The Powercrank Thread

[FrankDay]

Hi Frank,

I have a question for you from a friend of mine: the 145mm are the best choice for going uphill or it is ok even using something shorter (like 110mm)? He's 1.75m and the inseam is 87cm

thank you in advance!

This question would probably be best asked on the crank length thread but since you asked it here I will answer it here.

The answer to this is not particularly simple. The simple answer is the athlete should choose the crank length that optimizes him or her. For climbing this is primarily a power consideration as aerodynamics plays little role, especially on steeper slopes and if the rider doesn't also have to go downhill also.

That having been said there are two considerations to generating power, force on the pedal and pedal speed. It is easier to put force on the pedals if they are moving slowly but high power also involves high pedal speed. Longer cranks have an advantage because they allow a higher pedal speed at any given cadence. Short cranks have an advantage because it is easier to apply force to the pedal because the knee has better leverage if it isn't bent so much.

So, in my opinion, it is all about gearing. If you find that 110 mm cranks is best for your power can you find a gear that will allow you to keep your cadence up to something reasonable for the highest slope you might encounter. This will be a lot different for a 6% slope than a 20% slope. Let's say you can climb at a sustained wattage of 250 watts. What gearing would you need? Well, analyticcycling.com says you would be riding at 4.92 m/s on a 6% slope and 1.66 m/s on a 20% slope. On 700c tires the wheel would be turning 2.24 rps at 4.92 m/s and 0.75 rps at 1.66 m/s.

Now, let's calculate the gearing gain necessary to not go below 60 rpm. 60 rpm is 1 rps. So, to keep rpm above 60 we would need a minimum "gain" of 1/2.24, or 0.446, at 4.92 m/s and 1/0.75, or 1.33, at 1.66 m/s. What does this mean for gearing choices? On the 6% slope the rear cog can be no smaller than 0.446 of the front chain ring on the 6% slope and the rear cog can be no smaller than 1.33 larger than the front chain ring.

Now, lets look at crank length. Lots of people think longer crank lengths give more leverage but this is wrong. The leverage is really dictated by the ratio of the crank length and the radius of the front chain ring. If the crank length and the chain ring have the same diameter the leverage advantage is zero because the ratio is 1. So 175 cranks and a 52 tooth chain ring provides a leverage advantage of 1.75/105 or 1.66 which means that the pedal speed is increased and pedal force is decreased by this amount for the same power and cadence. To get the identical leverage advantage on 145 mm cranks one would need a 43 tooth chain ring and on 110 cranks one would need a 33 tooth chain ring.

So, what does this mean? On 700C tires and generating 250 watts on a 6% slope and keeping cadence above 60 rpm one could ride that using a 52/23 combination on 175 cranks, 42/19 on 145 cranks and 34/15 on 110 cranks. So, for ordinary climbs (6% slope) it is possible to be easily fit your bike with the gearing necessary to climb. If you find that one crank length gives you a power advantage over the others then you should choose that one. However, when the slopes get very steep the situation changes. To maintain cadence the front chain ring must be smaller than the rear chain ring and the smaller the cranks the smaller the chain ring. Let's put a 36 tooth cog on back and see what is needed. So, to climb a 20% slope at a cadence or 60 at 250 watts requires a 27 tooth front chain ring on 175 cranks, a 22 tooth front chain ring on 145 cranks, and a 17 tooth chain ring on 110 cranks. Such a set-up is almost impossible to attain (although we have made a set of PowerCranks with a 23 tooth front chain ring for someone racing Mount Washington).

So, in conclusion, when the slopes get really steep, the only option is longer cranks. When the slopes are moderately steep shorter cranks are probably just fine, as long as you are properly geared properly for them, so then choose the crank that is best for you.

Hope my math was correct. I am sure some of you will correct me if I made a mistake. Either way, the correct math won't lie and this will give you the general considerations for making this choice.

 

[coapman]

Using clock face, where should a PC rider's unweighting start and finish ?

 

[FrankDay]

Using clock face, where should a PC rider's unweighting start and finish ?

My current feeling is that the cyclist should start unweighting between 6 and 7 o'clock, be fully unweighted by 7:30, begin to relax at 10:30 and be fully relaxed between 11 and12.

 

[FrankDay]

One of the questions that I am sure people might have is whether it is possible to pedal in a perfect circle since most of the people we see and are testing have definite issues coming over the top. I am at the Challenge Atlantic City expo and one of our long-time pros, Petr Vabrosek, came over and wanted to hop on the bike and try out the iCranks. I was amazed at his smoothness and below is a typical screen shot. So, while some may still debate whether "perfect circles" is optimal I think we can conclude that it is, at least, possible to pedal in near perfect circles.

 

[sciguy]

Frank,

Did you scuttle your plans to race? Your name doesn't seem to be on the participant list.

It's interesting how asymmetric Petr is. It would appear that significant asymmetry is the norm for the folks you've tested so far. Hmmmmmmm I wonder who predicted that several months ago

Hugh

 

[FrankDay]

Frank,

Did you scuttle your plans to race? Your name doesn't seem to be on the participant list.

It's interesting how asymmetric Petr is. It would appear that significant asymmetry is the norm for the folks you've tested so far. Hmmmmmmm I wonder who predicted that several months ago

Hugh

Relay team #1158. They didn't have us down when we arrived which may account for us not being there. Our swimmer got sick a week ago so they had to find us a substitute so the Challenge CEO is our swimmer.

There is some normal variation in Petr plus I think the left crank measures a bit high (but can't calibrate to confirm). So, I think Petr is probably really well balanced. He certainly is "circular" both left and right which was the point.

 

[sciguy]

Relay team #1158. They didn't have us down when we arrived which may account for us not being there. Our swimmer got sick a week ago so they had to find us a substitute so the Challenge CEO is our swimmer.

The weather forecast sounds pretty nice for the day. A high temperature of 76F with dew point below 60F and winds 5 to 10 at most. I'd prefer cloudy over sunny but you get what you get. It should be fun racing with such a small field compared to a WTC race.

Good luck, ride safe and have fun. The race report will be interesting.

Hugh

 

[FrankDay]

The weather forecast sounds pretty nice for the day. A high temperature of 76F with dew point below 60F and winds 5 to 10 at most. I'd prefer cloudy over sunny but you get what you get. It should be fun racing with such a small field compared to a WTC race.

Good luck, ride safe and have fun. The race report will be interesting.

Hugh

I really don't have a clue what to expect. I am really marginally trained. About a month ago something happened to my knee and it blew up and I stopped the long training rides and really dropped back on the intensity. Then 4 days of sitting on my **** driving here followed by 3 days on my feet at the expo. I have lost my voice but at least I don't have to use that tomorrow.

Weather however looks perfect and if the winds cooperate that will help. So, we will see how it goes. Hopefully my bike will be faster than Tom's marathon (he is planning on 7 hours).

 

[sciguy]

I really don't have a clue what to expect. I am really marginally trained. About a month ago something happened to my knee and it blew up and I stopped the long training rides and really dropped back on the intensity. Then 4 days of sitting on my **** driving here followed by 3 days on my feet at the expo. I have lost my voice but at least I don't have to use that tomorrow.

Congratulations on surviving the day. I applaud you for putting your body where your mouth was. The marathon drive cross country in four days plus standing and chatting for three days certainly was a less than ideal taper for any sort of bike ride let alone one of 112 miles. Having a constant head wind right on the nose for the entire return trip to T-2 had be mind numbing as well.

Looking forward to a race report.

Hugh

 

[FrankDay]

Challenge Atlantic City Race Report

I did the bike portion of the relay but I will give my impressions of the bike and the swim.

I am told the swim was brutal for most. Lots of turns and a current. Our swimmer expected to do about 1:10 and ended up 1:30. First pro though did about 46 (6 min faster than 2nd) so not brutal for all.

Bike is similar to im wisconsin in that you ride out about 30 miles, do a couple of loops in the country, then come back. Pretty flat.

As I previously noted I was marginally trained for this race and it was made worse by the fact I had a knee swell up after a weekend of long training rides about a month before the race so I cut way back on distance and intensity of rides so whatever the issue was could heal. Then, 10 days before i had symptoms of a kidney stone and even though nothing was found I had 2-3 days of doing nothing. Then, we drove so 4 days of 12 hour days in a car and after we arrived 3 days on my feet working the expo. Hard to have a worse preparation.

The ride. The first 10 miles my legs felt dead and I thought this was going to be a long day. In addition I didn't see some upcoming "rumble strips" and hit those and lost my tool bottle and had to stop to go back for it. But then my legs woke up and I felt pretty good. The weather was good with little wind early on so was feeling confident especially as I went past my long training ride mileage and continued to feel strong.

Then, on the back of the first loop disaster. There were a few miles of really bumpy road and near the end of this portion my chain came off the front ring. I stopped to put it back on and I noticed why. I was missing 3 chain ring bolts and of the two remaining 1 was loose. I was amazed as I had checked them all before the race. I had been hearing some funny noises but thought it was a pedal issue. I moved the loose one so i had near 180 support and wondered if the town had a bike shop. This cost me at least 10 minutes plus I was afraid to trust what I had remaining especially since I still had to do the vibration stretch one more time. So, I eased up a bit and stopped at every aid station to check the bolts. (we had to do that section 2 times. On the second time I notices that section strewn with stuff having been lost from bikes that athletes would never discard voluntarily including a bottle holder and CO2 cartridges. I suspect I wasn't the only one to see some bolts loosen here. Up until this time I was on 6 hour pace and in retrospect felt I could have maintained this for 70-80 miles.

Stopping and going too slow is not good more time on the bike means more tired **** and shoulders and stopping lets you stiffen a bit. The first half of the ride took me 3 hours. The second 5. Despite having taken 8 hours I think my estimate of 6 hours to 7 hours was a pretty good one in view of all that happened. One more thing, there was a 17 mile stretch along the freeway to get back into town. Straight as an arrow and right into a headwind. Everyone found that hard.

i did learn a couple of things. 70 yo muscles do not fade like 30, 40,or 50 yo muscles. Rather than fade they crash. Also, I had adopted a very aggressive (for me) aero position and was especially worried about how my neck would stand up to supporting the head in such a position so I devised a bungie cord support system from the back of the helmet to the back of the seat. Pull the head back and you pull it up. It worked like a charm. Last two hours when shoulders and arms had trouble maintaining position for 2 minutes my neck was the only part of my body not giving me trouble.

I did the race on 125 mm PowerCranks and didn't have any issues per se with this. My only problems were mechanical and an inadequate base for 112 mile endurance at the pace I chose. I didn't race with power, HR, or even a watch so it was all by PE. Also, I chose to use my training wheels (which are tubeless) instead of the 404's because I had never changes a tubular tire and was afraid a flat would finish my day. I don't see much speed difference in them when training so I don't think I lost much.

Also developed an ulnar neuropathy in both hands. The little finger of my right hand is still numb as I right this. Shouldn't be too big an issue though as I don't use that finger to pick my nose but my right little finger is still pretty numb 24 hours later. Nerves regenerate about 1 mm a day so may be a few weeks before I am normal, depending upon the level of the lesion. I suspect it is the wrist.

Got back with little time to spare for our runner (81 yo Tom Knoll) to complete the marathon before cut off. He said he needed 7 hours and I gave him about 30 minutes to spare. Unfortunately most of the marathon was done on the AC boardwalk and late when the runners were sparse the tourists had no clue a race was in progress and a boy ran out in front of Tom, and Tom not being trained in high hurdles, fell and hurt his elbow. He got it patched up and continue but by then it was too late so a DNF for us.

I recovered quickly and was looking pretty normal when I walked after an hour lying down in the shade and water in medical.

One more story. When in medical this young man came in all bloodied. He had crashed his bike at mile 29 but kept going. I thought he was a relay person and the doctor said he had a dislocated shoulder. They cleaned out the gashes on his leg, bandaged those up, and immobilized his shouldet to his side. I was really impressed that he had ridden 85 miles or so on a dislocated shoulder. Later, when we were on the boardwalk looking for Tom I saw him run by, shoulder still immobilized, looking pretty good. He wasn't in the relay and I was doubly impressed.

All in all I was impressed with the race organization and I think with a couple of tweaks it will be a nice destination long-distance triathlon.

 

[sciguy]

I did the race on 125 mm PowerCranks and didn't have any issues per se with this. My only problems were mechanical and an inadequate base for 112 mile endurance at the pace I chose. I didn't race with power, HR, or even a watch so it was all by PE.

Not the Icranks so no data taken? It sure would have been nice to have actual data regarding the ride. It's tough to know how much of your early speed was power induced, tailwind induced or a combo platter.

It sounds like you need to fire your mechanic or hire one. I've had fillings shaken loose on rough roads but not chain ring bolts that were torqued to spec......... usually ~ 10Nm.

Looking at your race pictures, your aero position looks pretty darn good but the folds in your jersey are another matter entirely
http://www.marathon-photos.com/scri...lantic City&match=1158&name=Hugh&new_search=1

Well done on completing the race! When's your next one this time with Icranks?

Hugh

 

[coapman]

Looking at your race pictures, your aero position looks pretty darn good but the folds in your jersey are another matter entirely

http://www.stickybottle.com/latest-...wind-tunnel-energy-saved-time-gained-is-huge/

 

[FrankDay]

Not the Icranks so no data taken? It sure would have been nice to have actual data regarding the ride. It's tough to know how much of your early speed was power induced, tailwind induced or a combo platter.

No head unit available so not possible to gather race data yet. The early conditions (wind) were pretty mild and my 20 mile split speeds (from my phone) were pretty consistent through 60 miles (when I take off some time for the chain ring debacle) even though this included almost the entire first loop so some time into the wind also. I suspect my early power was pretty consistent on average.

It sounds like you need to fire your mechanic or hire one. I've had fillings shaken loose on rough roads but not chain ring bolts that were torqued to spec......... usually ~ 10Nm.

I am my own mechanic so I guess I should fire me. I had about 500 miles on that set up at home (I have changed to 94 BCD chainrings with a 46/30 tooth front chain ring combo) without any issue plus I checked everything the night before I took the bike in. S*** happens. Luckily I was able to McGyver a fix to get home.

Looking at your race pictures, your aero position looks pretty darn good but the folds in your jersey are another matter entirely
http://www.marathon-photos.com/scri...lantic City&match=1158&name=Hugh&new_search=1

I had a tight fitting suit all set but the wife wanted me to be stylin'. She was so worried about my well-being in view of my cardiac history I decided I wasn't going to fight over some of this little stuff since I wasn't expecting to be fighting for a podium spot.

Well done on completing the race! When's your next one this time with Icranks?

Hugh

It may be awhile before I do something like this again. As soon as we have a head unit available I will probably be loaning out the iCranks for people to race on so we can get some racing data. I am especially interested in seeing what changes in technique occur as people get tired.

 

[veganrob]

Frank,
You may have looked aero in the pics but perhaps it was not a position you could hold for long. Most of the pics show you holding onto the base bar, not very aero there. Looks like you are riding a P1 (P2SL same thing) is really a pretty aggressive geometry for an entry level bike.

 

[FrankDay]

Frank,
You may have looked aero in the pics but perhaps it was not a position you could hold for long. Most of the pics show you holding onto the base bar, not very aero there. Looks like you are riding a P1 (P2SL same thing) is really a pretty aggressive geometry for an entry level bike.

Most of those out of the aero bars pics were second half of the race when I was toast coming over little rises. Was in the aero position 98% of the time first half of the race. Bike is a 61 cm P3. Not sure why one would think that it not advantageous to get into an aggressive position just because a bike is entry level. Perhaps you could explain that to me.

Did you guys notice my red bungie cord? runs from the back of my helmet along my back and hooked over the back of the seat. Can see it behind my rear end going to the back of the seat. Copyright stuff prevents one from seeing it attached to back of helmet. Without that I would have never been able to sustain such an aggressive position. As I said, at the end of the race my neck muscles were the only ones in my body not crying for help.

 

[veganrob]

Most of those out of the aero bars pics were second half of the race when I was toast coming over little rises. Was in the aero position 98% of the time first half of the race. Bike is a 61 cm P3. Not sure why one would think that it not advantageous to get into an aggressive position just because a bike is entry level. Perhaps you could explain that to me.

Did you guys notice my red bungie cord? runs from the back of my helmet along my back and hooked over the back of the seat. Can see it behind my rear end going to the back of the seat. Copyright stuff prevents one from seeing it attached to back of helmet. Without that I would have never been able to sustain such an aggressive position. As I said, at the end of the race my neck muscles were the only ones in my body not crying for help.

Sorry. The bike looked like a P!, which is entry level, not a P3, Though they share the same geometry.
Getting into an aaero position is not advantageous if you can only stay in it for half of a 112 mile race.

 

[FrankDay]

Sorry. The bike looked like a P!, which is entry level, not a P3, Though they share the same geometry.
Getting into an aaero position is not advantageous if you can only stay in it for half of a 112 mile race.

But what does an entry level bike have to do with being too aggressive or not? And, it isn't clear to me that having a poor position for the entire race is better than an excellent position for 80 miles of the race followed by a more awful position.

Whether I was too aggressive or not this result is simply a lesson learned and to put into the computer for the next effort. The problem I expected from that position (neck fatigue) didn't happen (I presume because of my bungie cord fix) so I feel pretty good about that. Right now I personally feel my position was fine for the 6+ hours I anticipated. It wasn't for the 8+ it ended up taking me.

 

[CoachFergie]

At the 2nd World Congress of Cycling Science and the Mapei Biomechanist has just given a presentation of how they are optimising performance on the bike. No mention of Powercranks or Crank Length. Main measures the Mapei people use are Vo2, efficiency and Power. With power they are using Best Bike Split and Alphamantis to optimise position and performance on the bike.

 

[CoachFergie]

Asked the Mapei guy who said a couple of riders used Powercranks but only on the offseason. He didn't think they were of any benefit.

 

[JayKosta]

At the 2nd World Congress of Cycling Science and the Mapei Biomechanist has just given a presentation of how they are optimising performance on the bike.
...

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Was there any specific information about what they have found that actually does optimize performance? For example was any specific equipment or training method mentioned?

Tools such as 'Best Bike Split and Alphamantis' seem good for evaluating changes, but it isn't clear whether either one provides help in deciding what to change.

Jay Kosta
Endwell NY USA

 

[CoachFergie]

When testing they use both power and timed efforts on a variety of courses to measure differences in performance. Best Bike Split and Alphamantis both are power based models.

 

[CoachFergie]

Another interesting divergence between what is claimed about independent crank use and what is really happening. It was great to have so many groups represented and being so open about what they are measuring and how they are measuring and what methods are being used. Arguments were also made for low cadence training and gym training and I don't think the data was there to support the claims being made.

 

[Alex Simmons/RST]

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Was there any specific information about what they have found that actually does optimize performance? For example was any specific equipment or training method mentioned?

Tools such as 'Best Bike Split and Alphamantis' seem good for evaluating changes, but it isn't clear whether either one provides help in deciding what to change.

Jay Kosta
Endwell NY USA

I can't speak for BBS (although it's essentially just an online version of a pacing model that I and a few others developed many years back), but I don't think BBS is a tool for that purpose. You need to take it to the next step, which is something I have done, and develop the tool to analyse what you actually did and assess how you could improve race execution and quantify it.

As far as testing of aerodynamics goes, well that's the same issue for a wind tunnel or CFD analysis. You find out what to test for by doing. After a while you gain experience with what tends to work, and you do that first, but aero is pretty weird stuff so you never rule things out unless is really effing obvious not to bother, and even then you think about it.

Quite clearly, if a tool tells you A is better than B and by how much, then it's exceptionally valuable for making sound decisions about whether to go with A over B, rather than relying on belief or marketing hype or some other subjective assessment.

 

[JayKosta]

Another interesting divergence between what is claimed about independent crank use and what is really happening. It was great to have so many groups represented and being so open about what they are measuring and how they are measuring and what methods are being used. Arguments were also made for low cadence training and gym training and I don't think the data was there to support the claims being made.

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Knowing what 'methods' are being used for testing is interesting, and useful for those doing their own 'objective' testing. I'm most interested in learning about training methods that would be useful for me (and others) who are at the 'enthusiast' / 'beginning racer' level.

Also, I don't understand your focus on 'independent crank use' - did that standout as something thought to be 'not ever useful' or simply 'not necessary because of pro rider existing technique'? Surely there were many other training methods and equipment that were not mentioned in the presentation.

Jay Kosta
Endwell NY USA

 

[CoachFergie]

---------------------------------------------
Knowing what 'methods' are being used for testing is interesting, and useful for those doing their own 'objective' testing. I'm most interested in learning about training methods that would be useful for me (and others) who are at the 'enthusiast' / 'beginning racer' level.

Also, I don't understand your focus on 'independent crank use' - did that standout as something thought to be 'not ever useful' or simply 'not necessary because of pro rider existing technique'? Surely there were many other training methods and equipment that were not mentioned in the presentation.

It was a two day "Science behind the Tour de France" conference and included many talks I disagreed with. Strength Training for endurance cyclists and SFR or SE training where I felt the conclusions did not match the data or the research design was pretty poor. I only asked the Mapei chap about independent cranks because it was claimed they were big users of the product. That is a false claim. Just like the claims made about their use at Cycling Australia and British Cycling. Handy to know people in these operations

As an aside, watched the first day of the Tour de France in Leeds. Nothing in the cycling world can compare to the buzz around the event. I highly recommend it to any cyclist!