Dura Ace Q & A

[JasonW]

Would it be correct that in order to do the same work' date=' in the same time, on a shorter crank, you would need a higher cadence?[/quote']

 

This is a Chinese puzzle. Hou kop.

 

Your cadence would remain the same but you would have to apply more pressure throughout the pedal stroke. The upside is that your legs would travel a slightly shorter distance around the smaller circle.

 

 

 

 

 

Ok, so contrary to what I thought, you would acually need a stronger set of muscles, but they could be less fit! Or am I completely off track now?

[PPWTF]

 

adding my 2cents worth... there is a formal study which show that the performance difference is something like 0.1 % between crank lengths. The report concludes that crank length is therefore only truly significant, from a performance perspective, for Elite athletes.

 

The same report emphasized that bike fit is typically achieved through non crank length related means, and as such crank length is a 'feel' issue, akin to a swimmer describing a 'feel' for the water. There is no science to support such a 'feel' but it is formally recognized as playing a critical part in maximizing performance.

 

A long winded way of saying crank length is a personal choice issue, unless you are the next Lance Armstrong et al.....

 

I did post the link to the report on another thread here some time ago, but I'm damned if I can find it.........

 

PPWTF2008-09-02 02:27:33

[straatvark]

Sorry' date=' crank length is sometimes linked to knee pain.[/quote']

 

Very, very clever "sometimes" added there

 

Sometimes it rains on the day after i touch my left ear between 9 and 10 in the morning. But most of the time not...

 

At the end of the day you must read stuff and then think about it and use common sense - very handy to have a online calculator, but what shoe, innersole, cleat and pedal do I use? - all of these together can have big effect on the actual radius that your feet travel. So if crank lengh really really is such a concern on knee pain, why wouldnt Shimano etc make cranks at .1mm interval? Think about the money they can make with marketing campain around knee pain.

[Johan Bornman]

knee pain and crank leangth.

 

Commonly held belief is that the knee is at its most vulnerable when placed under load at an angle(bend) greater than 90 degrees.  therefore if your saddle is to low or cranks too long (but very long) your knee will bend more than 90 degrees and be placed under load as you pedal.

 

that is the logic of the statement.

 

I hand back to Johan now...........

 

My understanding of condramalasia is an inflammation behind the patella and femur head brought on by exercise stress on the knee in the presence of a strength imbalance of the two muscles that keep the patella centred about the knee. 

 

This is my own definition made up of scrappy bits of knowledge retreived from deep memory, so please modify it to perfection if you can.

 

I can wll imagine that a (very) too low saddle or (very) too long crank (of a length that doesn't exist in the bicycle world) in the presence of this muscle imbalance would create this inflammation. Alternatively, pushing a too big gear instead of spinning faster would have the same effect.

 

It is known that some physiotherapits and biokineticists treat condramalasia in cyclists by raising their saddle height. In  my view it just gives relief, but is not the key to preventing it in the first place. Prevention is better done by balanced leg exercises that works both muscles in the right proportions. Cycling tends to over emphasise the inner muscle.

 

No matter how we circle this baby, crank length just doesn't feature as a catalyst for knee pain.

 

 

 

[Canaris]

knee pain and crank leangth.

 

Commonly held belief is that the knee is at its most vulnerable when placed under load at an angle(bend) greater than 90 degrees.  therefore if your saddle is to low or cranks too long (but very long) your knee will bend more than 90 degrees and be placed under load as you pedal.

 

that is the logic of the statement.

 

I hand back to Johan now...........

 

My understanding of condramalasia is an inflammation behind the patella and femur head brought on by exercise stress on the knee in the presence of a strength imbalance of the two muscles that keep the patella centred about the knee. 

 

This is my own definition made up of scrappy bits of knowledge retreived from deep memory' date=' so please modify it to perfection if you can.

 

I can wll imagine that a (very) too low saddle or (very) too long crank (of a length that doesn't exist in the bicycle world) in the presence of this muscle imbalance would create this inflammation. Alternatively, pushing a too big gear instead of spinning faster would have the same effect.

 

It is known that some physiotherapits and biokineticists treat condramalasia in cyclists by raising their saddle height. In  my view it just gives relief, but is not the key to preventing it in the first place. Prevention is better done by balanced leg exercises that works both muscles in the right proportions. Cycling tends to over emphasise the inner muscle.

 

No matter how we circle this baby, crank length just doesn't feature as a catalyst for knee pain.

 

 

 

[/quote']

 

so there you have it folks, now refer to the 50/30 vs 53/39 debate to see how that has spun out of control.  https://www.bikehub.co.za/forum_posts.asp?TID=31848

KonaFan2008-09-02 02:34:54

[Minion]

 

Would it be correct that in order to do the same work' date=' in the same time, on a shorter crank, you would need a higher cadence?[/quote']

 

Power = Force x Crank Length x Cadence

 

So, yes, with a shorter crank and the same force, you need a higher cadence.

 

As Johan has said, the body produces power and the crank acts as a link. There are some efficiency issues with muscles not being able to develop maximum force at all positions, but over the range of common crank lengths (165mm - 180mm, giving 9% total variation), I think it would be unlikely to produce as significant effect as, say, setting your saddle to the correct height.

 

I have read some studies saying that crank length may have a measurable effect on power, but they have been performed non-rigorously on small samples. They admit this and conclude that there may be an effect, but further, more detailed, research is required to to prove this.

 

[Johan Bornman]

adding my 2cents worth... there is a formal study which show that the performance difference is something like 0.1 % between crank lengths. The report concludes that crank length is therefore only truly significant' date=' from a performance perspective, for Elite athletes.

 

c ut cut cut

 

[/quote']

 

I'm always sceptical when I see measurements relating to human motion that cite such small differences. Human performance is just not that easy to measure at that callibration. If I sneeze, it turns to 0,2% or, a 100% improvement, depending on how you want to emphasize the outcome of the study.

 

This whole "elite athlete" thing is also something to be taken with a pinch of salt. Elite athletes are the most superstitious, gullible and psychologically infuenceable people on earth. Many of their beliefs have a substantial placebo effect on their performance but these affects cannot be attributed to physics.

 

 

 

[FlyingCheetah]

knee pain and crank leangth.

 

Commonly held belief is that the knee is at its most vulnerable when placed under load at an angle(bend) greater than 90 degrees.  therefore if your saddle is to low or cranks too long (but very long) your knee will bend more than 90 degrees and be placed under load as you pedal.

 

 

Kona, This does not make sense...

 

A straight leg has an angle of 180 degrees. As soon as you start bending your knee, the angle will increase (except if you're an ostrich).

 

So bending past 270 degrees is actually the correct answer if you take the angle from the front of your leg, or less than 90 degrees if you measure it at the back of your leg.

 

 

[Canaris]

knee pain and crank leangth.

 

Commonly held belief is that the knee is at its most vulnerable when placed under load at an angle(bend) greater than 90 degrees.  therefore if your saddle is to low or cranks too long (but very long) your knee will bend more than 90 degrees and be placed under load as you pedal.

 

 

Kona' date=' This does not make sense...

 

A straight leg has an angle of 180 degrees. As soon as you start bending your knee, the angle will increase (except if you're an ostrich).

 

So bending past 270 degrees is actually the correct answer if you take the angle from the front of your leg, or less than 90 degrees if you measure it at the back of your leg.

 

 

[/quote']

 

thank you for the correction.  Most people see the 180 as a straight line and as the knee bends it bends by degrees from that straight line, thereby a 45 degree bend is actually 135 degrees and so forth.

[NotSoBigBen]

Does this make any sense to y'all? Saw it at Cyclingnews.com .........

 

"If we assume two identical riders and bikes with the only variable being crank length and also measure power at the rear wheel, then the same amount of power will be produced to carry an identical bike and rider up a hill. However the rider with the shorter crank will have a higher metabolic cost because the shorter crank length is a lesser multiplier of the work he performs. His 'twin' has a longer crank length that is a greater multiplier of the work the rider performs, which in turn means a lower metabolic cost, all other things being equal.

That example can't be extrapolated to suggest that longer is always better. There is a cost in turning a longer crank that my explanation above doesn't consider. Shear forces on the knee increase because the knee is flexed more at the top of the pedal stroke and the size of the 'dead spot' in the pedal stroke increases (not in degrees of arc, but in length). So a longer crank usually makes life easier at low to moderate cadences and life harder at high cadences particularly when high cadence is paired with high output. Individual differences in function, proportion and type of riding that the rider prioritises means there is no clear cut 'rule' to determine optimum crank length."

[Johan Bornman]

Sorry' date=' crank length is sometimes linked to knee pain.[/quote']

 

Very, very clever "sometimes" added there

 

Sometimes it rains on the day after i touch my left ear between 9 and 10 in the morning. But most of the time not...

 

At the end of the day you must read stuff and then think about it and use common sense - very handy to have a online calculator, but what shoe, innersole, cleat and pedal do I use? - all of these together can have big effect on the actual radius that your feet travel. So if crank lengh really really is such a concern on knee pain, why wouldnt Shimano etc make cranks at .1mm interval? Think about the money they can make with marketing campain around knee pain.

 

Don't worry Varkie, someone has already done this. Thankfully the infinitely adjustable crank has disappeared off the market.

 

I remember ten or so years ago, at the Argus expo a local inventor had a crank with a slot in which the pedal axle could travel up and down and be tightened at any desirable length.

 

I looked at his contraption and asked him: "So, what problem does this solve?" He got so angry at my rude question that he nearly stuck the crank down my throat. He started blustering, using huge technical terms and some amazing soundbites gleaned from a quantum mechanics textbook.

 

Funny enough, he memorised my name and maintained a grudge until today. Years later I encountered another one of his inventions, this time in a write-up in a local medical journal. It was a slotted or split saddle. He made some strange claims there about the iliac bones. What really annoyed me was that Tim Noakes put his name this it. I respect Noakes greatly, but he clearly didn't apply his mind to these claims.

 

I wrote a counter argument to the journal but they declined to publish it. After all, who is this Johan Bornman guy to call the inventor (forgotten his name) and Noakes bogus?

 

I find our scientific community's approach to counter arguments very interesting. Before they analyse your claims, they ask about your qualifications and weigh the argument accordingly. What happened to independent thinking?

 

 

 

 

[Canaris]

Sorry' date=' crank length is sometimes linked to knee pain.[/quote']

 

Very, very clever "sometimes" added there

 

Sometimes it rains on the day after i touch my left ear between 9 and 10 in the morning. But most of the time not...

 

At the end of the day you must read stuff and then think about it and use common sense - very handy to have a online calculator, but what shoe, innersole, cleat and pedal do I use? - all of these together can have big effect on the actual radius that your feet travel. So if crank lengh really really is such a concern on knee pain, why wouldnt Shimano etc make cranks at .1mm interval? Think about the money they can make with marketing campain around knee pain.

 

Don't worry Varkie, someone has already done this. Thankfully the infinitely adjustable crank has disappeared off the market.

 

I remember ten or so years ago, at the Argus expo a local inventor had a crank with a slot in which the pedal axle could travel up and down and be tightened at any desirable length.

 

I looked at his contraption and asked him: "So, what problem does this solve?" He got so angry at my rude question that he nearly stuck the crank down my throat. He started blustering, using huge technical terms and some amazing soundbites gleaned from a quantum mechanics textbook.

 

Funny enough, he memorised my name and maintained a grudge until today. Years later I encountered another one of his inventions, this time in a write-up in a local medical journal. It was a slotted or split saddle. He made some strange claims there about the iliac bones. What really annoyed me was that Tim Noakes put his name this it. I respect Noakes greatly, but he clearly didn't apply his mind to these claims.

 

I wrote a counter argument to the journal but they declined to publish it. After all, who is this Johan Bornman guy to call the inventor (forgotten his name) and Noakes bogus?

 

I find our scientific community's approach to counter arguments very interesting. Before they analyse your claims, they ask about your qualifications and weigh the argument accordingly. What happened to independent thinking?

 

 

 

 

 

His first name was Graham.  He also invented the adjustable bicycle.

[Johan Bornman]

Does this make any sense to y'all? Saw it at Cyclingnews.com .........

 

"If we assume two identical riders and bikes with the only variable being crank length and also measure power at the rear wheel' date=' then the same amount of power will be produced to carry an identical bike and rider up a hill. However the rider with the shorter crank will have a higher metabolic cost because the shorter crank length is a lesser multiplier of the work he performs. His 'twin' has a longer crank length that is a greater multiplier of the work the rider performs, which in turn means a lower metabolic cost, all other things being equal. [/quote']

 

BB, I don't understand the phrase "metabolic cost". However, lets for the sake of this argument simplify grossly and assume there are two types of energy systems involved in turning a crank.

 

Anaerobic and Aerobic.

 

Lets also assume that the act of applying a force to something requires only anaerobically supplied energy and the act of dragging that force around the circle only aerobic energy.

 

Now, you'll see that your twins are expendifferent types of energy. The one with the short crank is supplying more anaerobic energy and the one with the long crank is working more aerobically.

 

Since they are twins and genetically identical and, one is typically more pre-disposed to one energy system than the other (a shotputter vs a marathon athlete), one of the twins will be suffering a little and the other finding the ride a bit easier.

 

This in spite of them doing the same work.

 

Which one is suffering and how much more? There's the thumbsuck. It has to do with your muscle composition. A simple biopsy can indicate your predisposition but I for one stay away from donating chunks of muscle to lab technicians.

 

Back to metabolic cost. You can't say the metabolic cost of an anaerobic activity is higher than the cost of an aerobic activity, so the "Cost" is moot.

 

Depending on the hill's incline and the rate of ascent, we could probably figure out which one is metabolcally paying more, metaphorically speaking, of course but I think it is a silly statement to make.

 

I just ride with whatever crank the bike has on it.

 

 

 

[Johan Bornman]

 

 

 

Ok' date=' so contrary to what I thought, you would acually need a stronger set of muscles, but they could be less fit! Or am I completely off track now?

[/quote']

 

Jason, we often associate fitness with aerobic capacity. However, it is more than that and generally defined as a combination of flexibility, strength and stamina (aerobic capacity).

 

Us cyclists are therefore not quite as fit as we think, since we're weak and stiff. I proved this to myself some years back when I climbed a gum tree with a chainsaw and attempted to bring the tree down. On the bike I was a machine. In the tree like Tarzan I was a 90 pound weakling.

 

So, in your example above, the guy that prefers the shorter crank scenario will be stonger than you since you are more inclined to activities that requires stamina.

 

But please don't take this and attempt to quantify it. I'm talking delicate mixes and balances here.

 

Good athletes understand their natural predispositions and train accordingly. They will delicately balance strengh, endurance and speed training to achieve the body type they require for their activity.

 

You'll notice that the average Joe who trains for the Epic trains disproportonately at an aerobic level whereas the track guy works on anaerobic strength.

 

 

 

 

Johan Bornman2008-09-02 03:13:28

[GIRR]

http://www.ncbi.nlm.nih.gov/pubmed/11417428

Has anyone with a powermeter compared different length crank arms?  Pleeeease... so this "feel" thing can be put to rest.

http://www.ncbi.nlm.nih.gov/pubmed/11417428

 

Thanks jabba, I always prefer looking at the results of proper studies to rumour.

[Ox_Wagon]

Sorry to say it but the adjustable crank are back!