[Closed] Has VPP had it's day?

I think these are two different topics - chain growth, where the action of the suspension (some systems only) causes instantaneous changes in taut chain length due to bb and rear axle moving together or apart (e.g. while coasting over rocks), and chain tension applied by the rider, causing the suspension to compress due to what Midland has posted above.... ❓ these can both happen at the same time...and so interact..and it gets very complex...

I've just checked, and STW currently doesn't have a smashing my head against a brick-wall smiley 🙂

Here you go 😉
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blah blah blah. How does the bike feel? How does it ride? How easy is it to maintain?

sorry if i caused unnecessary frustration 🙁

Lovely debate and it has really got me thinking. I agree with this

I agree that there is no chain growth with a concentric bb but i think that if you tension the chain (the bit between the chainring and the rear wheel) on concentric bb pivot bike, that tension will cause the suspension to compress.

Obviously with a pivot concentric to the bottom bracket the position of the swing arm doesn't cause any chamge in the relative lenths of the chain top and bottom.

If you pick up the back of the bike and turn the pedals to accelerate the rear wheel this is what happens (we are ignoring bearing friction here)

The top chain now has more tension than the bottom chain (this applies a torque to the rear wheel causing its angular velocity to increase)

However it also applies a turning moment to the swing arm as the line of action of the force through the chain doesn't run through the pivot. This will cause the swing arm to rotate upwards. This rotation in the swing arm will compress the shock until the moment of the shock balances the moment of the tension in the chain. When you stop pedalling the swing arm will rotate downwards.

If the pivot is located higher up so the line of the chain (at the top) passes through the pivot then pedalling will not cause the swing arm to rotate.

All of this of course ingnores two other effects

The movement of the riders mass (legs going up and down)

The resulting acceleration of the bike if the wheel is on the ground. As has been mentioned this also effects suspension. Its not helpful to talk aabout mass transfer. When the bike acclerates the force is applied at ground level, but the bike and riders centre of gravity is much higher. So the force applied at ground level tends to make the bike rotate (front wheel up rear wheel down). This causes the reaction force at the rear wheel to increase and decrease at the front wheel.

I believe it is possible to combine these to effects for a given chain position so that pedalling has no effect on the position of the swing arm (the chain tries to rotate the swing arm down and this balances the increased reaction at the rear wheel)

But of course this only works for one chain line and ignores your legs going up and down

I dunnno, women go to all sorts of lengths to try to prevent it, but I find the sight of a faint outline quite a turn on actually.

So ade if you imagine a sp suss bike with a single chainring and the pivot a few inches behind the seat tube in line with the again in the middle gear (yes the pivots would be on the chainstay).

your theory means that in a low gear the suss contracts as the again line is above it, and conversely that in a high gear it extends because the chain is below it.

that doesn't make sense!

of course there is tension in the chain but it ALWAYS pulls the bb TOWARDS the hub axle because that tension is balanced or counteracted by traction of the wheel on the ground.

there used to be a Spanish website that explained it all but I can't find it.

I'm not reading all that, so

a: what's the verdict?

b: if you cobbled the belt on a treadmill.and put each bike on, would they take off?

Enjoyed reading this, hope it reaches some sort of consensus that I can understand!

Elfinsafety - Member
I dunnno, women go to all sorts of lengths to try to prevent it, but I find the sight of a faint outline quite a turn on actually.

So ade if you imagine a sp suss bike with a single chainring and the pivot a few inches behind the seat tube in line with the again in the middle gear (yes the pivots would be on the chainstay).

your theory means that in a low gear the suss contracts as the again line is above it, and conversely that in a high gear it extends because the chain is below it.

that doesn't make sense!

of course there is tension in the chain but it ALWAYS pulls the bb TOWARDS the hub axle because that tension is balanced or counteracted by traction of the wheel on the ground.

there used to be a Spanish website that explained it all but I can't find it.

Hi Cynic-al, could you please expand on your explanation? You say the chain always pulls the bb towards the rear axle but that statement doesn't disprove what Ade was saying, unless I'm missing something?

Ade says the suss extends when the chain line is below the pivot.

That would mean the axle-bb distance increasing.

cynic-al - Member
Ade says the suss extends when the chain line is below the pivot.
That would mean the axle-bb distance increasing.
POSTED 1 HOUR AGO # REPORT-POST

Suspension can extend under chain tension without the axle/bb distance increasing depending on pivot point location.
Though Ade may have over simplified with his chainline description.
I would have to make a jib crane type thing with string and lolly sticks to test.

Take a trail bike like the Orange 5, a Single Pivot bike with a pivot roughly level with the 32T ring. This is the optimal position according to Orange for the best trade off between Axle Path, Pedal Kick Back and whatever else they are considering in their design. As most people spend most of their time in the middle ring, the 32T PP is pretty good, PKB may be a problem for some people on larger hits and the AP generally arcs forward after the rider's sag point, draw a circle with the Pivot Point as the centre to see this.

Where the chain pulls on the rear wheel in relation to the PP can cause the suspension to extend/compress when pedalling. In simple terms Chain line above PP will mean compression and vice versa. There is also the Mass Transfer that DW talks about, ie accelerate in your car and weight moves rearward due to momentum etc.

The Virtual Pivot Point, as the name suggests allows suspension to pivot around a point on/around a frame which physically does not exist. So now a manufacturer can have an initial pivot point which appears to be mid wheelbase or 3 feet in front of the bars or wherever they want really. If you look at the 'bars' of the Four Bar system the Instant Pivot Point can be seen by drawing lines through the supporting bars, for better explanation go the DW website and draw a line forward between the bearings on the lower link and the bearings on the upper link, the intersection of these lines is the VPP (ignore the SC patent for now!) However this point is constantly changing throughout the travel and is normally set up for pedalling efficiency around the sag point, general 32T level but often forward of the down tube. This should help with pedalling.

Now as the suspension moves through its travel, the VPP will change, here the designer may decide that on a big compression, the rider is not pedalling and move the VPP in a way to limit Chain Growth or for whatever effect they want. This is part of the reason for the extra price, a 1mm difference in actual pivot placement may drift the VPP out by a lot more and upset the system, coupled with the countless options to whittle down and a bit of marketing to lure you.

As with any system the designer has to make some assumptions on what a rider wants and design around that. So having the high forward PP should counter 'bob' and keep the press happy! So VPP/DW/FSR will be around for a while but as with SP they all compromise something in the end.

However it comes down to personal preference in the end and usually geometry plays a bigger part in getting a fun bike.

Where the chain pulls on the rear wheel in relation to the PP can cause the suspension to extend/compress when pedalling.

A motorcycle engine isn't rotating at 60rpm with pistons that weigh 2 stone each.

Which is where we get back to my original point that the weight of the rider lunging on the pedals is all that matters when it comes to pedal bob.
The comparatively small force of the tension on the top run of the chain is insignificant.

MTQG trust me it matters...ride any high pivot bike like the 1st cannondale suss and you'll know all about it.

If you have read up to this point, is there a form you can fill in and submit to get the time lost added back on to your lifespan?

Think of a roller system on a rail and imagine a rope pulling on it at right angles and the roller would not move. Now move the rope up a few cm and pull again, the roller would want to follow and move up also. The swingarm and pivots control the path the axle will take on the bike but can still cause the axle path to be moved by chain tension.

Some systems take advantage of this and drive the wheel down a little, extending suspension but is cancelled out by your body momentum moving back in relation to the bike so there is little bobbing.

Standing up and can your whole body mass go up and down with each stroke will cause the suspension to react as will jumping up and down on the pedals or landing etc. The designer will generally assume the rider is seated for the majority of their pedalling and will design accordingly.

If you fitted an engine to a mountain bike, the bike may squat but as the power is constant you would not see bob. Plus the fact if you're providing the power to make you go forward you want to be as efficient as you can, if Yamaha is providing the power who cares!!

no idea what your roller analogy is about!

I'm unlikely to ever get the chance to ride an early Cannondale, what's the problem with them ?

Imagine a drag bike doing a static burn out, so weight transfer due to acceleration doesn't come in to it.
The suspension is designed for a total combined weight of bike and rider of 300kg.
The engine is putting out over 100hp to overcome the friction of the tyre and spin the back wheel.
The suspension will squat a little bit due to the tension on the top run of the chain.

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.
The suspension is designed for a total combined weight of bike and rider of 100kg.
The "engine" is putting out 1hp to drive the bike forwards.
Are you really saying that 1/100th of the power through a suspension system that is designed for 1/3rd of the weight will be noticeable ?

The rail travels vertically on the left hand side of your screen. There is a roller on it which is free to move up and down, almost frictionless if you will and it is in the middle of the rail.

Now a piece of string is attached to the roller and you bring it out to the middle of the right hand side of your screen and pull really hard, the roller doesn't move. Now relax for a minute, move your hand and string to the top right of the screen and pull, the roller will start to move up the rail.

I [s]think[/s] hope that might help!

A static burn out.

No cyclist could ever spin a tyre that wide on dry tarmac, therefore the bike is putting far more tension on the top run of the chain than any bicycle suspension is designed to deal with.
It's a simple single pivot swinging arm.
It's not squatting.

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...