So Why do heavy guys do better on Flats?

[11ring]

You think they go fast on the flats?
You should see them going downhill in a straight line...

Our club trains every Sunday on a flat stretch and depending on the wind the heavier guys have an advantage. Especially if there is a tail wind. They are disadvantaged in a head wind though as the momentum is fighting the wind. Assuming a heavier rider is bigger they also have more surface area/drag.

Well my explanation works also for downhill.

The heavier rider contains more potential energy at the top of a climb than the lighter rider. As any object (rider plus bike) descends, this potential energy is converted into kinetic energy and is also used to overcome wind and rolling resistance. At terminal velocity, almost all of the 'power' produced from this effect goes to overcoming wind resistance.

You can calculate the 'power' produced by descending by this simple equation.

P= V*Gradient* MG

Thus a rider and bike weighing 100 kg, which is descending at 20 meters second, or 72 kph, on a 1 in ten (.1) slope, is converting ~2000 joules of KE per second into what is essentially free 'power'. As Delta E/T = power then it is 2000 watts of 'power' from gravity.

Now, assume that this rider can also pitch in 500 watts from their muscles, and you have a whopping 2500 watts to overcome wind resistance.

Now, imagine a 50 kg combo of anorexic climber and bike, who can produce, say 300 watts. They only get 1000 watts from gravity, making a total of 1300 watts.

In this case, the 1300 watts may not be sufficient to overcome the wind resistance produced from going downhill at 72 kph, and the rider will slow down. Also, the 2500 watts from our 100kg rider/bike combo may be more than the wind resistance produced by smashing thought he air at 72 kph, and the rider will speed up.

At terminal velocity, the total power will ~ equal wind resistance. We can see that unless lighter riders have bigger power outputs than heavier riders, or greatly superior aerodynamics, heavier rider will tend to reach a greater terminal velocity. In this case, the lighter rider would have to have almost half the CdA of the heavier rider.

As Docspoc has demonstrated thriugh his example of cubes, this is just not the case.

To find terminal velocity going downhill, just solve the equation below

(V*Gradient* MG) + Rider power = CdA* V^3

 

[longfemur]

Weight does not matter as much when on the flats as it does climbing, once you're already accelerated and rolling.

Since heavier guys have bigger muscle mass (since as cyclists, the weight probably is not fat), they potentially can produce more power to keep themselves rolling than lighter guys on flat terrain. But muscles themselves weigh a lot (the quads being the biggest muscles in the body as far as I know), and when the road starts sloping up, the weight starts being more of a handicap than the power advantage, and so lighter guys have the potential to climb more easily, within reason (assuming they have pretty strong, well-trained muscles too). This is why "rouleurs" are rouleurs, and climbers are climbers, and why climbers need the rouleurs to keep them in the race in between the climbs.

Aerodynamics don't really come into the picture that much in this scenario, because there isn't really that much difference in frontal area between heavier guys and lighter guys.

But, as we all know, there are other factors that confound all this, such as overall talent, strategy, team ability, the effectiveness of the performance enhancement some can get away with, etc.

 

[doctorSpoc]

Weight does not matter as much when on the flats as it does climbing, once you're already accelerated and rolling.

Since heavier guys have bigger muscle mass (since as cyclists, the weight probably is not fat), they potentially can produce more power to keep themselves rolling than lighter guys on flat terrain. But muscles themselves weigh a lot (the quads being the biggest muscles in the body as far as I know), and when the road starts sloping up, the weight starts being more of a handicap than the power advantage, and so lighter guys have the potential to climb more easily, within reason (assuming they have pretty strong, well-trained muscles too). This is why "rouleurs" are rouleurs, and climbers are climbers, and why climbers need the rouleurs to keep them in the race in between the climbs.

Aerodynamics don't really come into the picture that much in this scenario, because there isn't really that much difference in frontal area between heavier guys and lighter guys.

But, as we all know, there are other factors that confound all this, such as overall talent, strategy, team ability, the effectiveness of the performance enhancement some can get away with, etc.

do you actually have a power meter? have you actually compared how much power a bigger guy has to put out to go at the same speed as a smaller guy on the same road at the same time? i suggest you go out and do this and you will quickly see that aerodynamics plays a significant roll, in fact the most significant roll... bigger guys need to put out a significantly larger power to get there bigger frames through the air. sure more powerful muscles, but as almost all of that advantage in increased power is used up by the increase in aerodynamic drag... think about it just for a second... a pair of Zipp 808's save something like 40Watts over standard box section rims... what would be the watts savings between Levi Liepheimer body and say... Tom Boonen or Thor Hushovd? answer... significantly more than 40Watts... just think about it for a few seconds and you'll see the error in your thinking..

 

[dhk2]

You think a pair of Zipp 808s save 40 watts over standard rims? My guess is that the savings is more like 4 watts at normal TT speeds of 25-30 mph. Wheels just don't have that much frontal area compared to the rider. Besides, if the tires stay the same, not much changes.

If we could save 40 watts @ 25 mph just by switching to aero wheels, my guess is everyone would have them by now. Just imagine the time I could gain on the fall club century with 40 more watts....I'd pay $1500 to save 40 watts tomorrow.

 

[doctorSpoc]

You think a pair of Zipp 808s save 40 watts over standard rims? My guess is that the savings is more like 4 watts at normal TT speeds of 25-30 mph. Wheels just don't have that much frontal area compared to the rider. Besides, if the tires stay the same, not much changes.

If we could save 40 watts @ 25 mph just by switching to aero wheels, my guess is everyone would have them by now. Just imagine the time I could gain on the fall club century with 40 more watts....I'd pay $1500 to save 40 watts tomorrow.

@ dhk2,

nope, not from what i've found... looks like you better get a pair of zipps then... watt saving in the 36 watts range @ 45km/hr (Tour Magazine - German)... that's what i've found in my search of testing...

in any case the point was that the assertion that the aerodynamics between small an large riders is insignificant... can safely be dismiss as obviously incorrect.

 

[alienator]

Well, this thread is headed the wrong way.

First some facts for the misguided: according to Zipp, their 808's save between 2 and 7 watts at 30 mph. So much for the 40 watt guess. Second, if we're going to start throwing around aerodynamics as a debate technique, let's get it right. Aerodynamics is a lot more than just frontal area, especially for wheels. Zipp wheels are not designed for minimized frontal area. Instead their designed to minimize drag in a range of relative winds from 0 to about 15 degrees. If frontal area was the only thing that tickled the gods' nads, Zipp wouldn't be making the move they're making toward wider rims, allowing wider tires. The new, wider rims are better aerodynamically than their more narrow predecessors.

Second, if you limit yourself to first order calculations, drag varies directly with frontal area, and for the population of pro cyclists, frontal area doesn't vary that much, especially when you remember we're not concerned with the frontal area of a rider standing up but a rider sitting in on a bike. One square meter is the number that's typically thrown around, and the variances from that aren't huge for the average pro rider.

Now, I'll leave everyone so they can get back to their territorial pissings (Thank you, Sr. Cobain.).

 

[doctorSpoc]

First some facts for the misguided: according to Zipp, their 808's save between 2 and 7 watts at 30 mph.

AHHHH no... Zipp claims the new shape yields about 2-7 watts savings... i.e. new shape vs old shape...

"The new shape yields to a savings on the road of 2-7 watts of power for a pair of wheels at 30mph"

http://www.zipp.com/wheels/detail.php?ID=21#

edit - if you scroll up you'll see you basically repeat what i've already said as well.. i.e. "aero drag is frontal area x drag coefficient.." anyway... thanks for coming out and you can pick up your participation ribbon at the door.. maybe next year... lol..

 

[alienator]

AHHHH no... Zipp claims the new shape yields about 2-7 watts savings... i.e. new shape vs old shape...

"The new shape yields to a savings on the road of 2-7 watts of power for a pair of wheels at 30mph"

http://www.zipp.com/wheels/detail.php?ID=21#

That's your interpretation. They don't seem to imply that at all.

At any rate, choosing Tour Magazine results as a point of reference is questionable, at best. They're not known for conducting scientifically sound tests.

 

[doctorSpoc]

That's your interpretation. They don't seem to imply that at all.

At any rate, choosing Tour Magazine results as a point of reference is questionable, at best. They're not known for conducting scientifically sound tests.

well the head engineer at Zipp didn't seem to have a big problem with their testing and numbers.. just thought the testing should be expanded a bit.. he had a bit of a problem that they put some wheels before the 808 and commented that the test was limited really to 0 degrees yah, which almost never happens in real world except on the track... but didn't comment that the numbers were somehow off by an order of magnitude like YOU claim... hmmm...

Interesting aero wheel test in German Triathlete Magazine
Watt savings over a 32 round-spoked Ambrosio Nemesis at 45kmh/28mph
Vuelta carbon pro -38 Watt
Xentis mark 1 -37 Watt
Zipp 808 -36 Watt
Bontrager Aeolus -34 Watt
Zipp 999 -29 Watt
Ritchey carbon -28 Watt
Easton Tempest II carbon -29 Watt
Lightweight TT -27 Watt
Mavic Cosmic Carbone -22 Watt
Corima 3 spoke+Disc -20 Watt
Corima 3 spoke -20 Watt
Lightweight 12/20 -19 Watt
Corima Aero -19 Watt
Tune Olympic Gold -16 Watt
Nimble Crosswind -5 Watt

http://www.zipp.com/support/askjosh/aerowheels.php#
after you get to the page click on "Wind Tunnel" then you can see Josh's comments by clicking on Josh's view.. hmmm.. who's opinion to i go with here... this is pretty hard... i think i'm going to Josh's... lol.

This is actually a repeat of a similar test they did last year. Funny enough I was just talking with Marcus from Triathlon DE just Monday of this week about the test. What they do is have the riders ride at a constant speed for so many laps and then take the average wattage from that run. They do all the wheels at the same speed and use the wattage difference at the same speed to determine the savings, so those wattage numbers they are quoting are watts saved at the same speed.
What we have been discussing with them is that this test really only holds water for indoor track usage as the airflow is completely stagnant in at the track they use, so from an engineering perspective we can consider all of the tests to be conducted at exactly zero degrees of yaw. Unfortunately, zero degrees of yaw will statistically occur less than 1% of the time in the real world, so to really make use of this data we have to either add similar testing done outdoors or wind tunnel data.
At zero degrees of yaw, not only are most wheels very similar, but many aero wheels with large surface area are at a slight disadvantage due to the predominance of skin friction drag over pressure drag, but with just a few degrees of yaw, the pressure drag becomes an order of magnitude more important than skin friction drag.
If you look at our white paper 'A Note on Rim Width' : you will see that all of the data is pretty compressed at zero degrees and that a disc actually gives up a little to both the 404 and 808, this is due to the predominance of skin friction at this angle (note that the zipp disc has less drag here than any other discs with the same shape...thank you dimples!). With just a little wind angle, though, the disc, or 808 suddenly becomes vastly superior to less deep rims. This wind angle phenomenon is part of the cleverness of the Xentis wheel, which has the spokes angled relative to the wind centerline so that at zero degress the spokes are at 10 degrees or so to the wind.
This works excellent at zero degrees, but you can also have too much wind angle and at the higher angles the drag begins to increase again as the Tour magazine test determined: you can see in their tour article Download Translated PDF wind tunnel graph that the Xentis is slightly faster than either the 808 or the disc at zero, but by 4 degrees the disc and 808 have a significant advantage. Using the numbers at zero from the Tour magazine test we extrapolate a 1.2 watt savings at zero over the 808 and 2 watts over the 999 (the data in the Zipp white paper mimics this identically), which is almost exactly what Triathlon DE found in this test.
As with any testing, the problem is determining the limitations of the test itself. In my opinion the Triathlon test is dangerous as they don't really adequately explain the very limited nature of the usefullness of the data. But when we combine testing methodologies you can start to really have something that is worthwhile. I think that this test is very interesting in that it more or less validates one of the data points seen in wind tunnel data, but it is dangerous in that wheel decisions made from this type of test will be very limiting in the real world. This also shows the give and take necessary in the design of these products. We spend about 50 hours per year in the wind tunnel trying to tweak and refine these shapes, but the reality is that you almost always have to give up something to get something.
Lately we have been giving up very low and very high yaw angle performance to improve mid range performance, and I am convinced that this methodology is really the future of design since real world wind angles are generally nothing close to zero degrees. I'm currently writing another white paper on this describing the vector resolution and wind angle distribution in percentages that we are now using for design.
For more information on Rim Shape and the aerodynamic “sweet spot” see our engineering white paper on rim shape:
Rim Shape: (PDF)

 

[alienator]

http://www.zipp.com/support/askjosh/aerowheels.php#
after you get to the page click on "Wind Tunnel" then you can see Josh's comments by clicking on Josh's view.. hmmm.. who's opinion to i go with here... this is pretty hard... i think i'm going to Josh's... lol.

Wow. You feel like you have a lot to prove, eh? Were you born with the overwhelming superiority complex? Or is it that you are just unable to discuss things in a civil manner? After all, scientific method is all about being snide and smug. You've got that down pat, fella. You're truly a credit to your profession.

I said I don't put much faith in Tour's tests, and I stand by that. Anyone that thinks they can quantify, in some manner, comfort, has issues with objective analysis. I am mighty impressed, though, that you went to the effort of looking up Josh Poertner's comments. Very impressive.

Is the snide attitude an important part of your "objective" analytical skills?

 

[doctorSpoc]

Wow. You feel like you have a lot to prove, eh? Were you born with the overwhelming superiority complex? Or is it that you are just unable to discuss things in a civil manner? After all, scientific method is all about being snide and smug. You've got that down pat, fella. You're truly a credit to your profession.

I said I don't put much faith in Tour's tests, and I stand by that. Anyone that thinks they can quantify, in some manner, comfort, has issues with objective analysis. I am mighty impressed, though, that you went to the effort of looking up Josh Poertner's comments. Very impressive.

Is the snide attitude an important part of your "objective" analytical skills?

yeah, i know... i've got some issues i need to work on...

 

[dhk2]

Doc, I don't claim to know much about aerodynamics (or anything else), but I'm always a little suspect when someone quotes the manufacturer's own man. Josh does work for Zipp, right?

From his page you posted, he first says the Tour tests should be taken with a grain of salt, as they were run in zero-yaw (no crosswind) conditions, not real world. He states that in zero-yaw, "most wheels are very similar". But looking at the test data, from 38W saved down to 5W, I don't see very similar results at all. Appears like a huge contradiction to me, but perhaps I'm missing something.

Another small issue turns up in the Wind Tunnel pdf, where Zipp 808s are claimed to save 81 seconds/27 watts (over an unnamed wheel) for a TT rider (eg, Cancellara) putting out 300W.
But then the explanation fine print says slower riders (ie, everyone else in the world) get even more time savings because they are riding longer. That statement just doesn't fit with my limited understanding of how aero drag works.....the part where drag is proportional to the cube of the velocity. Perhaps someone in marketing wrote this burb, thinking that the 27 W savings was a constant regardless of speed

Bicycling Mag had a test report from the Texas A&M wind tunnel a while back. IIRC, they found that a good aero position on the bike was by far the biggest factor. Next was a TT helmet, followed by a tight jersey or skinsuit kept zipped up. The conclusion was that the wheelset was the last thing a TT rider needed to invest in, not the first. Maybe I've got this all wrong; perhaps someone has the issue and can look up the results.

 

[11ring]

The savings for the slower rider are absolutely bigger, but smaller as % of ride time.

As the finish times at amateur level are also more variable, the equipment savings is doubly important at the higher level.

Doc, I don't claim to know much about aerodynamics (or anything else), but I'm always a little suspect when someone quotes the manufacturer's own man. Josh does work for Zipp, right?

From his page you posted, he first says the Tour tests should be taken with a grain of salt, as they were run in zero-yaw (no crosswind) conditions, not real world. He states that in zero-yaw, "most wheels are very similar". But looking at the test data, from 38W saved down to 5W, I don't see very similar results at all. Appears like a huge contradiction to me, but perhaps I'm missing something.

Another small issue turns up in the Wind Tunnel pdf, where Zipp 808s are claimed to save 81 seconds/27 watts (over an unnamed wheel) for a TT rider (eg, Cancellara) putting out 300W.
But then the explanation fine print says slower riders (ie, everyone else in the world) get even more time savings because they are riding longer. That statement just doesn't fit with my limited understanding of how aero drag works.....the part where drag is proportional to the cube of the velocity. Perhaps someone in marketing wrote this burb, thinking that the 27 W savings was a constant regardless of speed

Bicycling Mag had a test report from the Texas A&M wind tunnel a while back. IIRC, they found that a good aero position on the bike was by far the biggest factor. Next was a TT helmet, followed by a tight jersey or skinsuit kept zipped up. The conclusion was that the wheelset was the last thing a TT rider needed to invest in, not the first. Maybe I've got this all wrong; perhaps someone has the issue and can look up the results.

 

[swampy1970]

According to Contador, they don't!

Chris Boardman would agree with Alberto too...

 

[doctorSpoc]

Doc, I don't claim to know much about aerodynamics (or anything else), but I'm always a little suspect when someone quotes the manufacturer's own man. Josh does work for Zipp, right?

From his page you posted, he first says the Tour tests should be taken with a grain of salt, as they were run in zero-yaw (no crosswind) conditions, not real world. He states that in zero-yaw, "most wheels are very similar". But looking at the test data, from 38W saved down to 5W, I don't see very similar results at all. Appears like a huge contradiction to me, but perhaps I'm missing something.

yes, you need to look at the qualities of each of the wheels listed... the lower ranked ones are tri spokes the perform well in cross winds but not so good at 0 degrees, some like the cormina are only 40mm deep vs 80mm for the 808s and the better performing ones. of the ones with similar characteristics to the 808 they are all in the 25-35 ball park give or take...

Another small issue turns up in the Wind Tunnel pdf, where Zipp 808s are claimed to save 81 seconds/27 watts (over an unnamed wheel) for a TT rider (eg, Cancellara) putting out 300W.
But then the explanation fine print says slower riders (ie, everyone else in the world) get even more time savings because they are riding longer. That statement just doesn't fit with my limited understanding of how aero drag works.....the part where drag is proportional to the cube of the velocity. Perhaps someone in marketing wrote this burb, thinking that the 27 W savings was a constant regardless of speed

you have to remember that the drag of the wheels is not that much to begin (when compared to a persons body.. this is my point that started this tangent by the way) and so the speed differential is not enough to make much of difference in absolute terms (relative to the contribution from the wheel yes) Cancellara speed to normal human speed. secondly you have to remember that an increase of 27 watts at 30km/hr will change ones speed more significantly that a 27 watt increase at say 50km/hr... so as counter intuitive as it sounds, the slower you are the more impact aero equipment will have on your times because the faster you go the more and more incremental power it takes to go even faster...

Bicycling Mag had a test report from the Texas A&M wind tunnel a while back. IIRC, they found that a good aero position on the bike was by far the biggest factor. Next was a TT helmet, followed by a tight jersey or skinsuit kept zipped up. The conclusion was that the wheelset was the last thing a TT rider needed to invest in, not the first. Maybe I've got this all wrong; perhaps someone has the issue and can look up the results.

25-35 watts out of say 300-350 IS peanuts.. damn right! i'd be working on my position.. i have seen a really good article in cyclingnews (can find it now though) that gives a really good analysis of these comparisons and a cost benefit/value analysis too... for the money i think the helmet was the best kit to spend your money on but still position is very most important thing.. was interesting that most road bikes couldn't get riders into an optimal position... and again this is the point i was making... saying that the aerodynamics of big compared to small riders is insignificant just doesn't make any kind of sense... all you have to do is look over at your bigger or smaller buddies power reading as you ride and you'll see this.

 

[daveryanwyoming]

Here's one data point in terms of power savings of different components at constant speed for a single rider and single frame tested:

How Aero Is Aero? - BikeRadar

Not exactly an exhaustive test suite, but good food for thought.

-Dave

 

[doctorSpoc]

as swampy said... Chris Boardman (former world hour record holder) 5'9" and 150lbs.. that's not exactly what i'd call a "big" guy and yet in his time he was arguably the best on the flat of anyone on the planet.. kinda blows the big guys do better on the flat theory out of the water.. big guys are really just on an equal footing on the flat.. and maybe very slightly advantaged if any...

also look at the gold medal match in the sprint this year.. Bauge the mountain on the left ended up winning but, Azizulhasni on the right ended up with the silver medal and actually took one of the heats in the final...