There is air in only half of the fork right ? Shouldn’t that make the compresion of the fork uneven ?

And the next question….

I recently demo-ed a full suspension bike and noticed that the stancion is only 51mm on a 160mm bike , why is it this way ?

There is air in only half of the fork right ? Shouldn’t that make the compresion of the fork uneven ?

Correct, there’s typically air in the left leg and oil dampers in the right. It doesn’t matter though as the bridge between the two legs is very stiff and makes the whole thing move as a single unit so it doesn’t twist.

I recently demo-ed a full suspension bike and noticed that the stancion is only 51mm on a 160mm bike , why is it this way ?

Errr, that’s only 2″? Was this when you were sat on it (i.e. sagged) or when the bike was parked up?

Was that 51mm on the rear shock of a 160mm bike? If so, it’s due to leverage of the linkage.

Errr, that’s only 2″? Was this when you were sat on it (i.e. sagged) or when the bike was parked up?

Pretty certain he’s now talking about the rear shock.

noticed that the stancion is only 51mm on a 160mm bike , why is it this way ?

Levers innit.

Was that 51mm on the rear shock of a 160mm bike? If so, it’s due to leverage of the linkage.

Ah, yes. As his first question was about the fork, I assumed the second was too. Good answer 🙂

I recently demo-ed a full suspension bike and noticed that the stancion is only 51mm on a 160mm bike , why is it this way ?

As other noted leverage … but a fuller answer…
On the forks they go up/down… so 100mm is 100mm
On the rear shock the frame goes up/down (or rotates on a pivot point) and the shock provides the resistance to this. The actual travel is how much the bike moves, not the shock which you can view as there to prevent the bike moving without any force.

The amount of travel is very little to do with the actual absolute movement of the shock stanchion and far more influenced by the pivots and type of suspension…

I suspect the forces in the spring side and damper side are fairly close. The spring proceed a force relative to the displacement of the suspension – so how much travel you’re using, and the damper provides a force dependant on the speed of the suspension is working, so it’s not as if it is all one sided. If the damper was providing a force significantly less than the spring then you’d feel very under damped, and vice versa if the damper was providing too much force.

There is a whole load of twisting going on with the wheel, frame, large volume tyres etc. so you’re not going to notice the flex of the fork chassis too much.

Thansk for the explainasion guys

Sorry for my enghlish

Actually, the asymmetry is less of a problem than it seems at first glance. Think of a Cannondale Lefty fork, which only has one stanchion. The contact patch of the tyre is under the centerline of the bike. This means that there is no bending force at the headtube. There will be a bending force at the crown and stanchion, but it’s actually not that great because the offset isn’t that big.

I suspect a much bigger problem for fork designers is flex under hard braking on steep descents. The loads there will be much greater because nearly the entire weight of the bike and rider is trying to bend the forks back.