Shock absorbers in handle bars?



Friar Broccoli said:
..when I was accelerating or pushing up hills a LOT of energy from the
forward thrust was being LOST (as heat I guess) as the front forks were compressed by my downward pedal thrust. ....Thinking about this, it occurred to me that I really don't want my shock absorbers between the frame and front wheel where they are now; but on top between the handle bars and the frame.

With the shocks somewhere in the handle bar assembly, no thrust
energy
would be lost to the shocks, and my hands and arms would
still be protected from vibration.

Well, no. Wherever there is flex there are also losses. As long as you have your hands on the handlebars it doesn't matter (much) whether it is the wheel or the bar that is moving in relation to the frame. Only energy advantages I can see would be:
a) riding with very little weight on the bar would make a sus bar assembly less lossy than a sus fork.
b) a sus bar would typically have less travel than a sus fork. With less travel there is less energy lost.


Friar Broccoli said:
The energy loss on acceleration is so obvious and so extreme
with wheel fork suspension that I would have expected some
mention of it in the FAQ. Any idea why it was not brought up?
What I can think of is that bike suspension has been around for quite awhile now, and ALL designs has (to some extent) difficulties in separating the motion of rider bobbing up and down through vigorous pedalling from the motion of bike bobbing up and down beneath the rider due to an uneven surface. It might very well be that by now this phenomenon is so well-known that it is assumed to be part of general knowledge rather than a suitable subject for a specific question.

I would recommend you to look for an air-sprung fork with lockout, with extra preference given to Marzocchi. Air-sprung will make it really easy to adjust the "spring rate" by varying the pressure, and (some) Marzocchis use a "soft-stop" lockout that doesn't turn the fork completely stiff but rather leaves you with maybe half inch or so of travel.
 
dabac wrote:
> Friar Broccoli Wrote:
>>
>> ..when I was accelerating or pushing up hills a LOT of energy from the
>> forward thrust was being LOST (as heat I guess) as the front forks were
>> compressed by my downward pedal thrust. ....Thinking about this, it
>> occurred to me that I really don't want my shock absorbers between the
>> frame and front wheel where they are now; but on top between the handle
>> bars and the frame.
>>
>> With the shocks somewhere in the handle bar assembly, *no thrust
>> energy* would be lost to the shocks, and my hands and arms would
>> still be protected from vibration.

>
> Well, no. Wherever there is flex there are also losses. As long as you
> have your hands on the handlebars it doesn't matter (much) whether it
> is the wheel or the bar that is moving in relation to the frame. Only
> energy advantages I can see would be:
> a) riding with very little weight on the bar would make a sus bar
> assembly less lossy than a sus fork.
> b) a sus bar would typically have less travel than a sus fork. With
> less travel there is less energy lost.



I certainly get things wrong from time to time, but I don't
believe that to be the case here.

I BELIEVE that the energy loss occurs (during acceleration)
when I shift my weight to push the pedal down. Much of that
shifting action, which would normally push the pedal down, and
thus the turn the wheel is instead absorbed by the front shock,
via the frame. That is:


Pedal (acceleration load) => frame => fork shock (resisted by wheel)
==> with energy lost as heat in spring.

As others have suggested, I can avoid this loss by pedalling
"smoothly" (avoiding dramatic CHANGES in my pedalling action)
but I find this is difficult and unnatural.

Since this extra pedal compression load is transferred thru the
frame to the shock, if the shock is free above the frame (as
with a suspension stem shock absorber), then the only way this
energy can be lost is if I push down on the handle bars with my
hands, while I am pushing on the pedal. Since there is no
reason for me to do such a thing, no energy loss will occur.

Have I missed something?

[remainder snipped]

Cordially

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------
 
Friar Broccoli said:
...I BELIEVE that the energy loss occurs (during acceleration)
when I shift my weight to push the pedal down.
Correct.
Friar Broccoli said:
Much of that
shifting action, which would normally push the pedal down, and
thus the turn the wheel is instead absorbed by the front shock,
via the frame.
Correct, but not the whole picture. As long as you're pushing/pulling ever so little on the handlebar you're not only putting power into the bike through the pedals, but also through the bar, stem and steerer tube. And for that loss it doesn't matter much if it's the stem or the fork that's doing the bobbing up and down.


Friar Broccoli said:
...the only way this
energy can be lost is if I push down on the handle bars with my
hands, while I am pushing on the pedal. Since there is no
reason for me to do such a thing, no energy loss will occur.

Doing deliberately and doing inadevertently are not necessarily the same thing. I repeat:As long as you're pushing/pulling ever so little on the handlebar you're not only putting power into the bike through the pedals, but also through the bar, stem and steerer tube. (ASO)
The only time when a sus stem would be completely lossless is when you're riding hands off, or with only a negligible amount of force in the grip. So, for some sort of "average" riding style the amount of loss is more determined through length of travel rather than where the travel occurs, particularly if you're standing up or leaning forward while pedalling (which tends to coincide with pulling harder on the bar).

A sus stem might be better suited(less lossy) for you, but that would be primarily due to travel length and perhaps damping characteristics rather than through a superior location of the moving element. (unless you're riding with only a token force on the bar)

Bottom line is that where there is flexing there are losses, and that on a bike the rider is very much a part of the machine, so in terms of efficency you really want the parts of the bike that you brace against when pedalling to be rigid. That you might want them to flex for comfort simultaneously is what the engineering challenge is all about.

On a 'bent the situation is different. The rider is primarily bracing against the backrest and pushing against the pedals. With less of a conflict between pedalling motion(~lengthwise push/pull) and sus motion (up/down) a sus setup on a 'bent can be less lossy than a sus setup on a upright.
 
dabac wrote:
> ...
> On a 'bent the situation is different. The rider is primarily bracing
> against the backrest and pushing against the pedals. With less of a
> conflict between pedalling motion(~lengthwise push/pull) and sus motion
> (up/down) a sus setup on a 'bent can be less lossy than a sus setup on a
> upright.


It is my experience that "pogo" while pedaling, especially while
climbing is a significant problem with some suspended recumbent
designs, e.g. <http://www.recumbent.com/blackbikee.jpg>.

If one puts a jack-shaft concentric with the suspension pivot, pedaling
related "pogo" can be practically eliminated, e.g.
<http://www.ihpva.org/incoming/2002/Dragonflyer/df5.jpg>.

--
Tom Sherman - Post Free or Die!
 
Friar Broccoli wrote:
> Hello world;
>
> I recently had a touring bike made for me.
>
> Since I am now 56 years old and running to fat I have for years
> added front wheel suspension (shocks), mostly to keep the
> vibration from wrecking my wrists which seems to be effective.
>
> The shocks my bike shop put on my new bike have a 3 inch travel
> (compared to about 1 inch before) and I noticed that when I was
> accelerating or pushing up hills a LOT of energy from the
> forward thrust was being LOST (as heat I guess) as the front
> forks were compressed by my downward pedal thrust. (Actually I
> don't know exactly how the energy was being transferred to the
> shocks, only that it was.)
>


Sounds like your pedaling action is messed up. I can't understand why
your fork is compressing when you're accelerating on the flat (are you
standing up?). Do you stand up to climb hills, because any fork
(without lock-out) is going to start pogoing and sapping effort if
you're not seated. If you're seated and powering away from the lights,
mashing through those pedals, your front fork should raise/uncompress,
unless you've got way too much weight resting on those bars.

As other folks have mentioned, if your folks are bobbing up and down
through their entire range of travel they may need some adjustment.
When you get on the bike do the forks sag at all, for 3inch travel
forks they should just barely move. Grab the front brake and try and
compress the folks completely, how much efort does it take? You
shouldn't be able to compress them completely by just pushing down.
When riding along on smooth pavement you should notice a small bob at
the fork, a few mm. Other wise they're too loose OR you've got too much
weight resting on your wrists.

A mate of mine in Houston who's now 60 and doesn't have back problems
got a set of padded (plus some extra foam too) tri-bars fitted to his
flat mtb bars, brought his seat forward by an inch and raised the
handle bar to about 2 inchs above his seat and says it's the most
comfortable position he's ever ridden in. Horses for courses, but he
says shifting his upper body weight from his wrists to his elbows has
really helped.

laters,

Marz
 
Johnny Sunset said:
...It is my experience that "pogo" while pedaling, especially while
climbing is a significant problem with some suspended recumbent
designs,...

Well, I didn't claim perfection, only less of a conflict :) But with such a geometry re. pivot point and chainline as in the first link you posted the interference between pedalling and suspension is obvious.

Weren't there full sus MTB frames with a similar design some years ago? I seem to remember some hype about "Our design stiffens the frame while pedalling instead of making it sag" or similar. They seem to be all gone now though.
 
dabac wrote:
> Johnny Sunset Wrote:
> >
> > ...It is my experience that "pogo" while pedaling, especially while
> > climbing is a significant problem with some suspended recumbent
> > designs,...

>
> Well, I didn't claim perfection, only less of a conflict :) But with
> such a geometry re. pivot point and chainline as in the first link you
> posted the interference between pedalling and suspension is obvious.
>
> Weren't there full sus MTB frames with a similar design some years ago?
> I seem to remember some hype about "Our design stiffens the frame while
> pedalling instead of making it sag" or similar. They seem to be all
> gone now though.
>
>
> --
> dabac


Not gone, most decent bikes have stiffening incorported into the
design. It's just not something 'new' any more.

Most single pivot designs are built so they 'stiffen' when in granny
gear. Cannondale line up their pivot point with the middle chain ring,
which means when you're in granny gear your peddling action is also
attempting to extend the suspension, push the tyres into the ground.

VPP designed bikes work in a similiar way, hard pedaling extends the
suspension making the bike feel stiffer.

These days it's the actual shock that controls the effect of pedaling
on suspension movement, new shocks with stable-platform damping can
make a huge difference in pedaling efficiency, single pivot or horst
linkage.

Laters,

Marz
 
On Thu, 23 Nov 2006 20:21:19 +1100, dabac
<[email protected]> wrote:

[snip]

>On a 'bent the situation is different. The rider is primarily bracing
>against the backrest and pushing against the pedals. With less of a
>conflict between pedalling motion(~lengthwise push/pull) and sus motion
>(up/down) a sus setup on a 'bent can be less lossy than a sus setup on a
>upright.


Dear D.,

Enjoy:

http://www.kreuzotter.de/english/eschwinge.htm

Cheers,

Carl Fogel
 
dabac wrote:
> Johnny Sunset Wrote:
> >
> > ...It is my experience that "pogo" while pedaling, especially while
> > climbing is a significant problem with some suspended recumbent
> > designs,...

>
> Well, I didn't claim perfection, only less of a conflict :) But with
> such a geometry re. pivot point and chainline as in the first link you
> posted the interference between pedalling and suspension is obvious....


No, having the chain jackshaft and the suspension pivot concentric
ELMINATES the problem of pedaling induced "pogo".

--
Tom Sherman - Post Free or Die!
 
Johnny Sunset said:
...No, having the chain jackshaft and the suspension pivot concentric
ELMINATES the problem of pedaling induced "pogo".


?? Your first link from the top, this link <http://www.recumbent.com/blackbikee.jpg>. led to a bike that had the chainline well below the pivot point - which sure looks like it would lead to "pogoing".

Your 2nd link (this one<http://www.ihpva.org/incoming/2002/Dragonflyer/df5.jpg>.)led to a tadpole trike with what looks like a fairly concentric layout, which would be the "pogo-free" design.

So where's the argument?
 
dabac wrote:
> Johnny Sunset Wrote:
> > ...No, having the chain jackshaft and the suspension pivot concentric
> > ELMINATES the problem of pedaling induced "pogo".

>
>
> ?? Your *first link *from the top, this link
> <http://www.recumbent.com/blackbikee.jpg>. led to a bike that had the
> chainline *well below* the pivot point - which sure looks like it would
> lead to "pogoing".
>
> Your 2nd link (this
> one<http://www.ihpva.org/incoming/2002/Dragonflyer/df5.jpg>.)led to a
> tadpole trike with what looks like a fairly concentric layout, which
> would be the "pogo-free" design.
>
> So where's the argument?


Nowhere?

To clarify, the trike DOES NOT pogo, but the suspended BikeE DOES pogo.

Hopefully, this ends our confusion.

--
Tom Sherman - Post Free or Die!
 

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