I've been using 195mm Zinn custom cranks for several thousand miles. These were actually shorter than Zinn's formula called for. I've recently had the chance to try 175mm and 172.5 mm cranks (not Zinn) on the same bike. I think I am now ready and able to make some judgements about crank arm length.
One thing I noticed when I first started using the 195mm crank arms is that I got winded easier and long hard rides were more tireing. I figured this would go away when I became better adapted to the long cranks. To some degree this was true and I went back and forth between thinking the long cranks were an advantage and thinking they were a disadvantage.
Now that I've been able to put some miles on shorter cranks on the same bike, I'm quite certain the 195s are too long.
Here is what I think is going on: Though you are able to push with more force when your legs are near full extension, which works in favor of shorter cranks, I think there is a net gain in leverage with longer cranks. But I think the penalty (nothing is free) is that turning longer cranks takes more oxygen. That is, turning your legs in a big circle takes more oxygen than turning your legs in a small circle.
If you were able to graph the two (leverage vs. heart rate) at some point the two graphs would cross at your optimal crank length. (Complicating this is that I think your optimum crank length standing is longer than your optimum length sitting.)
For this reason, I think your VO2 max is probably as important in choosing a crank arm length as is your inseam measurement. That is, a short person with a good VO2 max might be able to use longer crank arms than a tall person with a poor VO2 max.
I've read the article at powercranks.com regarding the Martin study and agree with most of what he says. I too have found that I can lower my handlebars with shorter cranks, giving me a more aero position, but I'm not quite ready to go to extremely short crank amrs. Maybe I still have a bias toward longer cranks, but I'm inclined to think that 177.5 is probably the best length for me and, if my memory serves me, I have an inseam of 94cm.
Five years ago I would have said that most people are using crank arms too short for them. Now I would say that most people are probaly using crank arms that are about right or slightly too long.
Randy
One thing I noticed when I first started using the 195mm crank arms is that I got winded easier and long hard rides were more tireing. I figured this would go away when I became better adapted to the long cranks. To some degree this was true and I went back and forth between thinking the long cranks were an advantage and thinking they were a disadvantage.
Now that I've been able to put some miles on shorter cranks on the same bike, I'm quite certain the 195s are too long.
Here is what I think is going on: Though you are able to push with more force when your legs are near full extension, which works in favor of shorter cranks, I think there is a net gain in leverage with longer cranks. But I think the penalty (nothing is free) is that turning longer cranks takes more oxygen. That is, turning your legs in a big circle takes more oxygen than turning your legs in a small circle.
If you were able to graph the two (leverage vs. heart rate) at some point the two graphs would cross at your optimal crank length. (Complicating this is that I think your optimum crank length standing is longer than your optimum length sitting.)
For this reason, I think your VO2 max is probably as important in choosing a crank arm length as is your inseam measurement. That is, a short person with a good VO2 max might be able to use longer crank arms than a tall person with a poor VO2 max.
I've read the article at powercranks.com regarding the Martin study and agree with most of what he says. I too have found that I can lower my handlebars with shorter cranks, giving me a more aero position, but I'm not quite ready to go to extremely short crank amrs. Maybe I still have a bias toward longer cranks, but I'm inclined to think that 177.5 is probably the best length for me and, if my memory serves me, I have an inseam of 94cm.
Five years ago I would have said that most people are using crank arms too short for them. Now I would say that most people are probaly using crank arms that are about right or slightly too long.
Randy