Originally Posted by
Grumpy McTrumpy
Help me out here...
I am missing something. According to the posted study on pez, the variable is body position, and the control is 75%VO2Max. I can't find any mention of "maintaining same road speed". Sometimes I miss stuff though.
The article mentions similar cadence around 60rpm. This would indicate similar speed if we assumed the same gear, but I don't see that as a safe assumption based on what's in the article. I'm not claiming the speed will be the same, as aerodynamics will certainly slow you when out of the saddle, especially on a moderate climb of 5.3%, as mentioned in the article.
The big point of the article is that you're not burning any more energy up by standing. So any losses would have to be between the pedals and the rear tire, like from increased drag.
Originally Posted by
Grumpy McTrumpy
As far as the above graph goes, it looks to me like speed is going up while power is going down. The initial acceleration of pedal RPM starts at T12:41: P1500: V24. next second shows peak power, then power falls off as efficiency increases and more of the forces are being used to accelerate the bike. Max RPM indicates the point right before efficiency goes to its highest level, and speed then levels off. I would be interested in seeing what the power requirements would be to maintain V33, after the acceleration phase is complete.
I do not see this as a contradiction of what I said earlier.
The speed in a PowerTap lags behind a bit in my experience. Power doesn't fall off as efficiency increases, it falls off because maintaining 1651W is damned tough, and my NMP is mostly gone at that point. What efficiency are you speaking of here? Mechanical?
Originally Posted by
Grumpy McTrumpy
because a larger (meaning more frequent) number of accelerations have the advantage of working with, rather than against momentum. This is not rolling on a flat surface. The gravitational acceleration of the earth causes immediate backward acceleration at every moment that the bicycle is not under power.
Consider this:
Try pedaling one revolution of your crank per three seconds. Do a fast revolution, and then wait for three seconds "coasting". If you do it on a track, the bike will maintain velocity to a certain degree. If you do it on an uphill, the bike will possibly come to a complete standstill or even start to go backwards inbetween pedal strokes. Clearly this is an extreme example, but the physics are the same as what I am talking about. When you pedal out of the saddle in the traditional up-down way, there are stronger surges and longer "coasting" times per unit RPM than there are for spinning circles while seated.
These surges are not part of the mechanical inefficiency of the bicycle drivetrain. They are transmitted to the road. The only problem is that gravity is a constant acceleration pushing you literally backwards while you ride uphill. You need to have the most circular pedal stroke to overcome this and lose the least amount of forward (and upward) momentum, with the least energy expenditure. Also a faster cadence means that the dead spots in your stroke will have a lesser penalty since gravity has had less time to accelerate you backwards in each turn of the pedals.
We are speaking of climbing after all, and climbing is not anything like rolling on flats. The physical forces are vastly different.
If your average power is identical, there's no reason lower cadence will mean a lower speed.