Single speed bikes.

[Pottsy]

Excellent, that's that cleared up once and for all then.

 

[MartinC]

Hubgearfreak, from a simple physics or engineering standpoint you're right. However a bicycle is an ergogenic machine so you also need to take into account how the fixed wheel affects the ability of the (in fact, a particular) human body to do the work. This makes it far more complicated to the point where it's possible to sensibly hypothesise the claimed effect.

I certainly don't know enough to know whether the effect exists or not, to what extent and who for. If some people have the perception that it's easier then that seems credible to me as does the converse too.

 

[hubgearfreak]

If some people have the perception that it's easier then that seems credible to me as does the converse too.

you're right - if one believes something works, then for them, it works.
in medicine it's called the placebo effect.

 

[MajorMantra]

Ok, how about this: if you get up some speed on a fixed gear and then relax your legs, the cranks will keep your feet turning whether you like it or not. When you're pedalling you can effectively give your legs momentary (fraction of a second) rests during the upstroke or at TDC.

If you relax your legs on a freewheel bike then the cranks stop rotating instantaneously. If you want the pedal to move upwards and through TDC then you have pull it up and forwards or use the foot on the other side to carry out the equivalent movement.

A bit like a piston engine we tend to supply power in slightly cyclical fashion. Somewhat in the manner of a flywheel, the fixed connection with the back wheel on a fixed gear smooths out your power delivery. There's no free energy but under the right conditions a fixed gear makes slightly better use of the energy you supply it with.

By the way hgf, you make it sound like I've never ridden a freewheel. I do 100 miles or more a week on a geared road bike and around 20-30 a week on a fixed one.

Matthew

 

[MartinC]

you're right - if one believes something works, then for them, it works.
in medicine it's called the placebo effect.

That's a possibility, certainly.

A bike is driven by a very complicated set of pistons and levers operated by extending and contracting connections fuelled by a variety of chemical reactions triggered by a complex set of electrical impulses controlled by an enormously complicated processor. Do you know enough about this system (let alone every instance of it) to say that it might not drive a fixed wheel bike more efficiently than a freewheeled one in some circumstances?

 

[hubgearfreak]

By the way hgf, you make it sound like I've never ridden a freewheel.

i'm not suggesting that at all. but at a guess there's some differences between your geared bike and your fixed. are they the same size, same material, same tyres, rims, spokes & etc. even if they were (and i'll bet £1 that they're not) then it's still got a hub gear or a dérailleur making it not the same bike, at all.

so the question is - has anyone tried the same bike on the same day on the same hill, but with a fixed sprocket one time and a freewheel sprocket the other? i know i have

do you truly believe that the momentum of the bike can move your legs without effort expended by you or at the expense of the momentum, really, honestly?

 

[hubgearfreak]

a very complicated .... Do you know enough about this system

no i don't. but if you told me that people can levitate, i wouldn't believe you, regardless of my lack of biomedical knowledge. it's fairly simple Newtonian physics...all you (or I) need is to have studied it at GSCE or O level

 

[MajorMantra]

do you truly believe that the momentum of the bike can move your legs without effort expended by you or at the expense of the momentum, really, honestly?

Show me where I said that it could.

Matthew

 

[hubgearfreak]

here you go.

The forward motion of the bike keeps your legs turning through the top of the pedal stroke making it easier to keep going up a hill.

 

[MajorMantra]

here you go.

Where did I say it didn't cost you momentum? I didn't. TANSTAAFL and all that.

 

[hubgearfreak]

TANSTAAFL

we're agreed then?

you can either cycle up a hill and move your legs over the dead spot on a ss, or;
cycle up a hill and have you momentum move your legs over the deadspot. the very momentum that your legs gave the bike.

so what i took issue with is the oft repeated myth that fixed is easier to climb with

the higher end if running it fixed gear as they tend to be a bit easier to climb with

when in actual fact getting a mass (bike & rider) from one level up to another level (ie. uphill) will take the same amount of work

 

[Norm]

so what i took issue with is the oft repeated myth that fixed is easier to climb with

Hmm... whilst both will take the same amount of work, would the fixed not help carry the foot through the dead spot, a point at which you can't put in much power, by using some of the energy stored when you are going through the down-stroke?

In other words, it doesn't (can't) reduce the effort required but it uses "easy" momentum to carry you through the hard bits.

Never tried it myself, just postulating.

 

[MajorMantra]

when in actual fact getting a mass (bike & rider) from one level up to another level (ie. uphill) will take the same amount of work

You need to take efficiency into account.

An analogy: in an idealised world (neglecting air resistance and so on) it takes a fixed amount of work (force x distance) to move from A to B. Cycling 2 miles requires the same amount of energy as walking 2 miles carrying the weight of your bicycle.

In the real world, the bicycle plus you is a more efficient machine than you alone so you can travel 2 miles and use less energy than you would in walking the distance.

See where I'm going with this?

Matthew

 

[brodie]

This thread is going way off topic...

If someone is letting the momentum of the bike and rider push their feet round, then they are actually slowing down the bike!

Funny how the "flywheel effect" only seems to work uphill.

If fixed uphill is easier or faster, it's mainly because the bike is lighter than an equivalent multi-speed freewheel bike. The freewheel bike will also have slight losses due to the chainline and the chain having to bend around the jockey wheels.

 

[MajorMantra]

This thread is going way off topic...

If someone is letting the momentum of the bike and rider push their feet round, then they are actually slowing down the bike!

Way to jump into a thread without digesting a word anyone's posted.

Funny how the "flywheel effect" only seems to work uphill.

Says who? It's just more noticeable when climbing.

Matthew