Watts/kg and "Opposing Forces"
I read an article that says the following:
"Power to weight ratio is important because it requires more power for a heavier rider to travel the same velocity than for a lighter rider. However, it is important to remember that gravitational resistance is just one of many opposing forces while riding and only a small percentage of the opposing force on a flat road."* With the last sentence in mind I wondered: If I, a 69kg rider, maintain 1100 watts in a 20-second sprint (15.9 watts/kg) alongside an 88kg rider maintaining 1400 watts (also 15.9 watts/kg), who goes faster? To reduce the number of opposing forces we'll call this a drag race on a flat road with no wind and no wheelsucking/drafting. Two riders with different mass but generating identical power to weight ratios sprinting alongside one another. Who goes faster? *(C) Colin Sandberg |
Originally Posted by Davey
(Post 6284743)
I read an article that says the following:
"Power to weight ratio is important because it requires more power for a heavier rider to travel the same velocity than for a lighter rider. However, it is important to remember that gravitational resistance is just one of many opposing forces while riding and only a small percentage of the opposing force on a flat road."* With the last sentence in mind I wondered: If I, a 69kg rider, maintain 1100 watts in a 20-second sprint (15.9 watts/kg) alongside an 88kg rider maintaining 1400 watts (also 15.9 watts/kg), who goes faster? To reduce the number of opposing forces we'll call this a drag race on a flat road with no wind and no wheelsucking/drafting. Two riders with different mass but generating identical power to weight ratios sprinting alongside one another. Who goes faster? *(C) Colin Sandberg His watts/CdA ratio will almost certainly be greater. |
Big guy wins.
Here's a tangent: How is the "A" in CdA related to weight? If you make the crazy assumption that volume (mass) is equal to HxWxD and area is equal to HxW, then you would say that the square root of a rider's area should be proportional to the cube root of his mass... or that the rider's area is proportional to his mass raised to the 2/3 power. The [huge] assumption here is that the ratios of height to width to depth are fairly constant among riders. So maybe the metric for steady-state, flat, constant speed vs. drag power should be W/[kg^(2/3)]. Of course, a sprint is not steady-state; the riders have to accelerate against their masses. |
What speed are you starting from? If starting from a dead stop, the difference will be smaller.
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Originally Posted by Phantoj
(Post 6284826)
So maybe the metric for steady-state, flat, constant speed vs. drag power should be W/[kg^(2/3)]. http://www.cyclecoach.com/pageID-dow..._MAP_zones.htm |
There is a lot more to it than w/kg.... just sayin
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Originally Posted by Davey
(Post 6284743)
With the last sentence in mind I wondered: If I, a 69kg rider, maintain 1100 watts in a 20-second sprint (15.9 watts/kg) alongside an 88kg rider maintaining 1400 watts (also 15.9 watts/kg), who goes faster? To reduce the number of opposing forces we'll call this a drag race on a flat road with no wind and no wheelsucking/drafting. Two riders with different mass but generating identical power to weight ratios sprinting alongside one another. Who goes faster?
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Figure it this way - since frontal area is sort of similar for many riders, make it a minor point.
Major point is power, another is weight, since both vary greatly. Pure wattage relates to flat type speed. Threshold relates to TT speed. Watt/kg relates to climbing speed, minor is acceleration speed. Max (sub 10 second) wattage relates to jump in a sprint. 20-30 second wattage relates to sustainable top speed in a sprint. This is how I approach it. Seems to hold true at the most basic levels (i.e. 100-200 watt and/or 5 kg deltas). At fine tuning levels ("will that 4 watt savings with better tires make me faster in the sprint") then it's not right. hope this helps, cdr |
Originally Posted by carpediemracing
(Post 6285323)
Figure it this way - since frontal area is sort of similar for many riders, make it a minor point.
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Thank you all for reminding me why I went into television instead of physics...I now feel dumber than usual.
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Originally Posted by asgelle
(Post 6285382)
Comparing CdA values over a range of riders shows about the same variation as weight of bike plus rider.
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Originally Posted by Racer Ex
(Post 6285576)
In what riding position?
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Interesting. Any references you have bookmarked, asgelle?
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Originally Posted by Davey
(Post 6284743)
I read an article that says the following:
. Who goes faster? *(C) Colin Sandberg The one with the better positioning at the beginning of the sprint. |
Originally Posted by ElJamoquio
(Post 6286267)
Interesting. Any references you have bookmarked, asgelle?
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Originally Posted by brianappleby
(Post 6286269)
The one with the better positioning at the beginning of the sprint.
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Originally Posted by asgelle
(Post 6286045)
All positions.
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Originally Posted by ElJamoquio
(Post 6286267)
Interesting. Any references you have bookmarked, asgelle?
http://www.bikeforums.net/showthread.php?t=389702 post #16 tom d - .212? ryder h - .2298 just from those two measurements, there is about an 8% difference ~ 70kg rider and 75.9kg rider. i am sure there are extremes on both ends that would drastically increase the percent differences. |
Originally Posted by Racer Ex
(Post 6286631)
Hard to buy that based on the huge difference in frontal area between someone sitting up on the hoods and someone in a full TT position...
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What I want to know is how the heck does a little guy like Levi (relatively low steady state watts compared to much larger riders like Cancellara) ride a faster relatively flat TT?
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Originally Posted by Pizza Man
(Post 6286941)
... Levi (relatively low steady state watts compared to much larger riders like Cancellara) ...
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Originally Posted by Pizza Man
(Post 6286941)
What I want to know is how the heck does a little guy like Levi (relatively low steady state watts compared to much larger riders like Cancellara) ride a faster relatively flat TT?
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Originally Posted by Pizza Man
(Post 6286941)
What I want to know is how the heck does a little guy like Levi (relatively low steady state watts compared to much larger riders like Cancellara) ride a faster relatively flat TT?
Aero as anything. |
Originally Posted by Pizza Man
(Post 6286941)
What I want to know is how the heck does a little guy like Levi (relatively low steady state watts compared to much larger riders like Cancellara) ride a faster relatively flat TT?
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Originally Posted by Pizza Man
(Post 6286941)
What I want to know is how the heck does a little guy like Levi (relatively low steady state watts compared to much larger riders like Cancellara) ride a faster relatively flat TT?
Oh and as stated above, Levi seems to have the CdA of a small child :p |
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