Please critique this perception of full suspension anti-squat if you find this interesting.
I guess I may have been using the term "squat" incorrectly. I've always considered that when a full suspension frame pitch rotated rearward from a compressing rear suspension, whether or not the front end extended, this was “squat”. I guess this action is technically called "wallow". Squat is when the CM compresses overall when the front suspension doesn’t extend enough to compensate for the rear suspension’s compression. The attached picture below describes how the anti-squat line is determined. (Thanks to Strong-Like-Bull for the graphic.)
For example if the CM is half way between the wheels there is no squat when the rear suspension compresses 1 inch it the front suspension extends 1 inch and the CM remains at the same height. However, due to the practice of putting the seat quite rearward of wheel-base center, if the rear suspension compressed 1 inch and the front extended the same, then the CM would wallow rearward and compress (squat) significantly.
It's amazing to me that no one could point this definition of squat clearly in all these years of discussion I was involved in before. Maybe it should have been obvious.
Springs alone when coasting prevent squat unless there is a rolling surface (road or trail) induced compression of the CM when not pedaling or braking.
The Instant Center of Forces (ICF, also called the Pole of Moments) is where the drive-line such as a chain-line crosses the swingarm-line. A line drawn from the rear tire patch though the ICF is the net geometric acceleration reaction direction of any vehicle.
When the ICF is aligned with the anti-squat line, then the front suspension extends while the rear suspension squats, rotating the frame around a CM that remains at the same height (no matter where the CM was located horizontally). There is still acceleration wallow unless the CM is directly above the front wheel when ICF is aligned with the anti-squat line.
So only when an ICF is out of alignment with that anti-squat line will the rider input produce extension or squat to the CM.
I think this is a very non-intuitive definition of squat.
It is my experience that more than just a little wallow destabilizes confidence inspiring handling, traction consistency, and braking power.
Some varying amount of extension consistent with driving torque can counteract frame wallow for crisper acceleration while pedaling (like a runner leans low and forward at the start blocks and rises in height at a regressive rate while accelerating until obtaining full speed running height). On a bike that accelerating CM extension counters wallow without anti-wallow help from damping, but at the sacrifice of some bump compliance while accelerating that is translated into increased suspension kickback to the frame and/or pedals.
Furthermore, if the suspended CM (mostly rider weight) was able to spin the pedals in perfect circles to accelerate, I think that a line from the rear wheel ground patch, inline with the CM, produces reaction where the CM plus rear and front suspension all extend the same amount (“perfectly” stable extension while accelerating, with no wallowing.). If the rider, who is 80 – 90 % of the suspended mass, is leaned forward pressing mostly downward on the pedals in line with the ICF line, in a commonly normal pedal cadence, then there can be nearly 80- 90 % counter-extension bio-pace, so there would be nearly no extend bob either.
However, 100% stable anti-bob (no squat or wallow), in other words 100% bio-pace, would have rigid ride characteristics. So for bump compliance travel compression, some stable frame tolerant amount of squat is necessary to avoid noticeable reverse pedal cadence kickback (to avoid greater than 100% bio-pace). Actually some digressive rate of bio-pace as travel is compressed is more stable at the frame and more pedal spin compliant than hardtail like 100% bio-pace. Therein lies the elegance of fine-tuning the travel path sensitive dynamics to balance and hide the trade-offs in stability verses pedaling efficiencies into a bike’s suspension so that it simply rides great in a wide range of conditions.
“Stable Platform shocks”, digressive rate compression damped shocks aid the range of pedaling stability for more softly sprung longer travel suspension, and hide the awkwardness of less than elegantly tuned geometry in more firmly sprung shorter travel suspension.
Thanks for any critiques of this perception.
- ray
I guess I may have been using the term "squat" incorrectly. I've always considered that when a full suspension frame pitch rotated rearward from a compressing rear suspension, whether or not the front end extended, this was “squat”. I guess this action is technically called "wallow". Squat is when the CM compresses overall when the front suspension doesn’t extend enough to compensate for the rear suspension’s compression. The attached picture below describes how the anti-squat line is determined. (Thanks to Strong-Like-Bull for the graphic.)
For example if the CM is half way between the wheels there is no squat when the rear suspension compresses 1 inch it the front suspension extends 1 inch and the CM remains at the same height. However, due to the practice of putting the seat quite rearward of wheel-base center, if the rear suspension compressed 1 inch and the front extended the same, then the CM would wallow rearward and compress (squat) significantly.
It's amazing to me that no one could point this definition of squat clearly in all these years of discussion I was involved in before. Maybe it should have been obvious.
Springs alone when coasting prevent squat unless there is a rolling surface (road or trail) induced compression of the CM when not pedaling or braking.
The Instant Center of Forces (ICF, also called the Pole of Moments) is where the drive-line such as a chain-line crosses the swingarm-line. A line drawn from the rear tire patch though the ICF is the net geometric acceleration reaction direction of any vehicle.
When the ICF is aligned with the anti-squat line, then the front suspension extends while the rear suspension squats, rotating the frame around a CM that remains at the same height (no matter where the CM was located horizontally). There is still acceleration wallow unless the CM is directly above the front wheel when ICF is aligned with the anti-squat line.
So only when an ICF is out of alignment with that anti-squat line will the rider input produce extension or squat to the CM.
I think this is a very non-intuitive definition of squat.
It is my experience that more than just a little wallow destabilizes confidence inspiring handling, traction consistency, and braking power.
Some varying amount of extension consistent with driving torque can counteract frame wallow for crisper acceleration while pedaling (like a runner leans low and forward at the start blocks and rises in height at a regressive rate while accelerating until obtaining full speed running height). On a bike that accelerating CM extension counters wallow without anti-wallow help from damping, but at the sacrifice of some bump compliance while accelerating that is translated into increased suspension kickback to the frame and/or pedals.
Furthermore, if the suspended CM (mostly rider weight) was able to spin the pedals in perfect circles to accelerate, I think that a line from the rear wheel ground patch, inline with the CM, produces reaction where the CM plus rear and front suspension all extend the same amount (“perfectly” stable extension while accelerating, with no wallowing.). If the rider, who is 80 – 90 % of the suspended mass, is leaned forward pressing mostly downward on the pedals in line with the ICF line, in a commonly normal pedal cadence, then there can be nearly 80- 90 % counter-extension bio-pace, so there would be nearly no extend bob either.
However, 100% stable anti-bob (no squat or wallow), in other words 100% bio-pace, would have rigid ride characteristics. So for bump compliance travel compression, some stable frame tolerant amount of squat is necessary to avoid noticeable reverse pedal cadence kickback (to avoid greater than 100% bio-pace). Actually some digressive rate of bio-pace as travel is compressed is more stable at the frame and more pedal spin compliant than hardtail like 100% bio-pace. Therein lies the elegance of fine-tuning the travel path sensitive dynamics to balance and hide the trade-offs in stability verses pedaling efficiencies into a bike’s suspension so that it simply rides great in a wide range of conditions.
“Stable Platform shocks”, digressive rate compression damped shocks aid the range of pedaling stability for more softly sprung longer travel suspension, and hide the awkwardness of less than elegantly tuned geometry in more firmly sprung shorter travel suspension.
Thanks for any critiques of this perception.
- ray