Only with multiple chainrings.
1×9 or hub gear, it depends entirely on pedalling effort.

correct.

MidlandTrailquestsGraham – Member
Only with multiple chainrings.
1×9 or hub gear, it depends entirely on pedalling effort.

PEDANTRY ALERT!

How many full suss bikes are being ridden with single chainrings or hub gears?

Oh and you forgot to tick me off re crank length, nor the reaction from the suspension!

Every full sus DH bike ever runs a single chainring?

Ok, here we go…

I realised the other day that something was wrong with my analysis as I started to wonder whether the concentric pivot example was a special case. Consider a horizontal swingarm but with the BB directly below the pivot and a front chain ring that puts the chain line right at the middle of the pivot. If my statement above about chain line running through the pivot were true (chain force will not extend or compress the suspension), this scenario would produce no anti-squat effect as I had also stated that a horizontal swingarm has no anti-squat capability. It is clear however from drawing a standard anti-squat diagram that this setup will have a certain degree of anti-squat capability.

To explain what actually happens, you have to go a bit further into the force vectors and whatnot. When you are pedalling, there is obviously a force acting along the line of the swingarm in a forward direction, into the pivot. At the same time, there is an opposing force in the chain pulling backwards. Each of these forces can be separated into their vertical and horizontal components. The horizontal component of the chain line force must obviously be less than the horizontal component of the swingarm force, otherwise the bike would not move forward. The vertical components are what are important for calculating and understanding the anti/pro-squat.
Consider the scenario where the swingarm and chain line are parallel and both angled down towards the rear wheel – not an unlikely setup. The chain line force will have a vertical component acting down pulling the main frame (sprung part of the bike) down and so producing a pro-squat effect (compressing the suspension). The vertical component of the swingarm force however will be acting upwards pulling the main frame up and so producing an anti-squat effect (extending the suspension). I have already shown that the horizontal component of the swingarm force must be greater than that of the chain line force so it follows that the vertical component of the swingarm force must also be greater. It doesn’t take a genius to therefore work out that there will be an overall anti-squat effect as the vertical swingarm force component is dominant, outweighing the pro-squat effect of the chain line force.

In the first example I mentioned above in this post, the swingarm force is horizontal so has no vertical component. It therefore has no anti/pro-squat capability, as I mentioned in my original biblically long post. The chainline force however has a vertical component acting upwards, pulling the main frame up and producing an anti-squat effect.

So in quick conclusion it IS possible to have a chainline that lies above the main pivot but below the point where it would be parallel to the swingarm line and have an anti-squat effect (i.e. extension of the suspension rather than compression). Having the chainline coincident with the main pivot does not mean the chain force won’t act to compress or extend the suspension, it just means that the chain extension (and so pedal kick-back) and variation of antisquat throughout the range of travel can be minimised.

That is basically a simplified version of what Tony Foale states in his book so I’m counting on him being right!

Diagrams would help explain this and I could probably do some if anyone is interested 😯