Contributions to Aerodynamic Drag

[chainstay]

I once saw a thread here where someone gave the rough estimates of the percentage range contributions to aerodynamic drag that various components, meaning wheels, frame and rider, contributed to aerodynamic drag, but I can't find the thread or remember the conclusions. Does anyone have an idea what the rough, percentage ranges are? Also, is there a big difference between the contribution to aerodynamic drag lended by the front wheel versus the rear wheel?

I am aware that speed gains due to changing equipment and lessening aerodynamic drag are not even measurable at speeds below 40 kph (or was it 35 kph?), but I am still curious to know roughly what the above percentage ranges are. It seems like the aerodynamic properties of various wheelsets comes up fairly frequently on this forum, and I am wondering where the aerodynamic drag lended by the wheelsets fit in to the overall scheme of things.

 

[alienator]

I am aware that speed gains due to changing equipment and lessening aerodynamic drag are not even measurable at speeds below 40 kph (or was it 35 kph?), but I am still curious to know roughly what the above percentage ranges are. It seems like the aerodynamic properties of various wheelsets comes up fairly frequently on this forum, and I am wondering where the aerodynamic drag lended by the wheelsets fit in to the overall scheme of things.

Wheels account for roughly 25% of the total drag. Most drag, of course, is caused by the oddly shaped biped propelling the bike.

It's not right to say that something can't be measured below a certain threshold. You have to consider what is doing the measurment and, in this case, what aerodynamic changes you're talking about. The speedo will show a difference between a set of Ksyriums and a set of Zipp 404s, LEW VT-1s, Lightweight wheels, Mavic Cosmic Ultimates, and etc.

 

[dazman]

I can't find it anymore either - I think it's a dead link from here, but scroll down and good info:
http://ccforums.ipbhost.com/lofiversion/index.php/t4119.html

or


http://www.socalttseries.com/Training/Articles/AerodynamicsforTimeTrial/tabid/217/Default.aspx
http://www.westwoodvelo.com/archive/index.php?t-354.html
http://www.bikeradar.com/road/fitness/article/know-how-beating-the-wind-12090

Great real world:
http://www.bikeradar.com/road/racing/article/technique

sorry though, I know the one you are after!

 

[chainstay]

Wheels account for roughly 25% of the total drag. Most drag, of course, is caused by the oddly shaped biped propelling the bike.

It's not right to say that something can't be measured below a certain threshold. You have to consider what is doing the measurment and, in this case, what aerodynamic changes you're talking about. The speedo will show a difference between a set of Ksyriums and a set of Zipp 404s, LEW VT-1s, Lightweight wheels, Mavic Cosmic Ultimates, and etc.

Thanks! How about the frame versus wheels and rider? Cervelo seems to make a very big deal about their aero frames in their marketing, and they seem to be immensely popular for triatheletes and time trialing, but aero frames don't seem to be a big priority for weekend road racers, am I correct?

And why do Mavic Ksyrium SLs and ES sell so well? They are regularly panned on this forum as having very poor aerodynamic performance, yet many bike companies bike spec them on their higher end bikes, aftermarket consumers pay up to $800 a crack for them, and they are a common sight at weekend road races.

Questions. Questions. Questions.

 

[chainstay]

I can't find it anymore either - I think it's a dead link from here, but scroll down and good info:
http://ccforums.ipbhost.com/lofiversion/index.php/t4119.html

or


http://www.socalttseries.com/Training/Articles/AerodynamicsforTimeTrial/tabid/217/Default.aspx
http://www.westwoodvelo.com/archive/index.php?t-354.html
http://www.bikeradar.com/road/fitness/article/know-how-beating-the-wind-12090

Great real world:
http://www.bikeradar.com/road/racing/article/technique

sorry though, I know the one you are after!

Thanks! You have given me some good reading material!

 

[artemidorus]

And why do Mavic Ksyrium SLs and ES sell so well? They are regularly panned on this forum as having very poor aerodynamic performance, yet many bike companies bike spec them on their higher end bikes, aftermarket consumers pay up to $800 a crack for them, and they are a common sight at weekend road races.

Because they look great! People buy on looks, reputation, and perhaps weight, and Ksyrium SL/ES has all these. The fact that they don't deserve the reputation is another thing.

 

[531Aussie]

Might've been this, ripped off from Tour Magazine:

They first put Uwe Peschel on a 'normal' road bike

Required output (watts) to sustain 45kph.

Stevens San Remo bike with hands on hoods: 465 Watts
Same bike, hands down on the drops: 406 watts
Same bike, Easton Aeroforce aero bars: 369 Watts
Same bike Triathlon position (5.5 cm lower bar, saddle forwards): 360 Watts
Same as above, with 2 carbon Tri-spoke wheels: 345 Watts

Cervelo Tri bike + Tri spoke wheels: 328 Watts
Cervelo Tri bike + Tri spoke front + disk rear wheel : 320 w
Same as above with Giro aero helmet: 317
Same as above with speed suit: 307



ALSO.......


According to the "Great Wheel Test", some 'aero' wheels are only 5 to 10 watts more efficient than a $200 pair of Mavic Aksiums! According to the Kreuzotter calculator, 10 watts, at or around 30mph, provides a speed increase of 0.3mph on flat roads. If an aero wheel is 20 watts more efficient than a 'normal' wheel (32 spokes) at the same speeds, that's about a 0.5mph increase.
http://www.kreuzotter.de/english/espeed.htm

There are obviously other benefits with good wheels, such as stiffness and hub quality, but I reckon it's the aerodynamics that gives the real, quantifiable speed difference.

http://www.rouesartisanales.com/article-4934445.html


..............................."watts absorbed at 50kph"

Zipp 808....................................18.1
Ritchey WCS Carbon....................19.3
HED Hed 3.................................19.7
Vuelta Carbon Pro WR..................20.8
Easton Tempest II Carbon............21.6
CKT Splendor.............................21.7
Mavic Cosmic Carbone SL.............21.9
Shimano WH-7801 Carbon 50........22.9
Campagnolo Bora G3....................23.0
Rose Aerospoke..........................23.0
Corima Turbospoke .....................23.1
Bntrga Race X Lite Crbn aero........23.4
Fulcrum Racing Speed..................23.7
Gipiemme Carbon 5-5...................24.1
Tune Olympic Gold 2005...............24.1
Shimano WH-7801 Carbon............24.4
FRM FL-R 23 SD Aerolight.............24.6
Corima Aero...............................24.7
Lightweight Obermayer................24.8
Xentis Mark 1.............................25.0
Citec 3000S Aero........................25.5
Shimano WH-R560.......................26.1
Lightweight Ventoux/Standard.......27.3
Campagnolo Eurus.......................27.8
Tune Skyline 2006.......................28.1
FSA RD-600................................28.7
Mavic Aksium Race.......................30.0
Citec 3000S................................30.6
Ambrosio X-Carbo........................31.5
Campagnolo Hyperon....................32.1
Mavic Ksyrium ES........................33.2

 

[artemidorus]

According to the "Great Wheel Test", some 'aero' wheels are only 5 to 10 watts more efficient than a $200 pair of Mavic Aksiums!

Yep, the Aksium beats the Ksyrium ES as well.
BTW, that's 5-10W at 50km/h, a speed above the traditional hour record! The realistic benefit is less than that.
Equally interesting is the 17W difference between the road frame set up for TT and the Cervelo TT frame - I wouldn't have thought the advantage was that large.

 

[artemidorus]

Just for comparison, I have read that a pair of 36 (round) spoke box-rim (ie Open Pro) wheels takes 44W at 50km/h.

 

[531Aussie]

yeah, I'm dubious about the 17w for a TT frame; and 60w just for going down to the drops? Ah well, I guess every point could be questioned

I've also read similar numbers for 36-spoke, box rims, but what about 28 or 32-spoke, 25 to 30mm wheels? I wonder. I can't imagine

 

[chainstay]

http://www.rouesartisanales.com/article-4934445.html

Thanks for that info. I wish they had even more wheelsets in that article. Are any of those wheelsets in the so called semi aero class of wheelsets--- that have a 27-34mm rim? There seem to be a bunch of wheelsets that are 27 to 34 mm and are marketed as aero, (although most of you will quickly point out that 30mm isn't really "aero"), weigh 1,500 to 1,700 grams or so, and don't cost an arm and a leg---the Velocity Deep V, Niobiums, Easton Circuits. Neuvation R28 Aero 2s and American Classic 420s for example. I guess the 420s are more expensive than the others, but are these class of "semi aero" wheels with 30mm rims generally worth considering for the alleged additional aero properties over a standard box rim?

In looking at the Bontrager website, (yeah I know you guys don't like Bontragers but I got them as original equipment on a bike and then upgraded again in the Bontrager line when I had a warranty replacement issue), I see that there is a regular Bontrager Race X Lite rear wheel, which I believe is about a 23mm rim, weighs 860grams, and a Bontrager Race X Lite Aero rear wheel, which is a 31mm rim, weighs 890 grams and costs less than 23mm version. Assuming for a moment you had to choose between these two, wouldn't it be a no brainer to choose the 31mm rim at less money, but 30 grams heavier than the 23mm version, or is the aerodynamic gain likely so insignificant going from 23mm deep to 31mm deep that someone might still reasonably prefer the 30 gram lighter 23mm version?

 

[nerdag]

Because they look great! People buy on looks, reputation, and perhaps weight, and Ksyrium SL/ES has all these. The fact that they don't deserve the reputation is another thing.

Also because Mavic probably wholesales them to bike manufacturers at a massively discounted price (and they can because of their market dominance), and they look the part, so manufacturers don't care so much.

n

 

[artemidorus]

There seem to be a bunch of wheelsets that are 27 to 34 mm and are marketed as aero, (although most of you will quickly point out that 30mm isn't really "aero"), weigh 1,500 to 1,700 grams or so, and don't cost an arm and a leg---the Velocity Deep V, Niobiums, Easton Circuits. Neuvation R28 Aero 2s and American Classic 420s for example. I guess the 420s are more expensive than the others, but are these class of "semi aero" wheels with 30mm rims generally worth considering for the alleged additional aero properties over a standard box rim?

I have read a separate paper (I've cited it elsewhere on this forum, but can't remember it) that stated wind tunnel results showing that a 30mm elliptical section rim with 32-36 spokes was well ahead of a 20 spoke Open Pro wheel in terms of aerodynamics.

 

[chainstay]

Required output (watts) to sustain 45kph.

Stevens San Remo bike with hands on hoods: 465 Watts
Same bike, hands down on the drops: 406 watts
Same bike, Easton Aeroforce aero bars: 369 Watts
Same bike Triathlon position (5.5 cm lower bar, saddle forwards): 360 Watts
Same as above, with 2 carbon Tri-spoke wheels: 345 Watts

Cervelo Tri bike + Tri spoke wheels: 328 Watts
Cervelo Tri bike + Tri spoke front + disk rear wheel : 320 w
Same as above with Giro aero helmet: 317
Same as above with speed suit: 307

From looking at the above, it looks like the gain from going to the aero wheels is fairly similar to the gain from going to the aero tri frame, but I would guess the potential gain from seeking out a road "aero" bicycle, like the Soloist for example, would be much less?

In terms of road racing, would these rough generalizations possibly hold: Look for wheelsets to produce roughly 25% of the drag, frames to produce 10 or 15% of the drag and the rider to produce 60 to 70% of the drag? It doesn't seem like the aero properties of road frames are generally rewarded with much consideration by most road racers. In one of the articles cited above, one of the time trialists even seem to pooh pooh worrying about the aero properties of frames too much, noting that the most important thing in a frame is making sure you are comfortable on it and want to ride it!

 

[chainstay]

I have read a separate paper (I've cited it elsewhere on this forum, but can't remember it) that stated wind tunnel results showing that a 30mm elliptical section rim with 32-36 spokes was well ahead of a 20 spoke Open Pro wheel in terms of aerodynamics.

Thanks Artemidorus. From reading some of the links in this thread, it also sounds like front wheel aerodynamics is more important than rear wheel aerodynamics. This makes common sense since the rear wheel is protected by the frame. One guy gave aerodynamic improvements to the front wheel double the value he gave to aerodynamic improvements to the rear wheel.

 

[531Aussie]

In terms of road racing, would these rough generalizations possibly hold: Look for wheelsets to produce roughly 25% of the drag, frames to produce 10 or 15% of the drag and the rider to produce 60 to 70% of the drag?

The wheels wouldn't be that much, or I'd have some by now . In the TT position on the 'normal' bike, the rider is at 360w; the two tri-spoke wheels drops 15w, then the disk drops a further 8w. The disc rear and tri-spoke are obviously still producing some drag, but that's about as aero as it gets, so I reckon the 6.4% (23w/360w) is closer to the mark

 

[531Aussie]

Thanks for that info. I wish they had even more wheelsets in that article.

there are few more here: http://www.radplan-delta.de/rennradtechnik/aero_messungen.html

some here.
http://www.carbonsports.com/LW_Test_Tour2002.lasso

There's more stuff around, but I can't find it at the moment.


'Aeroness' isn't necessarily about getting a rim to a certain depth, it's as much about reducing spokes. A 30mm rim with 20 spokes should be more aero than a 26mm rim with 28 spokes, not so much coz it's 4mm deeper, but because it has 8 less spokes. HED said this somewhere (not an exact quote): "increasing a rim's depth by 4mm may not make it more aero per se, but if will if it means we can get rid of 2 or 4 spokes due to the rim being stiffer and stronger."



Also, I wouldn't fuss too much about weight on aero wheels.

Firstly, I reckon rotational mass on a bike is total BOLLOCKS, partly because a rider has the acceleration of an 1800kg sedan with small motorbike engine; but I'm not gunna get all flustered about that again. There's a bit on that here, inlcuding a couple of links. http://www.charles.whitaker.name/wheels.html

Many of the aero rims weigh around 500 to 600g! Much of the weight is cut from the hubs from fancy wheels, so that's obviously not gunna effect the mythical rotating mass anyway.

The wheels that the pros use for TT are heavy: some of the rear Mavic discs are 1200g alone! There's a Mavic Comete rear on here listed at 1472g!! For one wheel!! But I bet it's farkin fast! http://weightweenies.starbike.com/listings/components.php?type=roadwheels


So, there ya go!

I hope that's confused the issue. Every time I think about spending big bucks on wheels, I check out heaps of aero sites, and always return to the conlcusion that it ain't worth it for just about anything other than a time-trial.

 

[alienator]

The wheels wouldn't be that much, or I'd have some by now . In the TT position on the 'normal' bike, the rider is at 360w; the two tri-spoke wheels drops 15w, then the disk drops a further 8w. The disc rear and tri-spoke are obviously still producing some drag, but that's about as aero as it gets, so I reckon the 0.064% (23w/360w) is closer to the mark

I think you mean 6.4%, unless you're using some weird, new math.

 

[531Aussie]

I think you mean 6.4%, unless you're using some weird, new math.

ooops.....edited

 

[chainstay]

The wheels wouldn't be that much, or I'd have some by now . In the TT position on the 'normal' bike, the rider is at 360w; the two tri-spoke wheels drops 15w, then the disk drops a further 8w. The disc rear and tri-spoke are obviously still producing some drag, but that's about as aero as it gets, so I reckon the 6.4% (23w/360w) is closer to the mark

Thanks. It looks like you are talking about the maximum "improvement" that might be expected from going to a very aero wheel setup. When I said wheels might produce 25% of the total drag, I was quoting Alienator from the second post in this thread, but that 6.4% number is a more interesting percentage number to keep in mind, or even a lesser percentage, 15/360watts=4.2%, because that percentage may give a rough idea of the maximum gains you could hope for by going to the most aero wheel, group road race setup---although I am not sure folks enter regular road races with stuff like tri spoke wheels, do they?

Aeroness' isn't necessarily about getting a rim to a certain depth, it's as much about reducing spokes. A 30mm rim with 20 spokes should be more aero than a 26mm rim with 28 spokes, not so much coz it's 4mm deeper, but because it has 8 less spokes. HED said this somewhere (not an exact quote): "increasing a rim's depth by 4mm may not make it more aero per se, but if will if it means we can get rid of 2 or 4 spokes due to the rim being stiffer and stronger."

Thanks for pointing that out. I was wondering about it. I noticed that quite a few of these so called aero wheelsets in the semi aero category have more spokes than what I have now, which is 20/16 combination on one set and 20/18 on the other. So I will bet the 28mm deep "aero" Easton Circuits with 28/24 spokes probably aren't as aero as my new spare wheels, the 24mm Shimano WH5600s with 20/16 spokes.

So, there ya go!

I hope that's confused the issue. Every time I think about spending big bucks on wheels, I check out heaps of aero sites, and always return to the conlcusion that it ain't worth it for just about anything other than a time-trial.

I don't mind hearing that conclusion at all. It will save me a lot of time and money. Looks like you provided me with some more reading material. Thanks, I will check those links out!!