Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Suplex suspension upgrade .

Dan. If you decide to buy you may be able to get the Suplex kit fitted at the factory by Aero Racing. We had some items included on our order and fitted by them before we picked up our car.

PS. Hard to tell from the photo but it looks as though the Suplex shocks have silver grey springs over a black body. To me it looks quite good and blends with the black frame and the alloy of the engine quite well.

I agree Gambalunga , I like the look of the silver grey springs , I think all black looks a bit boring !

Gambalunga,

When you had Morgan fit your M3W with new upgrade kits, did they discount the kit as they’re not using all of their parts as a stock build? Or did they give you all the parts that would normally be removed when installing the upgrade kit? Kind of like Ford with upgraded wheels, you only pay the difference between stock and the upgraded wheels.

Thanks.

Our car is a 4 wheeler but the principal is the same. Put it this way. They did not discount but they did not charge the earth for installation either. In theory I think I could have asked for the original parts but I did not.

What happens is the car leaves the factory as a standard car in accordance with the homologation regulations. It is then taken across to Aero Racing, across the lane, to be fitted with the aftermarket items.

You would have to ask what they would charge in your particular case.

Today I managed to get some garage time and finally set the car up with the Spax adjustable shocks fitted.

Quick recap, standard shocks toe set at 0-0 deg. bump steer measured at .675"

New shocks, ride height set at 130mm front and 150mm rear.

Original toe went from 0-0 deg to off the scale i.e. more than 25 deg toe out at each side.

So I reset the tracking to 0-0 deg and then measured the bump steer.

.050" with 1" droop and 1" bump.

Thats down .625" to FIFTY THOU.

There is now no visual deflection of the front wheels when I bounce up and down on the chassis.

Job done.

Dab, are you saying that just changing out the coil overs you went from over 5/8" to less then 1/16" in toe deflection when bouncing on the front end?

I would think that you would check the bumpsteer with the shocks off but starting at ride height. Then move up/down a couple inches and measure the toe change over the full range of motion.

When I think of setting ride height on cars or bikes with coil overs, I try to set them up with 2/3 compression and 1/3 extension. So normal drive weight the shocks would be 1/3 compressed. Is this the way the coil overs are set on a M3W?

I'm curious enough to ask.

Hi Dan

Yes I took the coil overs off to check the bump steer and measured 1" either side of static ride height using a trolley jack to raise and lower the suspension in a controlled manner.

Measurement was taken using a DTI running on an aluminium plate fixed to the wheel rim.

The difference of dropping the car 30mm is unbelievable with regard to bump steer.

A bit of history. When the M3W was first set up (initial production) with the original SUPLEX units the ride height was set lower than it was later in production with the std basic SPAX units. This initial lower ride height meant that there was little noticeable bump steer and of course the bump travel was also restricted due to the rising spring rate in bump with these SUPLEX units. There was also very little rebound travel due to the internal stiff rebound spring in the SUPLEX units that significantly increases roll stiffness. So a nearer optimum ride height for minimum bump steer and less travel anyway.
When the production SPAX (non adjustable basic type) units were specified to replace the initial SUPLEX units the ride height was increased to allow more bump travel as the springs fitted by SPAX were linear with no 'spring assist' to give rising spring rate. Hence 'they' were trying to avoid full bump impacts by increasing bump travel.
Hence it is no great surprise that lowering the front again to the original ride height as used with the initial SUPLEX units reduces bump steer as that is how the M3W was setup originally; but doing so with the linear springs on the older and latest SPAX units risks full bump impacts, unless the bump damping is wound up that then can impact negatively on ride comfort.

I prefer to control bump travel with a progressive rising rate spring and then control front end rebound with very little travel also with a progressive spring, but then keep bump damping as low as possible to give good ride. Good turn-in being achieved with the outer suspension 'finding' the increased spring rate in bump and not a high 'low speed' bump damping that can destroy good ride.

Bump:rebound travel ratios. Indeed at the rear of a rear drive car (or a bike )a ratio of 2:1 bump:rebound travel is quite typical to allow the inner wheel to droop in roll to maintain traction powering out of a corner. This is of course not the same requirement at the front. Front rebound travel should be restricted as this enables the roll centre to move to the contact patch of the inner wheel thus nearly doubling roll stiffness! Aside - the SUPLEX RS front suspension on the 4 wheelers also uses a very stiff progressive (external) rebound spring and a quite soft main spring. This is done to give compliant ride but with high roll stiffness. This same concept was used on the early SUPLEX M3W units and of course on the latest release of SUPLEX M3W units in that there is an internal rebound spring (inside the damper) thus the Bump:rebound travel ratio is more like 8:1. Hence roll stiffness at the front (zero at back of course) has been significantly increased over both versions of the SPAX units.

One of the problems with a spring rate that rises in bump is that it will soften in droop. Hence in a corner the inner softer suspension will prefer to rise rather than the outer stiffer suspension compress, hence the C0G (Centre of gravity) rises, not desirable. So with a spring rate rising in bump the rebound travel has to be limited to make it stiffer in droop than in bump - thus a rebound spring. What this means is that in a corner, besides the shift in the roll centre to the inner wheel contact patch, the inner wheel suspension does not lift much and only the outer wheel suspension compresses, AND the CoG actually gets lower - oh that's nice.

This gives a bit of background behind the very different level of technology that the SUPLEX units use cf the SPAX units - and an indication of why there is such a price difference. Getting the nonlinear spring rates and the damping rates on the SUPLEX units optimum also took a lot of testing by SUPLEX and Morgan themselves of course.

Interesting (well I think so) the latest rear drive BMW and Mercs also are/will be using front dampers with internal rebound springs to increase roll stiffness but then to compensate reducing the stiffness of the (nasty) antiroll bars that produce poor single wheel bump ride.

Just a few thoughts to help/confuse - regards PJB.

Thank you Peter, as always very interesting.

Now that my Morgan is cornering with so little roll I find that anything else I drive seems to have excessive body roll. I recently drove a hired Mercedes family "wagon". I was expecting it to have good ride and handling but it was a great disappointment. A bit like driving a marshmallow

Obviously a model that does not yet have the rebound springs.

These explanations are very helpful thankyou .

But also annoying for those of us who test drove a Suplex car and received one fitted with Spax . Especially as we were told bumpsteer was a figment of our imagination ! ( Unless we were travelling at over 100mph in the USA )
Still at least it can now be sorted ....at our expense .