Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Suplex 5L: First Impressions

Yesterday was the first opportunity, since the fitting of the 5L, for Alis to go in the car. I was very interested in what she thought.

Firstly she thought that on the comfort side not a lot had changed (you really need back to back testing to notice the difference) but she immediately noted that the car seemed much better planted on the road and gave the impression of much more precise steering. After I dropped her off at her calligraphy class I decided to lower the damper settings to the minimum, as suggested by PJB.

We then took the same road home after enjoying a delicious pizza

Now keep in mind that when I picked up the car it was set 8 clicks down from full hard, I then set it 18 clicks down from full hard (that is where it was yesterday afternoon), and the 24 clicks down which makes it full soft. The difference between all these settings was noticeable but not to a huge degree. Even at the lowest setting, which I am told is more or less equivalent to the non-adjustable Bilsteins, the car has a sporty ride. Certainly it is very comfortable and I will probably go back up to 18 clicks down from full hard.

One thing that did come out though was the fact that the car drops a little more when passengers get in than when the car was fitted with leaf springs. This does mean that I will have to adjust the ride height a little as the car is a little too low. To be fair this is all covered in the instructions and not unexpected but each person is going to have their own requirments and the Plus 4 with the 195/60 tyres is particularly prone to ride height problems.

The next big test will be when we go away with full luggage mid April. By then I should have all the adjustments and checks completed.

Peter, ref your feedback - yes the ride height will drop with passenger, luggage and fuel, but then the stiffer rate in the spring stack comes in to cope with the increase in weight. Cheers Peter [PJB]

CBY, good question - I think you are nearly there though.

In full axle bump & rebound (like hitting a change in height across the full road width) the links all articulate; the top links articulate using only the rotational compliances in their rubber bushes (no radial compliance needed) and the lower links articulate with the standard rubber bush at the front and a spherical joint at the rear. Thus the arc prescribed by the rear pivots of the lower links is different from the arc prescribed by the rear pivots of the upper links. Thus the axle does rotate a little in full axle bump and rebound travel, but this is fine - probably no more than the axle experiences on a leaf spring in use.

In roll (axle articulation), one wheel goes up and the other wheel goes down. To enable this the 2 pairs of trailing links rotate in different directions across the car and 'fight' each other and also fight the Panhard rod. By this I mean that effectively there are triangles formed that resist distortion in roll. Triangles are rigid. So to allow roll the rubber bushes have to deform radially. Thus the stiffness progression in these top link rubber bushes actually sets the roll stiffness. But also as rubber and the bush design are such, this compliance is progressive. So for small angles of roll the roll stiffness is little, but as cornering forces build the forces on the bushes increase and then they really start to resist and progressively limit roll.

For single wheel inputs such as road surface deformations (eg broken tarmac surface) as in roll the rubber bushes in the top links deform and allow small displacement single wheel inputs to achieve good ride without softening the roll in hard cornering. (All helped with the progressive coil spring stack of course).

Thus the front 'RS' and rear '5L' suspensions are matched as a complete car in terms of bounce frequency, spring rate, spring rate progression & roll stiffness progression.

Hope this helps. This is quite a novel approach and is protected by the manufacturer. Regards Peter [PJB]

You'll need to join the BHM Goodwood Trackday
to earn your hooligan title ;-)

Thank you PJB for your technical explanations. Smart design.

A few months on - have you forgotten it's there?

Hi David
Interested to know just what suspension set up you have on your Roadster? I am thinking down the line about Panhard rod and adjustable AVOs to begin with but am attracted to the Suplex rear end 5L. I have heard that some owners have had the front Suplex removed as they didn't like the rolling.
Richard

Well I now have something like about 5,000km on the 5L.

A few adjustments have been performed and some of my findings, and those of others, have been incorporated both in the design and the fitting instructions. I have also fitted the car with 195/65 R15 tyres, this, in combination with the Suplex ride height adjustments, give me the ground clearance I need and excellent ride comfort.

The system has performed well without any problems on a fairly extensive trip across France (one week on tour) and in England (two weeks) and return via Belgium, Germany, and Swtzerland.

It is true that I have become so accustomed to it that I have almost forgotten it is there.

I have driven the car by myself and experienced excellent handling and ride comfort. I have carried both of us and an great amount of luggage for touring, and I have sat next to our PJB whilst he put the car through its paces (and believe me he does not hang about on his rough and undulating "test track")

I did want Jays to drive the car whilst I was in the UK but he is still recovering from his ankle injury, however he was a passenger in the car on the way to Prescott and in my two fairly slow ascennts. I think he was reasonably impressed by the ride comfort. Perhaps he could be persuaded to comment.

I have had some discussions with Suplex and may finish up fitting slightly higher spring rates in the rear to better cope with the loads I carry whilst touring. The increased rate will stiffen the car a little but not effect the comfort too much.