LarryOz
Cruzeum Curator & Sigma Wrangler
I'm sure I'll stir up something with this post!
As I'm sure you are all aware from my numerous posts that I am an advocate of shorter cranks. Changing from 170mm to 150mm saved my knees from certain early death. Now I ride pain free.
Not shorten cranks because shorter is better, but shorter cranks if you need them.
Primarily if your knee on your pull-stroke is bending farther than 90 degrees, assuming your boom is positioned correctly for your push-stroke which should have your knee at nearly full extension, you need to shorten your cranks.
Many people who swear by their long crank arms saying they will get better leverage because the crank arm is longer, therefore a longer lever, which means less force needs to be applied to the arm (lever) to achieve equivalent power (watts) when compared to a shorted crank. That is a logical assumption and it makes perfect sense to me. I'm sure it can be proven on paper with math, but I'm no mathematician! This all may be true and probably is, but what is the real benefit if you knee bends too much to help? I believe that if your knee is bent past 90 degrees on your pull-stroke, that when the pedal comes around and is ready for your "power" push-stroke, since your knee is bent so much, you can't apply as much power, therefore your power phase will be a shorter period of the pedal rotation when compared to a shorter (better fitted) crank. Another factor that is hard to quantify is that your legs are not having to "move" as much as the pedal goes around. In addition it is easier to "spin-up" the pedals from a slower rpm to a faster one. I think this is because of less leg movement also. There are obvious limits as well to both longer and shorter cranks.
...
Now I am on my quest to find the "best" crank length for myself for different types of riding: TT's, ultras, mountain rides. They will probably be different for each one.
I realize this might be a life-long quest with so many variables affecting the data: wind, tires, tubes, speed, grades, max speed, distance, etc., etc., etc., but I am young compared to my grandmother, who turned 101 today (May 14th), so I am looking forward to many years of testing!
So I have designed and fabricated a rather simple adjustable crank "bell", "leaf", "heart", whatever form you see when you look at it. I took a rather inexpensive SRAM Apex aluminum crank set and also machined it to receive the "other" piece,
I took very special care to make sure the crank arms are still parallel with the body and the pedals are perpendicular with the crank.
It has this strange shape to be able to accommodate the Garmin Vector Pedals which have a plastic arm that must wrap around the crank arm and plug into the back of the pedal to compete a circuit.
With this set-up, I can quickly unscrew the pedals and re-attach them and keep going. It only takes a couple of minutes.
..
Yes, I know they add some significant weight - That's OK - it is only for testing and gathering data.
Yes I know the Q-factor is increased slightly - That's OK too - only for testing.
So, I completed my first "testing" this morning.
Variables and set-up:
Road around a 1/4 mile high school track with average asphalt pavement.
Start time 7am - 5-10 mph winds and higher gusts. Winds also picked up to 10-15mph by the end of the testing, which makes the data a little hard to compare since it was not entirely constant and also gusting slightly.
Front wheel: 66 mm CF wheel with steel brake track - gator hardsheel wheels with thick slim filled rubber tube
Rear wheel: 88mm CF wheel with Conti 4000SII wheel and tube
XQL Q-rings (53-large ring) on OCP #! setting
Di2 components
no water bottle or cages mounted
very loose fitting long sleeve shirt (so, not the best aero)
Giro attack helmet - with face shield off.`
I started at 135mm setting and ran in a gear that would give me about 21mph at 100 rpm
then I up'd the gear by one to give about 23mph at 100rpm
then I stayed in that same gear and road at 110 rpm, which was around 25mph.
I repeat the above 3 benchmarks after changing the crank length to 130, then 125mm
Each benchmark was as close to a 2 mile distance as i could get.
I did one "extra" test with the 125mm cranks. I went down one more gear to avg speed around 26, and cadence around 100
I changed the crank length on the Garmin setup each time, and then re-calibrated the Vector pedals as well.
For consistency each test was started after getting up to speed and cadence and then starting the lap.
At the end I changed the crank length all the way down to 105. (The Garmin Vector software) will not allow any settings lower than 115, so the power data collected cannot be trusted), but the cadence, distance and HR data still are.
In the 105mm settings I rode:
23mph speed at 100 rpm
26 mph speed at 100 rpm
20 mph speed at 90 rpm
I recorded the data on a single Garmin ride and hit the lap button at the beginning and end of each test.
.........
attached is also a screenshot of the spreadsheet.
The wind did appear to make some of the data rather inconsistent.
My observations:
Well that's my 2 cents for now.
Welcome any feedback.
Larry
As I'm sure you are all aware from my numerous posts that I am an advocate of shorter cranks. Changing from 170mm to 150mm saved my knees from certain early death. Now I ride pain free.
Not shorten cranks because shorter is better, but shorter cranks if you need them.
Primarily if your knee on your pull-stroke is bending farther than 90 degrees, assuming your boom is positioned correctly for your push-stroke which should have your knee at nearly full extension, you need to shorten your cranks.
Many people who swear by their long crank arms saying they will get better leverage because the crank arm is longer, therefore a longer lever, which means less force needs to be applied to the arm (lever) to achieve equivalent power (watts) when compared to a shorted crank. That is a logical assumption and it makes perfect sense to me. I'm sure it can be proven on paper with math, but I'm no mathematician! This all may be true and probably is, but what is the real benefit if you knee bends too much to help? I believe that if your knee is bent past 90 degrees on your pull-stroke, that when the pedal comes around and is ready for your "power" push-stroke, since your knee is bent so much, you can't apply as much power, therefore your power phase will be a shorter period of the pedal rotation when compared to a shorter (better fitted) crank. Another factor that is hard to quantify is that your legs are not having to "move" as much as the pedal goes around. In addition it is easier to "spin-up" the pedals from a slower rpm to a faster one. I think this is because of less leg movement also. There are obvious limits as well to both longer and shorter cranks.
...
Now I am on my quest to find the "best" crank length for myself for different types of riding: TT's, ultras, mountain rides. They will probably be different for each one.
I realize this might be a life-long quest with so many variables affecting the data: wind, tires, tubes, speed, grades, max speed, distance, etc., etc., etc., but I am young compared to my grandmother, who turned 101 today (May 14th), so I am looking forward to many years of testing!
So I have designed and fabricated a rather simple adjustable crank "bell", "leaf", "heart", whatever form you see when you look at it. I took a rather inexpensive SRAM Apex aluminum crank set and also machined it to receive the "other" piece,
I took very special care to make sure the crank arms are still parallel with the body and the pedals are perpendicular with the crank.
It has this strange shape to be able to accommodate the Garmin Vector Pedals which have a plastic arm that must wrap around the crank arm and plug into the back of the pedal to compete a circuit.
With this set-up, I can quickly unscrew the pedals and re-attach them and keep going. It only takes a couple of minutes.
..
Yes, I know they add some significant weight - That's OK - it is only for testing and gathering data.
Yes I know the Q-factor is increased slightly - That's OK too - only for testing.
So, I completed my first "testing" this morning.
Variables and set-up:
Road around a 1/4 mile high school track with average asphalt pavement.
Start time 7am - 5-10 mph winds and higher gusts. Winds also picked up to 10-15mph by the end of the testing, which makes the data a little hard to compare since it was not entirely constant and also gusting slightly.
Front wheel: 66 mm CF wheel with steel brake track - gator hardsheel wheels with thick slim filled rubber tube
Rear wheel: 88mm CF wheel with Conti 4000SII wheel and tube
XQL Q-rings (53-large ring) on OCP #! setting
Di2 components
no water bottle or cages mounted
very loose fitting long sleeve shirt (so, not the best aero)
Giro attack helmet - with face shield off.`
I started at 135mm setting and ran in a gear that would give me about 21mph at 100 rpm
then I up'd the gear by one to give about 23mph at 100rpm
then I stayed in that same gear and road at 110 rpm, which was around 25mph.
I repeat the above 3 benchmarks after changing the crank length to 130, then 125mm
Each benchmark was as close to a 2 mile distance as i could get.
I did one "extra" test with the 125mm cranks. I went down one more gear to avg speed around 26, and cadence around 100
I changed the crank length on the Garmin setup each time, and then re-calibrated the Vector pedals as well.
For consistency each test was started after getting up to speed and cadence and then starting the lap.
At the end I changed the crank length all the way down to 105. (The Garmin Vector software) will not allow any settings lower than 115, so the power data collected cannot be trusted), but the cadence, distance and HR data still are.
In the 105mm settings I rode:
23mph speed at 100 rpm
26 mph speed at 100 rpm
20 mph speed at 90 rpm
I recorded the data on a single Garmin ride and hit the lap button at the beginning and end of each test.
.........
attached is also a screenshot of the spreadsheet.
The wind did appear to make some of the data rather inconsistent.
My observations:
- Yeah - it looks goofy - so what!
- You can pedal more easily at high rpm's 100+ since you legs are not having to "move" as much.
- I could really tell a difference with how how I had to push for each pedal revolution when at the 105mm length, especially at the higher speeds. (Shortest lengths harder on your knees at higher speeds due to more force needed)
- At the lower speed of around 20mpg, and at 105mm crank length, it seemed incredibly easy to maintain at 90rpm. Avg power only 96 watts for 10mph No problem pushing the pedal around at the power level.
- There does not see to be a consistent pattern or change of the amount of wattage needed to maintain a certain speed - but I would not expect that - it should take the same power to maintain the same speed if all other variables are the same. The only thing that might matter (a very little bit) would be home much or your legs are in the wind with the longer cranks. It would lessen with the shorter cranks, but I guess it would also be a fairly small amount. With the winds being inconsistent and gusty, rather impossible to see a pattern at this time
- best metric observed: 23.5 mph on 168 watts using 125mm length at 100rpm. nice!
- I am only starting out: obviously more testing is needed in a more "controlled" environement (i.e. no wind)
Well that's my 2 cents for now.
Welcome any feedback.
Larry
