How Suspension Reacts

[The Stranger]

We all know that under acceleration the front of a bike tends to lift and the front suspension unloads to some degree, possibly to the point where it is completely unloaded and the bike wheel stands.

What happens to the rear suspension during acceleration?

[Quasievil]

We all know that under acceleration the front of a bike tends to lift and the front suspension unloads to some degree, possibly to the point where it is completely unloaded and the bike wheel stands.

What happens to the rear suspension during acceleration?

It compresses, yeah ?

[DEATH_INC.]

Actually,no.The chain actually pushes the suspension down (extends it),it tries to shorten itself as much as possible,pulling the top of the sproket down.You do get a certain amount of compression from weight transfer though.

[The Stranger]

Don't know for sure.
On the one hand you tend to think there is now a rearward weight bias and therefore the rear suspension will compress, but does it?

I believe the front tries to lift because the front sprocket is providing lift via tension on the top of the chain which is anchored to the rear sprocket.

If so then the lift is being provided at about the centre of the mass and wouldn't this lift tend unload the rear suspension also?

Sure there is weight transfer front to rear and there is a relative difference in heights front to rear, but that would not necessarily preclude the rear from rising too.

Where am I going with this?

Well I see some prominent riders claiming that a bike gets taller under acceleration (front and rear) and thus you get increased ground clearance say when accelerating around a bend. Some also claim that this a big problem when taking a bend with a trailing throttle, as the opposite happens.

Now they don't state why the bike get taller and I have seen no evidence of this, but I like to know for sure and I was hoping someone may have video footage which could clarify this matter.

[T.W.R]

Actually,no.The chain actually pushes the suspension down (extends it),it tries to shorten itself as much as possible,pulling the top of the sproket down.You do get a certain amount of compression from weight transfer though.

have a wee re-think about that!

Under initial acceleration the chain is drawing (pulling) the rear sprocket towards the drive sprocket & as the swing-arm travels in arc & with suspension length etc & the rigid length of the swing-arm results in the compression.
The swing-arm actually sits slightly below the upward stroke of the arc in normal motion due to the direction of chain rotation, so under acceleration the swing-arm is drawn further up the arc thus compressing the suspension further ( thats why numerous motorcycle tests comment on the tested bikes sitting under acceleration) & why more powerful bikes will loft the front wheel under hard acceleration ( because the rear wheel is being pulled towards the front-end) its only once an equalibrium has been reached that the bike will level out & release the increased load on the suspension.

The only occassions were a bike will rise under acceleration is with the older style shaft drive bikes, this is why BMW designed the PARA-LEVER system to overcome the torque loading on the drive-train.

this is why any vehicle squats under accleration & lifts the front end (e.g dragsters etc)

[TwoSeven]

We all know that under acceleration the front of a bike tends to lift and the front suspension unloads to some degree, possibly to the point where it is completely unloaded and the bike wheel stands.

What happens to the rear suspension during acceleration?

It extends.

[SlowHand]

do a burnout. See what happens - but dont ask me how it works

[Hoon]

this is why any vehicle squats under accleration & lifts the front end (e.g dragsters etc)

But vehicles aren't chain driven are they?

Both are right.

Chain pulling on the sprocket causes the rear to extend.
Weight shifting to the rear causes the rear to compress.

Usually compression is the greater of the two so the other goes unnoticed but rear extension due to chain pull is real, thats what adjustable swingarm pivots are for.....to change the angle between the front and rear sprocket.

[The Stranger]

do a burnout. See what happens - but dont ask me how it works

No good, as so much resistance is lost when the wheel breaks traction.

[dhunt]

Twist of the wrist states


Most riders don't understand this simple fact: The harder they twist the gas, the less compiant the rear suspension is and the more the rear end tries to <B>rise</B>. Most riders believe that the back of the bike goes down they accelerate. It doesn't. (To test this, put the front wheel of your bike up against a wall and begin to engage the clutch with the transmiision in ger. The rear end will come up.)

"Whacking" the throttle on stiffens the rear suspension and reduces traction. That's a problem for most of us. Yet the best riders have figured out a way to completetly reverse the situation and use it to teheir advantage. In the case of a 500cc GP bike, when the power starts to come on and the suspension stiffens, the tire tends to spin because tractions is reduced. What do the best riders do? They let the tire start to spin for the drive out of the turn. The suspension actually becomes more compliant right when the tire begins to spin, because the reduced traction relieves some of the load. ...

[T.W.R]

do a burnout. See what happens - but dont ask me how it works

whats the first thing you do when doing a burn-out ? handful of front brake! so the arse-end is trying to push everything forward thats why the you get the rise in the rear!

[The Stranger]

That may appear to be the end of it, but, does anyone have proof?
Say a video.

Placing your front wheel against a stop may induce a false result as the rear wheel would tend to push swing arm up when it can not push the front wheel forward, so I don't believe that that is a valid comparison to real world riding.

[TwoSeven]

That may appear to be the end of it, but, does anyone have proof?
Say a video.

Placing your front wheel against a stop may induce a false result as the rear wheel would tend to push swing arm up when it can not push the front wheel forward, so I don't believe that that is a valid comparison to real world riding.

Put a data logger on your suspension and look at the pics. I had an example diagram years back, should be some around if you use google.

Generally the bike tries to climb the sprocket which extends the rear on accel.

[Hoon]

That may appear to be the end of it, but, does anyone have proof?
Say a video.

Watch any racing footage when a rider exits a turn and is hard on the gas. The rear is almost topping out.

[NordieBoy]

If it extends under load it's a bad design.

The turning motion of the rear wheel works to push the swingarm down (1) against the effort of the spring - loads the suspension up.
When the spring matches that effort then the rotational motion it translated to forward motion (2) and the spring unloads to an extent as there is less rotational force on it as it has overcome the inertia of the lardarse and bike.

Or something...

[TwoSeven]

Try examining it from the front sprocket in relation to the seat.

[T.W.R]

When a motorcycle is in motion and accelerated hard the initial reaction of the of the drive-train is compression then expansion (load transfer), the initial power delivered by the drive shaft upon then sprockets makes them contract towards each other, then as the power is transfered into momentum the expansion happens (the only reason that it looks as if theres just extension of the suspension is that it happens so fast, only the result is truely noticeable).
Its simply a pull push effect, the engine pulls the wheel towards it and the energy is transfered to the tyre which is pushing upon the ground & when in motion that push effect rises the whole motorcycle.

Check the attachment (even though the bike in it is a turbo powered V-MAX) watch closely at the first couple of meters, the bike is squating down until it gains full traction then once that happens it appears to rise)

[T.W.R]

[QUOTE=Hoon]But vehicles aren't chain driven are they?

factoid: maybe not in this day and age, but all the first cars and other assorted forms of transport were chain drive!

it doesn't matter whether its chain driven or shaft driven the transfer of energy has the same effect

[TwoSeven]

What if I was to say that the swingarm piviot point is above the axle would that make a difference. Would it be that the wheel base would shorten and the rear ride height increase, buggering up rake and trail and cornering ability.

You'd need to keep messing with the chain angle and pivot points and rebound in order to ensure the rear doesnt climb to quickly. Almost like an anti-squat system if one existed.

Have a look at the history of the swingarm on the R1 and see what I mean.

:)

[Brian d marge]

look would you lot stop posting interesting threads ...I am at work at must at least look like i AM WORKING ...

Actually ,,This one messess my head up ...I know what it does cos all the books tell me it does ,,,but my head goes all in circles and me brain gives up the ghost on this one ....

I have a computer prrgram that does all this sort of stuff when I gwet home Ill see if I can post anything worth while


Stephen

[HDTboy]

Look at your bike from the right hand side. As the bike accelerates with traction the wheel will turn clockwise in relation to the swingarm. The more torque the wheel can apply to the swingarm, the more the swingarm will try to rotate anticlockwise; Lifting the bike

[erik]

Interesting thread indeed.

I tried thinking about it, couldn't figure it out. It's bloody complicated.

the tension in the chain will try to make the swingarm rotate up towards the rear seat.
But this might be balanced by the force due to acceleration if it passes below the swingarm pivot. But it's hard to tell which force would be stronger, and it all varies with how fast the bike accelerates.

:wacko:

[TwoSeven]

The basic principle is that the chain pulls the wheel forward. Because the swingarm piviot is above the wheel axle height it pushes the swingarm piviot up and forwards which forces the suspension to extend. Think if it as trying to break the bike apart

[Draco]

have a wee re-think about that!

Under initial acceleration the chain is drawing (pulling) the rear sprocket towards the drive sprocket & as the swing-arm travels in arc & with suspension length etc & the rigid length of the swing-arm results in the compression.
The swing-arm actually sits slightly below the upward stroke of the arc in normal motion due to the direction of chain rotation, so under acceleration the swing-arm is drawn further up the arc thus compressing the suspension further ( thats why numerous motorcycle tests comment on the tested bikes sitting under acceleration) & why more powerful bikes will loft the front wheel under hard acceleration ( because the rear wheel is being pulled towards the front-end) its only once an equalibrium has been reached that the bike will level out & release the increased load on the suspension.

The only occassions were a bike will rise under acceleration is with the older style shaft drive bikes, this is why BMW designed the PARA-LEVER system to overcome the torque loading on the drive-train.

this is why any vehicle squats under accleration & lifts the front end (e.g dragsters etc)
No,you're wrong.The top of the rear sprocket is above the top of the front sprocket generally so it pulls the arm down,not up.Plus the bottom of the rear wheel where the drive force is transmitted is well below the swingarm pivot so it'll try to drive underneath,again causing extension.
As a side note,a well setup dragger will also extend under acceleration as do any well setup 4 bar circuit cars etc.Ever watched a sprinter sit up and down under acceleration/decceleration?
Death.(on draco's pooter.)

[erik]

The basic principle is that the chain pulls the wheel forward. Because the swingarm piviot is above the wheel axle height it pushes the swingarm piviot up and forwards which forces the suspension to extend. Think if it as trying to break the bike apart


But the chain passes above the swingarm pivot (at least it does on my bike) so it will pull the swingarm up, toward the mudguard etc.
But because the distance of the chain from the swingarm pivot is small, the torque created is small.
By the sounds of what Death's said, I'd guess the force from acceleration passing below the wingarm pivot makes the bike stand up.

But it would depend on the location of the swingarm pivot and the bike's centre of mass (and how hard the bike was accelerating).

I can't see any way other than the acceleration force passing below the swingarm pivot that would make the rear of the bike raise.

[TwoSeven]

But the chain passes above the swingarm pivot (at least it does on my bike) so it will pull the swingarm up, toward the mudguard etc.
But because the distance of the chain from the swingarm pivot is small, the torque created is small.
By the sounds of what Death's said, I'd guess the force from acceleration passing below the wingarm pivot makes the bike stand up.

But it would depend on the location of the swingarm pivot and the bike's centre of mass (and how hard the bike was accelerating).

I can't see any way other than the acceleration force passing below the swingarm pivot that would make the rear of the bike raise.

The Chain Run passes above the swingarm piviot but the force [well most of it] travels along the swingarm.

The chain run angle is slightly different from the swingarm angle which must be positive. The force if neutral would run from a line drawn from the rear axle to the front axle, but because the piviot is higher than this plane, it gets pushed up as the back wheel gets pulled towards the front.

[erik]

The Chain Run passes above the swingarm piviot but the force [well most of it] travels along the swingarm.

The chain run angle is slightly different from the swingarm angle which must be positive. The force if neutral would run from a line drawn from the rear axle to the front axle, but because the piviot is higher than this plane, it gets pushed up as the back wheel gets pulled towards the front.
In other words:
The force to accelerate the bike is all transmitted through the swingarm.
Because the swingarm is pivoted at both ends, it can only transmit force along it's axis, it can't transmit torque at the pivot (ignoring suspension here).
Because the innertia force (reaction resisting acceleration) of the bike and rider acts below the swingarm pivot, it tends to rotate the body of the bike downwards about the swingarm pivot (clockwise if bike is viewed from right side).
And since the weight has all transferred to the rear wheel, the front of the bike rises as the forks don't have so much weight on them.
In effect this makes the rear of the bike raise up and the swingarm rotate anticlockwise if viewed from the right.

The above can be more easily visualised if you imagine the swingarm at an exaggerated angle.
In the attached pic (sorry for the drawing quality ;) )
If the bike had the blue swingarm, it's fairly easy to imagine that the wheel would try to ride under the bike and the bike would kind of fold like scissors about the swingarm pivot, making the swingarm pivot raise.

But with the red swingarm, the innertia force acting from the bike's centre of mass passes way above the pivot, and it's reasonably easy to see the pivot would move down, the bike would fold in the opposite direction to before.

However, in both cases, if the front sprocket was moved with the swingarm pivot so that the chain passed above and below the pivot, the effect of the tension in the chain would try to rotate the swingarm around clockwise (relative to the body of the bike). This is easier to visualise if you imagine the rear sprocket fixed to the swingarm (ie, can't rotate around the rear axle). See pic 2.

[TwoSeven]

If I read that correctly, then yep, thats about right as I see it :) :)


Edit:
I take it your really good at math then. Having never done math, I have to draw lots of pictures and then spend days thinking about it. Would have never picked up the front end rotating bit.

[GeorgeR]

You can't assume that the sprocket is fixed to the swingarm - that allows torque to be transmitted into the swingarm which as you said is impossible.

Google makes things much easier to explain - no need to draw my own diagrams...
http://www.tootechracing.com/Engine%20torque%20-%20Suspension.htm

[NordieBoy]

You can't assume that the sprocket is fixed to the swingarm - that allows torque to be transmitted into the swingarm which as you said is impossible.

Google makes things much easier to explain - no need to draw my own diagrams...
http://www.tootechracing.com/Engine%20torque%20-%20Suspension.htm

On the MotoCycz the front sprocket is on the swingarm pivot.

Taken to an extreme is my Cannondale V3000.
The front sprocket is so far below the swingarm pivot that any engine/leg motion is first translated to rear suspension extension and then to forward motion as less energy is needed to extend the rear than propel forward.
Every time you push the pedals you first go up - then forward.

[Hoon]

it doesn't matter whether its chain driven or shaft driven the transfer of energy has the same effect

No it doesn't. Chain pull is totally seperate force of its own and very different to a rotating driveshaft which is at a 90 degree plane.

Heres another explanation from one of my fav reference books Sportsbike Performance Handbook (http://www.amazon.com/exec/obidos/tg/detail/-/0760302294/103-5897245-2512622?v=glance).



A Useful Semi-secret About Rear Suspension

Many riders and tuners don't know it, but when a chain-driven bike accelerates, chain forces try to extend its rear suspension. We are used to cars, which dip at the front under braking, and squat at the back under acceleration. We assume bikes squat the same way but they don't. The tension in the drive chain, acting at a slight angle to the plane of the swingarm, exerts a downward force that tends to extend the suspension. Chain force is greater in lower gears, and the lift it generates can equal or exceed the bike's normal tendency to squat under acceleration. Go and watch bikes coming off a first-gear turn, and see them lift or even top out their rear suspension as they hit second gear. Or watch a bike on a Dynojet dyno, rising at the rear as its power comes on.
The existence of this chain "tangent force" is the reason for all the current interest in adjustable swingarm pivot height for Superbikes. Chain lift force is determined by the angle between the taut upper chain run and the swingarm. The bigger the angle, the greater the lift force that will oppose squat. Raising the pivot height increases the lift force, and lowering it reduces it. Even changing rear sprockets can change this lift force somewhat, by changing the angle of the top run of the chain to the plane of the swingarm.


It then goes on about how to use this effect to go faster but you'll all have to buy the book if you want to know more!

[Brian d marge]

You can't assume that the sprocket is fixed to the swingarm - that allows torque to be transmitted into the swingarm which as you said is impossible.

Google makes things much easier to explain - no need to draw my own diagrams...
http://www.tootechracing.com/Engine%20torque%20-%20Suspension.htm

Thats a good one ,,See that was exactly what I was going to say !!! NOT ,,I will sit down with that later ..and digest it .....
I know it happens its just my brain wont let me get it clear enough for a simpleton like me to explain it / and if I can explain it I understand it ,,,,

one hopes !!!

Stephen

[erik]

You can't assume that the sprocket is fixed to the swingarm - that allows torque to be transmitted into the swingarm which as you said is impossible.

Google makes things much easier to explain - no need to draw my own diagrams...
http://www.tootechracing.com/Engine%20torque%20-%20Suspension.htm
The link doesn't work for me :(

Treating the sprocket as fixed to the swingarm is ok, as far as I can tell. All it does is stop you having to worry about what the road and wheel are doing.
When the wheel is turning, the tension in the chain has the same effect.
Say the rear sprocket was fixed to the swingarm, now because the chain passes slightly above the swingarm pivot, and because the front sprocket is in front of the pivot, if the swingarm rotates up, the distance between the top edge of the rear sprocket and the top edge of the front sprocket will reduce slightly, releasing the tension in the chain. This is what I mean about the chain tension making the swingarm want to rotate up.




A Useful Semi-secret About Rear Suspension

Many riders and tuners don't know it, but when a chain-driven bike accelerates, chain forces try to extend its rear suspension. We are used to cars, which dip at the front under braking, and squat at the back under acceleration. We assume bikes squat the same way but they don't. The tension in the drive chain, acting at a slight angle to the plane of the swingarm, exerts a downward force that tends to extend the suspension. Chain force is greater in lower gears, and the lift it generates can equal or exceed the bike's normal tendency to squat under acceleration. Go and watch bikes coming off a first-gear turn, and see them lift or even top out their rear suspension as they hit second gear. Or watch a bike on a Dynojet dyno, rising at the rear as its power comes on.
The existence of this chain "tangent force" is the reason for all the current interest in adjustable swingarm pivot height for Superbikes. Chain lift force is determined by the angle between the taut upper chain run and the swingarm. The bigger the angle, the greater the lift force that will oppose squat. Raising the pivot height increases the lift force, and lowering it reduces it. Even changing rear sprockets can change this lift force somewhat, by changing the angle of the top run of the chain to the plane of the swingarm.

If I may be so bold... I think he's got it wrong.

As I understand it:

The chain doesn't provide a lift force. The chain, like I described earlier, provides a torque that tends to rotate the swingarm up. The strength of the torque is determined by the tension in the chain and the distance the tight side of the chain passes above the swingarm pivot.
It is correct that raising the pivot point will make the rear of the bike stand up more on acceleration, but this is not because it increases the "lift force".
By raising the swingarm pivot, the distance between the tight side of the chain and the pivot is decreased, and this has the effect of reducing the turning moment that tries to rotate the swingarm up (turning moment is equal to the "chain tension" x "chain distance from pivot"). By reducing this turning moment, there is less resistance to the bike standing up on acceleration.
The reason why the bike stands up is because the innertia force resisting the acceleration passes below the swingarm pivot, hence the rear wheel tries to "walk under the bike". When the bike is on a dyno, the rear raises because the swingarm pivot is above the rear wheel axle, again making the rear wheel want to move under the bike.

Anyway, that's how I understand it.

I checked and it turns out they've got Sportbike Performance Handbook at the waitakere libraries, I'll have to get it out some time, it looks interesting.

[XP@]

Interesting question CaN :)

This guy has a few interesting ideas on the subject
http://www.tonyfoale.com/Articles/index.htm

From what I have been taught the rear does lift... why never been told that but how about this theory hot from the left field...

First pose the question what drives a bike? answer the back wheel.
So the back wheel is pushig the front. It is trying to catch up the front wheel, but is not succeeding because the frame is in the way. So something has to give, this is the swing arm.

If you go in to a corner with a steady throttle you will come out slower than when you entered the corner this is because friction has used mostly be the front wheel to help you turn and thus reduced your speed. To stop this happening we apply more throttle through and out of the corner, increasing the speed of the rear wheel. This makes the rear try and catch up the front and hey, presto the swingarm lifts.

I would suspect the best place to see this would be on a dirt bike setting off.

[Hoon]

The chain doesn't provide a lift force. The chain, like I described earlier, provides a torque that tends to rotate the swingarm up.

Are you assuming for a bike which has the rear sprocket higher than the front?? Then yes it would but sportsbikes rear sprockets (top edge) are lower than the front so it would pull down.


Treating the sprocket as fixed to the swingarm is ok, as far as I can tell.

This ignores another force of the chain pulling against the circumference of the rear sprocket. The chain has more contact with the upper half of the sprocket than it does with the lower half due to chain slack and centrifugal force (see pic). This net total results in another source of slight downward force.

The explanation in that book is by no means complete but it tells you all you really need to know in laymans terms i.e. what goes in (chain pull) and what comes out (downward force) without dwelling over what happens in the middle. The target reader is a rider/mechanic, not a physics student so has no real desire to analyse and breakdown each of the indivudual forces at work, only the net output.

[erik]

Are you assuming for a bike which has the rear sprocket higher than the front?? Then yes it would but sportsbikes rear sprockets (top edge) are lower than the front so it would pull down.

No, I'm not assuming the rear sprocket is higher than the front. The critical things that determine whether the swingarm tries to rotate up or down are the pulling force in the chain and the distance (measured at 90° to the chain) that the chain passes the swingarm pivot. Take a look at the attached drawing. In the top sketch, it's easy to see that the chain will pull the swingarm up. This is due to the turning moment about the swingarm pivot which is equal to the chain pull x radius R (measured tangentially from the chain to the pivot).
Next pic down, say the chain pull F is the same, but the radius is decreased. As the moment M = F x R, the moment is also smaller because R is smaller.
The third pic down is close to what a normal bike layout is. R is small, but still there, therefore there still exists a turning moment trying to rotate the swingarm up.

If the chain were to pass directly through the pivot point, R would be zero, and therefore the moment M would be zero.
The last pic shows that if the chain passed below the pivot, the moment would be reversed and try to turn the swingarm in the opposite direction.



This ignores another force of the chain pulling against the circumference of the rear sprocket. The chain has more contact with the upper half of the sprocket than it does with the lower half due to chain slack and centrifugal force (see pic). This net total results in another source of slight downward force.
I can't think how to prove it, but I'm pretty sure the only significant force the chain can apply to the sprocket is pulling on it tangentially (ie making the sprocket want to rotate about its centre). I might ask a lecturer about that.


The explanation in that book is by no means complete but it tells you all you really need to know in laymans terms i.e. what goes in (chain pull) and what comes out (downward force) without dwelling over what happens in the middle. The target reader is a rider/mechanic, not a physics student so has no real desire to analyse and breakdown each of the indivudual forces at work, only the net output.
I'll agree that he's got the relationship between accelerating and the rear of the bike raising correct, and also the effect of raising the swingarm pivot, that raising it will make the rear of the bike raise more on acceleration.

I guess that if you don't mind having an incorrect understanding of the mechanics behind it, then it's enough to just know that accelerating makes the rear stand up and that raising the pivot will increase this effect.

Still it would be better if he had the mechanics correct, even if he didn't go into detail proving them.

For me, I'm studying mechanical engineering and learning to work on my bike, so understanding this kind of stuff as well as I can is one of my goals in life. :niceone:

[Hoon]

No, I'm not assuming the rear sprocket is higher than the front. The critical things that determine whether the swingarm tries to rotate up or down are the pulling force in the chain and the distance....

The reason I ask is that I'm not disputing your logic which is sound so I suspect we may be talking about two different models here? My interpretation of how a swingarm works is closer to your 4th pic where the chain is pulling at a more downward angle to that of the swingarm due to the offset of the pivot and front sprocket i.e. the centreline of the two sprockets is below the pivot of the swingarm. Does this change things in any way?

[TwoSeven]

I usually find that when there is a thing that can be observed/measured in engineering/physics there ends up being a sinle word or phrase thats used to describe the phenomina. In this case we are talking about suspension extension, so I guess there should be a unique engineering term to try and describe it.

From my perspective I use design to try and improve how to ride in that understanding how something works allows me to develop and test riding theories for improved performance. In this respect, understanding how the machines traction and steering geometry changes under acceleration allows me to use rebound and throttle control for example to control accerlation more precisely (starts and corner exits), as well as how to use the front setup in tandem with the rear to control corner entry and mid corner control.

The other aspect is I can work out ways on how to improve shite bits of the bike that the original designers have done for cheapness purposes.

[erik]

The reason I ask is that I'm not disputing your logic which is sound so I suspect we may be talking about two different models here? My interpretation of how a swingarm works is closer to your 4th pic where the chain is pulling at a more downward angle to that of the swingarm due to the offset of the pivot and front sprocket i.e. the centreline of the two sprockets is below the pivot of the swingarm. Does this change things in any way?

I need a smilie with a cheesy grin here.

I think my fault was in imagining the sprocket fixed to the swingarm.

Take a look at the two attached pics. The first one is based on your dimensions, the second one on a photo of a zx10.

I think I should have considered the fact that the chain and sprocket are moving (as was suggested). Assuming that the chain is in constant tension which pulls tangentially from one sprocket to the other, when the swingarm moves down, the tangential distance between the sprockets decreases (as shown in the pictures). Therefore, the chain tension will try to make the swingarm move down to relieve the tension.

In my original idea, if the rear sprocket was fixed, moving the swingarm down would increase the tension, which is opposite to the above.

Assuming I've got the reasoning right this time, I stand corrected.

[edit]
maybe the third sketch is an easier way to see what's happening.

[cowpoos]

its not worth arguing about...because the facts have been stated....rear will lift under accereration....the only exception is when the axle is 5 degrees + higher than swingarm pivot....its to do with tractive force's...the chain is simply trying to shorten its self....and the wheel and rear sproket are causing a tractive resistance....so the the front sproket is trying to pull....the rear + the wheel is resisting...so the side effect force is the chain gets pulled incredibly tight....which starts to pull the swing arm down...causes bike to rise...if the rear wheel starts to spin alot of the force that causes this effect is lost in the spin....so there is the potentail to get a better drive if a small amount of spins is induced....

[Motu]

Oh dear,it's so simple it's hard eh? And the sportsbike expert got it wrong of course - my Pajero lifts the rear under acceleration,and not all cars nose dive under braking,like the Peugeot 306 I drove last week - it's all about geometry and how they set them up...each case is seperate - you need to be Rolf Harris to paint with a 6in brush....

[erik]

its not worth arguing about...because the facts have been stated....rear will lift under accereration....
Well, for me it was worth arguing/discussing because it's helped me understand things better.
If we didn't argue and instead just accepted the facts without really understanding them, it'd be like religion... :whistle:

[cowpoos]

Well, for me it was worth arguing/discussing because it's helped me understand things better.
If we didn't argue and instead just accepted the facts without really understanding them, it'd be like religion... :whistle:


true brother very true.....:2thumbsup

my bad