I fitted a brand new pair of genuine Rover cones (FAM3968) when I first built my Frame, following problems with a coil spring conversion (see other, earlier post)...Using Hilo's to jack the Buggy right up for Trialling and off road use, I noticed after a while that they had started to collapse, almost "rolling inwards" upon themselves where the cone meets the Hilo.
This is of a wider section on a Hilo, over the standard alloy suspension trumpet, and I believe that this increased lip alters the rubber cones mounting face, and uprates its "spring rate", the cone is less likely to roll around against this wider lip. However, it clearly was not working properly on my car, the more suspension movement you have, and the rougher the roads the quicker they seem to collapse, they just dont seem man enough for the job? I think that I've now gone through two or three new pairs since I built the car, and as they didnt seem to last, and it was getting a pain to keep changing them so frequently and the high cost of doing so, recently I've fitted a pair of new Minispares Innocenti Progressively Balanced rubber cones (C-STR687), to give them a try. Another local buggy owner, Jimmy the Frame has fitted some and says their brilliant, much better for off road/trialling than the standard ones. I've not used my Buggy recently, so I could'nt say for sure, but he says that you can really feel the rear suspension moving and working properly, and Minipares advertise them as the "ultimate cone" so they could be worth your trying. They HAVE to be used with Hilo's.
Afraid, as everything nowadays, their a bit more expensive to buy than the standard ones, but hopefully you only have to buy them once, and if they improve the ride/handling/traction etc, they could be well worth the extra expense?........