Single pivot rear suspension - pivot location

The Rookie

This is more a Tech than a workshop, anyway, looking at single pivot bikes (be they the obvious swing arms like Orange or the Santa Cruz Superlight for example or those with a linkage driven shock like the Mega's) there seem to be two common and very different locations for the pivot.

The two swing arm mentioned place the pivot on the downtube and roughly on the extended chain line when in the middle (or in vogue single) ring giving a much longer swing arm than the other common location (more often used with linkage driven shocks usually via pivot link on the seat tube) is just above and behind the BB.

I understand this affects the way it works, the first location gives more rearward axle motion that lasts for more of the travel (or all the travel for something with 4" travel) and the pivot being on the chain pul line is meant (as I understand it?) to help reduce bob. The latter location gives a more upward axle path, starting rearward, then going vertical and ending as forward, how much back and for being determined by the height of the pivot relative to the axle in the normal sag position (most actually seem about inline).

So what are the strengths and weakness of each, comparing reviews it doesn't seem to hold either design back and despite the apparent crudity of swing arm/single pivot designs they are still on many popular bikes that get excellent ride reviews (even Orange 5's!).

I'm guessing more modern (than 2000!) shocks with a pedal platform damper have helped them to be able to compete with more complex suspension systems which inherently add more weight (such as the whyte quad link, Horst, VPP, DW etc).

I have read http://en.m.wikipedia.org/wiki/Horst_li ... ngle_pivot but looking for a bit more info!

rockmonkeysc

Characteristics depend more on the geometry of the set up than which style it is.

The Rookie

But doesn't the single pivot location dictate the geometry?

nicklouse

Nope.

The single pivot position defines the wheel arc.

The Rookie

nicklouse wrote:

Nope.

The single pivot position defines the wheel arc.

Indeed, but what else dictates the rear suspension geometry to the same extent? There is the position of the pivot relative to the BB and BB height (so BB relative to rear axle). Shock linkage may effect the progression (+ve and -ve) but not suspension geometry as such.