change in static ride height. If there is a change in ride height, I wonder if its achieved by moving the lower damper mounting point.

Regards,
-Spencer

Will post some pics for you -but think that u will see hardly any difference - I could not really see any - but was told by one of the engineers building M3Ws that the tube profile was much thicker and has beefed up welds/joins throughout - hope this helps - pics to follow

I notice you say 'four wishbones' when dealer replaced mine only the lower two were replaced , couldn't really detect much difference in the steering.

I dialled in a fair amount of toe in to help with the high speed stability and noticed an improvement in bump steer. I suspect the static toe out in combination with the poorly optimized springs/dampers leads to substantial increase in tire-to-road pressure on bumps. That increase in pressure, combined with the toe out, causes the tire to generate cornering force, in turn causing the trike to veer. When you get rid of the toe out, the bump steer seems to get better, which corresponds well to my little theory.

There is likely a lot more going on, but I believe that the process I'm describing is causing some of the bump steer. Also, the way the control arms are configured really lends itself well to the addition of a set of adjustable eccentric cam alignment bolts on the inner upper arms. These would help by allowing the raising of the car (to deal with bumps using more suspension travel and less spring/aggressive-compression-damping) while maintaining reasonable static camber.

The front suspension is a work in progress, but I will sort it out and make the trike handle well at least up to 100 mph.

Hi gaius49 have posted a pic for you.

I am nowhere near your stratospheric understanding of suspension - but interestingly enough I understand that there is a mod in development which would add a new alloy (adjustable?) section to the top wishbone joint - if this is adjustable then it would maybe meet your idea for eccentric cam alignment bolts?

hope this helps

Oh, wouldn't it be great to have two people that understand the black art. Well done Gaius49, we're rooting for you.

Good point about the toe in, I will certainly try it on mine, though, it's funny the factory recommend a tad of toe out, or at least they did last year, this may have changed since I first took deliver in April. They must have a reason for that, just as the must, to have changed the angle of the steering arms from parallel to the ground, in early pictures of the car, to sloping down on production cars.

Surely with so much bump steer on M3W causing toe-in in bump, if you set a little toe-out unladen then the wheels will go parallel or even toe-in when laden, which is what is required typically. Unlike on the 4 wheelers that toe-out in bump. So do we all set the 4 wheeler toe angle laden then? It's enough to make your toes curl! PJB

The trouble with static toe out, is that it gives instability of straight ahead steering, and quite agressive initial turn in on corners, typically leading to lock having to be taken off to maintain an even turn radius, which is exactly what is happening to mine. Add to this, the bump steer aggravated toeing in on spring compression and it's no wonder the little thing doesn't know which way to go.

The problem is knowing quite how to fix the car the way it is now? The factory clearly don't have the answer, and, like other aspects of production, it is all rather hit and miss, whether they get it right or not.