Here are 2 suspension bushes made from doorstops in action:

bush made from 1 doorstop plus 1 10mm thick piece from another doorstop cemented on it, sanded down for smoothness:

Installed with me seated normally: Note how much it bulges out. Installed with mudguard washer.


Bush made from 2 shortened doorstops cemented end-to-end:


Installed with me seated normally: Note how much less it bulges out compared to the other one. It has a recess at each end, so no mudguard washer is needed.


I cannot explain why the 1st one bulges out more than the other. I guess I have to hand back my suspensionology PhD. The only attempt at an explanation is that the 2nd one is captured/constrained more due to the recess allowing it to go deeper into the frame socket.

The 1st one is noticably softer due to this effect. The 2nd one used to be 2 separate pieces, and it was stiffer then. It would be stiffer still if a mudguard washer was placed in between the pieces. You could tune it for rider weight this way.