[argylesocks]

here are 2 different riders:
80kg person with 320watts at LT (4watts/kg)
60kg person with 240watts at LT (4watts/kg)

riding at LT, who would be faster
a) on a flat 40km TT
b) in a rolling race
c) on a 8mile hillclimb

lets assume same bike, same body shape, same aerodynamics, etc... other than weight & power, all things are equal.

 

[shawndoggy]

here are 2 different riders:
80kg person with 320watts at LT (4watts/kg)
60kg person with 240watts at LT (4watts/kg)

riding at LT, who would be faster
a) on a flat 40km TT
b) in a rolling race
c) on a 8mile hillclimb

lets assume same bike, same body shape, same aerodynamics, etc... other than weight & power, all things are equal.

#1 will be faster in a TT (esp. using your unlikely assumption that they punch the same hole in the wind). Probably significantly faster (on the order of several minutes).

They should be equal on the hill climb as it gets steeper (equal power to weight ratios, same aerodynamics) but the flatter it is, the more the advantage tips back to raw watts. Can't remember where the breakpoint is... I think it's 6%ish?

In the rolling race it's probably going to depend on who has the better anaerobic capacity to get over the rollers.

In short, if those two riders live in Chicago (or Florida or some other very flat area), the big dude is going to be the big gun. If they live in Colorado or Norcal or somewhere with lots of climbing, the tables could be turned (though in truth, the big dude is going to have the advantage in the TTs and flatish crits, so he'll still be a force to be reckoned with).

 

[CC09]

then why do small guys usually make great climbers?

 

[Mark McM]

Power/weight

here are 2 different riders:
80kg person with 320watts at LT (4watts/kg)
60kg person with 240watts at LT (4watts/kg)

riding at LT, who would be faster
a) on a flat 40km TT
b) in a rolling race
c) on a 8mile hillclimb

lets assume same bike, same body shape, same aerodynamics, etc... other than weight & power, all things are equal.

Assuming all else being equal (or at least in proportion to body weight), the larger rider would be faster under all conditions. Aerodynamic drag is proportional to frontal area, and frontal area does not increase proportionally with mass, so the larger rider will have a smaller frontal area/mass ratio. Since these two riders have the same power/mass ratio, the larger rider will have a smaller frontal area/power ratio, and proportionately less drag for their power. Therefore, in a flat TT, the larger rider has the advantage.

For climbing, the larger rider in this example still has an advantage. The weight of the bike will be a smaller proportion of the total weight for the larger rider, so if you add in the weight of the bike, the larger rider will have a larger power/weight ratio than the smaller rider, so the larger rider will climb faster.

So, you might ask, why do smaller riders usually climb faster than larger riders? Because typically, smaller riders have a higher power/weight ratio than large riders. Muscle strength might increase proportionally to size, but aerobic capacity does not. If you were to compare the best time triallers in the peloton to the best climbers, you would find that the time triallers typically are heavier and generate more power than the climbers - but that though the climbers power output was smaller, their weight was much smaller, so they end up with a higher overall power/weight ratio.

 

[asgelle]

here are 2 different riders:
80kg person with 320watts at LT (4watts/kg)
60kg person with 240watts at LT (4watts/kg)

riding at LT, who would be faster
a) on a flat 40km TT
b) in a rolling race
c) on a 8mile hillclimb

lets assume same bike, same body shape, same aerodynamics, etc... other than weight & power, all things are equal.

In all three cases preparation, skill, pacing, and motivation (for B, there will be tactical ability as well) will play a greater role than any difference in power/wt or power/area. Success in racing depends on a lot more than just physical measurements.

 

[TurboTurtle]

In all three cases preparation, skill, pacing, and motivation (for B, there will be tactical ability as well) will play a greater role than any difference in power/wt or power/area. Sucess in racing depends on a lot more than just physical measurements.

Who are you and what did you do with Asgelle? TF

 

[The Flash]

Throw in that the bigger guy will pick up speed faster going down the hills as well....if he can maintain the same speed going up given the equal power output, he'll be way ahead....that's how I hang in the hills ....

The Flash

 

[Dwayne Barry]

In all three cases preparation, skill, pacing, and motivation (for B, there will be tactical ability as well) will play a greater role than any difference in power/wt or power/area. Success in racing depends on a lot more than just physical measurements.

Power by far will explain most of the variability in performance. Totally unmotivated pros just riding time trials to not get eliminated ride faster than all put a few people at your local district champs. All those "intangibles" you mention only come into play once you have riders who are relatively similar in their physical abilities.

 

[asgelle]

Power by far will explain most of the variability in performance. Totally unmotivated pros just riding time trials to not get eliminated ride faster than all put a few people at your local district champs. All those "intangibles" you mention only come into play once you have riders who are relatively similar in their physical abilities.

But in races (at least in the U.S.) we have categories for races so that the fields are comprised of riders of relatively similar abilities. Also note that the original question was concerned only with who would be faster (win) races. That's very diffferent from a pure performance metric.

 

[shawndoggy]

But in races (at least in the U.S.) we have categories for races so that the fields are comprised of riders of relatively similar abilities. Also note that the original question was concerned only with who would be faster (win) races. That's very diffferent from a pure performance metric.

'cept for the flat 40KTT -- the big dude, who has an 80w advantage, would have to ride like a COMPLETE moron to lose, even if the little dude were racing like his life were on the line.

 

[asgelle]

'cept for the flat 40KTT -- the big dude, who has an 80w advantage, would have to ride like a COMPLETE moron to lose, even if the little dude were racing like his life were on the line.

Using the defaults at analyticcycling.com and using a 2/3 power scaling for frontal area, the difference is the larger rider is 1:40 faster (2.7%) assuming a perfect race by each. Whether you have to be a "COMPLETE moron" to lose 1:40 or poor pacing, motivation, position, starts and turns, etc. could account for that is a matter of opinion, but I don't believe it beyond the realm of possibility for lower category or inexperienced riders.

 

[shawndoggy]

Using the defaults at analyticcycling.com and using a 2/3 power scaling for frontal area....

I'm not sure what you mean by "power scaling". I hope that doesn't mean that you gave the lighter guy a smaller effective frontal area, because that's not what the OP asked....

lets assume same bike, same body shape, same aerodynamics, etc... other than weight & power, all things are equal.

... all I changed was the weight of the rider/bike combo (I used 8K for the bike, so 68 and 88), the slope (set to zero, since it's supposed to be a "flat" TT), and the power. ....Not necessarily realistic, I know, but that was the question. I get 54:41 for the heavier rider and 60:00 even for the lower powered rider.

So I stand by my prior assertion that the heavier rider is very unlikely to lose the TT.

 

[asgelle]

I'm not sure what you mean by "power scaling". I hope that doesn't mean that you gave the lighter guy a smaller effective frontal area, because that's not what the OP asked....

That's exactly what i did. The OP wrote 'same body shape" not same size. Do you think it's realistic to say that you could cram an additional 20 kg onto a body without changing either the size or shape of the person. Humans don't show variations of body density of 33%.

Lets say our 60 kg friend is 20% body fat. That would be 12 kg. Since muscle is about 20% more dense than fat, if all that body fat were muscle, it would increase his weight by only about 2.5 kg. Far from the 20 kg proposed.

 

[shawndoggy]

Do you think it's realistic to say that you could cram an additional 20 kg onto a body without changing either the size or shape of the person.

No! absolutely not! 20kg is a lot of weight and the two riders are going to look really different. By the same token, let's say the two riders are 6' tall. The 60Kg dude is going to be rail thin, and the 80Kg guy isn't. But that increase in body mass IS
NOT going to result in a 33% increase in frontal area.

Remember, frontal area is a two dimensional measurement: height x width.

On the bike in an aero position, two people of equal height are going to have roughly the same height on the bike. The difference is going to occur because of the width of the riders. And no way no how will the heavier guy be a whopping 33% wider than the skinny guy. 5% sure, 10% maybe, but no way will he be 33% wider.

 

[asgelle]

No! absolutely not! 20kg is a lot of weight and the two riders are going to look really different. By the same token, let's say the two riders are 6' tall. The 60Kg dude is going to be rail thin, and the 80Kg guy isn't. But that increase in body mass IS
NOT going to result in a 33% increase in frontal area.

Who said anything about 33% wider (or greater frontal area)? I specifically said area would scale as the 2/3 power of weight. So if the weight ratio is 80/60, the frontal area ratio is (80/60)^2/3 or about 1.2, i.e., the heavier rider has about 20% more area.

Remember, frontal area is a two dimensional measurement: height x width.

Right. That's where the 2 in the 2/3 scaling comes from. The 1/3 comes from the relation of length to volume (or weight for constant density).

On the bike in an aero position, two people of equal height are going to have roughly the same height on the bike. The difference is going to occur because of the width of the riders. And no way no how will the heavier guy be a whopping 33% wider than the skinny guy. 5% sure, 10% maybe, but no way will he be 33% wider.

Or maybe 20%, who knows. The 2/3 scaling isn't perfect but according to the Andy Coggan quoting Heil et al., http://www.bicycle-forum.net/racing/Power_Profiling__good_stuff_325967.html the proper scaling ranges from 0.41 to 0.76 so my scaling of 0.67 might be slightly high (or it might not) but is in the correct range The point is the difference in time over a 40K TT is on the order of a couple of minutes, Anyone who's gone out too hard in a TT and died at the end knows it's possible to lose that much time from poor pacing.

 

[Angelracer]

Guy 1 would build gaps so big on guy 2 on a climb 20% +


Climbers rule, end of story.

 

[Kerry Irons]

Say what?

Guy 1 would build gaps so big on guy 2 on a climb 20% +

Climbers rule, end of story.

At the same power to weight ratio, both riders would climb at the same speed. On what do you base your fanciful claim?

 

[53T]

Clearly, the big rider would be riding at LT, while the small climber would be so hopped up on grennies and EPO that he would be at or above max HR from the foot of the climb all the way to the disco in the finishing town. Small guy wins, widow remaries someone with an office job.

You won't find that kind of output on analytical_cycling!

 

[toofast4u]

or...

Or you could just do what I do....put out 310 watts at LT while weighing 68 kilos and smoke them both.

 

[MaestroXC]

Can I have your autograph?