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Torsion Springs...why not??

As some of you know I am relatively new to the world of MTBing, and my experiences have to do with Aircraft and roadrace/rally vehicles..
But I have been pondering something and am curious about feedback on this subject..

Why have manufacturers NOT begun adopting and using Torsion spring technology?
The packaging and reduction in weight could be considerably better than what is currently available in metallic springs that are being used.
With the increasing number of multi-pivot and VPP systems being created I would have expected some manufacturer to at least try to make a frame set which utilized a torsion spring...

It is highly possible as I am new to this sport that this avenue has already been exhaustively explored and deemed inneffective..due ot cost or other considerations..
So please enlighten me.

This is more obviously directed towards the "engineering types"on this forum.
thank you all in advance for your time

PM
 

-BB-

I broke all the rules, but somehow still became mo
Sep 6, 2001
4,254
28
Livin it up in the O.C.
Originally posted by shootr
As some of you know I am relatively new to the world of MTBing, and my experiences have to do with Aircraft and roadrace/rally vehicles..
But I have been pondering something and am curious about feedback on this subject..

Why have manufacturers NOT begun adopting and using Torsion spring technology?
The packaging and reduction in weight could be considerably better than what is currently available in metallic springs that are being used.
With the increasing number of multi-pivot and VPP systems being created I would have expected some manufacturer to at least try to make a frame set which utilized a torsion spring...

It is highly possible as I am new to this sport that this avenue has already been exhaustively explored and deemed inneffective..due ot cost or other considerations..
So please enlighten me.

This is more obviously directed towards the "engineering types"on this forum.
thank you all in advance for your time

PM
please enlighten US...
what is a Torsion Spring?
 
Well that is somewhat what I was asking, but that is a fixed durometer damper/spring....what I was mor interested in was the removal of the coil spring, but not the damper, and utilizing a metallic torsion spring to suspend the bike..

in that set up torsion springs can be much MORE effective than a coil as when operated in their elastic region they have no bind point, only a fairly linear rate (note I said FAIRLY).

I built a few hillclimb and spec winter rally vehicles in my time and on more than one occasion we opted for torsion suspension for just those reasons.

for BB, pls do not think that I am trying to sound more knowledgeable..
A torsion spring is a bar or tube that functions as a spring when twisted. This can be done this way where you "wind" a spring helically and provide torsional twist to the ends

OR it can be done via a "torsion BAR"
(see next post)
 

-BB-

I broke all the rules, but somehow still became mo
Sep 6, 2001
4,254
28
Livin it up in the O.C.
Originally posted by shootr


for BB, pls do not think that I am trying to sound more knowledgeable..
A torsion spring is a bar or tube that functions as a spring when twisted. This can be done this way where you "wind" a spring helically and provide torsional twist to the ends

OR it can be done via a "torsion BAR"
(see next post)
No worries... I was just asking b/c obviously you ARE more knowlegale than myself. I just thought that it was an interesting question and I wanted more light shed on the subject.
 

ohio

The Fresno Kid
Nov 26, 2001
6,645
6
SF, CA
Well it might just be that no one's thought of it yet. But off the top of my head, I can think of a couple of reasons. The first is that I don't see the packaging as being any better. The pivot areas on bikes are already overly cluttered, with barely enough room for sufficient bearings, let alone a torsion spring. This can be worked around though, as the spring could be plaed at any of the pivots (for the most part).

The other thing is, you still have to package a damper into the frame somewhere, and it doesn't take up THAT much more space to run a coil spring around it. Q: are there quality "axial" dampers? Like a hopey steering damper, except with the same level of sophistication as current telescopic/linear dampers?
Coincidentally, my thesis work was on a low-cost commuter bike (aimed at developing countries where bikes are the primary form of transportation and used extensively for utility in addition to transportation) that used leaf springs.

-ohio
 
True that most "axial" dampers are underdeveloped, but the main benfit to running the torsional setup would be reduced weight, especially if it were a torsion bar, which could be placed in the link which attaches the damper, or conversly you could place the torsional spring around the lowest pivot, providing a lower center of gravity....
 

Phreaddy

Chimp
Jul 5, 2001
78
0
New York City
but check out softride.com and slingshotbikes.com for alternative suspension systems that have small number of but ardent supporters.

My first guess is that a true torsion system would be too unwieldy, heavy, or expensive to adapt to bikes, though I'm just talking out my a$$ here since I'm neither a metallurgist nor an engineer.
 
actually a "true torsion" system should be just the opposite, as packaging and size of torsional springs can be far smaller than their conventional "wound" compression spring counterparts...

I will give you an example. all the current crop of formula 1 cars use torsion bar springs, they loads that these springs face are in excess of 16,000 lbs, they have rates around 23,000lbs/in..
each of those springs weighs less than 2 ounces...


There are also very light spring applications, which are light, and cover a tremendous range of deflection such as the springs on the throttle of your car...
 

oldfart

Turbo Monkey
Jul 5, 2001
1,206
24
North Van
One big difference between a motorized vehicle and bicycle is weight. The rider on a bicycle is always far heavier than the bike. So you need a way to adjust the spring rate or preload. Would that be more difficult with a torsion bar? I could see how a torsion spring could be adjustable. I think there were some bikes using a flex plate like a slingshot but down at the bb with a damper up on a linkage instead of a complete spring shock unit. I think Bontrager did one but I guess it never went anywhere. And I did see something recently in a downhill frame which I think used a torsion spring. I'm pretty sure I saw a picture and link on www.mountainbike.com . It was polished aluminum and US(?) made. BIG travel.
 
total mass has actually very little to do with this, it matters not whether the bike weighs less/more than the rider, unless you are getting into a discussion about the interaction between the rider and the bike making the rider a "sprung" member..

for suspension engineering, you need only work within the realms of sprung and unsprung masses, and theyre interactions..

I will explain.
the car moving along a roadway experiences a deflection in the suspension (assuming a rigid vehicle structure) due to a bump, the mass of the vehicle is greater than the mass of the "unsprung" suspension components and therefor resists the change in direction that the energy of the impact wants to occur, since there is compliance in the suspension, the wheel assy. (of lower mass than complete vehicle and therefor lower inertia) travels in a new direction at the application of force, and this force is transmitted to the spring, which has this unique characteristic of storing energy, (the force of the bump), which eventually is released by the spring, throwing the wheel assy down again, but this is resited by the damper (and converted into heat) so that when the wheel travels downwards it has less kinetic energy in it than on it's upwards climb...

this occurs virtually the same in the MTB example.

The rider whose mass is coupled to and connected to the bike, this mass with the exclusion of the "unsprung" components, of the wheels, links, and approx half of the spring/damper assy completes the "sprung" mass, whos inertia is far greater than that of the suspension components,
so traveling down the road again, the same control of the energy occurs at the impact as did in the car..

I can also give many more examples of using a torsion spring arrangement in objects far smaller than an automobile...the device that closes the door in your office is torsionally sprung for example...
 
Apr 17, 2002
20
0
Santa Cruz, CA
Shootr,

This answer might be stupid and frustrating, but mountainbike suspension has always compressed springs in a linear manner. All of the current knowledge that frame designers have is based on this trend. Shocks have settled into certain eyelet to eyelet sizes, which deliver a certain amount of travel, so shocks are somewhat standardized and interchangeable. Riders like the ability to upgrade suspension components to deliver a better ride.

At the extremely low end, a coil shock unit looks like a shock to the completely untrained eye and can be recognized from a distance. In the showroom this can be an advantage.

I don't know much about torsion springs and their use in race cars, but mountain bikes generally like to keep lower compression ratios between shock and wheel travel. 3:1 is currently the highest compression ratio you will likely see, and performance starts to get better as you reach 2:1 and lower.

I hope this helps.
 

Lt.Dan

Thank you sir may I have another!
May 15, 2002
77
0
el cajon
if you have an older toyota truck they have torsions. i think its a great idea because it would be so much lighter and would have the benifits of less parts that could break. but coils just seem to have better tunability and are more geared toward bike setups
 

ohio

The Fresno Kid
Nov 26, 2001
6,645
6
SF, CA
Originally posted by GrahamKracker
Shootr,

This answer might be stupid and frustrating, but mountainbike suspension has always compressed springs in a linear manner. All of the current knowledge that frame designers have is based on this trend. Shocks have settled into certain eyelet to eyelet sizes, which deliver a certain amount of travel, so shocks are somewhat standardized and interchangeable. Riders like the ability to upgrade suspension components to deliver a better ride.

At the extremely low end, a coil shock unit looks like a shock to the completely untrained eye and can be recognized from a distance. In the showroom this can be an advantage.

I don't know much about torsion springs and their use in race cars, but mountain bikes generally like to keep lower compression ratios between shock and wheel travel. 3:1 is currently the highest compression ratio you will likely see, and performance starts to get better as you reach 2:1 and lower.

I hope this helps.
Sticking with convention is a reasonable argument for why we haven't but I don't think it's necessarily a good reason in and of itself not to try something completely different. Compression ratio actually has nothing at all to do with spring weight or quality of the spring action. Compression ratio only effects damper performance.

It is pretty feasible to use one of the current shocks on the market as a damper/bottom-out/top-out and drop the weight of the spring by placing a torsion spring at one of the pivots. You could get around the linear rate of the spring by placing it at a linkage pivot (same as is currently done with compression springs, effectively). As I said above the issue for me would be packaging the spring at the main-pivot, but it doesn't have to be there.

Shootr, do you have any links to some of the F1 setups you were talking about, or better yet, any motorcycles that have ever used torsion sprung systems?
 
Like I stated in the start of this thread, my reasoning for asking this Q was because from an engineering standpoint it is a natural evolutionary stage...
I was curious as to IF this has been as of yet done at ANY scale (R&D or even production), as it is becomming increasingly clear that at least on the production end this avenue has only been marginally explored (fixed durometer spring damper by GSR and Human Propulsion labs.)

I am also aware that there are a number of engineering personnel from some of the smaller more progressive bicycle manufacturers, and was most curious as to what their own experiences regarding this subject might be, or at least to spark some frank discussion on this subject and hypothetically explore this as a possibility in the future evolution of the suspended bicycle.
I have personally been exploring this avenue on my own, (though not very intensively as of yet)< and though I have encountered many obstacles I have also discovered a great deal of benefits (mostly in packaging and weight).

Ohio, we have already spoken on a few subjects, and you in particular were one of the people I was interested in hearing from, as far as information regarding their use in F1, you will find very little specific info regarding ANYTHING in F1, as it is all gaurded to the point of absurdity, and that context would actually provide very little beneficial info. anyhow, as those suspension systems are designed spcifically to exhibit certain characteristics under the loads produced by downforce...

BUT I will see what info I can dig up for you and send you, regarding it's use on motorcycles and other vehicles (note: it HAS been used before on motorcycles, but widespread use was never adopted due to being "niche" market, It's most prolific use can be found in GranPrix 500cc bikes)

I may be slow in obtaining this information, as the net, unfortunately provides VERY little real clear usefull documentation in these areas...
 

ohio

The Fresno Kid
Nov 26, 2001
6,645
6
SF, CA
Originally posted by shootr

Ohio, we have already spoken on a few subjects, and you in particular were one of the people I was interested in hearing from, as far as information regarding their use in F1, you will find very little specific info regarding ANYTHING in F1, as it is all gaurded to the point of absurdity, and that context would actually provide very little beneficial info. anyhow, as those suspension systems are designed spcifically to exhibit certain characteristics under the loads produced by downforce...
If you CAN find anything that'd be great. I really want to see how torsion springs are implemented because I've never worked with them before (except on a garage door). All the open-wheel cars I've ever seen (or seen pics of) internally used rocker-arm actuated dampers AND compression springs, usually mounted opposed and longitudinally for a narrow profile. I'm curious as to how they achieve the extreme rising rate necessary to handle the downforce with a torsion spring.
 
actually most current crop open wheeled race cars use dampers positioned as you mentioned, but they use torsion tube/bars attached to the rear of the lower wishbone for a spring, like wise virtually ALL race cars utilize torsion tube/bar assy for controlling roll rates (anti roll bar/sway bar) about the longitudnal axis.

I will dig up some pics and send them to you..
(note: all the same practices regarding rising/falling rate changes thru rocker actuation and position are identical to using compression coil springs)
 
I think a torsion bar setup would be great on a cross-country bike where weight matters and you do not need very much travel, but it would not happen on a downhill bike where weight isn't of much concern and you need a lot of travel.
 

oldfart

Turbo Monkey
Jul 5, 2001
1,206
24
North Van
Shootr: You missed my point. If the rider weight is far greater than the vehicle weight then the springs need to be more adjustable. With the coiled spring you showed that would be easy but a torsion bar maybe not??

I understand sprung versus unsprung weight.

I could see a small square torsion spring mounted at the main pivot which would act as the spring and pivot. Imagine that on a bike like the Fuel with a simple damper at the other end. That torsion spring could be made from fibergalss I'll bet, similar to the slingshot flex plate. I think Corvettes use fiberglass springs.
 
oldfart, adjustibility is NOT a factor of spring size, spring material, spring design etc...

a spring is a spring, once it is made, it is NOT adjustable, what you are thinking of is ajusting the amount of SAG in the suspension, that can EASILY be accomplished with a torsion bar Or torsion spring, (ask any guy with a lowered toyota/mazda/nissan small Pickup truck, all they had to do to adjust the sag was adjust the torsion bar)
(I hope that you do not take me to be arrogant in explaining sprung vs unsprung weight)
and yes, the material selection of such a device is wide open, for there are many that would work.

And PG this would probably be more applicable in a XC bike, for weight concerns, as it is not a major design point in a DH bike.(though it is still a consideration), and amount of travel does NOT negate the use of a torsion spring or a torsion bar..(I stated an example earlier in this thread).

and shocktower, to understand that mass is def. NOT a critical criterium in a springs ability to bear load, you may simply take a small spring from ANYTHING that has a spring in it, whether it be a compression spring. tension spring or torsion spring, and simply CUT half of it off, you will be reducing the mass by half, and you will also discover that you will have DOUBLED its rate...
try it.
 

6thElement

Schrodinger's Immigrant
Jul 29, 2008
9,113
5,962
Bot bump?

Also a coil spring is a torsion spring. Unwind one of the fuckers and try fitting it on a bike.
Well instead of riding your Ibis down the trail apparently you've been doing it wrong and should have been driving a 1992 Williams F1 car down the single-track.
 

HardtailHack

used an iron once
Jan 20, 2009
3,174
918
There was a Spot bike stranded in a shop near me, its torsion spring was a-broken and they ain't easy to get 'round here.