I have two bikes outfitted with two different power meters and have done a 30 minute Tempo/LT ride on each bike. I am trying to understand why there are slight variations between the two nearly identical efforts.
First the hardware configurations:
1). 2004 Cannondale CADD 7, 54 cm frame, 172 mm cranks, full aluminum bike, 53/39 and 12/26 Campy with Powertap SL.
2). 2005 Specialized Roubaix Pro, 54 cm frame, 172 mm cranks, full carbon fiber bike, 53/39 and 13/26 Campy with Ergomo Pro.
Next the ride information:
A 30 minute Tempo ride 1 week apart on the same indoor trainer. I have attached a Word file that lists key measures of both rides along with a min/max/avg comparison for other key measures. To my untrained eye, the ride statistics are very similar in terms of HR, cadence, and pace. However, I am seeing a 12 watt power difference between the two bikes. The aluminum Cannondale requires 12 less watts to produce .3 MPH higher speed at a virtually identical cadence than the Specialized.
Here is where I need help:
1). Could the more stiff aluminum frame of the Cannondale account for lower watts yielding a greater speed over the more pliant carbon frame of the Specialized?
2). Could the slight variation in rear cassette gearing cause the difference? I don’t know which rear gear I was using on either ride, but I was in the 53 front ring on both rides.
3). Could the variance be explained by the difference in accuracy between the two power meters?
4). Is the variance so small that it is insignificant and immaterial?
5). Could the rides truly be slightly different enough to account for the slight power and speed variation?
6). Do I need to repeat two more rides and attempt to exactly duplicate conditions before any meaningful conclusions should be reached?
A little background info……..I had ridden both bikes with Polar Power Meters since the bikes were purchased new. Even with the Polar units, I noticed I produced less watts but similar or higher speeds on the Cannondale than the Specialized during rides. Back then, I chalked this up to a potential quirkiness of the Polar units.
However, about 9 months ago, I converted my Specialized to the Ergomo and noticed that the Ergomo was yielding similar power results than the Polar I just removed. 9 months later, after converting my Cannondale to a Powertap, I see that it is yielding slightly lower numbers than the Specialized similar to the Polar. as a side note, I think I’ve proven at least to myself that the Polar Power Meter is a reasonably accurate meter for the price.
The reason for my post was after watching the DVD that came with my Powertap, I heard Dr. Lim explain that anything that causes you to produce the same speed with less watts is a GOOD thing. While this is usually attributed to aerodynamic positioning, it dawned on me that the Cannondale might be a better bike for me because I could use less watts to produce a faster speed than when riding my Specialized. Up until I heard this concept, I thought that my Cannondale with less watts might actually be a bad thing.
So now that I have two good meters, can the more astute power gurus of the group help me answer the 6 questions posed above? Or, perhaps help clear up what I may need to do in order to clear up this mystery?
First the hardware configurations:
1). 2004 Cannondale CADD 7, 54 cm frame, 172 mm cranks, full aluminum bike, 53/39 and 12/26 Campy with Powertap SL.
2). 2005 Specialized Roubaix Pro, 54 cm frame, 172 mm cranks, full carbon fiber bike, 53/39 and 13/26 Campy with Ergomo Pro.
Next the ride information:
A 30 minute Tempo ride 1 week apart on the same indoor trainer. I have attached a Word file that lists key measures of both rides along with a min/max/avg comparison for other key measures. To my untrained eye, the ride statistics are very similar in terms of HR, cadence, and pace. However, I am seeing a 12 watt power difference between the two bikes. The aluminum Cannondale requires 12 less watts to produce .3 MPH higher speed at a virtually identical cadence than the Specialized.
Here is where I need help:
1). Could the more stiff aluminum frame of the Cannondale account for lower watts yielding a greater speed over the more pliant carbon frame of the Specialized?
2). Could the slight variation in rear cassette gearing cause the difference? I don’t know which rear gear I was using on either ride, but I was in the 53 front ring on both rides.
3). Could the variance be explained by the difference in accuracy between the two power meters?
4). Is the variance so small that it is insignificant and immaterial?
5). Could the rides truly be slightly different enough to account for the slight power and speed variation?
6). Do I need to repeat two more rides and attempt to exactly duplicate conditions before any meaningful conclusions should be reached?
A little background info……..I had ridden both bikes with Polar Power Meters since the bikes were purchased new. Even with the Polar units, I noticed I produced less watts but similar or higher speeds on the Cannondale than the Specialized during rides. Back then, I chalked this up to a potential quirkiness of the Polar units.
However, about 9 months ago, I converted my Specialized to the Ergomo and noticed that the Ergomo was yielding similar power results than the Polar I just removed. 9 months later, after converting my Cannondale to a Powertap, I see that it is yielding slightly lower numbers than the Specialized similar to the Polar. as a side note, I think I’ve proven at least to myself that the Polar Power Meter is a reasonably accurate meter for the price.
The reason for my post was after watching the DVD that came with my Powertap, I heard Dr. Lim explain that anything that causes you to produce the same speed with less watts is a GOOD thing. While this is usually attributed to aerodynamic positioning, it dawned on me that the Cannondale might be a better bike for me because I could use less watts to produce a faster speed than when riding my Specialized. Up until I heard this concept, I thought that my Cannondale with less watts might actually be a bad thing.
So now that I have two good meters, can the more astute power gurus of the group help me answer the 6 questions posed above? Or, perhaps help clear up what I may need to do in order to clear up this mystery?
