She did not look happy (at all) getting off the bike. But, she gutted out a very strong run. So, good on her!


Steve,

She had ridden like this for years and had always ridden the back half of 1/2 and full IM's with a moderate amount of back pain.

We have played around with a number of things over the last few years( switching to Q Rings, Switch to the Cervelo P3, Changing the bike fit overall slightly, and finally, going to the shorter cranks). Trying to work with each one in isolation to solve the issues but the sum total is now what we feel is right for her. We are now at the point that she can ride 5 hours and feel strong and comfortable riding mostly in the aero postion - that's the point you want to get to. Reason: at her level, it invariably comes down to the run - you have to be able to get off that bike and lay down a strong run to be in contention and be where you want to be at the finish.

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Steve Fleck @stevefleck | Blog

can i give a grab bag of comments in response to several issues folks have raised?

1. the idea behind the shorter crank is this: for every 2.5mm you shorten your cranks, the distance between your knee, and your chest, increases by 5mm, assuming you keep the armrest drop a constant amount (several threads on this). in other words, if you preserve, say, 19cm of armrest elevation drop v your saddle height (i think that's about where jordy is), riding with 172.5mm cranks gives jordan an extra 5mm gap between knee and chest at top dead center. that allows jordan to either lower his front end by 5mm, or ride with better leverage at TDC.

2. yes, a shorter crank decreases torque, but power is torque X cadence, so, you get that power by increasing your cadence. still, it's not a lot. maybe 1 or 2 rpm to normalize. anybody want to math on this a little?

3. you will always see a lower HR when you lower your cadence. don't use this as your only metric, however, or you'll be riding around at 60rpm. there are two types of fatigue with which to be concerned during a race, aerobic and neuromuscular. yes, there is more stress on your aerobic system when you pedal faster but, again, power is torque X cadence, so, if you lower your cadence your torque increases, muscle recruitment increases, and fiber types used moves from type 1 only to types 1 & 2 (a less efficient way to perform a long distance race). so, it's not a matter of choosing a cadence, rather, choosing a cadence to fit the effort level. is 90rpm better than 95rpm? depends on the effort. the answer is yes, it is, if it's a half-IM. and it's probably more like 85rpm in an IM. but 90rpm would probably be too slow for most people in a stand-alone 40k TT. rule of thumb, on average: 95rpm in an oly-distance triathlon, 100rpm in a stand-alone 40k. 65rpm or so in RAAM. cadence ought to match the effort.

4. gearing must match the cadence.

5. gregx and francois, you might want to read our overview of this, which will give you each more battle ammo.

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Dan Empfield
aka Slowman

Background: height 5'11"; inseam 32"; age 58
After 20 years of riding 175 cranks I decided to experiement with shorter cranks. Thanx to the availability of inexpensive 150, 155, 160, and 165 cranks through the now defunct Chuck's Bikes I took advantage of this and bought all four sizes. I already had a set of 170 & 175 cranks.

Currently I am changing from 160 to 165 for September.

Since the beginning of May and using my same commuter route (the test hill is N30th in Old Town Tacoma) and this is what I've found:
170 (June) back pain went away and a slight increase in cadence. On the 175s I was comfortable at 80-85 max. There was no discernable sense of mechanical disadvantage on the one really steep climb when I dropped into the "grind" rpm (below 70)

165: Just starting my second trial (September) with these. For the two weeks in May the sustainable rpm was 95-100 and the biggest difference was maintaining the aero position. Again, I didn't notice any sense of mechanical disadvantage on the steep climb.

160: (August) All of the advantage of 165 and increased to 105 rpm easily in the aero position.
However I felt it was a bit more difficult to accellerate out of the grind rpm on the steep climb.

150 and 155 (July): small increase in rpm but lost nearly all acceleration grind climb.

My conclusion is the optimal crank length for me lays somewhere between 160 and 165. I've found it more difficult to go from shorter to longer but the adaption time was still less then an hour.

And, the best part!!!, it has had a lot to do with getting me off my ten year history of taking perscription Ibprofen.

Best of luck,

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Jay

Bingo. That's why I was experimenting with very short cranks before I gave up racing. I am one of those who experiences very high power losses in an aero position. (My FTP on a road bike was around 320, but only about 280 on a TT bike). The power loss all comes from the acute angle at the top of the pedal stroke. If you reduce that acuteness, you can increase power.

Some people get confused about this: they shorten their cranks, raise their seat and then say: MY POWER DIDN"T CHANGE!. They're probably right, but guess what? You raised your seat without raising your bars, so you are probably more aero now. Raise your bars as much as you raised your seat and you will probably find a power increase.


-jens

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Sure...at the BB spindle. But, as you should gather from that link to Sheldon Brown's article about "gain ratios" I posted above, you'll see that the crank arm is only one part of the total "leverage" between the force you put into the pedal and the force that's applied at the road.

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http://bikeblather.blogspot.com/

"they shorten their cranks, raise their seat and then say: MY POWER DIDN"T CHANGE!"

double bingo. you have to add the qualifier: if you keep your armrest drop constant. and if you do keep your armrest drop a constant, you're preserving a position that we assume is a good one for you, we're just granting a bit more mechanical advantage in the first quadrant of the pedal stroke.

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Dan Empfield
aka Slowman

And the cool part is you get to choose...more drop at the same hip angle, or the same drop with a more open hip angle. Great tool in a fitters belt.

Dan...I personally think it's helpful to NOT think of all of this in terms of torque and cadence, but rather pedal force and tangential pedal speed. This is because, for a given effort, your muscles will have a "preferred" muscle shortening speed. Think of this as the "constant" in this whole deal. Andy C's presentations on "quadrant analysis" really brought this home for me.

So...what does that mean to crank lengths, cadence, and gearing? Simple, it's the force at the pedal and the preferred muscle shortening speed (i.e. tangential foot speed) that determines both the cadence that will be expressed AND the gear ratio the rider will select to maintain the same force "feel" at the pedal. In other words, the cadence and gear ratio used are both DEPENDENT variables. Shorten the cranks and the tangential foot speed is lower for a given cadence. So what happens then? The body tries to keep the muscle shortening speed the same, and thus the cadence naturally rises for a given force at the pedal. That means that for a given ground speed (or, force at the road), the gear ratio needs to be changed to match both the new cadence and the ground speed (road force.)

This also means that those typical cadence ranges you state above MAY not be applicable very broadly, especially as people experiment around with different equipment. Sure, in general they'll apply, but I know in my own case with my TT setup I found out earlier this year that for TTs from 10miles up to 40km anything OVER 90 rpm resulted in my actually producing LESS power for a given PE. It seems my own personal "power band rpm range" for sustainable efforts is more like 85-90 rpm for the equipment I'm currently using.

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http://bikeblather.blogspot.com/

GregX - read the above carefully ...

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____________________________________
Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

Not sure I understand the gain ratio argument completely. At the limit (crank length going towards 0) it would be impossible to power your bike. Slowman's explanation of the lower knee lift of a shorter crank making a more aero position possible was the most logical sounding ito advantages. Still not 100% how the lower leverage gets compensated ito powering the bike.

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power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team

Easy...you shift your gears ;-) Seriously...

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http://bikeblather.blogspot.com/

"I personally think it's helpful to NOT think of all of this in terms of torque and cadence, but rather pedal force and tangential pedal speed."

what you write notwithstanding, it's nevertheless true that power is a function of torque and cadence, so, this being true, i think it's still a very relevant set of metrics.

but we do bring this up in all our discussions of crank length and cadence, that foot speed probably remains pretty constant as you shorten the crank and increase cadence. but i'm not convinced that this is the only metric to be considered. jim martin talks about negative power occurring at a particular cadence, not at a particular footspeed. when you're asking muscles to contract and relax, that's more cadence specific than footspeed specific. imagine riding 90rpm with 120mm cranks, keeping your footspeed the same as it is now. how many cycles of contraction/relaxation do each of your muscle groups go through? that's a function of cadence, not footspeed.

i don't think footspeed is an unimportant metric, just that i don't think it's the only relevant metric.

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Dan Empfield
aka Slowman

Sure...but people don't produce torque at the pedals, they produce force.



But there you're talking about a condition that's outside the "flat" range of acceptable crank lengths. It's sort of like jever98 on another thread asking about how torque gets compensated through gearing by asking about what happens when crank length goes to zero ;-) Just because at the limits "odd things happen", it doesn't mean that what's going in the "acceptable range" isn't different...just don't go to the limits :-)

Anyway...my suggestion of not focusing on cadence is that doing so tends to cause people to make equipment decisions based on cadence. As RChung has told us many times, "cadence is a red herring". Cadence will end up being whatever it needs to be for the particular load, the particular equipment, and the particular effort. Like I said above, it's a DEPENDENT variable in the whole thing.

That's part of the reason I was asking Mr. Cobb about his recommendations to go with a particular sized chainring when dropping crank length. I have a feeling (if his recommendation is to go to a larger chainring when putting on shorter cranks...I don't know...that's why I asked him about it) he may be making that recommendation due to a misunderstanding about what's happening at the pedal due to a focus on cadence rather than foot speed/foot force.

I don't know the particular reference to Jim Martin's comments about negative power, but I would guess that if he was talking about it in reference to cadence, then he was most likely assuming for a fixed crank length. Also, aren't the cadences (assuming a typical sized crank) where this starts becoming an "issue" fairly high, compared to the cadence ranges being discussed here? If you could point me to the references, that would be great...

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http://bikeblather.blogspot.com/

 
I should add as aside -- this is why the aft- or center- mounted cleats are generally a BAD idea for TTers and Triathletes.

It took me a while to figure this out (it should have been obvious): If you move your cleats back 3cm and lower your seat by 2cm, you end up with a much more acute angle at the top of the pedal stroke (particularly if you lower your bars by 2cm too.


-- jens

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

I recently put shorter cranks on my tri bike. I'm 5'9" with 33.5" inseam. I rode 170s from 1986-1999 on a road bike that I put clip-on aerobars on in 1990. In 1999, I bought a medium Softride Powerwing 700 that came with 175s. The Softride has a fairly tall headtube (13cm I think - only 1cm shorter than my old roadie) so I don't ride it in a real aggressive position, but I've never ridden it as fast the old roadie, even in 1999 where I raced the first half of the season on the roadie and the 2nd on the Softride (although the 1st half was short races and the 2nd half was 1/2IMs). After reading Slowman's article on crank length, I decided to swap cranks between the two bikes. So far I like it. But I don't have a lot of race experience with it yet. Just one race where I was really fatigued going in. I've made no changes to the gearing.

edit: and i did not change saddle height. i think it might have been a bit on the high side after my last reassembly after traveling. saddle height adjustment can be a PITA with the softride.

"Sure...but people don't produce torque at the pedals, they produce force."

you don't want this to be the directio of the conversation, do you? torque is force, applied around a circle. it's a twisting force applied to an object and, as such, i think it's a more descriptive term than force for the purpose at hand. now, yes, it's true that muscles individually don't produce force in a circle. but in the aggregate they can.

martin's negative power occurs at about 115 rpm, more or less and, as i recall, the problem is not a loss of force exerted by any particular muscle, rather it's a problem of muscle coordination (your brain anticipates, in advance, the need to contract or relax, like a bombardier letting the bomb go well in front of the target, and at a certain cadence the neurological pathways just can't keep up). the amount above or below 115 rpm where any particular individual will experience this loss probably depends on a lot of personal variables that andy or jim are better equipped to explain. nevertheless, it is not my understanding that this happens at a particular crank length, rather that the rate of cycles of contraction/relaxation over a given time increment is more key to the problem than the length of the crank.

i have no citation for you, this is just a recounting of conversations i've had with jim on the subject.

i don't think cadence as an issue is a red herring or a straw man or whatever the proper metaphor is, expect to say that there is no specific cadence that's good: your correct cadence for RAAM is a third less than your correct cadence for a 40k (more or less). there is a very good formula for determining the proper cadence for an effort. i just don't know what it is ;-)

but i have a rule of thumb, and it's this: 100rpm for a 40k standalone; 95rpm for a 40k inside of a triathlon; 90rpm for a 70.3 bike ride; 85rpm for an ironman bike ride. obviously, that'll change a bit for each person, but, does anyone have a big problem with this 'rule of thumb?'

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Dan Empfield
aka Slowman

"this is why the aft- or center- mounted cleats are generally a BAD idea for TTers and Triathletes."

i'm an agnostic on this. i'll let smarter people than i decide whether there's a benefit to aft mounting cleats.

but you're right: moving the cleats fore/aft effectively changes the seat angle just like moving the saddle fore/aft does. so, if you aft mount your cleats, you have to move your saddle forward the same amount (corrected for your plantar angle during the power phase of your pedal stroke) to preserve your relative seat angle.

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Dan Empfield
aka Slowman

I am 6 foot 5 and used to push 180's, then 177.5's, then 175's. Now I have 172.5 cranks (Cinqo Quarq's) (53) and 11-25 cassette - and to be honest I cant tell the difference. I am a huge grinder and am quite happy. I notice that if I spin more my power drops - so no point in that. I love having the 11 cassette - use it all the time on flats, tailwinds and downhills.

I recently rode the timberman 70.3 at 37kph with a avg cadence of 76.
cheers
MH

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Michael Hay - helped on the journey by the great folks at ZiZU Optics, (for the custom fit), and Bialkowlski's TRYSPORT

Not sure about the rule of thumb. But I'm pretty certain that because it's more comfortable for me to push big gears, I've let myself use bigger and bigger over the years, and shift less and less. It has affected my cycling and my running, and not for the better, and I think has caused the injuries I've had in the past few years. I'm hoping that shorter cranks will help a bit with going back to a higher cadence (along with the smaller chainrings)...to avoid the constant mashing in the mid (sic) 60s.

I don't have a lot to add to this discussion. I used 170 cranks in the 80's and then went to 172.5 through most of the 90's and 2000's with some playing around on 175s. With a 68.5 centre off BB to centre of seat height, these lengths are arguably all too long for me anyway.

Recently I bought a pair of 170 SRMs from Jens and I've done a half Ironman and three TT's on a course that is in the 70-75 minute range. I had the best 90K ride in several years in the half Ironman and my time on the 3 TT's has been consistently 1-3 minutes faster for similar conditions as the times I did before switching earlier in the summer.

Now we could argue that before I switched, I was in an Ironman buildup phase and carrying a bit of constant fatigue (but then again we can argue that post Ironman, I should be less sharp).

The most important thing I have noted is that knee issues that I have been fighting off and on for 7 years seem to have almost cleared up in a span of 5 weeks riding somewhat shorter cranks.

Now we can state that 170's are still "long" for my size, but less long than other cranks that I previously used.

I have gone down to 170's on all my bikes and I am considering seeing if SRM will retrofit my 170's for 165's for a winter long experiment based on inputs from all the smart guys here. At this point I can't compare "before and after power" going from 172.5 to 170's, however, I will if I go down to 165.

Bottom line, is that it is way easier to stay aero and that is worth a lot....and my knees feel much better which is like being 24 with bomb proof knees all over again (I hope...)

Actually...yes, I do ;-)

I do because it gets to the heart of the matter...when you press down on the pedals you don't feel "torque", you feel force. The torque that's produced is the RESULT of the lever arm of the crank and acts at the BB. In other words, the torque at the BB is ALSO a DEPENDENT variable.

On top of that, the "working" portion of the pedal stroke is more linear than circular anyway...the feet travel in a circle, yes, but they put the "power down" in a nearly linear manner.




OK...115 rpm is fairly high for sustained efforts, so that's not really applicable to the thread at hand, no? The "muscle coordination" effect makes plenty of sense.

So, yes, there begins to be a problem with how quickly a person can "repeat" a contraction...but for the types of efforts we're discussing here, you're going to be running some awfully short cranks for that to start becoming an issue. In the "wide, acceptable range" of crank lengths, this isn't going to be an issue for sustained efforts.



My only issue with it is that IME, the numbers you cite for the 40K efforts seem to be slightly on the high side...but, in any case, you seem to be agreeing with me that cadence will end up being whatever it needs to be based on the equipment selected AND THE EFFORT undertaken.

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http://bikeblather.blogspot.com/

The only thing is...as you admitted previously, you didn't change your seat height when swapping to the 170 SRM cranks. So, basically, all we can conclude is...in typical ST fashion...was that YOUR SEAT WAS TOO HIGH! ;-)

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http://bikeblather.blogspot.com/

"I'm pretty certain that because it's more comfortable for me to push big gears, I've let myself use bigger and bigger over the years, and shift less and less."

it's more comfortable for everyone to push big gears... in the short run... because it's more energetically efficient. it's over the course of a half-day or day of racing that it becomes potentially problematic.

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Dan Empfield
aka Slowman

"Actually...yes, I do ;-)"

while your point is arguable, i just don't see how this advances any thesis you're trying to make. the power you produce on the bike is determined by torque and rpm. that's just true. and for the purposes of this discussion, i don't see how getting into the tall weeds advances your thesis that angular footspeed trumps cadence as a metric. but if you do, i'm all ears (well, i'm all eyes).

"115 rpm is fairly high for sustained efforts, so that's not really applicable to the thread at hand, no?"

i don't know. 115rpm is where negative power becomes a real problem (according to jim). but did jim measure this during the 5th hour of a bike ride? what happens to triathletes, late in the ride, when neuromuscular pathways degrade? is that number lower where neuromuscular degradation happens? what's that cadence number during the 5th hour versus during the 1st? i don't know. maybe jordan can add to this with an analysis of his bike ride file. it's been my observation with some riders that cadence starts a bit higher, degrades a bit over the ride, but that power stays fairly constant during the ride (if you ride the ride the way you hope to ride it). so, a 265w average ride is one where 265 watts is fairly well held, but it's generated with a higher cadence early, and a lower cadence late, averaging out at 85rpm or so. but the power files tell the story. anyone?

"the numbers you cite for the 40K efforts seem to be slightly on the high side"

you think 100rpm for a standalone 40k is high? i think maybe one of obree's efforts is the lone hour record since before merckx occurring at a cadence less than 100rpm, and mostly they're up around 103rpm. certainly fixed gearing is not the same as what you experience on the road, but i don't think that ought to matter more than 5rpm on the outside, do you? (and i think this is fairly well seen during timed events at the pointy end of bike racing).

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Dan Empfield
aka Slowman