rear shock change

[yorkie_chris]

Originally Posted by Red Herring

Sorry to be pedantic YC but changing the length of the shock can also have an effect on the ratio as it alters the angles involved in the linkage, almost more than changing the dogbones.

The shock is attached to the centre of the linkage which is fixed to the chassis (and rotates around) at it foremost point. Lengthening and shortening the shock will move the linkage and alter the angle that it sits at.

The dogbones join the linkage to the swingarm and changing their length simply adjusts the angle that the swingarm sits at in relation to the linkage (a side effect of which is to alter the ride height), they do not alter the arc that the linkage will move through as the suspension flexes. They do have some effect on the ratio as they alter the angle that the swingarm operates at in relation to the shock, but it's nothing like as extreme as some persons suggest.

I've tried both avenues. First I raised the ride height by adjusting the length of the shock, then I tried keeping the shock the standard length and fitted shorter dog bones. Ride height was the same in both set-ups but the later configuration works much better for me.

Linkage geometry will give you a curve, think of a graph of wheel displacement vs. shock displacement. When you change shock length you are just changing where you start on that curve. Ratio is just the gradient of that line at any point.

[Red Herring]

So by changing the point on the curve that you start at you are changing the ratio, because the gradient at that point will be different.... Keeping the shock the same length though means the suspension will start it's movement at the same point on the curve, so the ratio will be the same (although by changing the dogbone it will actually be slightly different because the angle of the swingarm, and therefore it's leverage on the linkage, will be marginally different...) Anyone confused yet?

[yorkie_chris]

But you are moving starting point of dogbone-swingarm bearing closer to link and further down. So it will start harder and ramp up faster (I think).

Tell you what this needs a spreadsheet with the dogbone length and shock length as variables.
Any chance you could get me some measurements of linkage and frame?

(or maybe we should just leave alone, but pah, it's too cold to ride)

[Red Herring]

Unfortunately it's not that easy to measure in situ. I'll have to try and get some measurements next time it's all apart.

[yorkie_chris]

IMO until there is measurement before and after then it is pointless saying one works better than other, as change in linkage is going to affect equivalent spring rate and equivalent spring rate progression.

For example if your change makes link more progressive, same sag numbers will mean a softer eq. rate when nearly topped out, so it'd be a bit more compliant transitioning from braking to on the power. And maybe this would work better.

But there's lots of ways to skin a cat.

[Red Herring]

This is all getting a bit to technical even for me. All I know is that I started off with an SRAD 750 rear shock, which was nice but not perfect. I liked the ride height it gave, and the spring rate, but I couldn't get the damping right and in fairness after a while the shock started to go off. I changed to a GSXR600 K4 shock, which was great on the track, but not on the road, it was also slightly shorter than the SRAD one. I then went to an Ohlins, which I set up with the same ride height as the SRAD and after some tinkering with the settings I got that pretty much as I wanted it. I was however right on the limit of the shock length with no option to go any higher, so I fitted some shorter Dogbones (+30mm ride height) and shortened the shock so that when all fitted I retained the same ride height as before. The intention was to play with ride height some more but when I rode it like this the set up is the best it's ever been, so I'm a bit reluctant to change it. I didn't change the preload when I fitted the dogbones, just the shock length to that the bike rode at exactly the same height as before, so the only thing that changed was the angle that the linkage sits at.

[yorkie_chris]

Too technical? don't be pussy

Dunno about shock going off, one I put on 1gen was pretty toasted when I got it. When I tore it down it had 10psi of nitrogen in it lol

Originally Posted by yorkie_chris

Linkage geometry will give you a curve, think of a graph of wheel displacement vs. shock displacement. When you change shock length you are just changing where you start on that curve. Ratio is just the gradient of that line at any point.

Correct, reason shock length is preferred.

just wondering if a curvy shock would fit on a pointy or are they completely different
thanks

Originally Posted by rude

just wondering if a curvy shock would fit on a pointy or are they completely different
thanks

it will still be crap so no point might as well go for a gsxr shock