Testing the use of short cranks

[CoachFergie]

The research question is in two parts. Does using a shorter crank lead to a drop in the power one can deliver to the crank. There must be a tipping point where power drops off or you just can't hold cadence. To use the ridiculous lets say a 50mm crank. So if we hold the resistance applied by the trainer which shouldn't need to change as the crank length is adjusted and use the same cadence we hypothesise that as we go from 170mm to 60mm that there will be no change in wattage but as we go to 50cm the power drops away or you just can't pedal any more.

Once we have confirmed the shortest crank we can use and maintain wattage at a given load then we can test if this allows a rider to attain a more aerodynamic position with the shorter crank.

What I don't expect to see is an increase in wattage as we go shorter in just the same way that everyone on the wattage forum is just a tad skeptical of the chap claiming a 14% increase in power holding resistance and cadence constant going from 175mm cranks to 200mm cranks.

 

[FrankDay]

The research question is in two parts. Does using a shorter crank lead to a drop in the power one can deliver to the crank. There must be a tipping point where power drops off or you just can't hold cadence. To use the ridiculous lets say a 50mm crank. So if we hold the resistance applied by the trainer which shouldn't need to change as the crank length is adjusted and use the same cadence we hypothesise that as we go from 170mm to 60mm that there will be no change in wattage but as we go to 50cm the power drops away or you just can't pedal any more.

Once we have confirmed the shortest crank we can use and maintain wattage at a given load then we can test if this allows a rider to attain a more aerodynamic position with the shorter crank.

What I don't expect to see is an increase in wattage as we go shorter in just the same way that everyone on the wattage forum is just a tad skeptical of the chap claiming a 14% increase in power holding resistance and cadence constant going from 175mm cranks to 200mm cranks.

Fergie, why don't you actually do that and report back. As you know, some of us have actually done something similar.

 

[Vegan Dave]

The guys typically putting out the most watts are track sprinters...what length cranks do they use?

 

[CoachFergie]

The guys typically putting out the most watts are track sprinters...what length cranks do they use?

I am tempted to use a two week break in studies to nab the adjustable length track SRMs from our local Uni (if they are open in a city that has had three >6.0 earthquakes and nearly 7000 aftershocks in the last six months) to do a little testing. They also have a Velodyn and SRM erg with adjustable crank length.

The trend in sprinting has been to go shorter with some riders on 155mm cranks while pursuiters appear to be going longer with many on 175mm cranks which I would tend to disagree with.

I don't think you will gain power but if you don't lose power there would be some questions to answer about aerodynamics.

 

[CoachFergie]

Fergie, why don't you actually do that and report back. As you know, some of us have actually done something similar.

Yes but heart rate was the dependant variable and there is no way to determine what was causing that heart rate (heat, dehydration, hot lab assistant etc). Wattage if the stimulus at the pedal so what better DV to find the tipping point where crank length costs you power?

 

[CoachFergie]

I performed a test last night using the difference between wattage and roller speed as the DV and found a marked difference between a SRAM chainring on a SRAM power2max crank and a budget Truvative chainring I had initially put on. Using the recommended chainring reduced the variation so when I get my Powertap back will carry on testing to see if there is a difference between using the rings I had taken off my old cranks and using the recommended chainrings.

Performance, especially in an endurance sport, is not always about more power it is about sustaining power and in this test about finding where power is being lost. There is a marked difference in the 36t Truvative inner ring and the 34t SRAM inner ring. Not so much with the 50t FSA outer and the SRAM 50t outer.

 

[FrankDay]

Yes but heart rate was the dependant variable and there is no way to determine what was causing that heart rate (heat, dehydration, hot lab assistant etc). Wattage if the stimulus at the pedal so what better DV to find the tipping point where crank length costs you power?

Why don't you just do your experiment and report back. Then everyone can critique the various protocols one might use in making this determination.

 

[CoachFergie]

http://quake.crowe.co.nz/ is one reason that things are a little slow at my end.

Also not sure how short the SRM adjustable crank goes.

But the question does have my attention. Will make some enquiries on Monday.

 

[FrankDay]

Also not sure how short the SRM adjustable crank goes.

Don't you think your ignorance of this one little fact is reasonable evidence of how little attention has been payed in the past to this area by coaches such as yourself.

Anyhow, I look forward to your report.

 

[CoachFergie]

Silly me focusing on things that actually matter like training, recovery, nutrition race strategy and motivation.

A gain is a gain and we are still talking hypothetical gains here but I am not expecting any huge gains by comparisons to the factors above.

 

[FrankDay]

Silly me focusing on things that actually matter like training, recovery, nutrition race strategy and motivation.

A gain is a gain and we are still talking hypothetical gains here but I am not expecting any huge gains by comparisons to the factors above.

If you say so. Of course, one researcher (Martin) has already done something along these lines. I look forward to seeing your data and then we can discuss whether what you found was predictable or not.

 

[CoachFergie]

Yes, the chap on wattage claiming going from 175mm to 200mm is the reason behind his 10% increase in wattage is totally refuting all of Martin's work based on his n=1. Funny that any power meter does not require crank length as an variable to determine wattage.

I would concur with Martin that length doesn't have any effect on power delivery until one goes stupid short or stupid long and if the cranks at our local lab do go short enough I would expect to find a tipping point where one just can't physically pedal.

It is of interest to me because I have a rider in the NZ U23 track programme who sits a lot higher on the bars than the other riders. If we could get him lower without compromising his power delivery he would be faster.

 

[CoachFergie]

Hmmmmm, SRM adjustable only goes to 150mm. I run 170mm. All the tests indicate I should run 172.5mm but this has always felt too big for me. I have done road time trials on my track bike on 165mm cranks and this has always felt fine. Sadly fixed gear bikes are banned on road by UCI.

For 20mm it's not worth the time. The guy at the lab has been following the wattage forum thread with interest and has had the same "longer cranks = more power" debate with many in the NZ endurance track team. I was pleased that one of my riders came back from a session with the biomechanist with the suggestion to go from 172.5mm to 170mm cranks.

The chap on wattage claims that the longer cranks mean a better start in track sprint events which doesn't explain why many sprinters have decided to go shorter running 150 - 155mm cranks. Again I would take it is reasonably well studied that shorter doesn't cost power and running a shorter crank means the sprinter could achieve a more aero position. Quite relevant as the faster you go the more that aero counts. Most sprinters are now running 35cm handlebars to try and reduce frontal area.

 

[JayKosta]

My guess is that aerodynamics in actual riding conditions would be a significant factor.
Shorter crank length could give a smaller 'frontal exposure' to wind.

Also, individual differences in muscle type and usage might be more important than the 'mechanical lever length' of the crank.

Jay Kosta
Endwell NY USA

 

[FrankDay]

All the tests indicate I should run 172.5mm

which tests are those?

 

[CoachFergie]

My guess is that aerodynamics in actual riding conditions would be a significant factor.
Shorter crank length could give a smaller 'frontal exposure' to wind.

Also, individual differences in muscle type and usage might be more important than the 'mechanical lever length' of the crank.

Jay Kosta
Endwell NY USA

That would be my WAG on the matter. Crank length doesn't matter till you go stupid long or stupid short and the body would adapt to any subtle changes (although I never felt right on 172.5mm cranks). If I was going to race in any position and any length of crank then I would train using that crank and that position.

Only unanswered question is whether short cranks allow one to maintain a more aero position. Anecdotal observations seem to suggest they can and do. My research next year will focus on sprinter pacing and warm ups but subject to our wind tunnel coming back on line there is probably scope to test aerodynamics for the sprint cyclist from a 150mm to 180mm crank length.

All there is left is for someone to start marketing "Aerocranks".

 

[CoachFergie]

which tests are those?

Leg length, width of ****, length of willy and girlfriends star sign. You know, all the usual suspects. None have been scientifically validated.

 

[fatsprintking]

Hmmmmm, SRM adjustable only goes to 150mm. I run 170mm. All the tests indicate I should run 172.5mm but this has always felt too big for me. I have done road time trials on my track bike on 165mm cranks and this has always felt fine. Sadly fixed gear bikes are banned on road by UCI.

For 20mm it's not worth the time. The guy at the lab has been following the wattage forum thread with interest and has had the same "longer cranks = more power" debate with many in the NZ endurance track team. I was pleased that one of my riders came back from a session with the biomechanist with the suggestion to go from 172.5mm to 170mm cranks.

The chap on wattage claims that the longer cranks mean a better start in track sprint events which doesn't explain why many sprinters have decided to go shorter running 150 - 155mm cranks. Again I would take it is reasonably well studied that shorter doesn't cost power and running a shorter crank means the sprinter could achieve a more aero position. Quite relevant as the faster you go the more that aero counts. Most sprinters are now running 35cm handlebars to try and reduce frontal area.

I would have thought that a longer lever was going to help you get on top of a big gear at the start of a sprint/standing start, but that as a track sprinter you are trying to balance this against maximum cadence.

In a pursuit you can use a longer crank as you are pedling at a constant level a can mitigate the risks of hitting a pedal on the track with a smooth swing up at the end of your turn, where a sprinter will have more sudden changes in direction and hence a greater chance of grounding a crank with longer.

It would be interesting to know what structuaral issues are leading to a rider sitting high and looking at if these could be rectified before adjusting crank length to an extreme. I would think that you would also have to look at changing cranks on all his bikes, and so a long term study of what this means for his road training would be very interesting.

 

[CoachFergie]

I would have thought that a longer lever was going to help you get on top of a big gear at the start of a sprint/standing start, but that as a track sprinter you are trying to balance this against maximum cadence.

I understand BMX use up to 180mm cranks because the event is often won in the first three pedal strokes. In most track sprint events the start is of minimal consequence and the pace is winding up for longer so power delivery at high cadence over 15-30sec is a bigger priority than the ability to accelerate to maximum speed in as short a time as possible.

In a pursuit you can use a longer crank as you are pedling at a constant level a can mitigate the risks of hitting a pedal on the track with a smooth swing up at the end of your turn, where a sprinter will have more sudden changes in direction and hence a greater chance of grounding a crank with longer.

Yes most pursuiters are going longer but what is the rationale for this? Crank length with the exception of stupid long or stupid short doesn't affect power. You don't have to input crank length when setting up a power meter.

As for pedalling at a constant level it depends on what track you ride. Invercargill indoor track has very tight bends where you tend to pick up speed but power drops while on the straights speed drops and power increases. Manchester has easier to ride bends and many records are set there. Many suggest Moscow is the place to set pursuit records with a 333.333m track.

It would be interesting to know what structuaral issues are leading to a rider sitting high and looking at if these could be rectified before adjusting crank length to an extreme.

For sure. Armstrong had a fractured spine hence the hunch in his back. I think Indurain was the same. Both Boardman and Obree were very flexible. We are covering all bases with my rider and crank length is just one of them.

I would think that you would also have to look at changing cranks on all his bikes, and so a long term study of what this means for his road training would be very interesting.

Pursuiting in recent years has been a case study of just how rapidly one can adapt to the demands of the pursuit. In 1996 Boardman set a WR for 4000m 6 weeks after finishing the Tour de France and was able to adapt to the Superman position in that time. In 2000 the Germans (documented in MSSE) come off the road 14 days out from Sydney Olympics and their speed training was 5 x 5000m at 80% of goal pace and 6 x 2000m at goal pace before winning Teams Pursuit and Individual Pursuit Gold. In 2002 Brad Magee won Commonwealth Games IP Gold in 4:16 two days after finishing the TdF. Hayden Roulston was winning a stage race in France two weeks out from Beijing Silver in the IP and Taylor Phinney jumped off the plane as from Euro stage racing onto the track felt fast and set a 3000m junior world record the next day. Before the first of his World Pursuit titles he was racing a stage race in Mexico. Finally Jack Bobridge set the new WR this year on no track training hot off a win in Aussie Road Nationals and riding Tour Down Under.

My experience is that riders adapt to the different position for pursuit, the different intensity and different cadence rather rapidly. If coming from a base of good conditioning they can pick up pursuiting in as short a period as 2-4 weeks. One year a New Zealand track cyclist was released from his Pro Tour team 2 days out from track worlds. Two days of motorpacing was all he needed to get in tune with the bike and the cadence needed to perform at Worlds level track cycling.

 

[Alex Simmons/RST]

Boardman
the Germans
Brad Magee
Hayden Roulston
Taylor Phinney
Jack Bobridge

My experience is that riders adapt to the different position for pursuit, the different intensity and different cadence rather rapidly. If coming from a base of good conditioning they can pick up pursuiting in as short a period as 2-4 weeks. One year a New Zealand track cyclist was released from his Pro Tour team 2 days out from track worlds. Two days of motorpacing was all he needed to get in tune with the bike and the cadence needed to perform at Worlds level track cycling.

I venture that all of those riders had a significant amount of track riding experience under their belts though, meaning they adapt far quicker when they get back on the boards. I suspect it would be different for someone not brought up doing much track work in their younger days.

 

[fatsprintking]

I was thinking that changing crank lengths by 20mm or more is going to start working the major driving muscles through a different range of motion, which is differnet to just changing position.

I guess that pursuiters as they are maintaining a constant cadence might just like the "feel" of the longer cranks given the it seems that the way to success in the pursuit now seems to be to be able to ride a bigger and bigger gear while maintaining a constant cadence.

I am a bit of a believer that what feels right to us is often more important than what can be scientifically proven. Its like tied and soldered wheels. Scientifically they might not be stiffer but to me they feel stiffer and when you are lining up for the sprint this means a lot.

It does not surprise me that you dont input date for crank length for a power meter. I am guessing that power as measured by a strain guage does not need this variable to work out power output. In car terms a higher tourqe low rpm engine and a higher reving engine could both produce the same power output as measured on a dyno. The power meter doesnt even need to know what gear you are in does it to provide you with your power output. You could be producing the same power pushing 53 x 12 at a low rpm or 39 x 21 at a high rpm the output power is whatever it is.

I always asummed that the leverage gained by longer cranks simply allowed you to push a bigger gear at a given rpm, but that ultimately the longer the crank the lower your ultimate rpm capacity. I also assumed that riding a smaller crank with a higher rpm gave greater ability to change rpm quickly where a long crank and low rpm was limited in this regard.

Persoanlly I cannot tell the differnece between 170 and 175 cranks for in any way other than seat height which I am very sensitive to, and would need to be looking at 180 vs 160 to get any idea. Maybe my assumptions have been wrong.

 

[FrankDay]

Yes most pursuiters are going longer but what is the rationale for this? Crank length with the exception of stupid long or stupid short doesn't affect power. You don't have to input crank length when setting up a power meter.

I would submit it does affect power but the affect is small.

We are covering all bases with my rider and crank length is just one of them.

If you are making several changes, it is not possible to know which change is responsible for what, especially if one is dealing with a single rider.

 

[FrankDay]

I was thinking that changing crank lengths by 20mm or more is going to start working the major driving muscles through a different range of motion, which is differnet to just changing position.

Any change in crank length changes the ROM of the joints/muscles. I am coming to the conclusion that much shorter crank lengths optimize ROM for power production. Something has to explain the findings of Martin. If you would like to test this for yourself simply go to a gym and watch people on the stairmaster. Few take steps "higher" than 6 inches when trying to optimize sustained climbing rate. This suggests to me that when able to "freely choose" "crank length" (or joint ROM) to optimize power the athlete will choose something much shorter than what is typically used now.

 

[blutto]

....here are some words on the subject that I found interesting....hope they add to the discussion...

Steve Hogg says in an answer to a crank-length question )

G'day Aaron,

The short answer is I don't know. The longer answer is that if you are going to increase your crank length by 45mm, it is very likely that you will have to drop your seat post 45mm further into your frame to maintain the same seat height as measured from pedal to seat. In turn that will mean that your knee will rise 90mm higher than it does now at the top of the pedal stroke.

A much more bent knee means an increase in shearing forces on the knee joint. A shearing force in this case means that your femur is trying to push forward over your tibia. Whether this results in injury you will only find out by trying it.

Other issues that potentially arise are:

1. A longer crank means more leverage for the part of the pedal stroke you can apply it, but often less ability to apply leverage through as many degrees of crank arc as with the shorter crank. In short, the crank arm will have to move further past top dead centre before you can apply any given degree of mechanical advantage to it because of the increased bend in your knee at the top of the pedal stroke.

2. You will reduce toe of shoe / front wheel clearance (if you have any) by 45mm or increase toe overlap by the same amount. Whether this is a concern is a personal thing.

3. Unless you have a custom frame built, you won't be pedalling through many corners.

4. A seat drop of 45mm relative to the frame means that the seat will move forward by approximately 15mm. This may have other effects on your position on the bike that are not necessarily easily predictable. In a static sense your weight will be further forward but with pressure on the pedals with the further forward pedal (45mm further forward) and will offset that to some degree. Again, only experimentation will determine this.

5. The practical issue of how to try before you buy. There are adjustable cranks available in lengths of up to 220mm from High Sierra Cycles and Zinn Cycles sell cranks in a range of lengths of up to that size as well.

6. Will you benefit?

Who knows. We don't know what you do on a bike, how you do it or what your goals are. I would be personally surprised if they are of benefit for performance riding, unless you are freakishly proportioned, but I'm happy to be wrong about this. Only you can make the final decision. If it helps, have a look at this

Cheers

blutto

 

[CoachFergie]

At least there is a semblance of a biomechanical rationale to Steve's answer. Unlike making a recommendation for crank length based on what you see people do on the stair master or the chap on wattage forum who will test his long crank theory using hand timed starts over 125m on the track