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Retro Grouch
2,091 Posts
Discussion Starter · #1 · (Edited)
I know that someone out there will want to dispute my take on Chaos theory; please don’t because I have no intention of defending it. For those that don’t know, Chaos theory is a theory of physics; it is also contradicts Newtonian Physics, which tells us any phenomena can be reduced to mathematical equation and reproduced; Chaos theory tells there are simply too many variables in the real world for Newtonian Physics to replicate any real world phenomena.

So where is this going? A few posts ago Sparty and pursuiter bandied the difference in longer crank arm lenghth using both a “Newtonian” equation (rightfully defined by asphaltdude as Sheldon Browns "Gain Ratio") “It's all about the pedal's speed, linear speed (inches/sec), not rpm. A larger diameter circle requires faster pedal speed for the same bike speed if the gear isn't changed. If the crank is longer, then a larger gear is need to keep the pedal's linear speed the same for the same bike speed”.

And Sparty’s real life experiences:

“Gain ratio = written tables & theory.

Personally I'll rely on my 14 years of experience on the bike riding 195-202mm cranks. I'm not saying long cranks are for everybody. But just think, some folks with long legs might find more comfort &/or power &/or torque &/or other benefits turning larger circles. That's it. Ergonomics that defy definition & go beyond spreadsheets.

No one really knows the advantages & disadvantages until they experience the real thing for themselves. And that's something I don't understand -- why some people who frequent these forums offer "advice" about how long cranks are no different than shorter cranks with a lower gear. Without experiencing both short AND long cranks, their opinions are little more than conjecture”.

The reason I’m going with Sparty is pursiuter left a phrase out of his comparison and that would be “all things being equal”. But in the real world, nothing is equal. It’s possible that due to femur and tibia lengths, combined with muscle twitch speed, that by lengthening a crank arm, one person could easily maintain the same linear speed as with the shorter crank arm and have more stamina and torque; it’s the same reason many ride a singlespeed faster than a geared bike. Sports science tells us that maintaining a high RPM, regardless of terrain, using gearing, will give you the most speed for the buck, but as we all know we all have different abilities and strengths and sometimes the reverse works just all well. I say conventional wisdom is a good place to start, but it’s certainly not a final resting place.

4,667 Posts
CB2 said:
That is impressive.
The fastest I've spun is around 170 on the fixie.
That's how I've gotten good at spinning. Most of my riding is fixed and I don't use cars. Spinning that fast with 46:16 (on my track bike) on a slight downhill with a tailwind is scary. Especially with a roadie trying as hard as he can to catch you before the finish line. I got kinda scared and let him pass. The crash is never worth it.
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