[mojomike]

Quick and easy question:

When I dial the TALAS down from 140 to 120mm on those long and very steep climbs, It feels as though I'm adding a gear. Is it possible that the small rotation of the force vector towards the slope could cause a perceptible change in required pedaling force?

Should I entertain this line of thinking or better be served by adhering to that wise old axiom that is posted all over my lbs and even my own license plate frame, "shut up and ride"?

Thanks in advance. I must say I appreciate reading your posts vey much. If I see a thread with a technical bent, I often find myself scrolling through the posts to look for the Derby or dw responses first.

Mike

 

[miles wadsworth]

I have noticed the same thing or feeling but I could not think of a logical reason for this. Maybe you have found the answer.

 

[mx_599]

I must say I appreciate reading your posts vey much. If I see a thread with a technical bent, I often find myself scrolling through the posts to look for the Derby or dw responses first because no one else has a clue.

Mike

 

[derby]

Yea that's a strange feeling.

Yea that's a strange feeling. Lowering the fork when climbing and it's easier to keep the front wheel on the ground and maintain steering and balance, but it feels like it's harder to pedal up the climb.

It's interesting as a "lay-person" with casual interest to try to calculate the physics. I'm sure an advanced academic or professional vehicle designer could be very precise in calculations.

Lowering the front 20mm lowers the forward drive force vector angle less than 1 degree, which doesn't on the surface seem to be very much.

Calculating the forward drive force vector is a bit complex, at 100% anti-squat the forward drive force vector nets to driving the CM (center of mass) directly forward amd level with the ground, no matter the ground incline slope. The ground slope multiplies the squat reactivity to some degree.

In the past I've measured the Mojo's dw-link at near or even up to 10 or 15% over 100% anti-squat in the lowest granny gears depending on rider position with the Mojo's sag set equal front to rear and travel about 140 mm front and rear. The anti-squat measurements vary quite a bit depending on fork axle to crown, sag differences, but mostly rider position and the center of rider's weight center. (Those guys and gals with giant leg weight and strength but light upper body have such an advantage in anti-squat forward drive - and braking - efficiency over us relatively handicapped by a heavier upper body and lighter legs. End of whine.)

So why does it feel slower and harder when lowering the fork travel to help keep the front wheel on the ground?

Well, full suspension anti-squat effectively activates frame, centered at a point above the front wheel where a line from rear ground patch crosses the chain-line and axle path radius line (a line crossing axle and IC or monopivot) and projects to cross a line perpendicular to the ground through the front axle. I'll call the anti-squat point above the front wheel the "anti-squat center" (not really a physical pivot center it's dynamically changing in position, it's a virtual pivot with the CM for acceleration force).

When accelerating the frame is activated about the "anti-squat center", and pulls the CM forward. The CM, if above the height of the "anti-squat center", is pulled lower compressing the rear suspension, or if the CM is lower is pulled behind the "anti-squat center" higher and the rear suspension spring is un-weighted and the suspension extends. When acceleration rate reduces during the weaker 2/3's of the pedal stroke, the CM rises or falls to return to fork and shock equilibrium at non-driven (static) sag - the repeated oscillation of squat reactivity cause most of pedal-bob reaction (the riders vertical oscillation causes a small amount of bob reactivity unless technique is very vertical such as standing and pounding the pedals on level ground).

Lowering the fork reduces the anti-squat rate. By lowering the fork the CM is repositioned slightly forward although not significantly lower but the "anti-squat center" is reduced near 1 degree and the percentage of anti-squat (measured perpendicular to the front wheel base) would be roughly 2% less. For example, using my CM height at the height of the seat at 42 inches or 1070mm, and for argument using a 100% anti-squat rate where the "anti-squat center" is at height of CM. Then lower the fork 20mm to lower the "anti-squat center" to 1050. 1050/1070mm = 98% or 2% less anti-squat rate.

Less anti-squat is has a lower leverage angle or less torque for pulling the CM forward. Less leverage requires more effort to go the same distance forward, no matter the slope.

The angle of ground slope multiplies the anti-squat difference by some complex amount. I'll use a 1/1 rate to argue the trend. A 10% ground slope would (hypothetically and without accuracy) multiply the 2% anti-squat leverage loss 2 times as much as a 5% ground slope. The net effect is that the steeper the ground slope, the more magnified the loss in anti-squat leverage and increased effort to pedal the bike forward.

Going up 1 cog higher in the granny adds about 8 to10% more forward distance per crank stroke. At some rate of ground slope incline the loss in anti-squat leverage will require more extra effort to move the bike forward as using a cog higher gear rate.

If you can instead of lowering the fork, use a higher gear, you may use the same extra energy but go faster conserving momentum in bumps better and have less bob oscillation and be able to more easily keep the front wheel on the ground, with a net shorter energy use amount than lowering the fork to keep the front wheel on the ground.

What do you think?

 

[mtb143]

Are you twelve years old? OP's respect for Derby's technical prowess is clearly warranted, as evidenced by Derby's response, which hurts my head.

If you don't have anything nice, constructive, or germane to say, then please keep your "ass kisser" comments to yourself, thank you.

 

[mx_599]

Are you twelve years old? OP's respect for Derby's technical prowess is clearly warranted, as evidenced by Derby's response, which hurts my head.

If you don't have anything nice, constructive, or germane to say, then please keep your "ass kisser" comments to yourself, thank you.

i'll be 14 next month, so 12 yrs old whatever.

personally, i thought the photo was a little funny. you obviously got it...

mx

 

[le_buzz]

Well, full suspension anti-squat effectively activates frame centered at a point above the front wheel where a line from rear ground patch crosses the chain-line and axle path radius line (a line crossing axle and IC or monopivot) and projects to cross a line perpendicular to the ground through the front axle.

I was trolling around the forums and came across your post, sounded pretty
interesting. I think I vaguely followed most of what you said, except for the above
run on sentence, which seems poorly worded.
"antisquat activates frame centered...... ?" Not sure what you're trying to say here.
I'm not trying to come off as an English grammar purist, but it helps others to follow your posts if you're clear about what you're trying to say.

Anyway, thanks for your thoughts. BTW, what did you use to measure the
antisquat ? Just curious.

 

[derby]

I was trolling around the forums and came across your post, sounded pretty
interesting. I think I vaguely followed most of what you said, except for the above
run on sentence, which seems poorly worded.
"antisquat activates frame centered...... ?" Not sure what you're trying to say here.
I'm not trying to come off as an English grammar purist, but it helps others to follow your posts if you're clear about what you're trying to say.

Anyway, thanks for your thoughts. BTW, what did you use to measure the
antisquat ? Just curious.

Comma added. Thanks! It's a lot to edit before posting. I often later see my grammar errors, typos, and poorly chosen words. Communication is a huge challenge for me, I hope I'm improving. But I also hope the mistakes bring discussion to clarify and critique with better perspectives from others, and overall learning for everyone including me.

I'm a student of these things, not an authority. DW is an authority, a professor, a published author(ity), with patented validation of the discovery he professes. I'm not professing, I'm interpreting, seeking only peer validation and critique for my hobby of mechanical analysis and opinions. I'm a pundit at best. I've never claimed to be an authority, but I do like to encourage focused critic of concepts, such as from you and others having such interest. In this case there's a lot of concept and a complex set of variables to try to digest into a generalized and readable post that is concise and to the point without dragging in pages of pictures and calculations as an authority would do. It's just meant to give a generalized concept of the dynamics, not a proof. Proof is for authors and professors to produce. In DW's case, he can't reveal very much publicly and can only hint at the facts due to the increasing design thievery by a few "copy-cat" builders.

To calculate the Mojo anti-squat I used Linkage comparing different anti-squat rates to points in sag depth of the Mojo, and other bikes, about 6 months ago. Not long after getting my Mojo 2 years ago, I measured it and input the Mojo into Linkage and saved it to the subscribed on-line library. Linkage has mouse-pointer coordinates, and can show the distance of point-to-point during a click-and-drag. And in Linkage I can use Edit to choose a gear set, and it shows the chain line. And I can sag the suspension to a fixed static level with the slide bars in the Linkage graphics. IC and CC can be displayed for floating axle 4-bars. And by projecting lines on the screen with a straight-edge I could find the intersection of the chain-line with the axle through IC radial alignment swing-line. And by projecting a line, from the rear tire's ground patch through the chain/radial-swing line intersection, forward to cross a vertical line through the front axle, the anti-squat point at sag is found. Compare that point on the vertical line through the front axle with another point on the same line at the height of the CM and the percent of anti-squat can be calculated.

I used a rough anti-squat difference using the same 20mm measurement the fork travel was lowered for the example anti-squat alignment measurement change, it's close enough to show about 2% reduction in anti-squat rate for a generalized concept.

BTW, the "anti-squat center" I describe at the front wheel base as a virtual pivot was a new concept to me while writing that. I'll have to think about that some more. While accelerating the pedals, does the CM and frame swing as if pivoting behind that dynamically rising and falling "anti-squat center" point about the front wheelbase? It does feel like it when riding I think. And as always, the ride experience is the best test of a bike's performance.

Thanks for your comments!

 

[le_buzz]

Comma added. Thanks! It's a lot to edit before posting. I often later see my grammar errors, typos, and poorly chosen words. Communication is a huge challenge for me, I hope I'm improving. But I also hope the mistakes bring discussion to clarify and critique with better perspectives from others, and overall learning for everyone including me.

I'm a student of these things, not an authority. DW is an authority, a professor, a published author(ity), with patented validation of the discovery he professes. I'm not professing, I'm interpreting, seeking only peer validation and critique for my hobby of mechanical analysis and opinions. I'm a pundit at best. I've never claimed to be an authority, but I do like to encourage focused critic of concepts, such as from you and others having such interest. In this case there's a lot of concept and a complex set of variables to try to digest into a generalized and readable post that is concise and to the point without dragging in pages of pictures and calculations as an authority would do. It's just meant to give a generalized concept of the dynamics, not a proof. Proof is for authors and professors to produce. In DW's case, he can't reveal very much publicly and can only hint at the facts due to the increasing design thievery by a few "copy-cat" builders.

To calculate the Mojo anti-squat I used Linkage comparing different anti-squat rates to points in sag depth of the Mojo, and other bikes, about 6 months ago. Not long after getting my Mojo 2 years ago, I measured it and input the Mojo into Linkage and saved it to the subscribed on-line library. Linkage has mouse-pointer coordinates, and can show the distance of point-to-point during a click-and-drag. And in Linkage I can use Edit to choose a gear set, and it shows the chain line. And I can sag the suspension to a fixed static level with the slide bars in the Linkage graphics. IC and CC can be displayed for floating axle 4-bars. And by projecting lines on the screen with a straight-edge I could find the intersection of the chain-line with the axle through IC radial alignment swing-line. And by projecting a line, from the rear tire's ground patch through the chain/radial-swing line intersection, forward to cross a vertical line through the front axle, the anti-squat point at sag is found. Compare that point on the vertical line through the front axle with another point on the same line at the height of the CM and the percent of anti-squat can be calculated.

I used a rough anti-squat difference using the same 20mm measurement the fork travel was lowered for the example anti-squat alignment measurement change, it's close enough to show about 2% reduction in anti-squat rate for a generalized concept.

BTW, the "anti-squat center" I describe at the front wheel base as a virtual pivot was a new concept to me while writing that. I'll have to think about that some more. While accelerating the pedals, does the CM and frame swing as if pivoting behind that dynamically rising and falling "anti-squat center" point about the front wheelbase? It does feel like it when riding I think. And as always, the ride experience is the best test of a bike's performance.

Thanks for your comments!

Thanks, I'm also a student (freshman at best) at these things.
I think I need to get Linkage myself, I it would be a good exercise to learn what some of these terms really mean in the context of how they interact with each
other to define the suspension characteristics of a particular design.
FS design is definitely complex art, and getting everything right is definitely
a challenge, as evidenced by the multitude of crappy FS designs out there.
(It's amazing how effective marketing can convince people that a crappy design is good)

Anyway, I've been starting to pay attention to suspension squat in my recent rides. The ride that I've been doing is in the lower Catalinas (it's too hot to ride in the Valley these days) and involves nearly 1000 feet of elevation gain from the bottom to the high point in the ride. I definitely notice now how the lack of antisquat effects the ride in this very steep granny ring climbing. The acceleration force tries to make you go backward which compresses the shock, so it takes more energy to do the climb because of this. This kind of climbing would be very hard on any bike, but I'm getting tired faster on this bike than I would on a DWL and probably having to rest more due to the extra squat.
Also, the DHX Air is very supple early in the travel which I think contributes to the squat issue somewhat.
I don't believe in overdamping the shock, so I suffer through the tough parts of the climb and rest as I need to and put up with the squatty suspension which I generally like a pretty well except for this issue.
Oh well, I guess you can't have everything

 

[robbieracer]

DW has descibed it rather well
Bottom line: a lower fork is a small change but may be noticable to the sensitive rider.
Using granny gear= a larger change, quite noticable by anybody who is paying attantion

 

[Ridnparadise]

I am going to have to re-read your comments Derby. This is a tough subject and I have also asked this question. So far I have never had an answer, so many thanks. One thing I am sure of is that it is not an effect on rolling resistance. I have tried a gentle runnoff to a stop with varying fork travel and the Ibis rolls the same distance (give or take tiny amounts) regardless. Somehow I think I'll be counting CMs and anti-squats going uphill to get to sleep tonight .

 

[MB24]

It could just be the fact that the relative position of the seat and pedals changes, so your legs have to work differently. Think about how you can feel more powerful when climbing just by sliding your seat back. Just a thought.

 

[wheelhot]

aah, now my brain hurts.

By the way, another well done job derby

 

[jever98]

Derby et al,

one thing you seem to ignore completely is the relative weight that is on the front or back wheel, and the different resulting seat angles when lowering the fork.

My previous bike, a Bionicon, had a combined fork travel / BB lift action that would allow you to steepen the angles for climbing. Interestingly, the bike would feel like it rolling less well with the fork travelled and BB raised, even when rolling on a flat road without pedalling. To me, this suggests that the weight distribution between front and back wheels is very important.

Also, when cycling uphill your seat angle becomes flatter, changing the dynamics of pedalling (unless you apply your force perpendicular to the trial surface, which I don't think one does - look at people climbing out of the saddle). This could also affect perceived effort of climbing.

looking forward to hearing your thoughts,

Cheers
Jever

 

[Gregg K]

Different positioning also can utilize different muscles. Or different fractions of them.

When I want to get into my climbing mode, I slide forward on the seat. I have much more power there than if I slide rearward. And that's just the opposite of replies here. Go figure.

Now it could also be several other things. But I'd rather have another espresso and go stare at my Mojo.

 

[mojomike]

More Help?

Derby,

Thanks for the detailed response. Somehow I was hoping for a slightly more simple expanlation that I was actually able to fully comprehend. Nonetheless, I still enjoy the challenge and I'm sure I (and others) will learn something. If you will further indulge me with some basic suspension phyics, I would appreciate it.

At the level I understand your explanation, it seems to make sense, with the exception of one statement that seems counterintuitive-

When accelerating the frame is activated about the "anti-squat center", so the head tube rises and pulls the CM forward.

From experience, when a quick acceleration is initiated, the head tube certainly seems to rise (wheelie), but if the CM moved forward it should counteract this tendency, right?

On the other hand, the resultant additional pedal force when lowering the fork and obvious movement of the CM forward (front end plants) would tend to support your statement. I'm a little confused.

I look forward to some empirical testing of adding a gear to see how the front end will plant on the steeps.

Mike

 

[derby]

Derby,

"When accelerating the frame is activated about the "anti-squat center", so the head tube rises and pulls the CM forward."

From experience, when a quick acceleration is initiated, the head tube certainly seems to rise (wheelie), but if the CM moved forward it should counteract this tendency, right?

On the other hand, the resultant additional pedal force when lowering the fork and obvious movement of the CM forward (front end plants) would tend to support your statement. I'm a little confused.

I look forward to some empirical testing of adding a gear to see how the front end will plant on the steeps.

Mike

Yes the ride is what matters most. It's fun to try to analyze the mechanical dynamics. But I try to confirm my words with ride time experiences.

Regarding the quote from my original post (in quotes above). That was a mistake (and I've edited it). I think that the CM (not the head tube) is virtually pulled behind a virtual rope attached to a virtual pivot at the 'anti-squat center' along the front wheelbase driven by a virtual strut from the rear tire patch point during acceleration. And yes the CM position matters (and CM is about 85 - 90% rider weight) so the head tube may rise less or with nearly no change when the fork is lowered 20mm and the rider is positioned more forward within the wheels and anti-squat is about 2% less. With 2% less anti-squat the rear would squat more into the shock (or extend less if still over 100% anti-squat).

A 2% loss in anti-squat may be noticeable to very sensitive riders. But also the firmer and less compliant lowered fork and visually lowered site line change may really cause most of the sensation of increased effort when climbing with fork lowered.

I've never seen a good explanation for that strange feeling of increased effort to climb with fork lowered. Multiplying 2% less anti-squat times the percent amount of incline may be the significant factor. Maybe DW could answer?