just wondering what the advantages/disadvantages/purpose of the vpp on the santa cruz v10, or any bike for that matter. does it make for a more progressive shock feel? better race bike? braking under load?
Virtual pivot point??
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Lurch..
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from what i can tell ( i aint no suspension expert) it provides better pedaling because when the suspension moves through its travel the chainstay length doesnt change?? i think. ask kyle or konadude as they know HEAPS about this sorta thing.
since I don't have a great deal of time today, I will make this explanation as brief as possible.
A VPP (virtual pivot point), is exactly that. the rear axle of a FS bike travels in an arc around a pivot point. On a single pivot bike this is clear and obvious, it rotates around the swingarm's mount.
Every time you exert force on the pedals, the tension in the chain attempts to draw the axle forward, if this pivot point is significantly HIGHER than the the chain, the swingarm will descend, "jacking" up the bike as the torque is applied. This "jacking" effect stiffens the rear, as well as altering the bikes geometery, and if it is severe, it will result in bumps being loaded up the chain and into the rider.
Now if the pivot is significantly LOWER than the line of tension from the chain, the swingarm will pivot upwards, compressing the rear shock and "sagging" the back of the bike.
As you can guess both of these scenarios result in a bike that does NOT perform well over bumps while the rider is pedalling.
To alieviate this problem designers try to place the pivot in the most neutral position possible..
BUt this is sometimes impossible to achieve since there are other things (cranks, bottom bracket) interfering with the IDEAL placement of the pivot.
SO to engineer themselves AROUND this limitation, they add a series of pivots, which form a parrallelogram of sorts. This allows them to actually make the rear axle rotate around a point that is not ACTUALLY a physical pivot location, hence the "virtual" pivot.
And since they can adjust the location of this VPP, they can place is directly in the "ideal" location. Resulting in a rear suspension that is NOT acted upon by the tension of the chain, and therefore free to travel normally whether the rider is pedalling or not.
NOW, before any body jumps to correct me, I assure you that this is the most basic of explanations, as there are far more factors (brake torque, cog size selection etc.) that will make up a determining factor for pivot point selection.
The main advantage of "riding" a VPP bike is that you will feel much less energy exerted when pedalling it compared to a physical pivot point bike.
as with everything, if you would like a more complete explanation please PM me and I will try to make some time.
I hope that helped.
A VPP (virtual pivot point), is exactly that. the rear axle of a FS bike travels in an arc around a pivot point. On a single pivot bike this is clear and obvious, it rotates around the swingarm's mount.
Every time you exert force on the pedals, the tension in the chain attempts to draw the axle forward, if this pivot point is significantly HIGHER than the the chain, the swingarm will descend, "jacking" up the bike as the torque is applied. This "jacking" effect stiffens the rear, as well as altering the bikes geometery, and if it is severe, it will result in bumps being loaded up the chain and into the rider.
Now if the pivot is significantly LOWER than the line of tension from the chain, the swingarm will pivot upwards, compressing the rear shock and "sagging" the back of the bike.
As you can guess both of these scenarios result in a bike that does NOT perform well over bumps while the rider is pedalling.
To alieviate this problem designers try to place the pivot in the most neutral position possible..
BUt this is sometimes impossible to achieve since there are other things (cranks, bottom bracket) interfering with the IDEAL placement of the pivot.
SO to engineer themselves AROUND this limitation, they add a series of pivots, which form a parrallelogram of sorts. This allows them to actually make the rear axle rotate around a point that is not ACTUALLY a physical pivot location, hence the "virtual" pivot.
And since they can adjust the location of this VPP, they can place is directly in the "ideal" location. Resulting in a rear suspension that is NOT acted upon by the tension of the chain, and therefore free to travel normally whether the rider is pedalling or not.
NOW, before any body jumps to correct me, I assure you that this is the most basic of explanations, as there are far more factors (brake torque, cog size selection etc.) that will make up a determining factor for pivot point selection.
The main advantage of "riding" a VPP bike is that you will feel much less energy exerted when pedalling it compared to a physical pivot point bike.
as with everything, if you would like a more complete explanation please PM me and I will try to make some time.
I hope that helped.
The simplest answer, as it applies to the current crop of VPP bikes, is that the initial part of travel acts as if it pivots around a point somewear behind the rear axle. That is if you're looking at the bike from the drivetrain side, the axle path traces out a subtle S-shape, so that for the first 1/2 or 2/3 of travel, chain tension pulls the suspension into the "belly" of the S.
This means that while you're sprinting the suspension tries to stay about 1/3 into it's travel. It will compress to that point if the suspension extends, and it will extend back to that point if the suspension is compressed(note: those proportions are just for example)
I hope that makes sense.
This means that while you're sprinting the suspension tries to stay about 1/3 into it's travel. It will compress to that point if the suspension extends, and it will extend back to that point if the suspension is compressed(note: those proportions are just for example)
I hope that makes sense.
Ohio is 100% right on. The chain tension keeps the rear wheel in the shortest chainstay position (the "belly" of the S). I call it a "torque sensitive" suspension system. It's a clever system, but it has its downsides too.
I won't say anything 'till more people ride them and give their feedback.
Actually, your pivot point. or "virtual pivot point" can be below the imaginary projection of the chainline and still have extension. Your analysis is assuming that the rear wheel is locked to the swingarm, which is not truly the case. Draw a free body diagram of the system and it will make it easier for you to understand what I am saying.
The VPP bikes most certainly are affected by chain torque, and the ARE affected by the tension of the chain, not necessarily a bad thing.
In the simplest terms, the VPP bikes attempt to put this "Virtual Pivot Point" at an infinite distance from the center of the rear axle at the "preferred pedaling point". As with any design, there is a compromise with this, but it works very well. The design as governed by the Outland Design Patents holds great promise if executed correctly.
Feel free to contact me offline if you would like me to explain any more, constructing a *correct* free body diagram will go a long way to helping you understand all this jazz
dw
re read my post you will see in the section you are refering to (extension or compression of the rear susp.) you will NOTE that I am INDEED talking about single pivot designs, and NOT VPPs at in that text.
and I stated "significantly below the chain's prjected line of tension".
and unfortunately using an "infinite" distance as a reference point for the "arc" is quite impossible.
Now, NO I am NOT a mechanical engineer, and NEVER claim to be, and NO, I am NOT a specialist in the design and engineering of bicycles, but I have a fairly large amount of experience in suspensions relating to other things..
(and NO I am not some self serving ignorant buffoon who does not believe he can still learn every day! )
and I stated "significantly below the chain's prjected line of tension".
and unfortunately using an "infinite" distance as a reference point for the "arc" is quite impossible.
Now, NO I am NOT a mechanical engineer, and NEVER claim to be, and NO, I am NOT a specialist in the design and engineering of bicycles, but I have a fairly large amount of experience in suspensions relating to other things..
(and NO I am not some self serving ignorant buffoon who does not believe he can still learn every day!
)I'm sure youre a damn smart guy! The "significantly" part didnt register with me there, sorry about that!Originally posted by shootr
re read my post you will see in the section you are refering to (extension or compression of the rear susp.) you will NOTE that I am INDEED talking about single pivot designs, and NOT VPPs at in that text.
and I stated "significantly below the chain's prjected line of tension".
and unfortunately using an "infinite" distance as a reference point for the "arc" is quite impossible.
Now, NO I am NOT a mechanical engineer, and NEVER claim to be, and NO, I am NOT a specialist in the design and engineering of bicycles, but I have a fairly large amount of experience in suspensions relating to other things..
(and NO I am not some self serving ignorant buffoon who does not believe he can still learn every day!
Its just that I happen to be a Mech, and a bike suspension specialist, bla bla And I learn new stuff every day too man! If I stop learning, theres a problem, right? (i would guess that problem might be death in my case? 
heh)the V10 and blur do however at one very tiny unmeasurably small point in the trave have an "infinite" pivot point. It is at the exact point where the arc turns from a rearward facing arc to a forward facing arc. At that tiny tiny point, the path has no cuvrvature. not impossible at all.
VPPs and single pivots react exactly the same in terms of their reaction to chain forces in relation to pivot point placement, its just that SOME linkage bikes have a significantly moving pivot point.
dw
doooooood, you got me all wrong..
I am not sitting here fuming, saying
"hey dat guy said I'z dumb, didja hear that Daryll?? Hes up an gone und said I'z dumb!!!, hand me mu rifle Daryll!! I'z gonna teach dat schoolerd fellar a lesson 'r two!!"
quote: It is at the exact point where the arc turns from a rearward facing arc to a forward facing arc. At that tiny tiny point, the path has no cuvrvature.
A point is just that a point, it is NOT a path, and ANY point in a path will show NO curvature, as it is only a POINT, and even when you select 2 points in a path, they will only show angle not curvature, only thru EVERY point in a path can curvature be displayed.
YOU are correct, but even at that transition point in the "s" curvature, there is actually NO rise in the rear axle (or conversly fall), it is merely a flat instant when the suspension reaches it's maximum forward point of movement, and the corresponding "arc" of travel flips.
(if we are going to get REALLY picky)
Physically it is IMPOSSIBLE for ANY manner of geometry where a point is controlled thru links NOT to prescribe some form of arc.(in relation to what the links are eventually fixed upon).
And by all means, construct as many *correct* free body diagrams in whatever suspension format you choose to illustrate that fact to yourself. <said with stupid sound of smug satisfaction>
I, am also a mechanic, and I do engineering, but I am NOT a mechanincal engineer, that is all I was saying, if you read ANY of my posts you will note disclaimers attached, as I am HIGHLY aware of the incomplete nature of most answers I post, but unfortunately I do not have the luxury of the time required to explain things fully, and I highly doubt that most people reading the threads would care to hear complete explanations.
<my little rant>
(no real smugness here, jsut the appearance of it)
I am not sitting here fuming, saying
"hey dat guy said I'z dumb, didja hear that Daryll?? Hes up an gone und said I'z dumb!!!, hand me mu rifle Daryll!! I'z gonna teach dat schoolerd fellar a lesson 'r two!!"
quote: It is at the exact point where the arc turns from a rearward facing arc to a forward facing arc. At that tiny tiny point, the path has no cuvrvature.
A point is just that a point, it is NOT a path, and ANY point in a path will show NO curvature, as it is only a POINT, and even when you select 2 points in a path, they will only show angle not curvature, only thru EVERY point in a path can curvature be displayed.
YOU are correct, but even at that transition point in the "s" curvature, there is actually NO rise in the rear axle (or conversly fall), it is merely a flat instant when the suspension reaches it's maximum forward point of movement, and the corresponding "arc" of travel flips.
(if we are going to get REALLY picky)
Physically it is IMPOSSIBLE for ANY manner of geometry where a point is controlled thru links NOT to prescribe some form of arc.(in relation to what the links are eventually fixed upon).
And by all means, construct as many *correct* free body diagrams in whatever suspension format you choose to illustrate that fact to yourself. <said with stupid sound of smug satisfaction>
I, am also a mechanic, and I do engineering, but I am NOT a mechanincal engineer, that is all I was saying, if you read ANY of my posts you will note disclaimers attached, as I am HIGHLY aware of the incomplete nature of most answers I post, but unfortunately I do not have the luxury of the time required to explain things fully, and I highly doubt that most people reading the threads would care to hear complete explanations.
<my little rant>
(no real smugness here, jsut the appearance of it)
Oh yeah, theres no doubt at all that the average of any three points on the axle path is going to allow for the fitment of some curvature that represents the path of a 4 bar linkage. Printed text which I have always assumed to be correct is very clear on that. We are crystal clear on that, and I'm not inferring in any way that there is any "path (the sum of a curvature fit to 3 or more points)" with an infinite focal point, thats impossible. Thats why I was very careful to say "point" . At the sum of points directly before and after this "preferred pedaling point" the measured focus of this curvature that we have fit to any three points will be extremely far ahead or behind the bicycle, kilometers away. The closer you resolve this point towards the "preferred pedaling point" the farther away you go to infinity. Yeah, we're splitting hairs, not really neccesary. read below-Originally posted by shootr
Physically it is IMPOSSIBLE for ANY manner of geometry where a point is controlled thru links NOT to prescribe some form of arc.(in relation to what the links are eventually fixed upon).
And by all means, construct as many *correct* free body diagrams in whatever suspension format you choose to illustrate that fact to yourself. <said with stupid sound of smug satisfaction>
Your statement above is correct, if you are talking about a PATH
But if you read, I am not. I am talking about a point, a POINT at which there is a transition of the focus of the averaged radius of the linkage path curvature. Although you cannot measure this POINT (at its at infinity and cant be measured) it does exist for an instant. (and my *correct* free body diagrams do in fact illustrate this fact to me) (BTW, the reason I put correct in ** is to say "this point may be debatable, as I did not write the kinematics and physics books, but i have a damn good understanding of them, and it makes a lot of sense to me and all of the other engineers that I have consulted with it, including men with many years more experiance than I. So I am pretty damn comfortable with my analysis)
Text on particle physics and kinematics illustrate this, I'm not making it up off the top of my head, and by god if its wrong, someone at the university and the publisher's has some splainin' to do!
I dont mind saying flat out that I am correct
, took a long time to get there.OK, so I *believe* you and I are on the same page here, nothing a face to face talk about it with a couple pencils or sticks and sand couldn't square up
. At least if we got bent at each other we could wail on each other with the sticks!! later man, it will be a pleasure to meet nd discuss someday.
dave
Originally posted by Toshi
You guys are obsessive. Rock on.
obsessive and compulsive id say
but thats just how id like my suspension engineers, right obi1 and ohio?
OBI-1, YOu rock, seriously, I am super impressed, I usually see some people posting cut-n-paste info about technical subjects that they don't really understand, and I try to pick them apart...
It is obvious that YOU definetily DO know your stuff.
I must say without reservation that you surely have a stronger grasp of this than myself, and I feel mildly humbled..
But truthfully and honestly I am NOT a Mech. Engineer, (though one never knows what the future may hold, as I hold Mech, Engineers in the highest regard).
Yes I AM obsessive Astral, and I kinda like me that way, as it always makes me question myself in the search for better understanding.
I have to say, of all the diff. sites and forums I post on, this particular forum (tech talk) is my most favorite, even more than efunda.
You guys ALL rock.
ps obi 1, you would probably kick my ass, I am like three apples high!!
It is obvious that YOU definetily DO know your stuff.
I must say without reservation that you surely have a stronger grasp of this than myself, and I feel mildly humbled..
But truthfully and honestly I am NOT a Mech. Engineer, (though one never knows what the future may hold, as I hold Mech, Engineers in the highest regard).
Yes I AM obsessive Astral, and I kinda like me that way, as it always makes me question myself in the search for better understanding.
I have to say, of all the diff. sites and forums I post on, this particular forum (tech talk) is my most favorite, even more than efunda.
You guys ALL rock.
ps obi 1, you would probably kick my ass, I am like three apples high!!
Dave and Shootr, what an interesting discussion. I think you guys are saying very similar things and pretty much agreeing.
I read and understood it all, and agree with what you say as well.
It's good to see an educated discussion like this once in awhile. It reminds me of the old days on Empty Beer.
I read and understood it all, and agree with what you say as well.
It's good to see an educated discussion like this once in awhile. It reminds me of the old days on Empty Beer.
AAAAARRRRRGH!!
Sorry Toshi, I guess that is a whole lot worse than being called "obsessive".....
Sorry Toshi, I guess that is a whole lot worse than being called "obsessive".....