Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing series 1 Roadster sump damage

Method for cutting a rebound spring for those who want to do it.

Removal of the original set up of the front suspension.
Assembly of the front suspension without the rebound spring.
Car on the ground, bounce the car several times to get the balance position. The car sits only on the main spring.
I guess it would be better to do it before replacing the kingpins in order to have less friction.
Measure the free part of the kingpin along the lower part of the kingpin : gap between the hub stub bottom and the lug plate.
Cut the rebound spring at this size.

An estimated calculation for my PLUS 4 with original 110 lb/inch main spring :

intitial length of the rebound spring : 90 mm
final length of cutted rebound spring : ~44 mm

Roughly the half length and twice of stiffness for rebound spring + 110 lb/inch of main spring during rebound.

No problem with the sizes, but difficult to know with precision the stiffness of the main spring.

I am not queen of cutting a spring as explained previously. Having the SSL kit, I don’t have this concern.

What would happen if you ran without a rebound spring?
Nick

You would lose a lot of roll stiffness which would have an adverse affect on the handling.

Without the rebound spring there would be nothing to stop the main compression spring unloading on the inside wheel which would in effect jack up that side of the car and increase the roll. (i.e. reduce the roll stiffness)

The ideal is to have the 2 springs perfectly matched which is relatively easy on a nice known smooth race track but is quite difficult to achieve on unknown bumpy normal roads so a compromise is needed to get the best average handling.

The problem is that different drivers will have differing opinions on what that compromise should be.

Very difficult to get a one size fits all solution on the road which is where some adjustability comes in. ( If you know how the system works and understand what effect the adjustments will have.)

No need to correct much, just to confirm.
The high stiffness of the rebound spring if in compression at ride height adds to the softer main spring rate, so to only use the main spring in bump the rebound spring must be just kissing the hub.
The rebound spring thus set just kissing adds significantly to the front roll stiffness. If there is "zero droop" (Search Google) this doubles the front roll stiffness, hence no need for antiroll bars. But this alkso affects inner front wheel compliance in droop.
If the soft std rebound spring is fully compressed at full droop (jack front of car up to check) then in hard cornering the inner front wheel has no suspension, that is not good. The SSL rebound spring is progressive and never goes coil bound.
If the rebound spring is compressed at ride height then the roll stiffness, roll centre and roll moment all change as the hub comes off the rebound spring, just as you are turning hard into a corner, not ideal surely.
The little 'rate riser' spring on the kingpin above the hub gives the significant bump spring rate progression.
The ride height is defined by the length of the rebound spring or the short SSL rebound spring and its 20mm spacer. Fitting the spacer at the top with the 'rate riser' spring lifts the front of the car by 20mm, can be useful for those owners with cars with ground clearance issues on such as rough driveways.
The spring rate progression and roll stiffness progression of the RS front suspension and the 5L rear suspension is balanced. The 5L geometry has inherent roll stiffness progression.
Hope this brief summary helps.
PJB Peter Ballard.
Director SSL, originator of the 5L rear and joint on the RS front suspensions.