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From Peter’s post above;

“As for the different stifnesses, all I would ask is this. Has anyone ever seen any reference to ascertain exactly how the stiffness was quantiified by, say, fluid flow or a measure of resistance? Nope, me neither”

I wondered this as well, what actually was the difference between the different units ?

Was it just a different size valve ?

Exminiman wrote: ↑Sat Apr 19, 2025 8:16 am From Peter’s post above;

“As for the different stifnesses, all I would ask is this. Has anyone ever seen any reference to ascertain exactly how the stiffness was quantiified by, say, fluid flow or a measure of resistance? Nope, me neither”

I wondered this as well, what actually was the difference between the different units ?

Was it just a different size valve ?

In the BMC Australia engineering drawing I posted previously there two components that appear to affect the "stiffness" - the Flap Valve and the Spring Element Spec (i.e. the rubber bit).

Also from above - "The Spring Element Spec initials probably stand for Normal Rubber, Hard Rubber and Extra Hard Rubber - just a guess. There is more rubber in Cooper S displacers, the level being closer to the top of the displacer body where the hose exits when compared to a "standard" displacer. Maybe the rubber formula was the same in all displacers and the increased springing is due to the greater volume of rubber to be compressed in the S part".

Thanks, which to be honest makes sense.

So you couldn’t just change a valve in a non S unit, to get the same suspension performance.

Presumably, the rubber thickness difference is to make the suspension travel progressive