number9, 8/4/2015 at 8:06 PM
I spoke to Jerry at Öhlins and he was incredibly helpful. Unfortunately for me though, the 4th gen shocks are not a worthwhile swap into a 5th gen. The 5th gen shock is longer, it has less stroke, it has a different spring rate, it has different valving, it has a different mounting eyelet, it has a different body, it has a different shaft, it has a different length adjustment system...
It might be worth it if you can get a 4th gen Öhlins for free. Otherwise, go to a 5th gen.
I did some research before buying a second-hand RC36 Ohlins for my RC46, using Ohlins' own data, and I decided it would be possible to use a 4th-gen shock on a 5th-gen bike, and it could probably be made perfect with a re-valve and re-fresh. Of course, if I'd found a good second-hand HO 801 I would have gladly used that, but Ohlins doesn't (officially) make them anymore and there aren't many around!
RC36-II
Total length: 324mm
Stroke: 57mm
Spring: -79 (1,085lbs)
[image: images?q=tbn:ANd9GcRbYmQuqMDk9GTjwi3VdSG]
RC46-I
Total length: 325mm
Stroke: 58mm
Spring: -59 (857lbs)
[image: shock02.jpg]
So, the earlier shock is 1mm shorter in both length and stroke. Length can be adjusted, howewver, using a shim on the top shock mount on these bikes, so 1mm is not an issue with regard to total length. Stroke cannot be changed without opening up the shock, but I have been told that there is a small amount of adjustability internally, so I wouldn't expect that gaining 1mm to be a huge problem. The earlier spring is stronger, but could be just right, depending on the rider--I weigh 95kg and need a stronger spring, anyway (1,200lbs, according to Ed Sorbo at Lindemann). It's not clear from the crappy found-on-internet pics above, but the mounting eyelets look the same from here! (Perhaps Jerry was thinking of the earlier RC36 shock, which has a clevis at the bottom? And neither shock has a length adjuster, so what's he talking about?)
I plan on getting my 4th-gen Ohlins re-valved anyway, so any valving differences should be able to be changed then. I will find out soon enough...
Ciao,