# aero wheels? regular spoked wheels? HUH?



## omniviper (Sep 18, 2004)

I'm a lurker int hese forums but i post occassionally when i have questions. One thing that came to mind is the fact that a lot fo epopel keep mentioning areo wheels consistently. My question is what are aero wheels?

My softride only has the regular mavic xpc21 which are all spokes. Are those aero wheels as well? 

Whats the inherent different between aero and reg spoke wheels? It would seem aero has that coolness factor to it but aside from that i don't see anything else. Aerodynamically, wouldn't it be disadvantaged if wind was blowing perpendicular to you? In that aero wheels, having more surface area would have the most drag?


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## KonaMan (Sep 22, 2004)

*just had this discussion recently w/LBS*

basically "aero" wheelsets are varied with design, material and advantage (not to mention cost). depending on the race or intent of use (which will get you a million other answers), you'd use one style over another. For example, track bikes used for tt will typically use a "disc" or "solid" wheel. the advantage here is that you have no wind resistance on those wheels (most will only have this on the rear). 

so there are two basic designs, "squared" or "deep-V". Even some rims (Bontrager Selects for example) are "V"- shaped, but aren't deep enough to have an advantage. What I was told is that they need to be at least a 30 mm depth before you begin to get any advantage. Your Mavic's I believe are V shaped, but are not very deep, giving you little aeordynamic advantage. The number of spokes will vary, and some will even use a blade style spoke for more advantage (or if you look at FSA rims, mine are 28 mm deep and use fewer spokes that are blade style). We had a set of Deep V's built up for my wife (when she does triathlons) and they are a 32 spoke wheel, but are deep enough to get a slight advantage over her Mavic Open Pro wheels (used for training).

side winds, which you mentioned would have little effect on the wheels. if the wind is severe enough, there will be other factors to consider (since you'd be having to lean into the wind to stay straight). If you look at high end triathlon bikes (like Blue, Cervelo, etc) the down tube is usually very wide when looking at it from the side, but the front (aerodynamic) profile is where you gain the advantage. same principle applies to wheels.

If you're looking for a set that is reasonably priced (aero wheels don't come cheap) look at Velocity wheels. For their price, they do a great job. I've noticed more off the shelf entry level tri bikes with these this season.


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## Anti-gravity (Jul 16, 2004)

*Aero wheels and spokes*



omniviper said:


> I'm a lurker int hese forums but i post occassionally when i have questions. One thing that came to mind is the fact that a lot fo epopel keep mentioning areo wheels consistently. My question is what are aero wheels?
> 
> My softride only has the regular mavic xpc21 which are all spokes. Are those aero wheels as well?
> 
> Whats the inherent different between aero and reg spoke wheels? It would seem aero has that coolness factor to it but aside from that i don't see anything else. Aerodynamically, wouldn't it be disadvantaged if wind was blowing perpendicular to you? In that aero wheels, having more surface area would have the most drag?


Aerodynamics is a somewhat complicated method of design based on fluid dynamics, which is a difficult subject to understand for some people. Given that, the design of anything aerodynamic is not always obvious.

Additionally, with that said, the concept of aerodynamics in cycling is also contraversial and a source of much debate. In general, from what I have seen, most people consider wheels as a whole "aero" if the rim is deeper than 30mm. With my limited knowledge of the engineering aspects of aerodynamics (the physics I do understand for the most part) the idea of a deep rim is to reduce areas of low pressure and turbulence that manifest on the underside of the rim. The smoother the air can travel over a surface with as little turbulence as possible, the lower the drag force that opposes motion. Apparently there is a certain depth the rim should be at to start seeing this benefit, but that exact value is, of course, debateable.

Aero spokes can be seen on rims of any depth. They give slight improvements in aerodynamics over round spokes, can be made just as light, and are generally as strong or strong enough compared to regular round spokes.

-R


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## liu02bhs (Dec 30, 2001)

*Aero Wheels*

I think looks aside, aero wheel probably wouldn't make a significant difference in speed (as with aero frames). Aerodynamics is a very complicated subject. The drag from the bike pales in comparison with the rider. For my fluid dynamics class, I learned that the *entry doesn’t effect the drag as much as the exit*. This is because there’s pressure drop in the exit. The more the pressure drop, the more the drag. *Although a fin shape would have less drag, the tire is not fin shaped. So you get a reduction in drag from the front part of the wheel only*. Furthermore, perfectly laminar flow actually causes more drag in some cases, this is because the separation point of the flow moves from the back to the front. This is why golf balls have dimples (to induce turbulent boundary layer). Also, with larger surface area, you go skin (shear) drag resulted from the air molecules rubbing against the surface. 

When you add the ride everything gets more complicated because the air behind the ride is turbulent thus has random direction. So it’s hard to tell how much drag the back part of the bike is experiences. 

With side wind, aero wheel can be a pain in the arse. That’s why they don’t have disk for the front (except for track). Although you don’t get a lot of drag from side wind you get increase friction between the tire and the road, so you wouldn’t move sideways. You have to push harder to overcome the extra friction. Also you go a lot slower because you have to mind your balance. 

The manufactures say that the disk have a sail effect that help propel the wheel. I really don’t see how that happens, since the disk in the back is for the most part symmetrical, and the sail is not. And I think in sailing you have to zig-zag. But then again, I don’t know too much about the aerodynamics of the sail.

Personally, I think if you are a beginner, stick to the cheap stuff. *There is so little actual performance gain from the amount of money you have to dish out. The law of diminishing returns is at work here.* I think you get more psychological advantage than anything. 

This is the same with frames. As my materials professor told me, carbon fiber aside, you can make steel as light as aluminum and titanium because although Al and Ti has lower density they also have lower elastic modulus. Just look at the size of the steel bike tubes and the size of the Al and Ti bike tubes. So looking it as a whole, you have to use more material to get the same stiffness for the lighter metals. 

And Trek’s new OCLV 55 carbon, I’m not sure too many people know this, but the *lower carbon count severely lower the strength of the bike*, because almost all of carbon fiber’s strength comes from the graphite fibers and not the polymer matrix used to bond them. There is no free lunch.


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## MikeBiker (Mar 9, 2003)

Your CXP21's are more aero than the Mavic Open Pros, but less than what are considered 'true' aero wheels. The more aero a wheel gets, the more unstable they are in cross winds. The wheel weight and aerodynamics are not as important as the rider's weight and aerodynamic position. They are more important to the pros because they have less body fat and a more aero position and ride faster.

'Upgrading' your wheels would not result in any significant speed increase for 99% of riders. The CXP21's are essentially an OEM (Original Equipment Manufactures) version of the CXP30/33s.


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## al0 (Jan 24, 2003)

I would suggest you to take a look on the following link
http://www.analyticcycling.com/

Concrning aerodinamic advantage - it is usually considered that rwhile ims more then 30mm deep provide some advantage, but it is almost unnoticable. Some real aero advantage starts at ~45mm rims.

Anyway, to notice it you have ride 25mph (so for beginner aerowheels are completely useless). 

BTW, some measurements where published those shows some disadvantage for aero rims (and some other "aero" equipment) for speeds under 21-22 mph.


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## asgelle (Apr 21, 2003)

al0 said:


> BTW, some measurements where published those shows some disadvantage for aero rims (and some other "aero" equipment) for speeds under 21-22 mph.


Do you have a source for this. I've never seen anything like it, and it doesn't make sense unless factors such as additional weight are used to counterbalance the aero advantage. In that case, the results would be highly dependent on the equipment, rider, and course.

As for the advantage in reducing aero drag being noticable only over 25 mph. Well, I don't know how sensitive everyone is so I can't say what is or isn't noticable. However reducing drag provides a benefit at any speed, and in fact the slower the rider the more time is saved by reducing drag. This is clear from applying the models referenced at analyticcycling.com.


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## Kerry Irons (Feb 25, 2002)

*Some numbers*

The best aero wheels are good for about 0.4 mph at 25 mph. At 20 mph, this is worth about 0.23 mph. One of the best aero wheels is still the Hed 3 spoke (based on the old DuPont/Specialized design). Hed and Zipp also make fast aero wheels (very deep rims, very few spokes) along with a number of other brands. If you watch the time trials in the big tours, you will see a wide selection of styles, all with roughly comparable drag numbers. Advertisements by wheel companies tout various numbers as being better than the other guy's numbers. That is because each wheel has its own characteristic variation in drag with wind speed and wind angle, and the marketing department picks the set of numbers that makes their wheel look the best.

Despite the negative effects of crosswinds on handling, you actually get a sail effect and many designs, particularly discs, are actually faster with a cross wind - the power of the wind is transferred into the bike through the wheels, just like the sail on a sail boat. Disc wheels are only used on the front on the track or in low wind conditions due to the handling problems that can result, and any deep section rim will make steering more difficult in gusty cross winds.


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## KeeponTrekkin (Aug 29, 2002)

*Low spoke count, aero wheels have high cool factor...*

and high cost; not only to buy, but to maintain. Traditional wheels can be trued by any bike shop. Many specialized aero wheels require special tools to true. Break a spoke and you may be bikeless for weeks if the wheel has to be sent to the factory.

BTW, although some claim no crosswind effect with aero wheels, I claim they are brain dead. Aero wheels are highly sensitive to crosswinds, especially gusting crosswinds. If that's your idea of fun, you like spending a lot of money for a high zoot look, or if your riding conditions are such you rarely encounter them, then aero wheels may be for you.


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## orange_julius (Jan 24, 2003)

*One non-aero advantage to aero wheels*

While aerodynamic advantages have been covered, I've found one other advantage of using aero wheels: they are usually stiffer than the non-aero wheels. I have a set of lower-end Gipiemme semi-aero wheels that I love not because it's aero, but rather because it's damn stiff. Very nice for certain types of races. They're porky, as in very heavy, but in certain situations the stiffness more than makes up for it.


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## asgelle (Apr 21, 2003)

KeeponTrekkin said:


> BTW, although some claim no crosswind effect with aero wheels, I claim they are brain dead. Aero wheels are highly sensitive to crosswinds, especially gusting crosswinds. If that's your idea of fun, you like spending a lot of money for a high zoot look, or if your riding conditions are such you rarely encounter them, then aero wheels may be for you.


Of course there's a crosswind effect of high profile rims, then again there's an effect if a butterfly bats its wings in China. The question is how big is the effect relative to what is significant. I'd claim the effect of crosswinds on bike stability is negligible in all but the most extreme conditions. I've ridden deep profile rims in gusty crosswinds over 25 mph wihout any noticable instability. A lot goes into how stable these wheels are including bike geometry, rider size and rider skill. For some it's a problem, for many it isn't.


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