Rear shock spring rate

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tanto
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Posts: 218
Joined: Sat Oct 09, 2010 1:15 am
Bike owned: NC30, Raleigh Chopper
Location: Back in the UK.

Rear shock spring rate

Post by tanto » Wed Feb 08, 2012 7:04 am

My NC30 original "re-conditioned" rear shock is leaking. An O-ring in the oil res., by the looks of it. So while the shock is off I was thinking of replacing the spring.

I weigh around 11.5 stone/165lbs/75kg, + gear (I'd guess another 8-10kg). My question is what's the correct spring rate for the Showa shock?

The data I have is:
Shock spring free length 158.7mm (6.2 in.)
750-900 lb/in for a tapered spring, something like 2.25" ID
Nitrogen gas pressure 98 kPa (142 psi)

FWIW, the shock has been lengthened by 15mm, and the bike is running the 18" rear wheel.

Can anyone guide me to the correct spring rate for the shock? And if the spring is slightly over-length, what effect would that have? The bike's main use is fast-ish road riding over mountains, with 10% ascents & descents and quite a few hairpin corners, and occasional two-up 20-30 mile trips.
"A slipping gear could let your M203 grenade launcher fire when you least expect it. That would make you quite unpopular in what's left of your unit." - US Army manual of preventive maintenance.

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