Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Front Suspension Roadster GoPro

There are a several ways of achieving a rising rate spring. The one chosen by PJB was to use and inner spring which added to the overall rate as the outer spring became compressed. To look at the relatively light weight inner spring you would not think it does much but it seems to be cleverly calibrated to give just the correct amount of increasing rate.

The other thing to consider is that the correct setting for Morgan front springs leaves the lower rebound spring unloaded (enough so that you can just turn it by hand) at static ride height. Achiving this with the variables involved without an adjustable upper spring seat would seem to me impossible.

Worth mentioning also that the rebound spring should have a fairly high rate to limit the downward travel of the unloaded wheel in cornering. In Morgans this has the effect of reducing body roll in cornering. This is part of design that PJB has used successfully in both the Suplex RS kit and the Suplex race suspension.

I should make the usual disclaimers that I have no interest in Suplex other than being a happy customer but I have been intersted enough in the theory to seek some education on the topic. I am by no means an expert but I do understand at least some of the principles involved (with some help )

Interestingly at 2" the Suplex Kit will have also kicked in about 280 2"lbs as the "Rate Riser Spring" will be compressed also.

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Suplex is certainly and interesting concept. The "Rising Rate (I call it the overload spring)" is a lot stiffer than it looks. I think 80 inch lbs was what I measured but rising rate over the length of the spring. It sits above the stubaxle with only the main spring for about an 1". So this is why I can drive into potholes at about 40MPH and survive. I have mentioned my experience I think. 3 big touring Bikes were behind Me. 2 BMW and 1 Yamaha. When I stopped at Overlook near the Snake River Canyon (NE Oregon Forest Service Rd) they marveled that even though I was driving like a drunk from one pot hole to another they had difficulty keeping up. After I explained they understood. BTW: I made this test twice. Once in my +4-4Str and once in my DHC. Each test was a 2 day 1,500 mile run. Beautiful scenery and lots of fun.

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PJB lives not far from me, and a couple of years ago I wanted to know far more about the principles involved, so I traded a Facet full pump and regulator with Peter in exchange for a couple of hours of education on suspension design.

A splendid chap, I finally understood what was going on with Morgan front suspension, and he went away with the fuel pump he needed for his Zetec conversion.