[Closed] Has VPP had it's day?

The suspension will squat a little bit due to the tension on the top run of the chain.

Depends where the pivot is.

People say that virtual pivot bikes are a pain to maintain. But my experience of the Maestro is not like that. The main load-carrying bearings needed replacing after a two years and were just a few pounds.

I can vouch for very effective suspension while seated pedalling - on smooth trails, there is no sense of pedalling induced bob, but when climbing gets rough, the suspension is very active and gives loads of grip and helps you maintain steady cadence.

Wasn't keen on the 5 I demoed against the Giant. But I would be interested to try a more modern single-pivot trail bike like the ST4.

The suspension will squat a little bit due to the tension on the top run of the chain.

Depends on the relationship between chain and pivot but yes it could well squat.

Imagine a cyclist pedalling hard to maintain a constant speed in to a strong head wind, so weight transfer due to acceleration doesn't come in to it

If the cyclist can maintain a perfect output throughout the pedal cycle then no.

There are multiple different effects that cause rear suspension movement
1) - chain growth
2) - when the chain is not parallel with teh line between the wheel and BB centres ( viewed from teh side) You get squat or rise depending on the angle
3) weight transfer as you bounce on the pedals
4) brake jack
5) weight transfer back and forwards
6) hitting bumps of course

so these all interplay together to give various effects on rear wheel movement. Some designs these are set up to work against each other to reduce movement. You can even get different thinks happening at different points on the travel. Even with a concentric swingarm with no chaingrowth you can still get squat or jack under power depending on what gear you are in.# as yo can get a pull on the chain that is not parallel to the spindle / bb axis

Its all horribly complex and very few folk really understand what happens let alone what effect it has on riding. I can work out all the various movements in theory but have no idea how they actually interact or affect riding.

brant - Member

The suspension will squat a little bit due to the tension on the top run of the chain.

Depends where the pivot is.

Even with concentric it will squat as the top run of the chain is not parallell to teh wheel spindle / bb line. So no matter where the pivot is you stil get this force.

Cleverly set up systems with a single pivot will use this to counteract rise from chain growth in the most common gears.

Depends where the pivot is.

Mtqg

Actually squat on a chain drive motorcycle is significant. 1/3 of sus travel or more is possible . What is usually done is use the pivot location so chaingrowth produces rise in the rear sus - so the two forces balance. Rise from chain growth and squat from reaction to the angle of the pull on the chain.

A cyclist produces as much torque as a middleweight motorcycle. Torque effects can be very significant

I just spent a few minutes watching motorbike burn outs on youtube, which was amusing in its self.
None of them showed any significant squat caused by chain tension.
I suspect this 1/3rd of travel you mention is caused almost entirely by rearward weight shift due to acceleration, with maybe a little bit of torque reaction form the engine.

Sit on a bicycle, leaning on a wall.
With no pressure on the pedals, there is no chain tension.
The suspension is reacting solely to the riders weight on the seat.
Lock the back brake on.
Slowly, transfer as much weight as possible to the leading pedal.
There is now maximum tension on the top run of the chain.
How does the suspension react to that tension ? Does it even move ?

Having actually ridden motorbikes.................................

Teh rear sus will react differently with the brake on.

It all depends on the various angles and as I said there are two different effects that can be made to work in opposite directions to cancell out squat.

Altering chain length causes a reaction, the angle between the chain run and the line bb / wheel spindle causes another reaction

Back to the OP:

1. Yep, they require more design consideration, tighter manufacture and a downhill team to sponsor to show off their products!

2. Sub 125mm with VPP, never ridden one but you may have a point

3. DW Link is nice, I think it’s personal preference as to which makes the better bike.

4. Platform shocks are good but may limit suspension movement when activated, not always for the better

5. Pedalling performance is a big part in a press review; people will still want lockout even if they never use it!

6. Not necessarily but it can be expensive.

So:

Virtual Pivot systems will be around for a while as they also offer a design flexibility if the manufacturer wants a crazy axle path, pivot point, leverage ratio etc. From that, I imagine the SC VPP will stay with us and it can be tailored for whatever use they like, hence VPP2.

All designs will be compromised in one way or another, bob, reliability, price. Assumptions have to be made about what a rider wants, these may not tie in with what you actually want. As TJ says, various factors will influence suspension movement.

All manufacturers will claim their system is the best.

Geometry plays a big part, arguably even more than suspension on how a bike behaves and if you will enjoy it.

Single pivot will still be around too.

I’m in no way a suspension/vehicle/mechanical designer so please feel free to correct me if I’m wrong!!

2) - when the chain is not parallel with teh line between the wheel and BB centres ( viewed from teh side) You get squat or rise depending on the angle

Not sure it depends on whether it's parallel or not, it's (Chain tension) x (Perpendicular distance from taut chain line to pivot point) that counts surely. e.g. if the chain ran straight through the pivot point then chain tension wouldn't affect the suspension.

can you sort out your tehs. it's driving me nuts 🙂

Having actually ridden motorbikes.

Forget the rear brake bit then, I was just trying to come up with a way of studying the chain tension in isolation.
Lean your bike against the inside corner of two walls.
With the front wheel up against one wall so the bike doesn't roll forward, put maximum pressure on the leading pedal.
Does the chain tension cause the suspension to move ?

2) - when the chain is not parallel with teh line between the wheel and BB centres ( viewed from teh side) You get squat or rise depending on the angle

Not sure it depends on whether it's parallel or not, it's (Chain tension) x (Perpendicular distance from taut chain line to pivot point) that counts surely. e.g. if the chain ran straight through the pivot point then chain tension wouldn't affect the suspension.

can you sort out your tehs. it's driving me nuts

I actually lost sleep on some of this last night. I agre with TJ that chain angle is a variable. But I'm further out of my depth than I thought.

I get the whole moment equation but the problem is that the chain force isn't applied directly to the swing arm its applied to a wheel thats free to rotate. The chain tension causes a reaction at the axle. Which seems to elimenate the height of the chain but not the angle as a variable. I'll try and draw a photo if anyone cares.....

I care.
I'd like you to draw a photo.

Does the chain tension cause the suspension to move ?

Depends on the angle of the chain, any distance between the swingarm pivot and the bb and the height of the pivot

It could stay still, rise or fall depending.

Your test still does not mimic what occurs in real life tho as the front is not anchored.

I actually lost sleep on some of this last night. I agre with TJ that chain angle is a variable.

Chain angle - think of force vectors. There is a force acting along the chain - it can only be resisted by the swingarm. if the two are not parallel there will be a resulting force that makes the third side of the triangle - this could be either up or down depending oin the gear you are in. 22/34 puts the chain at a very different angle to 48/11

This is not the same as the effect from having a bb / wheel spindle distance that alters. (chaingrowth)

You can by clever geometry get these two forces to balance out at least in part in some gears - this is why some setups work best in middle ring only.

But I'm further out of my depth than I thought.

Teh main advantage of a multilink set up and virtually all of the m are variables on a couple of basic setups - is that you can tailor the axle path and leverage rations to create specific effects.

How crucial this is with modern sophisticated shocks I don't know

MTQG the difference between motorcycles and bikes is 2 heavy pistons rotating erratically at around the resonant frequency of the suspension system.

"2 ) - when the chain is not parallel with teh line
between the wheel and BB centres ( viewed
from teh side) You get squat or rise depending
on the angle"

I'm not entirely sure what you are saying here but do you mean irrespective of pivot placement?

Is anyone arguing for or against my point re. pivot placement? or caring? 😀

It could stay still, rise or fall depending.

Another video.

170hp on a dyno and there is negligible movement of the rear suspension.

My bike goes boing! [img] [/img]

...2 heavy pistons rotating erratically...

Yes - its a separate issue from the effects of pivot position

It happens even with a concentric pivot.

Pivot position is important but not in isolation

A carefully chosen pivot will allow the force I describe above and the effects from the non concentric pivot to balance ( in some gears)

MidlandTrailquestsGraham - Member

It could stay still, rise or fall depending.

But it doesn't, because the force is so small it has no effect.

Nope. It all depends on the balance of forces - that vid shows clear squat and rise on a very short travel system

Some motorbikes don't squat or rise much - good sus design balancing the forces out.

The simple force created by the chain being not parallel to teh swingarm is easily big enough to cause squat or rise. However you can balance this by clever placement of the swingarm pivot.

It needs paper and pencil to describe all this stuff adequatly.

I shall give up.

TJ is your point above based on separating the again tension into its components along and perpendicular to the axle-bb line?

if so then it seems you are with Ade re. chain tension and pivot placement?

cynic-al - Member

TJ is your point above based on separating the again tension into its components along and perpendicular to the axle-bb line?

Yes

Dunno what ADE has said.

There are two different effects being confused here.

Pivot placement has an effect that can create a vertical force on the wheel. the angle of the chain produces a different vertical force. These two are completely separate.

Thse two can both be in either direction or zero depending on the variables.

Clever positioning can make them equal and opposite in some gear combos

With a simple swinging arm, the only variables are the position of the swinging arm pivot, the point where the chain meets the chain ring and the point where the chain meets the rear sprocket.

These three points form a triangle.

The chain forms one side of the triangle.

By putting tension on the chain, it tries to shorten that side of the triangle.

With the swinging arm pivot below the top run of the chain, it will try to raise the swinging arm, or squat the suspension.

However, the angle between the chain and the swinging arm is so small that the force required to move the swinging arm is too great and chain tension has no effect on suspension movement.

Back to this picture.
[img] [/img]

Imagine the jib almost horizontal so that the top rope is nearly parallel with it.
It would take a lot of effort raise a load on the hook by pulling on the top rope.

Now imagine the jib nearly vertical.
It takes very little effort to raise the jib all the way to vertical.

Jib = Swinging arm
Rope = Chain

However, the angle between the chain and the swinging arm is so small that the force required to move the swinging arm is too great and chain tension has no effect on suspension movement.

This is simply not shown by what you say.

You are still confusing the two different effects.

On the motorcycle clip you linked to it was moving 1/3 of the travel easily.

With respect sir, that did not move 1/3rd of the travel.

Anyone else care to estimate how much the suspension on this bike moves when the power is applied ?

Incidentally, I'm trying to work my way round to explaining why the Santa Cruz VPP [i]does[/i] use chain tension as part of the suspension system, but after 5 pages we're still not clear on what's happening with a single pivot, so I don't know if we'll ever get there.

The harley on the dyno I meant You can see it rise and fall. A harly sportster only has about 4 inch of rear travel.

A burnout is no test at all - not much power used at all.

ah ok. I don't believe analysing the tension in the chain that way is correct as I've said. happy to be proven wrong.

Al - its basic mechanics. vector addition - triangle law

I have attempted to explain it to you twice without success. if you have a force along the chain that is resisted by the swingarm / chainstay then if these two are not parallel you get a resultant vertical force.

http://hyperphysics.phy-astr.gsu.edu/hbase/vect.html

Ah, OK, wrong video.
The thing is, even with the swinging arm pivot below the top chain line, the back of the bike rises.
How could chain tension cause that ?

What I think is happening is the triangle thing again.
The three points are the rear tyre's contact with the roller, the swinging arm pivot and the front tyre's contact with the wall.
As the rear wheel pushes forward it tries to shorten the bottom line of the triangle by pushing the swinging arm upwards.

I think you're misleading yourself with the parallel thing as well.
Two sides of a triangle can't be parallel.

MTQG

You have got two different things confused. Its really impossible to explain without diagrammes.

This shows the effects of the chain and swingarm being non parallel. Both are force triangles.

[img] [/img]

This shows the effects of the swingarm pivot not being concentric to the bb

[img] [/img]

Both those diagrammes are horribly oversiplified as well

TJ I get vectors, I just disagree that looking at the position and angle of the chain is the correct analysis.

wish I could fine that Spanish website, it was linked to loads here back in the day and I thought this point was well established.

Al - there is a basic misunderstandfing / lack of comnprehension

If the chain and swingarm are not parallel then there will be a vertical force produced irregardless of the position of the swingam pivot. this is simple basic mechanics.

Have a look at the diagrammes

Al http://www.sportrider.com/tech/146_0404_motorcycle_traction_geometry/photo_02.html

Remember that on a bicycle you generally have a larger front sprocket so the vertical force is opposite that on a motorcycle - reffered to as "chain pull" here it is a squatting force on a bicyle in a typiocal gear.

The three forces all act on the swingarm at the rear axle, and their moments about the swingarm pivot can be calculated. As the rear suspension compresses, the geometry of the force diagram changes--sometimes significantly. Note that while the chain pull always creates an antisquat tendency, the driving force torque changes from antisquat to pro-squat as the suspension compresses and the swingarm passes horizontal.

hmmm. I'm still not sure it's ap relevant on I bike given the disparity in power and torque.

oh and perhaps it's fairer to say we disagree than I misunderstand?

it is fascinatng reading about suspension forces as written by a solicitor, a mental health professional, and a bus mechanic.

what will the three wise men do next

Nope - I think there may be confused concepts but you cannot state that this clearly demonstrated effect does not happen. Sorry.

A cyclist produces as much torque as most motorcycles

Cycle springing is much lighter.

MTQG

I'll try and do a picture later

But I've just been out on my bike. A single pivot (Fuel ex 6.5)

Before I set off I sat on the bike and leant on the shed. Locked the front fork and pulled on the front brake

In the middle ring waiting the leading pedal contracted the suspension visibley. I assume this was due to chain tension but obviuosly as you wait a pedal other thing happens like the reaction force on your bum decreases. The pivot is below the middle ring. The effect seemed less in the the big ring.

Then I got bored and went for a ride

ch well in that case TJ you misunderstand too 😀

LOLLERCOPTERS at the tag.

oh and spunkyard I'll have you know I studied Physics at university 😀

I think the whole motor bike thing is taking us no where. Obviously no one would design a motor bike so that chain tension had a huge effect. It seems obvious a motor bike designer has lots of options to reduce or control the effect of chain tension. Its not obvious to me that the tension in the chain on a motor bike is more than on a push bike. A motor bike has greater power but this could be achieved through greater chain velocity not greater chain tension

read these, they may not settle your arguments but if you guys are genuinely interested in these things then they can be an enlightening read.

[url= http://raystrax.com/PathAnalysis/index.htm ]Path analysis 1[/url]

[url= http://www.rdrop.com/~/twest/mtb/pathAnalysis/ ]Path analysis 2[/url]

what always fascinates me is how hung up on axle path some people get when in reality all the major players are so close that it's not really worth even dsicussing. Even the tiny spend VPP paths are so close to a simple arc that it is of almost no relevance.

pivot placements, spring rates (both shock and system) and the rider have a far bigger impact thatn anything else.

Over the years I've used a lot of different designs, SP both linkage driven and directly actuated , 4bar, VPP, and various softails which blur the lines and I know what I prefer and it genrally depends on what kind of riding I do. I still own and ride a single pivot, and two different 4 bar designs on a regular basis but believe it or not the bike I get on best with is a 2001 schwinn straight 6 which is a lawill design trail bike. It has its quirks, it's a bit heavy and has a horribly tendancy to extend under heavy breaking but good use of compression damping at the front end and running a smaller than normal rear rotor tames that to the point where I can cope with it, and it's bump performance is probably the best of any bike I've ever owned and ridden.

what you all seem to be doing is focusing on the back end, dont forget that on trail performance is a harmonic blned of system, shock, setup and the front end, a poorly performing or set up front end can accentuate the good and the bad of any rear end, remember to treat the bike as a whole and not just think of the back and front as seperate.

above all suspension feel is such a personal thing I dont think you can ever say one type is 'better' or 'worse' they all have their ups and downs even the same sytem in different guises so just ride and see what you get on with best 🙂

[img][URL= http://inlinethumb36.webshots.com/6115/2136887990036898833S600x600Q85.jpg [/IMG][/URL][/img][img][URL= http://rides.webshots.com/photo/2006672680036898833Xezzvp ][IMG] http://inlinethumb28.webshots.com/3611/2006672680036898833S600x600Q85.jpg [/IMG][/URL][/img][img][URL= http://rides.webshots.com/photo/2629527740036898833uDdUZk ][IMG] http://inlinethumb29.webshots.com/21468/2629527740036898833S600x600Q85.jp g" target="_blank">http://inlinethumb36.webshots.com/6115/2136887990036898833S600x600Q85.jpg [/IMG][/URL][/img][img][URL= http://rides.webshots.com/photo/2006672680036898833Xezzvp ][IMG] http://inlinethumb28.webshots.com/3611/2006672680036898833S600x600Q85.jpg [/IMG][/URL][/img][img][URL= http://rides.webshots.com/photo/2629527740036898833uDdUZk ][IMG] http://inlinethumb29.webshots.com/21468/2629527740036898833S600x600Q85.jp g"/> [/IMG][/URL][/img]

ok we seem to have opened a huge can of worms here,, lets ignore the motorbikes for a while but bimota used to put a lot of effort to making the swingingarm pivot concentric to the engine sprocket,,

sorry side tracked there,,

i seemed to have massivly oversimplified the whole thing here,, there are lots of forces at play and all combined ,,

there are three screendumps from linkage one with pivot obove chainring one below and one to give 0 anti squat,,

the anti squat graph on the left is the one we are looking at the blue graph give you the amount of antisquat a +ve number means it's not squating and a -ve number means it is squating

it auto scales so take note of the vertical scale

i was surprised how low the pivot position needed to be to get zero antisquat ,, so there is someother force acting here

when pivot is placed on the bb it gives about -200% anti squat

what is not taken into account is the change in wheel rate (spring) due to the change in lever length of me moving the pivot

it goes from 1.9 pivot at bb to 3.5 pivot obove the chain,,

in conclusion we are all right ,, the height of the bb does alter the antisquat but there are other forces involved and it is a combination of these which determins the reaction of the swingingarm to pedaling forces and these cannot be taken in isolation

so there is someother force acting here

Thrust force from wheel acting along line from hub to pivot point?

my mistake al what a true polymath you are
TJ still knows noting though can we at least agree on that 😉

1) - chain growth
2) - when the chain is not parallel with teh line between the wheel and BB centres ( viewed from teh side) You get squat or rise depending on the angle

colinear works for me TJ but not simply parallel. parallel [but offset] will cause movement of the rear axle. take moments about the swingarm pivot - there is an unresolved moment that must be resisted by the suspension.

"in conclusion we are all right"

I KNEW I WAS RIGHT 😀

parallel [but offset] will cause movement of the rear axle. take moments about the swingarm pivot - there is an unresolved moment that must be resisted by the suspension.

This is where I get stuck. The chain tension doesn't act on the swing arm it acts on the sprocket/wheel, which are attached to the swing arm but via an axle which can't transmit any torque. If the chain tension is parallel to the swing arm this pushes the axle straight towards the pivot. So the force of the axle on the swing arm has no moment about the pivot

I'm not saying I'm correct I'm just saying I'm confused

the freehub can transmit torque to the wheel only, you're right. that's how they work. pawls etc. but the wheel will then exert a force perpendicular to the swingarm if it's [the wheel's] rotation is resisted by something e.g. contact with the ground, or the brake being applied for example as this locks the cassette in rotational position relative to the swingarm.

Forget about parallel. it's not a helpful term. think force = magnitude and direction instead. there are no shortcuts to understanding this, except computer software. basically you have to get into forces, moments and free body diagrams for various components of the assembly, from the rider to the wheel, the swingarm etc etc. This needs A level physics as a minimum I would say, not to discourage anyone or put anyone down in the slightest.

but via an axle which can't transmit any torque

there is a torque otherwise there would be no tension in the chain, and the chain line is offset from the line linking the axle and pivot as the chain leaves the rear sprocket at a distance from the axle even if the pivot is on the point where the chain meets the front ring

I think part of the issue is inexact use of words to describe concepts and thus misunderstandings over who means what.

Teh other issue is its hard to explain without drawings

ok back at linkage software this time std marin single pivot

only change is 36 rear sprocket and change to 11 tooth rear sprocket

36 gives 90% anti squat
11 gives 42% anti squat

well I think its interesting

I think you need to explain, carefully, and slowly 😉 what "90% anti-squat" means in the context of the software.

you don't get any chain tension effects with a BB-concentric-single-pivot.

i don't care how many long words, diagrams, or *****ng screen grabs from linkage we can link to.

you just don't.

so there.

X

think you need to tighten up on your terms a little there, ho ho ho 😀 no pedal feedback from suspension movement perhaps...

I think you need to explain, carefully, and slowly what "90% anti-squat" means in the context of the software.

i think i have to admit I am unsure as there is no units

what I do know is a positive number means the the swinging arm is being forced open trying to lift the back of the bike

a negative number is the the opposite back end being compressed

so in my last example 11 to 36 tooth give roughly twice as much anti squat

who has a single pivot bike near by put bike in big ring and biggest rear put the front wheel up against wall balence on bike and load pedals see how much rear end rises now try the same on smallest rear see if there is any differenc dont use the brakes

just been on t'internet on the forum for linkage

a1 curve is suspension's anti-squat curve. Anti-squat is suspension's resistance to compression due to acceleration. Over 100% of anti-squat (AS) means suspension will extend under acceleration. With 100% AS suspension won't neither extend nor compress. Under 100% AS means tendency to compress under acceleration. It is determined based on actual linkage IC, chain force line and center of mass height. I would say that pedal-kickback effect is a byproduct of anti-squat characteristics of the suspension.

a2 curve depicts suspension reaction under rear-braking without front-braking. Again, value > 100% means suspension will extend under rear-braking, value < 100% means it'll compress under rear-braking. This curve depends on actual IC position and center of mass height.

this is realy good,

yes it is, thanks 🙂

This needs A level physics as a minimum I would say, not to discourage anyone or put anyone down in the slightest

Oh dear, which what I teach for a living. I think it hasn't been helpful to over simplify things in my case. I was imagining spinning the rear wheel with it off the ground to isoloate the effect of chain tension

there is a torque otherwise there would be no tension in the chain, and the chain line is offset from the line linking the axle and pivot as the chain leaves the rear sprocket at a distance from the axle even if the pivot is on the point where the chain meets the front ring

There is a torque applied to the sprocket/wheel. The 2 forces in the couple at the reaction at the axle and the tension the chain. These two forces roatate the wheel. But the the only 2 forces acting on the swing arm are a force at the axle and a force at the pivot. If the line of action of the reaction is through the pivot then it has no moment. So I believe, but may be wrong, that if the chain stay pivots at the BB and the chain is parrallel to the chain stay then spinning up the rear wheel with it off the ground will not change the force in the shock

you don't get any chain tension effects with a BB-concentric-single-pivot.

That is my current conclusion. I'd be greatful if you pointed me toa supoorting argument

At some point I'll try and do all the forces with the wheel on the ground

you don't get any chain tension effects with a BB-concentric-single-pivot.

i don't care how many long words, diagrams, or *****ng screen grabs from linkage we can link to.

you just don't.

so there.

X

nice well reasoned point sir

ampthill - Member

That is my current conclusion. I'd be grateful if you pointed me to a suporting argument

easy:

it's *****ng obvious!

you can quote me on that.

thankyou.

X

(you will get mass-of-rider's-body/legs-accelerating-up-and-down-effects)

I,m not very good at maths etc so i try to look at things diferently

imagine a piece of wood laid on the ground with a piece of string tied to one end,, the wood is hinged to the ground at the other end now pull the string in line with the wood towards the hinge ,, waht is the result the wood is in compression but it stays on the floor

now lift the end of the string up to about the radius of the front ring and pull the string and what will happen now ,,

Ade that is sooo different to chain tension!

sorry most of what you have said is now tainted with "I ,m not very good at maths etc"

imagine a piece of wood laid on the ground with a piece of string tied to one end,, the wood is hinged to the ground at the other end now pull the string in line with the wood towards the hinge ,, waht is the result the wood is in compression but it stays on the floor

now lift the end of the string up to about the radius of the front ring and pull the string and pull what will happen now ,,

Thats all fine. Now glue a block of wood to the un pivoted end and tie the string to this. Now pull the string parrallel to the ground. The wood still lifts from the hinge

But really the string isn't tied to a block its round a wheel that can rotate.

I think this means that with the string parallel to the ground you can't bend the hinge. But it certainly isn't obvious to me.....

al why is it different from chain tension ? chain tension string tension forgive me but I really dont see why this isnt a valid model

isnt the point of max chain tension and torque to the rear wheel is when the rider is just stalling on a climb and the rear wheel not revolving

probably not, no. the point of maximum torque is probably when you are honking out of the saddle, pulling up really hard on the bars, out over the front of the bike to push back on the pedals, after just dropping into a slightly higher gear and really flying along wearing spds. under these circumstances you can mobilise quite a lot more than your body weight onto spinning the cranks, something you cannot really do while stationary. you need the gyroscopics of the wheels to stabilise the bike against you throwing your weight around everywhere. you know when you see the tour guys really accelerating and the bike is 45 degrees over one way then the other with each pedal stroke? that's maximum torque right there.

funny thing is after reading the definition of anti squat from the linkage forum
i moved the pivot point to the point where the chain meets the front chain ring and with the 11 tooth rear the anti squat reads 100.5 so virtualy no reaction to chain forces

move the pivot up by 10mm gives a AS figure of 160
move the pivot 10mm below the chain line give a figure of 50

Over 100% of anti-squat (AS) means suspension will extend under acceleration. With 100% AS suspension won't neither extend nor compress. Under 100% AS means tendency to compress under acceleration

if we go back to my original statment i think i said that a pivot point above the chain line would tend to extend the swinging arm and a pivot point below the chainline will tend to compress the the suspension

and a pivot point on the bb give a value of -260 %

now my maths may not be up to speed but the guys who wrote this software should be so i am going with the results from linkage

al why is it different from chain tension ? chain tension string tension forgive me but I really dont see why this isnt a valid model

that's a good enough model of chain tension.

i moved the pivot point to the point where the chain meets the front chain ring and with the 11 tooth rear the anti squat reads 100.5 so virtualy no reaction to chain forces

I seem to recall saying this about three pages back 8)

I just spent a few minutes watching motorbike burn outs on youtube, which was amusing in its self.
None of them showed any significant squat caused by chain tension.

Motorbikes do squat under power. A burn out isn't loading the suspension as the tyre isn't in traction, thus cannot load the suspension. I dial out squat on my track bike using the damper adjustments, it has a big effect on the ride of a motorbike. Chain tension and free play is used on motorbikes to adjust the squat effect as well as the suspension settings.

WTF did my post go?

Ade the difference is you are ignoring the effect of the wheel on the ground and the resulting forces.

WTF did my post go?

the physics police intervened... 😀

WTF!

harsh TT 😀

I dial out squat on my track bike...

I'm trying to find the effect of tension on the top run of the chain on the suspension.
I believe it is insignificant compared to the weight of the rider, but I accept that I may be wrong.

So, one question for those who understand the maths or have got use of the software.

A cyclist puts a 100kg load on a pedal horizontally forwards.
The crank is 170mm long.
The chainring is 85mm radius.
There is now a 200kg load on the chain. Have I got that right ?
The swinging arm pivots around the BB and is 450mm long.
The distance from the point where the chain meets the chainring to the point where the chain meets the rear sprocket is also 450mm.
We now have a 450/450/85mm triangle.
With a 200kg horizontal force along one long side of the triangle, what is the vertical force at the sharp end ?

Say 50-150 Newtons if you want a number depending on angle. The point is that this force is varying cyclically with crank revolutions, whereas, unless you are lunging around all over the bike, the force from your body weight is pretty constant and is already being handled in the sag of the suspension. unless you can suddenly alter your body weight, or accelerate your body around by lunging all over the bike, the system is in balance and the suspension will not compress any more or less due to body weight while just trundling along the trail. Whereas, the small but varying lateral load at the rear axle can, especially if near the resonant frequency of the system, turn into quite a noticeable bob.