# Wheels in Crosswind



## Maniton (Dec 26, 2011)

I had a bike mechanic at my LBS tell me that aero wheels, deep rim and discs, create drag on a cross wind as they increase surface area for wind. He said they are only meant to increase aerodymanics going directly into the wind, within a 15 degree variance left or right. 

Is there any truth to this? It came up because I told him I'd love to get some 50 or 80 mil wheels.


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## dcgriz (Feb 13, 2011)

Deep rims were derived from disks and disks were derived from the sails on the sailboats. The idea is to catch the wind and be propelled by it the same way a sailboat does. However, since the bicycle wheel orientation can not change as the sailboat mast does, the effectiveness of the wider rims is limited to a wind angle of around 20 deg depending on speed. HED has a yaw calculator on their website if you want to further get into it.
Cross winds with the deeper rims are a challenge and the lighter you are the more challenge it becomes.


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## Mike T. (Feb 3, 2004)

"Drag", or lack of, caused by crosswinds will depend on how well the rim has been engineered. There are probably test reports on the out there on the internet but for most of us who post here, it's all immaterial as we don't go fast enough for it to be important. What any of us, no matter how slow we go, will notice with deep rims is the effects of crosswinds on bike stability. And probably the biggest effect is when a passing vehicle removes the crosswind that we're leaning on. Oh my goodness! My 50mm deep wheels don't play nice in those situations.


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## c_h_i_n_a_m_a_n (Mar 3, 2012)

Mike T. said:


> ... And probably the biggest effect is when a passing vehicle removes the crosswind that we're leaning on. Oh my goodness! My 50mm deep wheels don't play nice in those situations.


Does that mean that you tend to be 'dragged' towards the passing vehicle?


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## Mike T. (Feb 3, 2004)

c_h_i_n_a_m_a_n said:


> Does that mean that you tend to be 'dragged' towards the passing vehicle?


That means, for me, I was leaning on a strong crosswind on a 40mph freewheeling downhill when, 3x over 3 rides, a vehicle passed me on the windward side and took my prop away. I swerved over, towards the wind (or instant lack of) about the width of the lane I was in. I wasn't expecting it the first time but I was for the next two, and it still happened. Now if I'm using those 50mm deep wheels I slow right down on that downhill if there is a crosswind. That kinda defeats the purpose of 'aero' wheels doesn't it?


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## rruff (Feb 28, 2006)

15 degree yaw is a lot. That's definitely more of an angle than you would normally see when riding fast. But a deep carbon wheelset will only get you ~0.2mph increase compared to a good set with a rim in the 25-30mm range anyway.


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## Elpimpo (Jan 16, 2012)

Wait, wait, 

Your name is Scott and you DON'T ride a Scott bike!?

Dude, C'mon.


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## looigi (Nov 24, 2010)

rruff said:


> 15 degree yaw is a lot. That's definitely more of an angle than you would normally see when riding fast.


Tan of 15deg = 0.27. A crosswind of 6.7 mph will produce a 15 degree yaw angle at when riding at 25 mph.


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## dcgriz (Feb 13, 2011)

The January edition of Tour included an interesting article on wind resistance and yaw angles based on wind tunnels tests they did. 

The yaw angle depends on riding speed as well as the direction and strength of the crosswind. Slow riders (19 mph) mainly experience yaw angles between 7.5 and 17.5 deg, with a max of approximately 35 deg. The relevant range for fast speeds (31 mph) lies between 2.5 and 10 deg; angles greater than 15 deg do not matter. Both cases for wind speeds of 6 mph.
They tested a bunch of wheels for yaw angles between 0 and 25 deg. The Zipp 808 was the only spoked wheel that showed negative wind resistance (propulsion) between 13 and 22 deg yaw. The rest of the spoked wheels ( including a lot of the 50 mm variety) never reached the negative resistance range.

The significance of all of this? The 808s were simulated to finish a 112 miles course 4:46 minutes faster than any of the other wheels tested when ridden at an avg. speed of 22 mph. You decide if that's important to you.


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## superjesus (Jul 26, 2010)

I can't speak to the numbers for aero wheels, but I can share an experience of mine. About 3 weeks ago, I had the opportunity to ride a set of 404's rather than my normal mismatched, cheap-o wheelset. I rode them on my usual 30 mile route. Course is essentially flat with generally well-paved rural roads. Wind was constant out of the west-northwest 6mph, gusting to 11. I couldn't have asked for a better, more typical day to test the wheels. I average ~19mph.

Except when riding with a pure tailwind, I felt like I was fighting the wind much more than usual with the 404's. Normally, I feel crosswinds tug at my body, but with the deep rims, I felt the bike was being pulled from under me. I really felt for most of the ride that I was fighting winds somewhat stronger than they actually were. I was surprised at how fatiguing it was to fight such mild winds. I really did not expect the way the 404's handled crosswinds to be so exaggerated. 

Everything else about the wheels was heavenly, though. I could elaborate, but it wouldn't be pertinent to this discussion.


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## dcgriz (Feb 13, 2011)

I have a set of 45mm carbons I ride occasionally. I have experienced crosswind push with wind speeds from the high teens upwards. Wind speeds to 10 mph have not caused me any lateral movement memorable enough to be recalled.


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## pletharoe (Sep 17, 2010)

There are three types of lies: Lies, damn lies and statistics.

The crosswind angle of an "average" cyclist is frequently discussed. As looigi pointed out these figures can be misleading. Take a look at the figures below for the yaw angle experienced by a rider going at 25mph with the wind perpendicular to his track:

Wind speed Yaw angle
0----------------0
5----------------11.3
10--------------21.8
15--------------31
20--------------38.7
25--------------45

Of course, most of the time the wind isn't perpendicular to our track, let's say it's at 30 degrees. The faster you go, the less your yaw angle becomes. However, using a rule of thumb I use in my every day work (as a pilot), the crosswind component at 30 degrees is half of the total wind. So the table for 30 degrees looks like this...

Wind speed Yaw angle
0----------------0
5----------------5.7
10--------------11.3
15--------------16.7
20--------------21.8
25--------------26.6
30--------------31

So it doesn't actually take much wind before an aero wheel gets to it's "stall angle".

But what exacly is this stall angle anyway? It is the angle at which there is no longer "laminar flow" over the wheel. Imagine holding a plank of wood at the end and dipping it into a river. If it's aligned with the flow of water, the water washes past it easily. As you twist it (say 5 degrees) it continues to wash past easily. As you twist it further there comes a point where the water downstream of the wood becomes turbulent (white and frothy) This is the stall. Now imagine that your plank of wood is the wheel and the water is a head wind. At low yaw angle the aero wheel cuts through the air nicely. As the yaw angle increases it eventually stalls. At this point aero benefits of the wheel are nullified. On top of this, the large surface area that the aero rim presents to the wind now gets blown sideways.

We must remember, though, that (at high yaw angles - say above 50 degrees) the majority of this force is PERPENDICULAR to the direction of travel and therefore does not manifest as extra drag. Therefore it DOES NOT slow you down. However it does push you over and steer the bike where you don't want it to go. This will slow you down, particularly in gusty conditions where you will be constantly correcting. This is what happened to Mike T. (Assuming he rides on the left hand side of the road) The wind was coming from the right. Aero wheels present a large cross section to the cross wind, so he had to lean into it (leaning right).

To add to this, a crosswind will push the leading edge of an aero wheel more than the trailing edge (the leading edge is bigger, acting like a larger aerofoil, producing more lift). This contributes to the feeling that the wind is "steering" you away from the wind. You essentially have to put pressure on the bars to stop the wheel turning left (if the wind is coming from the right). This is a phenomenon that Zipp have tried (with some success) to address with the firecrest wheel.

When the truck passed Mike T, it sheltered him from the wind, instantly removing these two factors. Mike had been compensating for them and suddenly found himself overcompensating as there was no more crosswind. A scary situation.

If I recall correctly, most manufacturers claim that their wheels stall at around 12-15 degrees (I may be wrong on this). Using the figures I calculated above, an aero wheel is advantageous at wind speeds up to 15 mph when the yaw angle is 30 degrees and the rider is going at 25mph. Beyond this angle, the aero wheels will produce (slightly) more drag up to (I estimate) 50 degrees. Unfortunately there are so many variables (wind direction, rider direction, wind speed, rider speed) that it is virtually impossible to say what is ideal. In the right conditions (headwind, high speed) aero wheels are definitely beneficial. In the wrong conditions (crosswind, causing difficult handling. Climbing with extra rotating weight) they are a curse.

It can be tempting to get aero wheels as they look like they go fast. But as I've just outlined, they can be a mixed blessing. I would only recommend them if you're already fast. For general use (not flat TT stuff) for a large rider (stronger upper body with more intertia to comabt crosswinds) I wouldn't go above 50-60mm, for a smaller rider I'd say 40-50mm.

Sheesh, it's time I stopped talking! I hope that helps.


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## orange_julius (Jan 24, 2003)

pletharoe said:


> There are three types of lies: Lies, damn lies and statistics.


YES! Excellent post. These kinds of questions have to be answered quantitatively. But is it possible to back-compute from what you said such that riders can get some guidance as to whether wheel A or wheel B is the most appropriate? 

To the OP: there are several lab and modeling results shared online if you want to have a look. Here's an old one that was among the first to consider yaw angle.
Wheel Aerodynamics

Keep in mind though the testing methodologies themselves vary, and manufacturers love to pick and choose one that shows superiority of their own wheelset.


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## Enoch562 (May 13, 2010)

I'm beginning to believe that a good strong medium height (25-38mm) wheel is all the average rider needs. The real tall rims sure do look nice, but for mere mortal weekend riders they are just fashion statements.


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## Mike T. (Feb 3, 2004)

pletharoe said:


> Mike T. (Assuming he rides on the left hand side of the road) The wind was coming from the right. Aero wheels present a large cross section to the cross wind, so he had to lean into it (leaning right).


Actually I was riding on the right side of the road and the wind coming from the left. Will this make a difference? 



> When the truck passed Mike T, it sheltered him from the wind, instantly removing these two factors. Mike had been compensating for them and suddenly found himself overcompensating as there was no more crosswind. A scary situation.


That it was. I damn near $#it my $horts.


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## coachboyd (Jan 13, 2008)

looigi said:


> Tan of 15deg = 0.27. A crosswind of 6.7 mph will produce a 15 degree yaw angle at when riding at 25 mph.


Wind speed is measured 10meters above ground. At the ground level wind speed is always 0mph and then exponentially rises the higher you get above ground. So if the measured reported wind speed is 6.7mph the actual wind speed you will see at wheel level will more likely be 1.5 to 3mph.

Plus, wind speed, wind angle, your speed, your angle are constantly changing. You may see 15 degrees of yaw angle and then 200 meters down the road it will be 3 degrees of yaw angle. As rruff said (and I think he's pretty handy with that physics topic), 15 degrees of yaw angle is more than you would normally see when riding fast.


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## pletharoe (Sep 17, 2010)

OJ: I'm not sure what you mean by "back compute". The figures I churned out apply to all wheels.

The aerodynamic disadvantages (getting blown about and the wind "steering" for you) scale linearly, so if you double the height of the rim, you get "double trouble".

The aerodynamic advantages are a law of diminishing returns. Double the height of the rim and you don't half the drag.

Your point about manufacturers publishing data which cannot be compared is very true. Both Zipp (very expensive) and Flo (very inexpensive) tested their wheels at the same wind tunnel at the same speed. If you compare Zipp's figures with Flo's, Flo claim to produce significantly less drag for the same rim depth. Zipps are undeniably lighter, but you would expect that (being more expensive and having all that wizardry they claim in the company) they would be more aero.

Enoch562: I agree with you wholeheartedly. A small fairing (aero bit) will probably help. But to most riders a good quality wheel will probably produce better results than a deep deep rim. Rotating (rim) weight will make a big difference to acceleration and handling. Stiffness will help under high loads (like sprints and climbs)

Mike T: Oh, you didn't tell me you were riding on the right - that makes all the difference. You weren't by any chance in the Southern hemisphere too? Then we'd have to redo all the calculations!


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## pletharoe (Sep 17, 2010)

coachboyd said:


> Wind speed is measured 10meters above ground. At the ground level wind speed is always 0mph and then exponentially rises the higher you get above ground. So if the measured reported wind speed is 6.7mph the actual wind speed you will see at wheel level will more likely be 1.5 to 3mph.


Actually, if you use the Power Law Method (explained here NDBC - Does NDBC adjust C-MAN and buoy wind speed observations to a standard height? )
6.7mph = 3mps.
3mps at 10 meters extrapolates to 2.1mps at 0.35m (half way up the wheel)
2.1mps = 4.64mph

So while you are correct in principal, the effect of moving from 10m down to "wheel level" is not as dramatic as you might think.

What you say about winds changing, though is spot on and frequently overlooked in discussion.


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## coachboyd (Jan 13, 2008)

pletharoe said:


> Actually, if you use the Power Law Method (explained here NDBC - Does NDBC adjust C-MAN and buoy wind speed observations to a standard height? )
> 6.7mph = 3mps.
> 3mps at 10 meters extrapolates to 2.1mps at 0.35m (half way up the wheel)
> 2.1mps = 4.64mps
> ...


That may be true for sailing on open waters but on land you have to apply the Hellman exponent as trees, building, hills, and such will also affect the wind speed above the ground.
Wind gradient - Wikipedia, the free encyclopedia
scroll down to the wind turbines section.


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## rruff (Feb 28, 2006)

pletharoe said:


> Using the figures I calculated above, an aero wheel is advantageous at wind speeds up to 15 mph when the yaw angle is 30 degrees and the rider is going at 25mph. Beyond this angle, the aero wheels will produce (slightly) more drag up to (I estimate) 50 degrees.


An important thing to mention is that a 15mph wind *at the level of the wheel* is a very strong wind... probably ~30mph as reported at the airport. For an average daytime airport wind of 10mph, you are looking at ~5mph and 5.7 deg of yaw. And as measured in the wind tunnel even at extreme angles, the deep rims produce less drag than a shallow one... but steering stability is another issue.


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## rruff (Feb 28, 2006)

pletharoe said:


> So while you are correct in principal, the effect of moving from 10m down to "wheel level" is not as dramatic as you might think.


That might be true on a dry lake bed... or similarly flat barren land. Having ridden lots of miles with an iBike, the wind speed even at handlebar level is rarely half of 10m height... on open land with sparse junipers. If there are a lot of trees and buildings it will average far less.


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## pletharoe (Sep 17, 2010)

coachboyd said:


> That may be true for sailing on open waters but on land you have to apply the Hellman exponent as trees, building, hills, and such will also affect the wind speed above the ground.
> Wind gradient - Wikipedia, the free encyclopedia
> scroll down to the wind turbines section.


I have been out-geeked! Well done choachboyd :thumbsup:

Using the Hellman equation for a 10m wind of 6.7mph, in unstable air in a human inhabited area the 0.35m wind is 2.7mph. In stable air it's as low as 0.9mph.

(You can tell if the air is stable because you get stratiform (flat) clouds. Unstable air produces cumuliform (lumpy / thundery) clouds)

Just to be picky, though (cos it's fun), I don't think this equation factors in the funnelling effect of valleys or roads between high buildings. Winds at the base of high buildings can actually be faster because the high level wind is deflected by the building.

Just another example of how there are way too many variables to ever give a definitive answer to the aero wheel debate!


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## JimP (Dec 18, 2001)

I understand about winds aloft and wind at ground level but... Yesterday we were riding in the Davis Mountains southwest of Ft. Davis, TX with a reported wind of only 14 with gusts to 20 mph. The road surface is chip seal and the wind is at 90 degrees to the road. I weigh 185 lbs riding a Felt with ENVE 2.45 rims with Conti Sprinter tires at 85 psi. I was riding at 32 mph and felt the front wheel being blown sideways and skittering on the chip seal. How strong were the wind gusts?


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## bwbishop (Sep 17, 2011)

dcgriz said:


> Deep rims were derived from disks and disks were derived from the sails on the sailboats. The idea is to catch the wind and be propelled by it the same way a sailboat does. However, since the bicycle wheel orientation can not change as the sailboat mast does, the effectiveness of the wider rims is limited to a wind angle of around 20 deg depending on speed. HED has a yaw calculator on their website if you want to further get into it.
> Cross winds with the deeper rims are a challenge and the lighter you are the more challenge it becomes.


Ok, I can't help but comment on this because I use to be an engineer before Uncle Sam ground down my ability to do complex math...

An aero bike tire has nothing to do with a sailplane, or an airplane propeller (like I've heard other folks say). An airplane generates life essential perpendicular to the cord of the wind (excluding AoA). The cord of an aero rim profile is front to back on the bike, so the "lift" or airfoil effect would be to your right, and to your left and would not add to your speed at all. And since all aero rims are symmetrical about the center line, any benefit you think you would get would be cancelled out by the equal and opposite effect on the other side. Sail boat references are just are incorrect. I have a sailboat, and if you run with the boom exactly down the center of the boat, your ass isn't going anywhere. The boom has to be off to the side somewhat when tacking upwind, and you go forward based off the lift minus cosine losses.

Aero rims decrease drag by decreasing the turbulent low pressure area behind the rim, which "pulls you back." The wind angle calculator just tells you when the "airfoil" stalls and no longer maintains laminar flow.

So unless you're riding your bike sideways across some ice, your aero rim is nothing like a propeller or sail.

*Caveat - I haven't done any fluids calculations in over 10 years, so feel free to correct me if I'm wrong


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## bwbishop (Sep 17, 2011)

pletharoe said:


> Mike T: Oh, you didn't tell me you were riding on the right - that makes all the difference. You weren't by any chance in the Southern hemisphere too? Then we'd have to redo all the calculations!


All your calculations would be upside down then! Everything is so much harder down there.


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## Mike T. (Feb 3, 2004)

bwbishop said:


> I have a sailboat


Slightly off topic, I had a sailboat too for many years and if all sporty cyclists learned to sail they would be much better at judging wind and its effects on a moving body especially as that moving body increases its speed. Their drafting skills would certainly improve.


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## Mike T. (Feb 3, 2004)

pletharoe said:


> Mike T: Oh, you didn't tell me you were riding on the right - that makes all the difference. You weren't by any chance in the Southern hemisphere too?


Heck no. I had enough troubles when I came from the UK to N.Am and had to go left to right. Going upside-down would have been way too much overload. 



> Then we'd have to redo all the calculations!


I had enough trouble with math as it was. See my excuse above.


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## bwbishop (Sep 17, 2011)

Mike T. said:


> Slightly off topic, I had a sailboat too for many years and if all sporty cyclists learned to sail they would be much better at judging wind and its effects on a moving body especially as that moving body increases its speed. Their drafting skills would certainly improve.


And if all pilots learned to fly a sailplane first, they'd be better off as well! There's lots to be learned from those natural, un-powered sports.


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## pletharoe (Sep 17, 2010)

@JimP
Ummmm, haven't you answered your own question higher up in your post? You said the wiind was 14, gusting 20mph.

I'm not sure where people tend to get their wind data, but if you want information for every hour (or sometimes every half hour), I suggest that you get a METAR. This is the raw data produced by the weather men at the airport. I guess that your nearest airport is Dallas Fort Worth, so here's what you need to do,,,

- Go to http://euro.wx.propilots.net/
- Select from the drop down box at the top left "METAR history"
- Enter in the box "KDFW" (the ICAO code for your airport) and select how much history you want (6, 12 or 24 hours)
- Decode the metar as follows.

The current METAR is:
KDFW 150653Z 35007KT 10SM BKN023 OVC055 18/15 A3021 RMK AO2 SLP223 T01830150=

Which means:
KDFW - Is the ICAO code for Dallas Fort Worth.
150653Z - Infor released on the 15th at 06:53 Zulu time. I think Dallas is UTC-6, so the data was released at 00:53 Local time.
35007 - The wind was coming from 350 degrees at 7 knots. If the wind was gusting, it would say something like 35007G20, meaning 350 degrees, 7 knots, gusting 20.
It might say VRB10, meaning the wind is coming from variable directions at 10 knots.

Then all you have to do is convert that to miles per hour by multiplying by 1.15.

Now if you really want to take it to silly levels of geekery, open excel and...
- Enter the METAR wind into cell A1
- Enter the appropriate Hellman exponent (explained at http://en.wikipedia.org/wiki/Wind_gradient) into cell A2.
- Copy the following line into cell A4.
=(A1*(0.35/10)^A2)

The figure produced in A4 will be the wind speed at wheel height. This does not include local variations such as the funnelling effect of local terrain or buildings.


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## Mike T. (Feb 3, 2004)

bwbishop said:


> And if all pilots learned to fly a sailplane first, they'd be better off as well! There's lots to be learned from those natural, un-powered sports.


So true. Sailplane pilots will definitely know the direction and effects of both horizontal wind and vertical "wind". I led many group training rides for years and sometimes, before we were riding, I'd ask the riders to point to where the wind was coming from. Some of them got it right. Then, when doing 20mph, I'd ask them to point to it again. Almost no-one got it right.


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## bigreen505 (Jun 10, 2007)

Take this with some salt as I am not an engineer, aero wheel owner nor particularly good rider. While it is easy to point to charts that say even in a strong cross wind it is barely blowing at wheel level so this this stability issue is purely mental, riding in gusting, rotoring cross winds above tree line is a totally different issue. I have a set of Ksyriums and almost got sent into oncoming traffic the first time I got hit with real breeze. The final straw came this past weekend when some cross winds created such a speed wobble on a descent that I could barely control the bike. No idea on wind speed, but it was noticeable. 

My point is that charts and real world riding conditions don't always match up



Mike T. said:


> Slightly off topic, I had a sailboat too for many years and if all sporty cyclists learned to sail they would be much better at judging wind and its effects on a moving body especially as that moving body increases its speed. Their drafting skills would certainly improve.


Because then we could all ride Zipp 808s and lee bow the windward rider?


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## JimP (Dec 18, 2001)

pletharoe said:


> @JimP
> Ummmm, haven't you answered your own question higher up in your post? You said the wiind was 14, gusting 20mph.
> .


You missed where I am riding. There is no metar in the Davis Mountains. The mountains tend to create their own weather. The readings are taken at Midland-Odessa which is over 100 miles away.


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## Superdave3T (May 11, 2009)

coachboyd said:


> Wind speed is measured 10meters above ground. At the ground level wind speed is always 0mph and then exponentially rises the higher you get above ground. So if the measured reported wind speed is 6.7mph the actual wind speed you will see at wheel level will more likely be 1.5 to 3mph.
> Plus, wind speed, wind angle, your speed, your angle are constantly changing. You may see 15 degrees of yaw angle and then 200 meters down the road it will be 3 degrees of yaw angle. As rruff said (and I think he's pretty handy with that physics topic), 15 degrees of yaw angle is more than you would normally see when riding fast.


Yes, but the wheel speed at ground level is also 0mph. At the top of the wheel it is twice the bicycle's velocity. Some low pressure areas have even higher speeds.
The varying wind speed along your path of travel is why shape is critical and why maintaining airflow is critical. When air stalls or detaches it needs some added energy or in some cases a great deal of time to return to normal flow, it doesn't just "jump" back onto the surface.
-SD


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## coachboyd (Jan 13, 2008)

SuperdaveFelt said:


> Yes, but the wheel speed at ground level is also 0mph. At the top of the wheel it is twice the bicycle's velocity. Some low pressure areas have even higher speeds.
> The varying wind speed along your path of travel is why shape is critical and why maintaining airflow is critical.  When air stalls or detaches it needs some added energy or in some cases a great deal of time to return to normal flow, it doesn't just "jump" back onto the surface.
> -SD


Killer post bump Dave 

We have a white paper coming soon about the new rims we are releasing and it's all about air flow over all angles. In part of designing the rims we made physical prototypes out of aluminum and then joined them together. One of the problems with our first prototype was that we had to bolt them together, then fill the holes and sand it smooth. Unfortunately it wasn't perfect and we found flow separation at higher yaw angles. You can see the spots in this picture. There was also an issue on the bottom of the rim with the joining together. Once the air started to separate there was no way to get it back onto the rim.









So, in making a better prototype we had the same process, but added a heavy clearcoat to the rim to simulate the clearcoat on carbon as much as possible. It gave us results much better and much closer to the finished results of the rims (not getting separation at higher yaw angles)


With the variety of yaw angle that we see. It depends a ton of riding speed, wind speed, and wind direction. Somebody riding along the coast may see over 15 degrees for most of their ride (happens to me whenever I am on the coast of Florida). But a pro cyclist doing a time trial on a calm day may never see above 5 degrees. Having a wheel (or bike  ) that performs on all those angles is key. . .because over the course of your riding and racing you will encounter all of them.

But I will stand by my post from 2012 that when riding fast, you are unlikely to encounter a lot of 15 degree yaw angles.


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## MercRidnMike (Dec 19, 2006)

bwbishop said:


> And if all pilots learned to fly a sailplane first, they'd be better off as well! There's lots to be learned from those natural, un-powered sports.


I'll agree 100% on this...you learn a lot about the wind by having to rely upon it. Though, in my case, my 3rd solo (in a sailplane) involved a cold front and more wind than I could shake a stick at (winds went from [email protected] to [email protected]+, a 737 aborted its landing at a nearby airport and went to its alternate landing site....I didn't have that luxury in my 600 lbs of engine-less sailplane). The higher you get, the higher the wind.

Getting back to the larger topic at hand....The fluid dynamics of airflow, especially in such a complex flow channel as what we get near ground level (trees, valleys, structures) is a really big PITA to try to work with. In general, though, what the airport reports will be far less than what we experience out on the bike.

In terms of deep wheels...realistically, unless you are racing and seconds matter, they are more of a fashion statement for the average joe rider except that there is the possibility of a stronger wheel build for us big guys (again, lots of variables to deal with in that conversation). 

Myself, I'm looking at building up a shallow profile aero rim (Flo 30's, actually) with a low drag hub for my long distance and occasional high speed runs (recently cracked 51 mph on a sweet downhill run). As a bigger guy, I could spring for deeper wheels and my weight would mean more resistance to to cross-wind forces, but the benefit would only be minutes on my Metric and Century rides...probably not the best return on investment. Deep rims would look cool though.


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## SwiftSolo (Jun 7, 2008)

If you are riding at 20mph in a 15mph tail wind, you are going directly into the apparent wind. Wheels only experience apparent wind, not true wind. a 5 mph wind blowing directly across your course of travel will likely far into the 15 to 20 degree apparent wind angle in which deep aero wheels claim to be effective. The apparent wind velocity would likely be less than 3mph at the mid height of the wheel.



Maniton said:


> I had a bike mechanic at my LBS tell me that aero wheels, deep rim and discs, create drag on a cross wind as they increase surface area for wind. He said they are only meant to increase aerodymanics going directly into the wind, within a 15 degree variance left or right.
> 
> Is there any truth to this? It came up because I told him I'd love to get some 50 or 80 mil wheels.


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## Mike T. (Feb 3, 2004)

pletharoe said:


> When the truck passed Mike T, it sheltered him from the wind, instantly removing these two factors. Mike had been compensating for them and suddenly found himself overcompensating as there was no more crosswind. A scary situation.


That was the scariest moment in decades of cycling. I sold those wheels (50mm deep Gigantex) and have not have a heart-stopping moment since. I now use 25mm deep Pacenti rims.


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## Pirx (Aug 9, 2009)

Mike T. said:


> I now use 2mm deep Pacenti rims.


*2mm* deep? Whoah...


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## Mike T. (Feb 3, 2004)

Pirx said:


> *2mm* deep? Whoah...


Yeah I'm such a good customer, Kirk had a special run of rims made just for me - not affected by crosswinds one iota.


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