mountainbike simulator "fs-kinematics"

igorion · Nov 9, 2005

during the past few months i have been working on an interactive mountainbike kinematics simulation tool. the online part of my tool is now finished and the programm can be used on the internet.

the project started when i first rode a full suspension that had noticeable pedal kickback and rose to zero sag with every pedal stroke. before that i had only ridden fsr bikes with quite neutral kinematics and pedal kickback seemed like a myth to me, so i wanted to know. now, some 4-digit number of working hours later, my software is used by "BIKE", europe's largest mountainbike magazine, to evaluate kinematics data for their test bikes and to support practical riding experience, and there has been very positive feedback by several bicycle manfacturers.

program features include:

simulation of virtually any suspension system available
several simulation modes
rider simulation
editable damper characteristics
effects of damper- or fork length change on geometry
center of gravity simulation
many diagrams showing system properties
export to several file formats (jpg,pdf,dxf,xml)
...

if you are interested, have a look at:

https://fs-kinematics.igorion.com

looking forward to your visit,

Hannes Fleischer

Moto'n'PushBiker · Nov 9, 2005

Very nice! Didn't get a chance to play with it a lot, I'll do that when I get to work.

Some comments I have:
- the font is really small in the web app
- some text isn't translated when you mouse over something in the bike/rider graphic (e.g. tretlager instead of crank)

igorion · Nov 9, 2005

Moto'n'PushBiker said:
Very nice! Didn't get a chance to play with it a lot, I'll do that when I get to work.

Some comments I have:
- the font is really small in the web app
- some text isn't translated when you mouse over something in the bike/rider graphic (e.g. tretlager instead of crank)

Hi,

i've just changed the labels in the "_system" bike to english, so anything based upon that bike is correct from now on. thanks for pointing this out to me. generally all these terms can be edited by the user, so for examle "swingarm" can become "VPP-LINK-A" if desired.

as for the font, i tried to keep everything around the bike as small as possible to give maximum room to what's important, the bike itself. yet, you are not the first one to complain about that. i am still thinking about the offline layout, and will definitely choose a less "web-design" approach in favor of a more pragmatic, down to the facts appearance there.

regards, hannes

Greyson45 · Nov 9, 2005

Your site looks good. I haven't had a chance yet to play with the software.

Does your program settle any questions in the debate between Horst Link supporters (Specialized FSR, Titus, etc.) and non-Horst faux-bar designs (Turner, Ventana, Kona, etc)?
There has especially been alot of uproar over Turner's decision to drop the Horst link license and move his pivot up to the seatstays. Some independent hard data would be useful in resolving this debate.

igorion · Nov 9, 2005

Greyson45 said:
Your site looks good. I haven't had a chance yet to play with the software.

Does your program settle any questions in the debate between Horst Link supporters (Specialized FSR, Titus, etc.) and non-Horst faux-bar designs (Turner, Ventana, Kona, etc)?
There has especially been alot of uproar over Turner's decision to drop the Horst link license and move his pivot up to the seatstays. Some independent hard data would be useful in resolving this debate.

hi,

i gave my best to capture as good as possible pivot locations from the video on turnerbikes.com. unfortunately, the horst link is barely visible on the video, so there might be some inaccuracy for that specific pivot.

below you will find links to the data sheets generated by my program for those two bikes:

http://www.igorion.com/_hf_files/5spot_old.pdf

http://www.igorion.com/_hf_files/5spot_new.pdf

you will see that the horst link version has slightly more pedal kickback on all three gear ratios, meaning that it should have a little more anti-squat than the TNT version. considering that the horst link position could in reality be a little further up, that difference would be even smaller. even with things like in the pdf files i doubt that you would be able to tell a difference in suspension vs. drivetrain interaction between those two bikes.

as for braking, the difference would be just the same as between a single pivot and a horst link bike.

personally, the six pack would have been one of my favorites if given the choice (even though turner's are hard to get a hand on in austria), but is out of question now after the change.

cheers, hannes

Greyson45 · Nov 10, 2005

igorion said:
hi,

i gave my best to capture as good as possible pivot locations from the video on turnerbikes.com. unfortunately, the horst link is barely visible on the video, so there might be some inaccuracy for that specific pivot.

below you will find links to the data sheets generated by my program for those two bikes:

http://www.igorion.com/_hf_files/5spot_old.pdf

http://www.igorion.com/_hf_files/5spot_new.pdf

you will see that the horst link version has slightly more pedal kickback on all three gear ratios, meaning that it should have a little more anti-squat than the TNT version. considering that the horst link position could in reality be a little further up, that difference would be even smaller. even with things like in the pdf files i doubt that you would be able to tell a difference in suspension vs. drivetrain interaction between those two bikes.

as for braking, the difference would be just the same as between a single pivot and a horst link bike.

personally, the six pack would have been one of my favorites if given the choice (even though turner's are hard to get a hand on in austria), but is out of question now after the change.

cheers, hannes

That is very helpful as there isnt much objective, hard data on this subject - only lots of subjective evaluations by persons that may or may not have preconcieved expectations. Thanks for evaluting these designs.

Ridge Rider · Nov 10, 2005

"as for braking, the difference would be just the same as between a single pivot and a horst link bike."

Can you elaborate on what you think the difference in the braking would be?

igorion · Nov 11, 2005

i think it's philosophy. one would say he'd want suspension to compress a little under braking to compensate weight shift, another one would want as much neutrality as possible.

i doubt one would feel the difference, but looking at the numbers, braking moment on the old turner would have less than half the effect it would have on the new tnt version.

on the x axis you see the angle of the brake caliper with respect to the ground, on the y axis there is wheel travel in percent. you can see that the caliper rotates more on the new version (but that's no secret from the beginning). all this is based on the assumption, that, if suspension movement doesn't cause the caliper to rotate, momentum at the caliper will not be able to induce movement in suspension.

Ridge Rider · Nov 11, 2005

I don't understand this statement

"all this is based on the assumption, that, if suspension movement doesn't cause the caliper to rotate, momentum at the caliper will not be able to induce movement in suspension."

especially "momentum at the caliper"

igorion · Nov 12, 2005

obviously a translation error (gotta refresh my english).

what i think: if suspension movement doesn't cause the brake caliper to rotate with respect to the ground, torsional force ("braking moment" or whatever the correct english term is), will not cause the suspension to move due to braking influence.

hopefully this time i got myself i little more clear.

Steve from JH · Nov 12, 2005

igorion said:
obviously a translation error (gotta refresh my english).

what i think: if suspension movement doesn't cause the brake caliper to rotate with respect to the ground, torsional force ("braking moment" or whatever the correct english term is), will not cause the suspension to move due to braking influence.

hopefully this time i got myself i little more clear.

That's clear enough. But it's not entirely true. Suppose you have a parallelogram linkage so that the axle carrying link does not rotate with respect to the ground or to the frame. If the linkage is not also parallel with the ground, there will be a rearward component to the wheel's movement, and braking will tend to move the suspension.

igorion · Nov 12, 2005

is it right you are talking about changes in wheelbase?
if so that's a subject i would very much like to discuss a little further.

especially interesting would be how torsional moment and changes in wheelbase would relate to each other.

Steve from JH · Nov 12, 2005

igorion said:
is it right you are talking about changes in wheelbase?
if so that's a subject i would very much like to discuss a little further.

especially interesting would be how torsional moment and changes in wheelbase would relate to each other.

No, not talking about wheelbase change. That is another topic.

If the unit of wheel and link together has a trajectory other than purely vertical, than the braking force at the contact point will tend to compress or extend the suspension, depending on which direction the linkage slants.

True neutrality occurs if a parallel linkage is also parallel to the ground or if the instant center lies along the ground line.

Ridge Rider · Nov 12, 2005

Steve from JH said:
No, not talking about wheelbase change. That is another topic.

If the unit of wheel and link together has a trajectory other than purely vertical, than the braking force at the contact point will tend to compress or extend the suspension, depending on which direction the linkage slants.

True neutrality occurs if a parallel linkage is also parallel to the ground or if the instant center lies along the ground line.

Which slant direction produces compression and which produces extension?

Steve from JH · Nov 12, 2005

Ridge Rider said:
Which slant direction produces compression and which produces extension?

Parallel linkage slanting up toward the front produces compressing moment from the braking force at the ground.

Ridge Rider · Nov 13, 2005

Steve from JH said:
Parallel linkage slanting up toward the front produces compressing moment from the braking force at the ground.

So then an Astrix or Lawill parralel linkage produces a compressing moment in the first part of the travel when the axle path is slanting backwards and an extending moment futher into the travel when the axle path is slanting forwards?

Steve from JH · Nov 13, 2005

Ridge Rider said:
So then an Astrix or Lawill parralel linkage produces a compressing moment in the first part of the travel when the axle path is slanting backwards and an extending moment futher into the travel when the axle path is slanting forwards?

No. A Lawill is not completely parallel. The rear link rotates counter clockwise (viewed from the drive side) when compressing from a bump. That means it is rotating around a point behind the axle. Rearward force at the contact patch causes an extending torque by making the link want to rotate clockwise.

I don't know about the Astrix.

Ridge Rider · Nov 14, 2005

Steve from JH said:
No. A Lawill is not completely parallel. The rear link rotates counter clockwise (viewed from the drive side) when compressing from a bump. That means it is rotating around a point behind the axle. Rearward force at the contact patch causes an extending torque by making the link want to rotate clockwise.

I don't know about the Astrix.

By measuring graphically from Linkage plots the Astrix is also not completely parallel. The Astrix Huckster's rear link rotates counter clockwise approximately 10 degrees relative to the ground in 8 inches of travel and the Yeti Lawill DH's (2000) rear link rotates counter clockwise approximately 17 degrees in 8 inches of travel. Many of the floating brake set-ups shown on Brake Therapy's website also have a slightly non parralel arrangement with the IC behind the bike although some of the set-ups may be compromised from ideal due to available positions for mounting the connecting rod clamp on the down tube.

In most bikes on the market today the axle path is close to circular but is mostly vertical throughout the travel , or the horizontal vector components are small compared to the vertical components. The same could be said about the motion of the rear link being mostly vertical with a smaller rotational component. Does that mean that the effects discussed above are relatively small?

Steve from JH · Nov 14, 2005

Ridge Rider said:
By measuring graphically from Linkage plots the Astrix is also not completely parallel. The Astrix Huckster's rear link rotates counter clockwise approximately 10 degrees relative to the ground in 8 inches of travel and the Yeti Lawill DH's (2000) rear link rotates counter clockwise approximately 17 degrees in 8 inches of travel. Many of the floating brake set-ups shown on Brake Therapy's website also have a slightly non parralel arrangement with the IC behind the bike although some of the set-ups may be compromised from ideal due to available positions for mounting the connecting rod clamp on the down tube.

In most bikes on the market today the axle path is close to circular but is mostly vertical throughout the travel , or the horizontal vector components are small compared to the vertical components. The same could be said about the motion of the rear link being mostly vertical with a smaller rotational component. Does that mean that the effects discussed above are relatively small?

I just posted an analysis comparing the HL and TNT versions of the Turner Sixpack when applying the rear brake. These are actual force calculations based on reasonable assumptions, I think. The link is:
http://forums.mtbr.com/showthread.php?p=1340228#post1340228

Ridge Rider · Nov 14, 2005

Steve from JH said:
I just posted an analysis comparing the HL and TNT versions of the Turner Sixpack when applying the rear brake. These are actual force calculations based on reasonable assumptions, I think. The link is:
http://forums.mtbr.com/showthread.php?p=1340228#post1340228

Nice post. Doing some more approximate graphical methods from Turner's TNT page the HL caliper rotates approximately 10 degrees clockwise (viewed from the drive side) and the TNT caliper rotates approximately 20 degrees or twice as much. Can we correlate twice as much caliper rotation to the twice as much compressive moment as caculated in your other post?

mountainbike simulator "fs-kinematics"

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