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I have an Orbea Occam AM with 140mm of rear wheel travel.
For some rides I'd like to reduce that to 100-110mm of travel, but without otherwise affecting the geometry of the bike.
Current shock is 200x51.
I'm thinking that something around 200x35 to 200x44 would have the desired effect.
Can someone else take a rough stab at the numbers without knowing all the linkage details etc?
Why?
Unless you change the i2i of the shock it wont have any useful purpose. Better to fill the shock to the max with tokens/oil to increase progression, that will have somewhat the same effect but still allow you to reach that max travel when you really slam it hard.
Id buy a shorter travel bike, for rides that would suit a shorter travel bike...
Or just ride the one I have. Seems a lot of faff to swap the shock out to suit different rides.
Pump up it a bit more.
You will effect the geometry anyway as you'll be running less sag
Just leave it on the firm setting and stick more air in.
Rode my Occam AM 50 miles around the South Dales today and only really needed to open up the shock fully for a handful of sections.
What shock's on it? I did a similar thing with my Cube Stereo 140 with a 200x57 X Fusion shock because I wanted a strongish short travel FS with ISCG tabs, and the frames were cheap new.
Basically, and this is very basic and assumes that it actually has 140mm of travel (in the case of my frame) and not 135 or 145, the amount of travel divided by the shock stroke will give you (roughly) the ratio of rear wheel travel to shock travel, so in the case of the Cube it's 2.46:1. I wanted around 120mm which meant reducing the shock stroke down to around 48mm to get it roughly there or thereabouts.
Shock out, air can off, clip a 5mm nylon spacer around the 10mm piston shaft to reduce the travel on compression and a 2mm O-ring (I just used the travel indicator ring that came on the shock) on the other end that the air can slides over (is this called a stanchion?) to stop it topping out as far and the overall effect is a reduction in rear wheel travel to around 125mm and a slightly lower BB and slacker head angle (because the BB's dropped).
I've tried just putting more air in it and reducing the compression travel and it didn't really work, it needed to have the overall length reduced slightly too to make the bike sit lower, unsagged.
I've probably made it sound way more complicated that it actually is, if the shock's basic enough it takes about an hour which includes making a cuppa and it's really easy to go back to standard if you want to.
Why?
So that I can load up an under-saddle type seatpack without any chance of the rear tyre hitting the underside of it.
I don't want to change the BB height. I don't want to change any angles (I'll accept there's maybe a very slight change due to sag). I don't want to the shock to hit a "hard stop". Putting more air in will make it too firm and still not guarantee no tyre/pack interface.
Id buy a shorter travel bike, for rides that would suit a shorter travel bike…
Shoosh! I'm trying not to do that 😉
Store stuff elsewhere
I don’t want to the shock to hit a “hard stop”
Just sticking a travel-limiting spacer on the compression stroke side won't make it hit a hard stop; you'd need to add more air to get the sag right for the reduced travel anyway, the spacer reduces the air can volume so it'll be slightly more progressive and there's already a 'hard stop' in there as standard (usually an O-ring to give a bit of cushion if it bottoms out.)
or this-
Store stuff elsewhere
😆
Your leverage ratio on the shock will be changing throughout the travel so it's a pain to calculate. If it doesn't have to be a specific travel and just has to be clearance for a seatpack then you could measure it directly.
Put the seatpack on. Take all of the air out of the shock and move the rear wheel as close as you'd like it to get to the seatpack. Hold it there while you measure the eye to eye of the shock and the difference between the extended eye to eye (200mm) and measured eye to eye is the amount that you need to reduce the shockstroke by.
i.e 200length
and
51 stroke minus eye to eye change
I don't know the bike but does it have linkages driving the shock? If so altering the linkage will do what yo want
I don’t know the bike but does it have linkages driving the shock? If so altering the linkage will do what yo want
Should be easy enough.
As above - ram it full of the max no of tokens. If you reduce pressure you may not alter sag dramatically.
I would think adjusting the seatpack to avoid clashing with the tyre at bottom out would be a simpler approach, you're not going to gain much space by reducing the travel and you'll end up sitting at the wrong point in the travel unless you run more sag, or a shorter(eye to eye) shock - but it's not like you can spec them in mm increments, so you'll bottom out all over the place.
The suggestion of moving the travel o-ring (after a good clean) to inside the shock and using a nylon spacer to decrease volume and move the top- and bottom-out in a bit is probably the best approach, but I'd just move the seat pack up or use one that's ~20mm less deep.