# When does the aero affect kick in?



## skyliner1004 (May 9, 2010)

At what average speeds does the aerodynamic affect really kick in?

Lets use some standard "base" set of wheels such as the BWW Blackset race, heres the basic specs: ~1450g, 24mm deep rim.

At what speeds will a 40mm deep rim's aerodynamic profile start to benefit it? Keep in mind the cost of the added weight of a 40mm deep rim.

What about a 60mm deep rim + extra weight?

What about 80mm deep rim + extra weight?


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## kritiman (Jul 31, 2006)

I read somewhere that at 17mph you start to use more energy to overcome air resistance than you do to propel the bike.
But sorry, no source.


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## fa63 (Aug 16, 2007)

The aerodynamic advantages are always in effect. Whether you will notice it or not, even at high speeds, is debatable. For example, based on published data the difference between a typical non-aero box section rim and an aero wheel like Zipp 808 is about 0.25 mph at 25 mph. At best this obviously will be barely noticeable to the casual rider, but can provide a big advantage to anyone who races, especially for pros where seconds can make all the difference in a time trial.

Also, aero trumps mass every time (within reasonable ranges) unless all you are doing is climbing steep hills at very low speeds all day.


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## fa63 (Aug 16, 2007)

With that said, don't let the facts stop you from getting deep section aero wheels if that is what you are after. After all, the placebo effect can have a huge impact on performance (no kidding).


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## rruff (Feb 28, 2006)

skyliner1004 said:


> At what average speeds does the aerodynamic affect really kick in?


0+ mph. 

If you'd like to now how *much* difference it makes, then pick some numbers off the graph below and plug them into analyticcycling, or a similar calculator.


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## Mainebikah (Sep 1, 2009)

fa63 said:


> The aerodynamic advantages are always in effect. Whether you will notice it or not, even at high speeds, is debatable. For example, based on published data the difference between a typical non-aero box section rim and an aero wheel like Zipp 808 is about 0.25 mph at 25 mph. At best this obviously will be barely noticeable to the casual rider, but can provide a big advantage to anyone who races, especially for pros where seconds can make all the difference in a time trial.
> 
> 
> > So pedaling along at 20 mph with a 20 mph tail wind, the aerodynamic advantage is still in effect? Maybe not so much. Under those conditions, a box section or deep aero wheel of similar weight should feel about equal.
> ...


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## fa63 (Aug 16, 2007)

Mainebikah said:


> So pedaling along at 20 mph with a 20 mph tail wind, the aerodynamic advantage is still in effect? Maybe not so much. Under those conditions, a box section or deep aero wheel of similar weight should feel about equal.
> 
> As head winds increase, you actually get increased benefits from aerodymic shapes. That's why we reach for the drops when we ride against a strong head wind. Sit up and you'll feel the aerodynamic effects in action right away. I may not race, but I'm pretty sure that any aero advantage would be appreciated on longer distance rides.
> 
> ...


You have to keep in mind that the frontal area of a front wheel is a fraction of the frontal area of a rider (about 1/50th). This implies that no matter how aero a wheel is, it is still a very small fraction of the total drag of a rider. So one shouldn't expect an aero wheel to be noticeably faster than a box section rim even under headwind conditions. The difference is essentially nil unless you are racing against the clock and seconds can make a difference (like in a TT or a sprint). 

Nonetheless, this didn't stop me from buying "aero" wheels; I just like how they look and they make me want to get out and ride more. So you can say they make me faster in a different way.


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## gibson00 (Aug 7, 2006)

Pretty much agree with everything fa63 said.
Also, people sometimes assume that in a TT, someone going 25mph will see more benefit than someone going 20mph, but you also have to remember that the guy going 20mph will be on the course longer, and thus will still get a good overall benefit.

But for casual training/racing, weekend warriors, yeah, the difference is mainly mental. Lighter wheels will feel a bit more lively underneath you, but won't change your speed much, even while climbing, unless climbing -long- -steep- hills (Alps, etc). But aero wheels do sure look nice! That is why I use them.


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## rruff (Feb 28, 2006)

fa63 said:


> You have to keep in mind that the frontal area of a front wheel is a fraction of the frontal area of a rider (about 1/50th). This implies that no matter how aero a wheel is, it is still a very small fraction of the total drag of a rider.


From the chart above, typical wheelset drag is in the .020-.035m^2 range for wheels with minimal aero spokes. The full drag of a cyclist is typically ~.35m^2 for road bike riding on the hoods, to .25m^2 for a full TT setup, so the wheels are around a 1/10th of the total drag. On a flat road you can figure that the change in speed will be approximately inversely proportional to the drag change to the .38 power. 

So if your CdA is .350 using the slowest wheels on that chart, and you are going 20mph... then you get some Zipp 808s, the total drag drops by .018 to .332. The new speed is (.35/.332)^.38 x 20mph = 20.4mph. That isn't enough to feel, but it's pretty significant.


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## Mainebikah (Sep 1, 2009)

OK, then, I hope to find out if lighter aero wheels will help out some in physical terms or mental, or both. There has to be something to the weight/aero advantage thing, or the pros would just use any old bike and wheel combination. 

I bike a couple of long stretches that tilt upward a little and are also aligned right into the afternoon sea breeze that develops almost on a daily basis when we get sunny days. The sea breeze funnels through this area and generally stays at a steady 10 to 15 mph. Add that to an average riding speed of 16 mph or so on this section of road, making it around a 25 to 30 mph wind on the nose. 

As soon as I get a chance to ride this section back to back on both sets of wheels, I'll report my impressions. 

Looking forward to some aero advantage!... or not.


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## ohvrolla (Aug 2, 2009)

What I want to know is when the aero effect drop out? I mean surely people aren't buying deep rims because they time trial all the time. If I'm riding in a pace line is it that big a deal to be on 22mm deep rims compared to 30mm? What about in the middle of a pack? Do people with 50mm rims go to the front and pull the whole way?


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## blackjack (Sep 7, 2010)

rruff said:


> From the chart above, typical wheelset drag is in the .020-.035m^2 range for wheels with minimal aero spokes. The full drag of a cyclist is typically ~.35m^2 for road bike riding on the hoods, to .25m^2 for a full TT setup, so the wheels are around a 1/10th of the total drag. On a flat road you can figure that the change in speed will be approximately inversely proportional to the drag change to the .38 power.
> 
> So if your CdA is .350 using the slowest wheels on that chart, and you are going 20mph... then you get some Zipp 808s, the total drag drops by .018 to .332. The new speed is (.35/.332)^.38 x 20mph = 20.4mph. That isn't enough to feel, but it's pretty significant.


So that's about 2% faster.

I'll get the least aero wheels in that case, because I'm in no hurry to get my 40 milers over a couple of minutes faster.

I'm riding, and mostly by myself, because I want to get away from everyone and everything except being out riding.

Different strokes I guess.

When I'm with a group I'll just wheelsuck, or put out 20 more watts for the few minutes I'm on the front.


If I was racing I'd come to you to save me a few minutes over a bunch of hours. Or if I wanted a pretty set of wheels.

Thanks for the information. It's kind of the only thing that clears up people's thinking.


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## Kerry Irons (Feb 25, 2002)

*Nope*



kritiman said:


> I read somewhere that at 17mph you start to use more energy to overcome air resistance than you do to propel the bike.
> But sorry, no source.


Bicycling Science, Wilson, 3rd Ed., MIT Press. The power to overcome aero drag is equal to the power to overcome rolling resistance/friction at roughly 10 mph (16 km/hr).

The best aero wheels available will give you 0.4 mph (0.6 km/hr) advantage at 25 mph (40 km/hr), zero wind conditions. Those same wheels will offer 0.3 mph at 20 mph. Etc. Of course the effect never "kicks in" or "kicks off." How could it?


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## cdhbrad (Feb 18, 2003)

In my experience, the riders with the deepest wheels often tend to do the least work....go figure. Wheelsucking becomes an artform when rolling on Reynolds 66 Tubulars.


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## Ghost234 (Jun 1, 2010)

cdhbrad said:


> In my experience, the riders with the deepest wheels often tend to do the least work....go figure. Wheelsucking becomes an artform when rolling on Reynolds 66 Tubulars.



When you are racing that is the goal: to conserve the most energy for the end of the race. 


The aero benefit of wheels and TT gear seems to be more beneficial the faster you go. Personally I wouldn't bother with most aero gear until you start to break speeds of 35-37km/h. Until then, just use the drops.


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## cdhbrad (Feb 18, 2003)

Agreed when truly "racing", but I'm referencing the weekly "Saturday World's Championship" group rides I participate in around home. Seems the guys with the deepest wheels tend to forget its not a "race."


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## den bakker (Nov 13, 2004)

cdhbrad said:


> Agreed when truly "racing", but I'm referencing the weekly "Saturday World's Championship" group rides I participate in around home. Seems the guys with the deepest wheels tend to forget its not a "race."


which of course is irrelevant to the discussion. 
(who gives a sh!t what other do at a group ride anyway as long as they don't crash people)


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## blackjack (Sep 7, 2010)

den bakker said:


> which of course is irrelevant to the discussion.
> (who gives a sh!t what other do at a group ride anyway as long as they don't crash people)



I think the problem is that people who exhibit the behavior cdhbrad talks about often *do *crash people.

I also think that riders who "need" this kind of equipment for non competitive group rides don't have the faintest idea of how little it contributes to riding in a group.

Kind of like how bad drivers on the freeway need to race around in high performance sports cars driving erratically, disrupting traffic flow, because they envision themselves as F-1 drivers


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## cdhbrad (Feb 18, 2003)

My original comment was in response to the following question posed immediately above my response: " Do people with 50mm rims go to the front and pull the whole way?"
In my experience, even in racing, the answer is a resounding "NO", but even more so in spirited group rides that some view as psuedo "races". We have one guy who rides the Reynolds I referenced and this past Saturday, he was second heading to the finishing sprint, which he lost. He later complained to someone that "No one would help me in the sprint." He was second wheel behind the eventual "Winner" heading to the line, what more help did he expect?


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## AvantDale (Dec 26, 2008)

ohvrolla said:


> What I want to know is when the aero effect drop out? I mean surely people aren't buying deep rims because they time trial all the time. If I'm riding in a pace line is it that big a deal to be on 22mm deep rims compared to 30mm? What about in the middle of a pack? Do people with 50mm rims go to the front and pull the whole way?


99.9% of the people that buy deep section wheels is for looks. Lol...that's why I got em.

For the guys that actually race...every bit of energy saving helps.


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## woodys737 (Dec 31, 2005)

AvantDale said:


> 99.9% of the people that buy deep section wheels is for looks. Lol...that's why I got em.
> 
> *For the guys that actually race...every bit of energy saving helps.*


This is what I thought everyone was thinking? In Kerry Irons example of an aero wheel giving a rider 0.4mph advantage at 25mph an online calculator calculated a 17W difference. May not seem like much but in terms of FTP I think it is significant.


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## Wookiebiker (Sep 5, 2005)

woodys737 said:


> This is what I thought everyone was thinking? In Kerry Irons example of an aero wheel giving a rider 0.4mph advantage at 25mph an online calculator calculated a 17W difference. May not seem like much but in terms of FTP I think it is significant.


In a race...an extra 17 watts or .4 mph can be the difference between a break away making it to the end and being caught...In other words the difference between winning and being swallowed up by the pack a few "K" before the line :thumbsup:

In a group ride...the look nice


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## mcsqueak (Apr 22, 2010)

Wookiebiker said:


> In a race...an extra 17 watts or .4 mph can be the difference between a break away making it to the end and being caught...In other words the difference between winning and being swallowed up by the pack a few "K" before the line :thumbsup:
> 
> In a group ride...the look nice


Yes, they do look nice... I was considering a semi-aero rim, like the BWW Pure Aero or the Soul S3.0, but since I don't yet race I won't gain anything from them, and they will be heaver than something a bit more low profile such as the BWW Raceset or the Soul S2.0.

My current wheels (Alexrim r500) weigh around 2055g without tires or tubes, as far as I can tell based on information found online. The Soul S2.0L weigh 1330g, which would probably benefit me far more than any aero benefit from deeper rims.


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## dgeesaman (Jun 9, 2010)

ohvrolla said:


> What I want to know is when the aero effect drop out? I mean surely people aren't buying deep rims because they time trial all the time. If I'm riding in a pace line is it that big a deal to be on 22mm deep rims compared to 30mm? What about in the middle of a pack? Do people with 50mm rims go to the front and pull the whole way?


Aerodynamics never drops out. It just becomes less significant the slower you go and the better your draft (if in a pack). It's more significant in a headwind.

Dave


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## fa63 (Aug 16, 2007)

rruff said:


> From the chart above, typical wheelset drag is in the .020-.035m^2 range for wheels with minimal aero spokes. The full drag of a cyclist is typically ~.35m^2 for road bike riding on the hoods, to .25m^2 for a full TT setup, so the wheels are around a 1/10th of the total drag. On a flat road you can figure that the change in speed will be approximately inversely proportional to the drag change to the .38 power.
> 
> So if your CdA is .350 using the slowest wheels on that chart, and you are going 20mph... then you get some Zipp 808s, the total drag drops by .018 to .332. The new speed is (.35/.332)^.38 x 20mph = 20.4mph. That isn't enough to feel, but it's pretty significant.


I have seen a value of 0.5 m^2 commonly used for the frontal area, and I calculated very roughly about 0.01 m^2 frontal area for the front tire, which is where the 1/50th came from. Anyways, regardless of the values I agree that the differences are too small to feel but significant to a rider racing against the clock.


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## ohvrolla (Aug 2, 2009)

AvantDale said:


> 99.9% of the people that buy deep section wheels is for looks. Lol...that's why I got em.
> 
> For the guys that actually race...every bit of energy saving helps.


Thanks for the honesty. I pretty much already figured that even if people don't come right out and say it.

Dgeesaman that's the whole point I'm making. This whole aero advantage is taken away when riding behind someone, and a smooth rotating paceline doesn't put you at the front long enough for the difference between 22mm rims and 27mm rims to make or break you.


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## fa63 (Aug 16, 2007)

mcsqueak said:


> Yes, they do look nice... I was considering a semi-aero rim, like the BWW Pure Aero or the Soul S3.0, but since I don't yet race I won't gain anything from them, and they will be heaver than something a bit more low profile such as the BWW Raceset or the Soul S2.0.
> 
> My current wheels (Alexrim r500) weigh around 2055g without tires or tubes, as far as I can tell based on information found online. The Soul S2.0L weigh 1330g, which would probably benefit me far more than any aero benefit from deeper rims.


Well, don't get too hung-up on weight either unless you climb the whole time you ride. My personal priorities when buying everyday wheels are: 1) durability/stiffness 2) hubs 3) aerodynamic properties 4) weight. It is also a plus if they happen to look good.


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## frdfandc (Nov 27, 2007)

Aero occurs at 1.21 gigawatts of power.


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## al0 (Jan 24, 2003)

What is interesting the difference between tires with lower rolling resistance (e.g. Veloflex Record or Conti 4000RS clinchers) and tires with higher rolling resistance (Schwalbe Ultremo clinchers or virtually any tubulars) is on par with difference between wheels like to Mavic Aksium or Shimano RS-30 and "true" aero wheels (like Zip 808). then compare the price differences 

You may look into the test in the last edition of the TOUR.


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## Kerry Irons (Feb 25, 2002)

*Future boy*



frdfandc said:


> Aero occurs at 1.21 gigawatts of power.


Great Scott!


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## andre71144 (Aug 25, 2003)

After reading two pages of information my orginal thoughts are now confirmed. 
I should buy the cheapest most reliable best looking aero wheel That i can get a good deal on.

I'm old, overweight, and slow but I excel in drafting so I will at least look good when I pull up to the group ride.


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## gibson00 (Aug 7, 2006)

andre71144 said:


> After reading two pages of information my orginal thoughts are now confirmed.
> I should buy the cheapest most reliable best looking aero wheel That i can get a good deal on.
> 
> I'm old, overweight, and slow but I excel in drafting so I will at least look good when I pull up to the group ride.


Or, quite simply, buy the wheelset that you are going to enjoy the most. The set that will make you want to ride your bike more!
If the only reason you are buying aero wheels is to go faster, then you are probably wasting your money. 
Reality sucks, eh?


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## andre71144 (Aug 25, 2003)

tell me about it I'll probably be a little faster just because I think I look faster.


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