Cranksets
02-15-14 | 01:41 PM
#51
Ride, Wrench, Swap, Race
Joined: Jan 2010
Posts: 9,808
Likes: 1,775
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I've always expected Triple arms to be similar in offset to similar Double arms, but that a wider and/or more-offset spindle is used when 3 rings are in place.
Track arms again my use an extra-narrow bb, noting also how many fixies end up with the chainring mounted to the back side of the spider tabs for proper chainline.
Track arms again my use an extra-narrow bb, noting also how many fixies end up with the chainring mounted to the back side of the spider tabs for proper chainline.
02-15-14 | 05:41 PM
#52
Senior Member
Joined: Sep 2011
Posts: 1,168
Likes: 25
From: The First State.
Bikes: Schwinn Continental, Schwinn Paramount, Schwinn High Plains, Schwinn World Sport, Trek 420, Trek 930,Trek 660, Novara X-R, Giant Iguana. Fuji Sagres mixte.
I am not assuming a significant peak, and I suspect that there is a macho thing that says to use a larger crank. I am also assuming that there is a peak, that is all. Every person has an ideal fit of a bicycle for their physique. We have different seat heights and angles, different stem lengths, different frame sizes, yet somehow in all this all people can all use the same size crank?? That does not follow logically.
If you look at the crank, foot, and leg, there is lever action in each part. The most significant part of the lever mechanism is your leg, not the crank. For this reason the crank has less effect than your leg does, but to discount it entirely would be a mistake. I covered this already in a prior post.
The study only shows that with the lengths used, there is not much difference. It simply does not have the resolution to show that there isn't a peak in performance with a particular length- that would be an unscientific conclusion. It certainly does not disprove the French formula. I suspect that the people who did the study were not even aware that the French *had* a formula.
I agree that the improvement in rider performance is not going to be much, but why leave that on the table?
If you look at the crank, foot, and leg, there is lever action in each part. The most significant part of the lever mechanism is your leg, not the crank. For this reason the crank has less effect than your leg does, but to discount it entirely would be a mistake. I covered this already in a prior post.
The study only shows that with the lengths used, there is not much difference. It simply does not have the resolution to show that there isn't a peak in performance with a particular length- that would be an unscientific conclusion. It certainly does not disprove the French formula. I suspect that the people who did the study were not even aware that the French *had* a formula.
I agree that the improvement in rider performance is not going to be much, but why leave that on the table?
Here's another study with recumbants that shows no significant difference in efficiency with crank length:
https://www2.gcc.edu/dept/math/jackso...-%20poster.pdf
Sram offers some opinion around crank lengths and references the Martin study I previously linked to. They opine that we are using cranks that are too long, at least for some types of riding.
https://www.theroaddiaries.com/2013/0...-with-options/
They also state that shorter cranks are less efficient at slower cadences such as for hill climbing. What may be going on here is that at shorter crank lengths, the cadence can increase, although with less torque, and at longer cranks lengths you will have a lower cadence but with increased torque. So efficiency tends to level out over crank length as the rider compensates. Somewhere in there a rider will find the crank length that gives them a cadence and torque combination that feels best to them, and possibly will give them their peak output. Apparently, however, we can adapt over quite a range of crank length, although a specific crank length may feel best to us for a variety of reasons.
02-15-14 | 06:02 PM
#53
multimodal commuter
Joined: Nov 2006
Posts: 19,810
Likes: 597
From: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
Part of the problem here, that makes it difficult to experiment properly, is the way bicycles are designed. On any given bicycle, you can raise or lower the seat a hundred times no problem, or swap out the stem for a longer or shorter one, but you can't change the height of the bottom bracket. So if you change the crank arm, experimentally, you also need to change the seat height (obviously) and nice the seat fore or aft, and change the stem length to correspond to the change on seat position. Otherwise you're changing too many variables of fit and your results will be nonsense.
For a given rider, you would have to set up a bike on which the seat height and handlebar position remain fixed, in relation to the road, and you can easily move the crank up and down, fore and aft, and change the crank arm ad infinitum (not just between 140 and 190mm or whatever). With that, you could determine the ideal crank arm length for that rider. Maybe.
For a given rider, you would have to set up a bike on which the seat height and handlebar position remain fixed, in relation to the road, and you can easily move the crank up and down, fore and aft, and change the crank arm ad infinitum (not just between 140 and 190mm or whatever). With that, you could determine the ideal crank arm length for that rider. Maybe.
__________________
www.rhmsaddles.com.
www.rhmsaddles.com.
