How do you measure the rear shock size whilst its still on the bike, also the stroke?.

Bike should be 120mm front/rear travel.

Google the make and model of your frame.You don,t even need a tape measure… 😉

with a ruler…

or more helpfully:

Eye-to-eye length really is that simple, measure the distance between the centres of the bolts holding the shock at each end.

Stroke length can be trickier as the entire exposed shaft length may not be fully used so to be 100% sure it’s best to refer to the manufacturer, however there are ‘common’ sizes like 165×38, 190×51, 200/57 etc.

what year and model is the bike?

Bike is 2012 , Marin East Peak.

Eye to eye is 165mm/6.5″, stroke??? (this is the figure that i am trying to work out.

Fox Float R

if its a 165mm e2e the 99 times out of a 100 the stroke length is 38mm (or 37mm, or 37.5mm on some shocks, but that small a difference you can ignore)

(6.5 inch x 1.5inch stroke in old money)

Although thats a short shock for 120mm travel, normally 165mm shocks top out at about 100mm at the rear wheel, that Marin must have quite a high leverage ratio…

from the pics it definitely looks like a 165mm shock

Thanks for the info and help. Would that translate into 5″ rear wheel travel or is that determined by the bikes design?

think we crossed posts ^

travel at the rear wheels is a function of the shock stroke and leverage ratio of the rear end, its a tad unusal for a 38mm stroke shock to be used to give 120mm of travel, but not unheard of.

mostly a shock that length would be used on 80 – 110mm travel bikes and then above that normally would start to use 50mm or greater stroke, but thats a guide, not a rule…

Ok, its funny as in the UK Marin site the spec lists an X Fusion shock even though it shows in the picture the Fox Float that is on it. Also to confuse things its also described elsewhere as having 100mm rear travel and 120 front??!!??.

On the Marin site it is listed in the Quad XC 120 so i am assuming its 120 rear/front?

This has all come about as i neglected rather badly i might add to look at the shock in the LBS and didnt realise it had no lock out which i found annoying on todays climbs (only first proper ride today) talk about sapping power.