I may combine the spring fitting with a shock rebuild and I'm inclined to modify the front fork valving as per Roger Ditchfield as well. I'll post updates as and when.
Iain, you most likely have taken into consideration the inside diameter of the spring needed for your Fox shock as you mention ISD. The reason I mention this is, on the standard Firestorm shock the inside diameter of the spring needs to be a different size at one end, a parallel spring won't fit on it's own. The way Maxton have got around this for the Firestorm is to supply a reducing collar.
Hopefully you are one step ahead of me on this, but I thought it was worth mentioning,
Apart from a guy that weighed in excess of 21st. I have NEVER used a 1000lbs/in (18kg/mm) rear spring on my Penske dampers. I am sure there are some guys out there with Revolution Penskes that can confirm that the springs I use very suitable. IMHO major manufacturers generally "overspring" and consequently "over damp" their products on "V" twins especially VTRs and SPs. They generally work to a simple weight formula for all dampers and where they have vast amount of worldwide feedback on parallel twins and inclined fours there is little info on "v" twins where the weight distribution is different as well as the torque deliverance. For the record I generally use the following spring rates on VTRs:- Rider weight inc riding gear.
10st - 12st = 800lbs/in (14.25kg/mm)
12st - 14st = 825lbs/in (14.75kg/mm)
14st - 16st = 850lbs/in (15.25kg/mm)
This may vary slightly dependant on the rider's usage
Trust me you do not want a 1000lbs/in (15kg/mm) spring unless you are in excess of 20 stone.
Hope this helps in your deliberations
I currently have an 850lb spring and the preload required to set the sag is immense, I'm talking over 40mm on the adjuster, so we'll see when it turns up.
Not really a comparison but I have an 1100lb spring on my mountain bike [FEARFUL FACE]
The best way to set the static sag with the rider stood at the side of the bike is as follows:-
Rear Sag for “aftermarket” adjustable dampers
It is important that the rear sag is 8mm. Measure from underside of rear subframe to wheel spindle
1) Take all the rebound off - adjuster at bottom of the shock.
2) Push firmly down on seat and allow to return. (Do not bounce) -- Measure
3) Hold rear subframe and lift to "top out" the shock -- Measure. This should be + 8mm greater than measurement 1)
4) Adjust until it is.
5) Set rebound to "fastest possible return, but under control"
6) If you have an OEM STD shock use level 1 up to 80kg rider weight .
Level 2 for 80kg – 100kg and so on.
It does not matter how much pre-load you use as long as you arrive at 8mm where possible
According to that calculator, i should have somewhere around 22kg spring
Roger did my penske a few years back for about 19st and its feels fine to me. I'm sure he wouldnt have put a 22kg spring on it.
We know the racetech spring calculator is very questionable on the fork springs (usually oversprung) so I expect it's the same with their rears. I don't think their calculator should be used for other spring manufacturers. Maybe if using all ratech gear including their valving then they may be more accurate. Also don't forget it's orientated towards pure racing and not street use.
Finally got the rebuilt shock and spring on the bike today, took ages to get the static sag set.
Anyway, the ride to work was much better, the high speed weave over rough roads has gone and it feels less wallowy in the bends.
Just need to mod the front forks as they feel really poor now.
Well done mate. It's funny how improving one area shows up the imperfections in other areas more. For me it was the other way around when I done my forks. I've still yet to do the rear shock.
It's never ending with me, but I enjoy sorting out niggles. I find I end up selling things after I get them just right.
The fox shock I bought 5 years ago and was told it needs a service when I bought it, sure feels better for it, the handling had been going off further every year.
