Unicycle approach to MTBking?

General
21

Re: Unicycle approach to MTBking?

In article <U-Turn.mku1n@timelimit.unicyclist.com>,
U-Turn <U-Turn.mku1n@timelimit.unicyclist.com> wrote:
)Your statements, Tom, are of the form “No, it’s not!”. I haven’t heard
)anything that would speak to a unicycle being less efficient. A bicycle
)may have a nicely lubed chain, but a unicycle doesn’t have one to lube.
)The aerodynamics are worse on a unicycle, but at low speeds is probably
)not a factor. The wobble of the wheel, like non-circular pedaling on a
)bicycle, is a matter of less-skilled unicycling, not a “force to
)overcome.” In what way does a bicycle “use its momentum”? Finally, what
)does gearing have to do with efficiency? We have to define terms
)better.

My statements are of the form “no it’s not” because the problem really
seems too obvious to be worth arguing. But if you insist, let us
define “efficiency” in this context as a measure of the ratio of
ground speed to energy input. A person who can go 10 kilometers per
hour while expending 300 calories per hour is operating more
efficiently than one who goes 10 kilometers per hour burning 500
calories per hour, and a person who can go 20 kilometers per hour
while burning 300 calories per hour is operating more efficiently than
one who goes 10 kilometers per hour while burning 300 calories per
hour.

I am not a particularly fast bicyclist. I can ride 100 flat
kilometers in 4 hours, for an average speed of 25 kph. If I were to
do a fast 4-hour unicycle ride, I would be at least as tired (burn at
least as many calories), and realistically would be more tired than I
was after the bike ride. And there is no unicycle in the world which
would take me anywhere near 100 km in 4 hours.

I do not think it is a great leap to assert that this is true for all
reasonable values of “bicyclist” and “unicyclist.” If you want to
trot out the fastest unicyclist in the world and say he could do it, I
get to trot out Lance Armstrong and point out that he could go twice
that far on a bike.

All unicycle wheels wobble, all the time. Experienced unicyclists wobble
less, but they still wobble visibly–just look at the tracks one of them
leaves. That curvy track represents energy constantly being injected
back into the system.

A bicycle “uses its momentum” in the sense that if you suddenly stop
putting energy into the system (stop pedaling), the bicycle will tend
to continue moving forward with only incremental speed loss. (OK, if you
want to be pedantic, there is still energy being expended to balance the
bike, even if you’re not pedaling, but it’s miniscule). If you suddenly
stop putting energy into a unicycle–if it were even possible, which it’s
not–it would almost immediately fall over. Just try coasting with no
feet on the pedals and see how far you get–even Sem can’t do that for
any distance.

Gearing has to do with efficiency, as I’ve defined it above, because
for a given power output, it will be more efficient to be in a certain
gear, and what’s more, more efficient to have multiple gears to choose
from.
-Tom

22

Re: Unicycle approach to MTBking?

In article <Vi2ra.11008$8Z5.67484@sea-read.news.verio.net>,
Tom Holub <doosh@inl.org> wrote:
)
)A bicycle “uses its momentum” in the sense that if you suddenly stop
)putting energy into the system (stop pedaling), the bicycle will tend
)to continue moving forward with only incremental speed loss. (OK, if you
)want to be pedantic, there is still energy being expended to balance the
)bike, even if you’re not pedaling, but it’s miniscule). If you suddenly
)stop putting energy into a unicycle–if it were even possible, which it’s
)not–it would almost immediately fall over. Just try coasting with no
)feet on the pedals and see how far you get–even Sem can’t do that for
)any distance.

By this, I meant coasting with no feet touching the frame–obviously
Sem and others can coast without touching the pedals.
-Tom

23

Hey, what happened to my thread over the last 24hrs?

All I wanted to do was to set up my mountainbike with some of the efficiencies of my YUni 29’er:

Unicycle efficiency:
*Very good power transfer- direct drive to the wheel
*Lightweight
*Low drag- one wheel only
*150mm cranks seem to be about right for my height/ leg length

Mountainbike:
*Gear efficiency- able to keep cadence constant
*Potential energy/ gravity allowing you coasting efficiency

With this in mind I find that over a given time, say 3hrs, my legs feel a lot more knackered after a mountainbike ride, even if I have gone a further distance/ more efficiently. All other factors being equal. I think this might be due to the longer cranks, since I feel about the same after riding 170mm cranks on a MUni. So I think I might be more efficient on two wheels with shorter cranks (150mm). In theory if I had low enough gears I can cranks up a similar cadence to my YUni 29er.

Also I’m sure that weight plays a significant part as well. My 11kg/24pound bike is 18% of my bodyweight, whereas my unicycle is only 8% my bodyweight. If I was riding up the perfect gradient for my unicycle gear (29’er, 150mm) I’m sure I go faster on my unicycle. I’ve passed MTBkers much fitter than me on a unicycle.

So it’s not about which is more efficient. I’d just like to transfer some of my unicycle efficiencies over to my MTB. Namely, lightweight, shorter cranks, and maybe a single speed for better power transfer. This would still allow coasting efficiency which I think is the main disadvantage of unicycling.

Tony, that link doesn’t work! But I’ve got some Doteks anyway. (Minus the spider :frowning: )

Ken

24

Re: Re: Unicycle approach to MTBking?

The world cycling speed record is over 80mph. I thought cheetahs did around 70mph (ref: top trumps)

25

Re: Unicycle approach to MTBking?

Your 170 cranks on your MTB may be too long. There are 165 MTB cranks available. Shimano has 165s in their XT and XTR lines. I know the 165s are used on the smaller womens mountain bikes. Not everyone carries the shorter cranks, but they are in the Shimano catalog
<http://bike.shimano.com/mtb/index.asp&gt;

It looks like DaVinci Designs makes 160 and 165 cranks.
<http://www.davincitandems.com/comp.html#cranks&gt;

I’m sure there are other short MTB cranks available.

Find a local bike shop that knows about bike fit and see what size cranks they recommend for you.

26

So we were, in fact, talking about different types of efficiency, which means that the problem is not obvious (most “obvious” things aren’t).

If you are looking for more downhill efficiency on a unicycle, consider a handbrake. It helps take the braking action out of your legs. If you brake skillfully, you can transform a leg-wracking downhill into a slope that is actually helping your forward progress. So you can get out of the hill some of what you put into it.

27

Re: Unicycle approach to MTBking?

On the flat, a properly set up bicycle is THE most efficient way of
converting muscular energy into movement. A bicyclist is more efficient than
a swimming dolphin or a running cheetah.

How come cyclists are so much slower, then, than dolphins or cheetahs?

Because they’re putting in far less energy than dolphins or cheetahs do when
they have a burst of speed. A fit bicyclist can ride at a good fraction of
his top speed for 8 hours or more; a cheetah uses so much energy that it can
only run quickly for short bursts.

That doesn’t address the question: why is the cyclist’s top speed so much
slower than the cheetah’s or dolphin’s if he’s so efficient?

It does address the question. The cyclist’s top speed is slower because he
is putting in less energy. Surely you don’t believe an 18-wheeler is more
efficient than a bicycle because the 18-wheeler goes faster.

I was comparing animals - cheetahs and cyclists - not internal combustion
engines and cyclists. They both use ATP and muscle and so forth, so there’s
no possibility of the cheetah using THAT much more energy - it’d cook.

So why’d you snip the dolphin 8-hour example?

And of course, THE unicyclist can coast without using friction to balance,
he’s done it in front of witnesses and cameras. The reason we can’t do it is
that, compared to him (I’m thinking here of Sem Abrahams) we suck.

I am sure that Sem spends a lot of energy while coasting–far more than a
bicyclist does.

Doing what?

Adjusting the position of the unicycle frame to maintain balance. A highly
talented unicyclist will require less energy to do this, but it’s absolutely
a requirement for any kind of coasting, while a bicyclist uses negligible
energy to coast.

Imprimus: bicyclists have to balance too.

Secundus: I doubt it takes Sem a lot of energy.

–
“Quemadmodum gladius neminem occidit, occidentis telum est.” – Seneca

28

Re: Unicycle approach to MTBking?

Tom Holub wrote:
> In article <Vi2ra.11008$8Z5.67484@sea-read.news.verio.net>,
> Tom Holub <doosh@inl.org> wrote:
> )
> )A bicycle “uses its momentum” in the sense that if you suddenly stop
> )putting energy into the system (stop pedaling), the bicycle will tend
> )to continue moving forward with only incremental speed loss. (OK,
> if you )want to be pedantic, there is still energy being expended to
> balance the )bike, even if you’re not pedaling, but it’s miniscule).
> If you suddenly )stop putting energy into a unicycle–if it were even
> possible, which it’s )not–it would almost immediately fall over.
> Just try coasting with no )feet on the pedals and see how far you
> get–even Sem can’t do that for )any distance.
>
> By this, I meant coasting with no feet touching the frame–obviously
> Sem and others can coast without touching the pedals.
> -Tom

How does coasting with your feet on the frame put energy into the system?

–
“Quemadmodum gladius neminem occidit, occidentis telum est.”
– Seneca

29

Re: Unicycle approach to MTBking?

nb wrote:
> Scott Kurland wrote:
>> *Tom Holub wrote:
>>
>> That doesn’t address the question: why is the cyclist’s top speed so
>> much
>> slower than the cheetah’s or dolphin’s if he’s so efficient?

> The world cycling speed record is over 80mph. I thought cheetahs did
> around 70mph (ref: top trumps)

Egad.

I was wrong.

I hate that.

–
“Quemadmodum gladius neminem occidit, occidentis telum est.”
– Seneca

30

Re: Unicycle approach to MTBking?

There are several kids cranks available at 150 mm with 3 chainrings.

e.g. some on
http://www.sjscycles.com/store/cat599.htm

I’m using 140mm cranks on my fixed gear road bike and 140mm on my 29er (hoping for some synergy in training).

I’ve never got round to putting shorter cranks on a multi-geared bike but I’d be interested to hear of the results.

I once had my bike set up with 125mm cranks and it was still pretty efficient (I was only 1min 30 secs off my best time for 10 miles).

Leo White

31

Re: Unicycle approach to MTBking?

In article <vaq6m2svhb33c2@corp.supernews.com>,
Scott Kurland <skurland@juggler.net> wrote:
)Tom Holub wrote:
)>
)> By this, I meant coasting with no feet touching the frame–obviously
)> Sem and others can coast without touching the pedals.
)> -Tom
)
)How does coasting with your feet on the frame put energy into the system?

Try standing on a very narrow beam–it requires constant adjustments to
remain balanced.
-Tom

32

Re: Unicycle approach to MTBking?

In article <U-Turn.mlc3n@timelimit.unicyclist.com>,
U-Turn <U-Turn.mlc3n@timelimit.unicyclist.com> wrote:
)
)So we were, in fact, talking about different types of efficiency, which
)means that the problem is not obvious (most “obvious” things aren’t).

The problem is still obvious. Even under your definition of
“efficiency”, which is fairly dubious to begin with, it’s still
obvious that the bicycle is more efficient. Let us take the most
advantageous unicycling example–say, riding on a flat road at 15 kph
on a big wheel or Blue Shift. The amount of energy the unicyclist is
putting in at that speed would propel a bicyclist faster (if you accept
that the bike is more efficient under my definition of efficiency).
It then follows trivially that the amount of energy a bicyclist would
have to put in to go 15kph is less than the amount the unicyclist does.
-Tom

33

most of the cranks smaller that 165mm in the byke world are going to be made of heavy-crapy steel.you could always get 145mm Profiles :slight_smile: if you have been reading other threads then you would know 145’s have the hole for the chain wheel now.

(EDIT they also make 150’s and 155’z)

34

There is some debate in cycling circles about the optimal crank length. Here is one site that proposes that your crank length should be 20% of your inseam length.

http://www.cranklength.info/cranks.htm

there is also a crank length calculator: http://www.cranklength.info/crankCalc.htm

BTW, if my figures are of any help, since dolphins can swim 40km/h and I can pedal 2 km/h underwater, that makes dolphins 20 times more efficient than me.

To be fair, you should also consider that cheetahs only run 70 km/h if they are enticed with food at the end of the trip. Bicyclist also attain much higher speeds if they know there is beer waiting for them at the end of the trip.

byron.

I assume that is what is meant by ‘drafting’, and a bicycle that is drafting can attain speeds of over 300km/h.

35

Re: Re: Unicycle approach to MTBking?

So your definition of efficiency eats mine? There’s nothing trivial about that situation. You have to accelerate up to speed, and a bike is 2-3 times heavier than a unicycle. You haven’t stated why you believe my measure of efficiency is dubious, just that it is. And I don’t necessarily accept apriori your definition. When it comes to efficiency, faster is not necessarily better. These matters are not trivial, nor obvious.

But I do see clearly that it’s time for me to bow out of this discussion.

36

Re: Unicycle approach to MTBking?

In article <U-Turn.mm1bz@timelimit.unicyclist.com>,
U-Turn <U-Turn.mm1bz@timelimit.unicyclist.com> wrote:
)
)Tom Holub wrote:
)> *In article <U-Turn.mlc3n@timelimit.unicyclist.com>,
)> U-Turn <U-Turn.mlc3n@timelimit.unicyclist.com> wrote:
)> )
)> )So we were, in fact, talking about different types of efficiency,
)> which
)> )means that the problem is not obvious (most “obvious” things
)> aren’t).
)>
)> The problem is still obvious. Even under your definition of
)> “efficiency”, which is fairly dubious to begin with, it’s still
)> obvious that the bicycle is more efficient. Let us take the most
)> advantageous unicycling example–say, riding on a flat road at 15
)> kph
)> on a big wheel or Blue Shift. The amount of energy the unicyclist
)> is
)> putting in at that speed would propel a bicyclist faster (if you
)> accept
)> that the bike is more efficient under my definition of efficiency).
)> It then follows trivially that the amount of energy a bicyclist
)> would
)> have to put in to go 15kph is less than the amount the unicyclist
)> does.
)> -Tom
)>
)> *
)So your definition of efficiency eats mine?

If the bike is more efficient under my definition, it is also more
efficient under your definition, unless you believe that a bicycle
requires more energy to ride at 15kph than at 25kph.
-Tom

37

On bicycle vs. unicycle efficiency:
Anyone who wants to prove something, bring over any unicycle you want, and race me on my bike. I’ll only use one gear. You pick the distance. I’ll win.

Then we’ll switch places, and you’ll win. Assuming you are trying.

Any other forms of efficiency may or may not be measurable, but I think the above covers practicality.

Dolphins are very slow out of water. We are very slow in water. Since dolphins are incredibly aerodynamic and are made of muscle from head to tail, I’d hesitate to propose that a human on a bike is more efficient.

The cheetah can hit up to 80mph (or so) in short bursts. So how far can it go in 8 hours, assuming plenty of Gatorade and food? Results there would count for the “average” cheetah, and should be compared with the “average” human. I think the cheetah would still kick ass. If not, what does it prove?

Bikes are hella efficient. There is energy loss in the drivetrain and extra weight, but the unicycle does not make up for these by requiring the rider to attend to balance all the time, and have only one gear. The bike still wins.

On crank length:
Somebody suggested that bike crank length is what it is based on tradition more than anything else. That’s like proposing that bike pedals are threaded the wrong way, because it seems like they should be the other way around.

Bike racing is a multi-million dollar industry. Lots of people are paying lots of attention to how to get the best efficiency out of the machine. The results of this “research” trickle down into the consumer bike industry, in the form of the crank lengths on today’s bikes. Surely there are other factors determining the crank length on a given bike, but they are based on real-world results, not laboratory figures.

I believe there should be a correlation between rider leg length and optimum crank length. Mostly for bikes, and to a much smaller extent for unicycles. Since the unicycle (usually) does not have gears, the cranks do a different job than they do on a bike. Bikes have longer cranks, because you don’t have to pedal them as fast!

38

Ohhh, a physicsy - mathsy thread. My turn:

The official definition for efficiency is energy out over energy in. Energy in is calories used by the rider (although joules are better, being SI units). Energy output is work done, which is force * distance moved.

At constant speed on a bike or a uni, force is constant, and it is equal to friction, balancing out that friction so that you don’t slow down or speed up. The difference between friction on a bike or a uni depends on the bike or uni. A bike with fat, low pressure tyres and a badly oiled transmission will require a large force at any speed, whereas a well maintaned road bike with thin tyres requires almost no force.

A uni is fairly efficient in that sense, in that there isn’y that much frictoin in the transmission, because there isn’t one, although there is friction in the bearings.
What is more important on a uni is the small forwards and backwars forces needed to maintain balance. These mean you are constantly accelerating or deccelerating slightly, so are putting a force in. How big this force is depends on the riders ability.

All that doesn’t help answer any questions, but it possible explains the situation a bit. Its just that its an answer starting with “it depends…”

The other issue mentioned is speed. A bike is faster than a unicycle and it takes less effort to go at a steady riding speed on a bike than a uni. At those speeds, a bike is more efficient, simply because on a uni you end up putting lots of effort into moving your legs in big circles which don’t help much. Like a motor, a person has a certain cadence at which they deliver cadence most effectively (around 60 rpm, I think, but don’t quote that) A unicycle ridden at that cadence may well be more efficient than a bike, it depends on the variables I mentioned earlier. IT’s all a bit irrelevant though, because few people ride at this most efficient speed, because on a uni it’s very slow, whereas on a bike it can be maintained through the use of gears.

Right, that’s the physics bit over. Aplogies for length of gibberings.

I’m not too sure how that works with gizmoducks list of ‘unicycle efficienct’. The direct drive is an advantage, but not a huge one. The friction in a bike chain isn’t much more thatn a unicycle bearing. And drag may be a bit less, but all the weight is on one wheel so that increases drag, as friction force is proportional to reaction force, ie weight, although that means that lightweight is a definate advantage, and probable the most significant for a uni.

The advantage of a bike of ability to coast makes things more complicated. downhill bikes have an advantage, because they can just make gravity do the work, whereas a unicyclist on a hill has to do more work than normal to stop gravity speeding them up, or they pedal too fast and fall off. (I’ve done extensive research into that bit.)
A uni does make up for that a bit uphill, where lightweight becomes much more important than low friction, and a low gear suddenly means a unicyclist is pedling at around the most efficient cadence.

Right, I really have finished now.

John

39

I don’t know how my thread ended up with the wildlife but I’ll reiterate the point that I am not saying one form of transport is more efficient than the other, only that each has it’s own efficiencies. And that I would like to see some of those unicycle efficiencies transferred over to my bike. (Seeing as I’m riding my unicycle so much these days :slight_smile: )

John, I take your point that a properly lubed chain is pretty efficent at transferring energy, but you should see the gloop that has built up on my drivetrain :smiley: . But aside from my laziness and the resulting sticky drivetrain, I still feel that a solid direct-drive connection sucks up less energy- I can feel it! I don’t know if it is just psycological but there is definitely a feeling of power when you turn a unicycle wheel that you don’t get with a bike wheel.

I think on an incline with the exact gradient matched to your particular uni gear ratio you can go as fast or faster on a unicycle. I’ve no idea how fit you are, but next time you’re passing through town I’ll be happy give you a race!

Your point about crank lengths not being a factor in bikes:
Although having gears on a bike means you don’t need to pedal faster to go faster, a suboptimal length means a larger dead spot in the pedalling circle (if too long), or not enough leverage (if too short).
Having gears also doesn’t take into account cadence vs cycling efficiency. You may pedal at a max comfortable cadence of say, 100rpm on 170mm and 120rpm on 150mm with the lowest connecting gear. Whichever cadence is more efficient depends on the rider/physiology. I feel happier with a higher cadence than most people.
Lastly, having a big pedalling circle for a short guy like me means that you have large degrees of motion in the lower limbs. That is, a greater range of flexion/extension; muscle contraction/relaxation, which contribute to fatigue. Of course if the cranks are too short then the fatiguing factor will be the increased force required by the muscle due to the decrease in leverage.

Ken

Thanks for those links everyone, they were really useful.

40

Ken,

To find those Dotek cranks (masquerading as ‘Bulletproof’) go to www.bikepartsusa.com. Choose ‘Crank’ from the ‘Show me’ list. The ones I’m talking about are the first on the list that pops up.

You might also consider Monty 152mm cranks which are available in NZ thru the Monty bikes agent. These are typically ridden by bike trialists with one chainring and a bash guard. I don’t know if that means you can take off the bash guard and put a second chainring on or not. If you are really keen on these, I’ll ask my bike trials friends about this.

Hurrah for short cranks!

T