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| Image courtesy of BMC Bikes |
First, the posts. The first one I'll link to was the "Current Carbon Gravel Bike Design - What I Would Change" post. The second was the "Road Bike Trends Toward "All-Road" Territory".
Second - You folks who commented. You do know this is on the internet, right? I mean, polite, thoughtful discussions just do not happen on the internet, or so we are led to believe. Ha! So, thank you for being the good people you are. I truly appreciate the decorum and great discussion your comments brought to the posts linked here.
Okay, so with this said, I wanted to react to a few points made in the comments which I may delve into further in a subsequent post. The first being crank length. I found it interesting that a few of you touched on the aerodynamic aspects of shorter vs longer cranks. This is something which doesn't get spoken about enough. Position on the bike being tangentially important here as well. I say this because longer cranks were used in the past with time trial bikes, so I think crank length is less important to body position on the bike for the finely tuned athlete.
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| Image courtesy of SRAM |
According to Zinn's formula I should be riding 181mm cranks. Ironically I have used 180mm cranks off and on for many years. Most recently on my "Ride For Jacob" last Summer. (Link to my gear review where I discuss what I thought about 180mm cranks)
Another interesting side-point was made in the road bikes becoming gravel bikes post. It had to do with perspectives of riders being different based upon their primary riding style and bike choice before transitioning over to gravel bikes.
I find this is a valid way to think about gravel riders currently. However; this won't be so easily delineated when riders start on gravel bikes and go into adulthood/age with gravel bikes. I think this is starting now, to be honest.
At some point, a drop bar bicycle with fatter tires won't be "gravel" or "road", it will just be an all-around bike with drop bars. This has already happened with 29"ers. Back 20 years ago you were riding a 29"er MTB or a "mountain bike" which was understood to be a 26"er, but no one said "twenty-sixer" then. Eventually 29"ers became "mountain bikes". Almost no one calls these bikes 29"ers anymore if they are under 30 years old.
Once "gravel bikes" become just another bicycle, I think those who grew up on them will not perceive gravel bicycles as having to be "more road" or "more MTB" anymore.
Okay, those are some initial thoughts I had after the comments on those two posts. Let me know iof you have any further thoughts as well.
6 comments:
Short crank aerodynamic efficiency? I guess as a result of lower bottom brackets... Why the pros are using them is the same reason racing teams spin engines faster: our bodies get less efficient the faster we make repeated movements (much like internal combustion has less time to work properly at higher engine speeds), but doing a little less work *faster* makes more horsepower/watts. This is the bio-*mechanics* part of cycling.
That said, the pros can & will destroy their bodies for the money/fame they make by doing so. IMO, it's best to have a crank proportional to the femur length (which the knew in the 1890's), *but also feel good*, since not everyone's body is in perfect alignment with a bicycle. Those that have had *good* professional bike fits done, & ridden many miles with different options on their own rig, will understand this intuitively.
I definitely don't need anyone to tell me what crank length I should be riding. That argument was done and dusted decades ago, and while I revisit it unwittingly ever so often (when I ride a bike without 175mm cranks), I immediately know it's not right.
And on your take that 'gravel' bikes will just become drop bar bikes, I think it's already happening in some circles...
Here is a quote from Lennard Zinn explaining your short crank aerodynamic efficiency question. It is not about lower bottom brackets. I think it is important given that he is arguably the #1 proponent of crank length proportional to leg length idea.
"While tall riders could produce incrementally more power by using longer rather than short cranks that are better matched to their legs from the perspectives of leverage, muscle extension/contraction, and knee angles, this power output increase can be more than offset by increased aerodynamic drag. If the handlebars have to come up higher to prevent the knees from hitting the chest, the hips from impingement, and the low back and hamstrings from strain, then the upper body is going to be pushing more air ahead of it. It often takes more power to overcome this than was gained by using longer over shorter cranks. Road bike riders may choose to use short cranks to allow the upper body to get closer to horizontal as a solution."
@JR.Z. - Aero is a concern with regard to cranks because, unless I am mistaken, moving legs through a longer radius disturbs more air than a shorter radius would.
Additionally, I feel crank length is something we've adapted to more than anything. Humans are extremely adaptable creatures. I recall Miguel Indurain running 180mm cranks on everything back in the day. Jan Ullrich rode in massive gears up mountains at a much lower cadence than what is common today.
While it could be argued both those athletes were "drug fueled" thus discounting any performance metrics they produced, I still think it is a notable thing. Those guys trained in a different way and adapted to that equipment and training which was available to them at the time.
But the point is more, "You find what you are looking for". I also agree with your comments that for the average cyclist, none of what the Pros are doing has a lot of relevance to our enjoyment of riding bicycles. I agree with you that feeling good on the bicycle will lead you to certain outcomes, and this could be short cranks, long cranks, and even the fact for some that it just doesn't matter.
I have no doubts that moving legs through a longer radius disturbs more air than a shorter radius but that is not the primary aero benefit of shorter cranks. It is all about how low of a body position you can comfortably maintain during hard efforts. Here is another quote from Zinn commenting on Wiggins move from the 177.5 cranks used in his TDF win to the 170mm cranks used on his hour record bike.
"Wiggins a few years later reduced his crank length to 170mm to allow him to fold further forward and reduce his aerodynamic drag on his aero bars to set the world hour record on the track"
Crank length affects how open or closed your hip angle is when pedaling and shorter cranks help with bike fit and aero positioning of upper body.
To be fair I was stating that the are aero advantages to shorter cranks, though you all expanded on my thoughts farther than I had taken them. What I was trying to point out is that shorter cranks for a given ride sizes produces higher rpm, and, as a result more power. Longer cranks produce more *torque*, but at a lower relative rpm; therefore longer cranks produce *less power* for a given rider height (that is to say, with limitations at the extremes).
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