Regarding low air resistance wheels

[sksig]

Hello.

I´m preparing myself for a BSc thesis in mechanics, and I was hoping to get some inspiration from you guys.

What I'm after particularly is what professional cyclists look after when choosing wheels for their bikes regarding air resistance? Are there any kind of wheels on the market that can perhaps use side wind to give the cyclist a boost?

Any thoughts or comments are well appreciated

 

[vspa]

wind is a force of nature and as such very often impredictable, so racing cyclists prefer equipment capable of performing in different conditions, when you do get tailwind average speeds climb up considerably, im not sure about a tail-sided wind, it could be a boost, im not sure,

 

[alienator]

Hello. I´m preparing myself for a BSc thesis in mechanics, and I was hoping to get some inspiration from you guys. What I'm after particularly is what professional cyclists look after when choosing wheels for their bikes regarding air resistance? Are there any kind of wheels on the market that can perhaps use side wind to give the cyclist a boost? Any thoughts or comments are well appreciated

There are aero wheels that can, given a sidewind in the appropriate direction, can generate lift with a component in the direction of bike travel....or so one company, Zipp, claims. I suggest you try contacting Josh Poertner at Zipp. Aero wheels, in general, are highly prized in the pro peloton. It used to be they were only used for time trials. Then they started to be used for flat-ish races or stages. Now you'll see pro's on aero wheels in virtually every race or stage. The factors that riders look at when choosing aero wheels are depth, cross-secitonal profile, and weight. The deepest wheels tend to be used in flatter stages/races and time trials, while more shallow aero wheels tend to be used in mountain stages/races or on very tough roads. The shallower rims are less susceptible to the forces generated by the unpredictable crosswinds in mountains. In terms of cross-section, some cross-sections manage crosswinds significantly better than others. When it comes to weight, riders tend to want lighter wheels. Note that in the professional ranks, many of those factors are sacrificed in order to gain or satisfy sponsors.

 

[sksig]

Ok, thanks a lot. I'll take a look at it

 

[wbkski]

I wanted to ask a related question, but, as it pertains to race preparation. I have 3 different wheelset configurations. 27cc front/back, 58cc front/back and a 85cc rear. I've looked at the configurations of the pros over the last few races which I recorded and it seems the climbers prefer a shallow depth wheel, while the sprinters go a bit deeper. Can anyone confirm this or add to why pro's make certain choices? I think everyone will concede that time trial wheelsets are pretty straight forward with the deep front wheel and the full disk in the back (but not always! LOL)

I just started racing crits and hill-climb TT's and I'm trying to get dialed in. Any help, comments or constructive criticism is welcome!

 

[wbkski]

Originally Posted by sksig .

Ok, thanks a lot. I'll take a look at it

You can also contact Keith Williams at Williams Cycling. www.williamscycling.com. He's very accessible and I'm sure would give you all the info you need. They make some pretty fine wheels.

 

[alienator]

I wanted to ask a related question, but,  as it pertains to race preparation.  I have 3 different wheelset configurations.   27cc front/back, 58cc front/back and a 85cc rear.  I've looked at the configurations of the pros over the last few races which I recorded and it seems the climbers prefer a shallow depth wheel, while the sprinters go a bit deeper.  Can anyone confirm this or add to why pro's make certain choices?  I think everyone will concede that time trial wheelsets are pretty straight forward with the deep front wheel and the full disk in the back (but not always! LOL) I just started racing crits and hill-climb TT's and I'm trying to get dialed in.  Any help, comments or constructive criticism is welcome!

There are a few possibilities why pros might make such a wheel choice:

• Part of professional racing is to try to take every legal advantage possible, and in the case of climbing that can include using the lightest weight wheels/the wheels with the lowest moment of inertia, even if the actual performance difference is very small.
• Climbing generally comes with descending in races, and some descents can have gusty winds from unpredictable directions. It's the nature of winds in the mountains. Shallower wheels make the effect of such gusts on steering less severe.
• The rider might just feel better about a set of wheels without having a reason for feeling as such. There are no shortage of times in racing when a racer will make a decision based on the idea that it just feels right.

There are of course other reasons. One thing to keep firmly in mind is that there may be no scientifically based reason. There are some choices still made in racing that are counter to what testing, data, or facts suggest.

 

[alienator]

You can also contact Keith Williams at Williams Cycling.  www.williamscycling.com.   He's very accessible and I'm sure would give you all the info you need. They make some pretty fine wheels.

Note that Williams aero wheels are not of his design. They are someone else's design, an open mold design. I don't believe that Williams manufacturers any of its wheel components. They are all made by other companies and not made just for Williams, excepting the decals of course.

 

[joroshiba]

It is my understanding that the Hed 3 trispoke wheel design is such that a cross wind generates a forward propulsive force due to the shaping the the "spokes". If you were to freely support them and put a fan at 9 degrees to the wheel it would start spinning in a forward motion. I am not sure whether this causes a significant difference in power loss to wind from a cross wind, but I don't think the wind tunnel takes this into account (HED 3's typically do very well at a low yaw angle and poorly in higher yaw situations in the wind-tunnel)

 

[alienator]

It is my understanding that the Hed 3 trispoke wheel design is such that a cross wind generates a forward propulsive force due to the shaping the the "spokes". If you were to freely support them and put a fan at 9 degrees to the wheel it would start spinning in a forward motion. I am not sure whether this causes a significant difference in power loss to wind from a cross wind, but I don't think the wind tunnel takes this into account (HED 3's typically do very well at a low yaw angle and poorly in higher yaw situations in the wind-tunnel)

I don't think that's the case. I can't think of any aero cross section off hand that generates lift at an angle of attack of 90°. All air flow in the shadow of the spokes and rim would almost certainly be turbulent. I also don't know if the Hed 3 is even the top aero wheel that it once was anymore. As for wind tunnel results, if a wheel generates a component of lift in the direction of travel (theoretical direction of travel since the wind tunnel won't be traveling anywhere), the force balance will read this as a lower drag force (Fdrag-Flift,z, where z is the direction of travel). CFD programs would be able to break out the components of lift and drag generated. With pressure sensors embedded in the surface of the spokes and rim, it's possible that you might be able to dig out the z-lift component from the tests.

 

[wbkski]

Originally Posted by alienator .


Note that Williams aero wheels are not of his design. They are someone else's design, an open mold design. I don't believe that Williams manufacturers any of its wheel components. They are all made by other companies and not made just for Williams, excepting the decals of course.

You may be correct, however, their website would suggest otherwise.

 

[alienator]

You may be correct, however, their website would suggest otherwise.

I see nothing on the sight that suggests otherwise.

 

[cyclintom]

The forward velocity of the bike both reduces the drag of the rearward revolving spoke but also increases the lift of the forward revolving one. Whether or not this is significant is a question but certainly you could measure it in a wind tunnel with a proper setup. Because of the rather slow speeds of bicycles, turbulence probably plays a smaller role than you might think.

 

[alienator]

The forward velocity of the bike both reduces the drag of the rearward revolving spoke but also increases the lift of the forward revolving one. Whether or not this is significant is a question but certainly you could measure it in a wind tunnel with a proper setup. Because of the rather slow speeds of bicycles, turbulence probably plays a smaller role than you might think.

Please justify your claim that turbulence "probably plays a smaller role than you might think". Feel free to use other resources to make up for any lack of knowledge in the areas of aerodynamics and specifically, sources of energy loss in fluid flow. Also feel free to look up the relationship between spoke count and drag.

Golly, I wonder what that chaotic flow downstream of the wheel is...?

 

[cyclintom]

Were you one of those telling everyone that you couldn't use windpower to go downwind faster than the wind?

 

[alienator]

Were you one of those telling everyone that you couldn't use windpower to go downwind faster than the wind?

Imagine things all you want. in only 6 posts you're already showing your troll powers. Again, what's the basis of your claims about turbulence?

 

[cyclightning]

re: forward push from sail even into headwind. Yes, it's possible to sail into a headwind, but on a sailing ship the boom can be turned at a large angle to the direction of movement, while a bicycle wheel just points straight into the direction of movement, except when turning. An aero bicycle frame adds a slight forward thrust in crosswinds as round front and elongated and tapered towards the rear down tubes and seat tubes redirect air towards the rear, thus giving a slight forward thrust. A symmetrically round tube will deflect air equally towards the front and rear.

 

[CAMPYBOB]

here toy go again...

 

[dhk2]

Quote: Originally Posted by cyclightning .
re: forward push from sail even into headwind. Yes, it's possible to sail into a headwind, but on a sailing ship the boom can be turned at a large angle to the direction of movement, while a bicycle wheel just points straight into the direction of movement, except when turning. An aero bicycle frame adds a slight forward thrust in crosswinds as round front and elongated and tapered towards the rear down tubes and seat tubes redirect air towards the rear, thus giving a slight forward thrust. A symmetrically round tube will deflect air equally towards the front and rear.


Amazing what kind of forward thrust can be produced by the wing sails on the America's Cup boats isn't it. I'd like to see Oracle put up some more of that today...at least more than Team NZ. Don't really care who wins the Cup, it's just not fun to watch a one-sided playoff.

But, those AC 72 sail/wings consist of two airfoil sections, which are shaped/tuned precisely for wind speeds and angles of attack constantly by the grinders onboard, and "flipped" each time the boat is tacked. If the two wing sections of the sail were kept centered and flat, and the boom kept dead on centerline (like a bike frame must be), I don't believe you'd see any forward thrust at all, just induced and parasite drag, like an aircraft wing.

 

[alienator]

re: forward push from sail even into headwind. Yes, it's possible to sail into a headwind, but on a sailing ship the boom can be turned at a large angle to the direction of movement, while a bicycle wheel just points straight into the direction of movement, except when turning. An aero bicycle frame adds a slight forward thrust in crosswinds as round front and elongated and tapered towards the rear down tubes and seat tubes redirect air towards the rear, thus giving a slight forward thrust. A symmetrically round tube will deflect air equally towards the front and rear.

I want to see numbers justifying this claim.