Suspension power losses/savings

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thelawnet
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Suspension power losses/savings

Postby thelawnet » 5 Feb 2019, 5:04pm

It is given here https://janheine.wordpress.com/2016/06/ ... confirmed/ that 183W on a flat smooth road results in a speed of 25kph. If 7%, or 13W, is lost to the drivetrain, and 40W to the tyres, then that means 130W is lost to air resistance.

On a rumble strip, with a similar 130W of air resistance, then 473W is required. If the drivetrain is slightly more efficient, at ~5%, say 25W is lost there, meaning that the rolling resistance increases from 40W to 318W.

It is shown that if we reduce vibration, by reducing tyre pressure, LESS power is required for a given speed as there is less vibration.

We could also reduce vibration by fitting a suspension fork.

Road carbon forks weigh from around 300-600 grams, MTB carbon forks are around 700g-800g, and MTB suspension forks weigh from around 1600g.

So:

* noting that damping is configurable on high-end suspension forks, what effect does a suspension tuned to work harder have on tyre pressures, and therefore on minimising vibration, and hence increasing speed
* on a very smooth road with suspension locked out what are the losses in to a good quality fork (in other words, besides weight, what is the suspension penalty)
* and on the same road with the suspension active?

This study

https://pdfs.semanticscholar.org/017f/1 ... 811f84.pdf

suggests that suspension systems, both front & full, have nil/negligible cost in terms of energy on a smooth surface, and even on a steep hill, the power loss to a full suspension system is negligible. It also notes that full suspension increases speed on rough surfaces, while front suspension might not do so, but certainly increases perceived comfort, which is a significant consideration for recreational cyclists.

Obviously there are other costs in full suspension in terms of cost, maintenance, and weight (a high-end full suspension XC MTB is essentially 1kg heavier than a high-end hardtail, and at least 2kg heavier than a high-end road bike, and with a different gear range (typically 1x, for MTBs at this point)).

Different riders & different surfaces in different countries suggest different bikes. New cyclists seem to like squishy bikes with forks. The forks are not necessarily slowing them down (although very cheap ones may be worse in this respect) of themselves, but the extra weight (around 2.4kg ona
typical entry level 'fork') needs to be carried around, and the very upright posture essentially prevents achieving any kind of speed.

Brucey
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Re: Suspension power losses/savings

Postby Brucey » 5 Feb 2019, 6:45pm

it rather depends on the terrain, the suspension system in question and the properties of 'the engine' as to whether it is a net gain or not.

I've done many thousands of miles on bikes equipped with suspension and TBH most of what you can buy is a bit crap. Even the stuff you can buy that isn't crap usually only doesn't interfere with pedalling if you either

a) turn it off (in which case why do you have it?) or
b) pedal in a very particular way.

Pedalling in that particular way is easy when you are not trying hard and you are fresh. It is virtually impossible when you are a bit knackered and/or are required to try hard.

The possible benefits of having suspension vary from a reduction in fatigue (during long spells of steady state pedalling) to an ability to travel on some surfaces without wasting a lot of effort, or at all. Horses for courses.

Given that no single ride comprises of the same surface throughout, the best you can hope for is that the bumpiest bits are made tolerable and in the least bumpy bits the suspension doesn't soak up too much of your effort.

My take on it is that (small wheelers aside) anything that is tarmac or 'gravel' is probably best addressed via correct choice of tyres/tyre pressures. Anything worse than that and suspension becomes a viable choice, provided it makes up enough of your journey to be worthwhile; you can do a few miles of quite gnarly stuff without, simply by standing up on the pedals.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

PDQ Mobile
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Re: Suspension power losses/savings

Postby PDQ Mobile » 5 Feb 2019, 6:49pm

Ah but if one likes to really fly downhill on potholed loose twisting forest trails and worse then good suspension really does increase the security of grip.
Or does increase MY FEELING of security of grip anyway!

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foxyrider
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Re: Suspension power losses/savings

Postby foxyrider » 5 Feb 2019, 7:47pm

Brucey wrote:it rather depends on the terrain, the suspension system in question and the properties of 'the engine' as to whether it is a net gain or not.

I've done many thousands of miles on bikes equipped with suspension and TBH most of what you can buy is a bit crap. Even the stuff you can buy that isn't crap usually only doesn't interfere with pedalling if you either

a) turn it off (in which case why do you have it?) or
b) pedal in a very particular way.

Pedalling in that particular way is easy when you are not trying hard and you are fresh. It is virtually impossible when you are a bit knackered and/or are required to try hard.

The possible benefits of having suspension vary from a reduction in fatigue (during long spells of steady state pedalling) to an ability to travel on some surfaces without wasting a lot of effort, or at all. Horses for courses.

Given that no single ride comprises of the same surface throughout, the best you can hope for is that the bumpiest bits are made tolerable and in the least bumpy bits the suspension doesn't soak up too much of your effort.

My take on it is that (small wheelers aside) anything that is tarmac or 'gravel' is probably best addressed via correct choice of tyres/tyre pressures. Anything worse than that and suspension becomes a viable choice, provided it makes up enough of your journey to be worthwhile; you can do a few miles of quite gnarly stuff without, simply by standing up on the pedals.

cheers


+1 - you've articulated my thoughts on the subject. I used to ride all the local trails long before suspension on bikes was a thing. A live suspension eats energy like a rabbit on cheap batteries!
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

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squeaker
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Re: Suspension power losses/savings

Postby squeaker » 5 Feb 2019, 8:45pm

thelawnet wrote:...We could also reduce vibration by fitting a suspension fork. ...
Only for a minority of cases, IME. Given that the losses are in the tyres, it has to be a pretty special suspension that reduces tyre losses on relatively high frequency surface roughness eg with cyclic repetition within the tyre footprint length ;)
YMMV, of course :roll:
"42"

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Re: Suspension power losses/savings

Postby PDQ Mobile » 5 Feb 2019, 8:52pm

There is another big plus of a decent front suspension fork, that is the improved tyre adhesion under heavy braking, especially on wet and slightly uneven surfaces.
The tyre really sticks down onto the surface and doesn't skitter.

A nimble mountain bike is a great urban steed.
Fearless curb hopping and descending steps. Powerful brakes.

So yes for the dedicated long distance tourer or roadie, light weight, large wheels increase distance ability.

But a quality (mudguarded) xc mountain bike takes on many things well that a lightweight will have significant disadvantages with. All IMHO.

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squeaker
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Re: Suspension power losses/savings

Postby squeaker » 5 Feb 2019, 9:24pm

thelawnet wrote:...We could also reduce vibration by fitting a suspension fork. ...
Only for a minority of cases, IME. Given that the losses are in the tyres, it has to be a pretty special suspension that reduces tyre losses on relatively high frequency surface roughness eg with cyclic repetition within the tyre footprint length ;)
YMMV, of course :roll:
"42"

thelawnet
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Re: Suspension power losses/savings

Postby thelawnet » 5 Feb 2019, 10:17pm

squeaker wrote:
thelawnet wrote:...We could also reduce vibration by fitting a suspension fork. ...
Only for a minority of cases, IME. Given that the losses are in the tyres, it has to be a pretty special suspension that reduces tyre losses on relatively high frequency surface roughness eg with cyclic repetition within the tyre footprint length ;)
YMMV, of course :roll:


MMMV quite a bit, as I get rather different terrain when I'm in Indonesia from in the UK.

UK off-road is typically ridiculously smooth with a relative absence of rocks, while the road is either smooth or sometimes you get a sort of rough sandpaper-like surface.

In Indonesia the roads I use are either tarmac (with sometimes hidden sleeping policeman, disguised as well as possible) which may be smooth or maybe rough, with sometimes large potholes/totally broken sections, or else unsurfaced with lots of rocks like this

surface.jpg


Sometimes there are fairly steep descents with larger rocks embedded.

I find that a low tyre pressure (I use around 20psi on 2.25" tyres) is the key to a smooth ride. I have a cheap coil fork, and it only really is noticeable when there are big bumps/rocks - for normal sort of road conditions it doesn't make much difference whether it's on or off.

I do find that I'm more confident/faster descending than the local mopeds are on the unsurfaced roads. I think the suspension gives you more ability to sort of charge down the hill without worrying too much about the line?

However, if you look at a half-decent air fork on rough ground they seem to move quite a bit?



Here's a basic coil fork for comparison



The questions for me personally is if I'm going to cycle 20km on a rocky unsurfaced road and then perhaps cycle back on tarmac, do I want suspension? I find that with (rubbish) suspension + low tyre pressure then it's only pleasant if I have good grips that absorb some of the vibration that otherwise goes into my wrists. I'm not really sure how much of a problem the bumps that suspension works on are, IYSWIM. If you don't have suspension then you will sometimes be jarred, but it's not necessarily the end of the world, and it might be better to take the bumps than to avoid them using suspension. But maybe not?

I think it is in any case hard to find people doing long rides WITH suspension, so presumably there are significant losses from it somewhere....

thelawnet
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Re: Suspension power losses/savings

Postby thelawnet » 5 Feb 2019, 10:20pm

foxyrider wrote:+1 - you've articulated my thoughts on the subject. I used to ride all the local trails long before suspension on bikes was a thing. A live suspension eats energy like a rabbit on cheap batteries!


according to the various studies referenced above, it doesn't. But it certainly seems like it does. Perhaps someone has some study that demonstrates significant measurable losses ?

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foxyrider
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Re: Suspension power losses/savings

Postby foxyrider » 5 Feb 2019, 10:57pm

thelawnet wrote:
foxyrider wrote:+1 - you've articulated my thoughts on the subject. I used to ride all the local trails long before suspension on bikes was a thing. A live suspension eats energy like a rabbit on cheap batteries!


according to the various studies referenced above, it doesn't. But it certainly seems like it does. Perhaps someone has some study that demonstrates significant measurable losses ?


There might not be any noticeable losses if you can ride/pedal smooth enough to prevent any bobbing. -n the real world that doesn't happen very often, get out of the saddle, bob, put the gas down, bob, bumpy road surface, lots of bob! If there is movement there is energy loss which doesn't matter on a gnarly downhill but does when climbing and on smoother surfaces (it's why they fit the lockout afterall)

The 'suspension' on some top end road bikes is really just damping which could, as Brucey says, be achieved with different tyre set ups.
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

peetee
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Re: Suspension power losses/savings

Postby peetee » 5 Feb 2019, 11:02pm

I did all my serious off roading with no suspension. You develop techniques to deal with it like dropping the saddle a couple of inches and 'sitting' on the saddle mid-thigh and never locked your elbows. I had very few offs, none serious. I have always wanted my rides to be fun and rewarding and slowly picking my way down a mountain using my limited bike handling skills was brilliant, exhausting fun and infinitely preferable to bombing my way down on a boing bike.
I have never been able to produce a lot of power and, frankly, I don't want any of it wasted by compressing suspension.
Current status report:
Latter side of fifty and feeling less than nifty.
Too many bikes on pegs and too few miles in the legs.

Samuel D
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Re: Suspension power losses/savings

Postby Samuel D » 6 Feb 2019, 7:32am

squeaker wrote:Given that the losses are in the tyres, it has to be a pretty special suspension that reduces tyre losses on relatively high frequency surface roughness eg with cyclic repetition within the tyre footprint length

Which losses are you referring to here? The major energy losses in riding a bicycle on rough terrain are so-called suspension losses, which are hysteretic losses in the human body. The body’s viscous soft tissues are heated by jiggling motion. That is what properly tuned suspension greatly reduces, even while it absorbs a small fraction of the saved power in its damping system.

The scale of these suspension losses (in the body) on rough ground can be glimpsed by the much lower speeds achievable on cobbles compared to smooth tarmac when riding a road bike. Assume rider output remains similar.

It’s easy to show by experiment that a bicycle with suitable suspension goes faster than a rigid one on very rough terrain. But most terrain that we cycle over is not that rough. On typical tarmac the benefit is minor and has to be weighed against the unpleasant indirect sensation of bobbing (which may even reduce pedalling efficiency or limit the maximum pedalling power), any small energy losses in the suspension’s damping system (especially when standing, not tested in the Nielens & Lejeune study), and the purchase cost and maintenance requirement of the suspension system. We don’t need to prove that suspension absorbs significant power on smooth tarmac to know it’s not a good idea in that case.

foxyrider wrote:-n the real world that doesn't happen very often, get out of the saddle, bob, put the gas down, bob, bumpy road surface, lots of bob! If there is movement there is energy loss […]

If much energy was absorbed in the suspension by this bobbing, it would show up in any study and heat the suspension components obviously. The direct energy consumption must be low albeit not necessarily negligible.

foxyrider wrote:The 'suspension' on some top end road bikes is really just damping which could, as Brucey says, be achieved with different tyre set ups.

The ones I’ve seen have had minimal damping such that they’re practically springs. Tyres have minimal damping too. Much of the suspension of a pneumatic tyre comes from averaging rough spots in the contact patch to reduce displacement of the bicycle.

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squeaker
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Re: Suspension power losses/savings

Postby squeaker » 6 Feb 2019, 10:29am

Samuel D wrote:
squeaker wrote:Given that the losses are in the tyres, it has to be a pretty special suspension that reduces tyre losses on relatively high frequency surface roughness eg with cyclic repetition within the tyre footprint length

Which losses are you referring to here? The major energy losses in riding a bicycle on rough terrain are so-called suspension losses, which are hysteretic losses in the human body. The body’s viscous soft tissues are heated by jiggling motion. That is what properly tuned suspension greatly reduces, even while it absorbs a small fraction of the saved power in its damping system.

I was taking the statement made in the [url]Jan Heine article linked in the OP[/url]
Riding on the rough surface took up to 290 Watts more than riding on the smooth surface (below).
and assuming that power into the pedals had been measured (to get such precision) and the extra Watts needed on a rough surface where dissipated in the mechanical connection between the rider and the road. I don't wish to buy the Bicycle Quarterly referred to, which might explain - but if anyone has and can explain just what these extra Watts refer to, then I'd be interested in finding out!
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Samuel D
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Re: Suspension power losses/savings

Postby Samuel D » 6 Feb 2019, 11:32am

Almost all of those watts are spent on ‘suspension losses’, a confusing term in the context of this thread that refers to the human body’s dissipation of energy as it is shaken. One reason that being shaken is uncomfortable is that it generates heat deep inside our bodies whose tissues are not perfectly elastic but viscous. Since the law of conservation of energy applies, that energy must have come from our efforts to propel ourselves forward.

Sometimes this is described as wasting energy on motion in the vertical plane that should be in the horizontal plane, but that is too simplistic to be useful in a thread like this, because motion in the wrong direction does not straightforwardly represent wasted energy: there is always the hope that the motion can be channelled back into the right direction. For example, a bicycle wheel that bounces up a bump is just as likely to land on the far side of the next bump and thus recover the energy that was briefly diverted to vertical motion. The real problem is therefore not the vibration itself but our bodies’ inability to conserve that energy. Put another way, the body dampens the bicycle’s vertical motion so that, ironically, it bounces less than it should.

It may help to imagine a bouncy ball of highly elastic material that, if thrown down a street, will keep going a long way despite bouncing up and down as it goes. Our bodies bounce badly by comparison and that is the source of Heine’s suspension losses.

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squeaker
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Re: Suspension power losses/savings

Postby squeaker » 6 Feb 2019, 12:45pm

Samuel D wrote:Our bodies bounce badly by comparison and that is the source of Heine’s suspension losses.
But how does he measure these internal losses?
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