"The 33"-Road Bike Racing - Are all watts created equal?

Will a rider putting out 150 watts, no matter what gear he is in, go at the same speed? (ignoring minor chain friction differences)

For examole, a rider puts out 150 watts while mashing a big gear at a cadence of 60 and then the same rider puts out 150 watts while spinning a small gear at a cadence of 120, will his speed be the same?

yes.



A watt is a watt, is a watt. It's watt's up.

do all your gears make you go the same speed? 53/14 and 200w on the flat or 39/25 and 200w up a hill, do you think they are going to be the same speed?

They are the same effort(or close to) but speed will not

Yes. Ignoring friction and aerodynamic effects, power is constant across geared/chain speed changes.

do all your gears make you go the same speed? 53/14 and 200w on the flat or 39/25 and 200w up a hill, do you think they are going to be the same speed?

He's asking more of a physics problem.

do all your gears make you go the same speed? 53/14 and 200w on the flat or 39/25 and 200w up a hill, do you think they are going to be the same speed?

They are the same effort(or close to) but speed will not

I should have added on the same flat, windless course, like a track on a calm day.

if the watts go out to the ground, yes

but at very high cadences more watts are burning as heat and breathing and that
becomes inefficient...total watts generated goes up but not all to the ground


for biking though you'd only measure forward moving guatts [so for all intents...mostly yes]

if the watts go out to the ground, yes

but at very high cadences more watts are burning as heat and breathing and that
becomes inefficient...total watts generated goes up but not all to the ground


for biking though you'd only measure forward moving guatts [so for all intents...mostly yes]

So for watts measured by a power meter, the answer would be yes?

Correct.

incorrect

It depends on what time interval are you measuring the power.

Take a 150W 3s ave power measurement with the cyclist riding at 60 cadence. He is actually producing 3 power peaks and 3 power valleys during that time interval which averages to 150W. A cyclist riding at 120 cadence would have produced 6 smaller power spikes but would come up with the same average power.

Even if your computer says you are traveling at a constant speed your bicycle is actually accelerating and decelerating with each pedal stroke. With the aerodynamic drag increasing exponentially with speed the large-surge/low-cadence rider will experience greater drag forces and a trivially slower speed.

What if said rider is going uphill?

This thread-----> :rolleyes:

incorrect

It depends on what time interval are you measuring the power.

Take a 150W 3s ave power measurement with the cyclist riding at 60 cadence. He is actually producing 3 power peaks and 3 power valleys during that time interval which averages to 150W. A cyclist riding at 120 cadence would have produced 6 smaller power spikes but would come up with the same average power.

Even if your computer says you are traveling at a constant speed your bicycle is actually accelerating and decelerating with each pedal stroke. With the aerodynamic drag increasing exponentially with speed the large-surge/low-cadence rider will experience greater drag forces and a trivially slower speed.

well thats more an issue of the measurement method than the actual physics of the situation. Over an interval of more than a few seconds those effects would average out anyway.

Under the same conditions, the an identical number of watts (by any combination of cadence and torque) getting to the ground WILL produce identical speeds.

maybe flailing at 180 rpm will make more wind resistance and be every so slightly slower, but that would be because your drag increased, not that your power was somehow diluted by higher rpm.

incorrect

It depends on what time interval are you measuring the power.

Take a 150W 3s ave power measurement

Now we're really splitting hairs, and incorrectly I might add. Note that the Powertap (for example), even though you can set the interval for 3 seconds, actually samples at 60 hz, which, for bicycling crank rotational speeds, will be precise enough to accurately measure power in both of your example cases. Your speed would be the same.

Now over a period of time, the metabolic cost of varying power can be != to the average power, which led Coggin et al to come up with the norm power construct.

Will a rider putting out 150 watts, no matter what gear he is in, go at the same speed? (ignoring minor chain friction differences)

For examole, a rider puts out 150 watts while mashing a big gear at a cadence of 60 and then the same rider puts out 150 watts while spinning a small gear at a cadence of 120, will his speed be the same?

if everything else stays the same (position, bike etc.) basically yes

if you had a large rider sitting up and a small rider on a tt bike with a good aero position which have completely different frontal areas then, no you will only go as fast as the watts of drag you have to overcome allow

Now we're really splitting hairs, and incorrectly I might add. Note that the Powertap (for example), even though you can set the interval for 3 seconds, actually samples at 60 hz, which, for bicycling crank rotational speeds, will be precise enough to accurately measure power in both of your example cases. Your speed would be the same.

Now over a period of time, the metabolic cost of varying power can be != to the average power, which led Coggin et al to come up with the norm power construct.

I agree with that. I was just trying to illustrate that two people with the same average power over a time period may produce significantly different average speeds if the power is applied unevenly, and that power is ALWAYS supplied unevenly to some extent.

Compare 5min average power and 5min average speed in these two cases

Rider one goes out too hard and then fades (say first min 500W then minutes 2-5 are at 250W). He would average 300W for the 5min. Rider two just holds a steady 300W for the entire effort. Rider two will make it further than rider one and therefore will also have a higher average speed.

Rider one will also experience a greater metabolic cost due to time above FTP etc, but that is irrelevant.


well thats more an issue of the measurement method than the actual physics of the situation. Over an interval of more than a few seconds those effects would average out anyway.


Are you sure?

What if said rider is going uphill?

What weighs more; a pound of feathers or a pound of lead?

You people are trying to make this way too complicated.

i think this is a good discussion. best i've seen on these boards all winter ('course, that's not setting the bar very high). here's what i believe i've read, and what it means to me, and it brings up a question:

-first, keep the assumptions consistent. it's just me, on my TT bike, in the same position, on a flat road, no wind, same atmospheric conditions. if i maintain a constant 200W for the same amount of time, it doesn't matter what gear i'm in or what rpm i turn
-i'm listening to this discussion from a training standpoint. and i read this as mashing vs. spinning. and what this seems to be telling me is that i get the same speed on this time trial by mashing 75 rpm and producing 200W as i do by spinning on this time trial at 100 rpm and producing 200W.
-if this is so, then what's the big deal about spinning? why is it all the rage? i know lance made it the method du jour, but if it extracts a higher physiological price for the same speed, why isn't it better to mash at 75 rpm?
-the previous post also seems to explain to me why pacing a TT is so important. i hadn't really understood why that was so, i've just always accepted that it was true

-i'm listening to this discussion from a training standpoint. and i read this as mashing vs. spinning. and what this seems to be telling me is that i get the same speed on this time trial by mashing 75 rpm and producing 200W as i do by spinning on this time trial at 100 rpm and producing 200W.

But you haven't asked about how the mode of power production affects fatigue.

To cut to the chase, experienced riders will choose the best cadence for themselves. If you don't feel you're experienced enough to choose optimal cadence, experiment riding in higher and lower gears to build up an experience base. Efficiency is a red herring and plays no role; speed is somewhat more relevant, but only for constant or final efforts as it doesn't account for minimizing fatigue in the present to be able to go faster at a later time.

Smoke - Spinning higher rpms is generally less efficient, that is you use more energy to generate your 200W at 100rpms than you do at 75 rpms. However, you are applying a higher peak force to the pedals at 75rpms. For some people, this higher peak force causes more leg fatigue (or sometimes just more fatigue the next day which is a factor in a stage race). Thus, there is a balance between higher efficiency and higher peak force. The point where you realize this balance depends on the individual and the event.

This thread should be moved to foo

incorrect

It depends on what time interval are you measuring the power.

Take a 150W 3s ave power measurement with the cyclist riding at 60 cadence. He is actually producing 3 power peaks and 3 power valleys during that time interval which averages to 150W. A cyclist riding at 120 cadence would have produced 6 smaller power spikes but would come up with the same average power.

Even if your computer says you are traveling at a constant speed your bicycle is actually accelerating and decelerating with each pedal stroke. With the aerodynamic drag increasing exponentially with speed the large-surge/low-cadence rider will experience greater drag forces and a trivially slower speed.

Bingo.. Semantically,
Instantaneous power applied to BB vs time = function of bio mechanics and non-linear.
Drag vs Speed = non linear. /endthread.

=> differing speeds for differing RPMs

This thread should be moved to foo

If you’re looking for mindless drivel watch tv. Personally, I prefer my drivel complicated. :)

It seems that many get offended by any suggestion that their power meter doesn’t have all the bloody answers.

You people are trying to make this way too complicated.

Simpleton

Simpleton

No, he is correct for all intents and purposes.

Simulation: http://static.howstuffworks.com/flash/fpte-curve2.swf
Description: http://science.howstuffworks.com/fpte5.htm

In before 1.21 jiggawatts.

Rider one goes out too hard and then fades (say first min 500W then minutes 2-5 are at 250W). He would average 300W for the 5min. Rider two just holds a steady 300W for the entire effort. Rider two will make it further than rider one and therefore will also have a higher average speed.


I see what you are saying, but it's splitting hairs and distorting the question.

power will only be proportional to speed under steady-state conditions. throw those out by averaging parameters over different intervals (as you have done), and you can get the numbers to tell you anything you want. It doesn't mean the physics is wrong, it just means you aren't looking at it properly.

the slight variations in power have essentially no effect on the overall momentum of the rider at normal speeds. do you swing back and forth from 20-30 MPH with every pedal stroke? No. For the sake of this thread its appropriate to assume steady-state conditions. Doing otherwise is just being a smart ass.

Ah yes assumptions and qualifiers make the situations equivalent… in your mind at least.

Math done like an engineer; technically got the wrong answer due to approximations, but it is close enough that nobody dies.

It seems that many get offended by any suggestion that their power meter doesn’t have all the bloody answers.

Except this thread* has nothing to do with power meters. Hint: power exists even in the absence of measurement.

*With the exception of where you introduced it for no reason.

Smoke - Spinning higher rpms is generally less efficient, that is you use more energy to generate your 200W at 100rpms than you do at 75 rpms. However, you are applying a higher peak force to the pedals at 75rpms. For some people, this higher peak force causes more leg fatigue (or sometimes just more fatigue the next day which is a factor in a stage race). Thus, there is a balance between higher efficiency and higher peak force. The point where you realize this balance depends on the individual and the event.Yeah, it depends upon your physiology and I doubt most people would have the leg-muscle strength to go for very long at 75-rpms at LT. Also you have to separate oxygen-consumption from carb-calories consumed in producing that 200w.

If you’re looking for mindless drivel watch tv. Personally, I prefer my drivel complicated. :)

It seems that many get offended by any suggestion that their power meter doesn’t have all the bloody answers.

I dont have a power meter and find my time better spent training than worrying about if a watt going up hill is the same as a watt on the flat with a headwind.....


im going to ride now.

Smoke - Spinning higher rpms is generally less efficient, that is you use more energy to generate your 200W at 100rpms than you do at 75 rpms. However, you are applying a higher peak force to the pedals at 75rpms. For some people, this higher peak force causes more leg fatigue (or sometimes just more fatigue the next day which is a factor in a stage race). Thus, there is a balance between higher efficiency and higher peak force. The point where you realize this balance depends on the individual and the event.

that was my understanding. i've always read that you should spin a high rpm, and if you get too tired, finish a ride at a low rpm, since it requires less oxygen to do so. i'm a masher; always have been. i'll turn 80 rpm all day. and i've been like that for 12 years; my legs are used to spending hours at a time doing that. but since lance, everyone and his coach wants you to change your spin to a high rpm. but why, if it's less efficient? just cause it works for lance doesn't mean it's right for everybody. i've never understood the you-should-spin-100 rpm idea. and this thread indicates to me that there is no advantage in speed to doing so. in fact, with its lack of efficiency, it may be better for you to turn 80 rpm (assuming you can do so for the length of the ride). heck, i think everyone should work on their spin to bring their rpm's down, not up.

that was my understanding. i've always read that you should spin a high rpm, and if you get too tired, finish a ride at a low rpm, since it requires less oxygen to do so. i'm a masher; always have been. i'll turn 80 rpm all day. and i've been like that for 12 years; my legs are used to spending hours at a time doing that. but since lance, everyone and his coach wants you to change your spin to a high rpm. but why, if it's less efficient? just cause it works for lance doesn't mean it's right for everybody. i've never understood the you-should-spin-100 rpm idea. and this thread indicates to me that there is no advantage in speed to doing so. in fact, with its lack of efficiency, it may be better for you to turn 80 rpm (assuming you can do so for the length of the ride). heck, i think everyone should work on their spin to bring their rpm's down, not up.


There is no question that there is a correlation between high cadence and high speed (wattage). There is no way track riders could be fast in the flying 200 meter if they were spinning at 80. They are in the 150+ range. Even stage race sprints, where most guys legs are pretty shot after hours in the saddle, riders are sprinting at 100+.

If you are talking about steady riding for a long period of time, then it al depends on the individual, as many have pointed out. You can mash at 80 all day. I can't go very long at 80 because my legs fatigue, but I can go for a long time around 100. If I tried going at 120+, then my legs would be ok but I'd get winded quickly and not be able to maintain. Trick is to experiment with cadence and find the range where you can get the max speed (and therefore max power) for the type of riding you do.

Will a rider putting out 150 watts, no matter what gear he is in, go at the same speed? (ignoring minor chain friction differences)

For examole, a rider puts out 150 watts while mashing a big gear at a cadence of 60 and then the same rider puts out 150 watts while spinning a small gear at a cadence of 120, will his speed be the same?

No, they would only be the same if you are using in-lbs for power output.

What about watts created in Watts? I think those would be better watts.

With the aerodynamic drag increasing exponentially with speed ...

Huh?

http://en.wikipedia.org/wiki/Watt

FTW

Notice, that this reference does not go into all of the bull-minutia covered in this thread. It is straight forward. A watt is a watt is a watt.

That is all.

Huh?

http://www.kreuzotter.de/images/P_equ.gif



P Rider's power
V Velocity of the bicycle
W Wind speed
T Air temperature (reduced to deg. Kelvin) (influences air density)
HNN Height above sea level (influences air density)
rho Air density
rho_0 Air density on sea level at 0° Celsius (32°F)
P_0 Air pressure on sea level at 0° Celsius (32°F)
m Mass of the bicycle (influences rolling friction, slope-dependent pull-down force, and normal force)
M Mass of the rider (influences rolling friction, pull-down force, and the rider's frontal area via body volume)
A Total frontal area (bicycle + rider)
Cw Air resistance coefficient
g Gravitational acceleration
Cr Rolling resistance coefficient
Cm Coefficient for transmission losses and losses caused by tire slippage (the latter can be heard during powerful pedal strokes at low speeds, for instance by their echo when you're riding along a vertical wall)

stg Inclination (grade) of road (unit: percent)



rho = rho_0 * (273/T) * e-rho_0*g*HNN/P_0 (air density via barometric formula)
(pull-down force plus normalized rolling friction force on inclined plane)



Note the exponent in the velocity term

http://www.kreuzotter.de/english/espeed.htm

http://en.wikipedia.org/wiki/Watt

FTW

Notice, that this reference does not go into all of the bull-minutia covered in this thread. It is straight forward. A watt is a watt is a watt.

That is all.

Far less entertaining.

Note the exponent in the velocity term

Things that grow as the square or the cube, etc., show algebraic growth, not exponential growth. If you have something in the form a raised to the power b with a as the variable and b fixed (like the function f(x)=x^2) it isn't exponential. To have that you need a fixed and b as the variable (like the function f(x) = e^x).

http://www.spursdynasty.com/uploaded_images/manu_tiger-794868.jpg

Things that grow as the square or the cube, etc., show algebraic growth, not exponential growth. If you have something in the form a raised to the power b with a as the variable and b fixed (like the function f(x)=x^2) it isn't exponential. To have that you need a fixed and b as the variable (like the function f(x) = e^x).

Ok

http://www.spursdynasty.com/uploaded_images/manu_tiger-794868.jpg

:lol:

Everytime I see that pic it makes me laugh

but since lance, everyone and his coach wants you to change your spin to a high rpm. but why, if it's less efficient? just cause it works for lance doesn't mean it's right for everybody. i've never understood the you-should-spin-100 rpm idea. and this thread indicates to me that there is no advantage in speed to doing so. in fact, with its lack of efficiency, it may be better for you to turn 80 rpm (assuming you can do so for the length of the ride). heck, i think everyone should work on their spin to bring their rpm's down, not up.

It's more efficient from a purely mechanical standpoint, yes, but our bodies are convoluted organic fuel cell engines.

Dervs are geared differently than their gasoline counterparts because it can take advantage of inherent strengths and mitigate weaknesses. The human body on a bicycle is generally more effective when used as an aerobic system. You train long enough at 120rpm and you'll feel the difference.

No, they would only be the same if you are using in-lbs for power output.

This is completely backwards. They would be the same speed if they have the same power, ignoring small aerodynamic relations with cadence and small changes in chain friction.