Motorcycle cast wheel spokes

[V8Pinto]

Anything to be gained by shaping the "spokes" of cast motorcycle rims?  I was staring at my Hayabusa rims yesterday and noticed the three spokes on the early bike's wheels are symmetrical.  Then I looked at the rims on my Gen II Busa and noticed that they angled the 3 spokes in a gentle arc and shaped the trailing edge of the spoke to look more aero.  The spoke is scimitar shaped on the later wheel.

Probably, the wheel/rim area is really turbulent otherwise we wouldn't have Moon discs on cars....so does this aero shaping of the wheel spokes really have any effect?

[fredvance]

Shane, I think that the air is pretty much torn up by the rotating tire. Since we cant put discs on the front wheel, not much we can do about it.

Fred

[Unkl Ian]

The US Olympic cycling team spent a ton of money on aero,
for the 84 Olympics in Los Angeles.

One thing they came up with, was flat spokes, instead of round.
IIRC, the rules specified the number of spokes, but not
the cross section of each spoke.

I can only assume this was done to reduce drag.
So while the air within the wheel is turbulent, drag still exists.

[nrhs sales]

There are also motorcycle wheels that are designed to actually catch wind to help cool the brakes in road racing applications. These ARE NOT what you want on a LSR bike!!

[Dean Los Angeles]

Since we cant put discs on the front wheel

Well, not so fast. Between discs and spokes there is a wide gap.  I don't remember the mandated amount that has to be open on the front wheel. 25%? If you take the wheel and calculate the area required to be open and then drill the disc with small holes to hit that number you have a ventilated disc that would probably have less turbulence than spokes.

5,162 1/8 holes and you have it whipped!

[Dean Los Angeles]

I did a design study when I was contemplating making a set of wheels.

"It is required that front wheels be cross-ventilated by an area equal to at least 25% of nominal rim circle area."

"Nominal" I take to mean the part of the wheel that isn't covered by the tire or hub. I was looking at a 17" wheel that had an area of 164 sq in. Minus the hub of 35 sq in there was a nominal area of 129 sq in. 25% of that is 32 sq in.

660 1/4" holes equals 32 square inches.

[sockjohn]

Just because it looks aero doesn't mean it is.  Pedal bicycles have spent lots of wind tunnel time refining wheels, unfortunately I'm not sure any of that is applicable here.

Would love to see Dean's design in the wind tunnel against something with a smaller number of larger holes, and a Hayabusa wheelset. 

I also wonder how the specifics of the motorcycle such as forks, fender, fairing would alter the results.

[1212FBGS]

totally wrong about bicycle wheels.... i did quite a bit of work with Aerospoke wheels several years ago, and they had a different agenda.... there is tons of data available about a spinning mass (wheel) there big concern was in lowering the inertia of the wheel with attention to aero so the rider didn't have to expend energy to turn the wheel..... easier for the rider less hp out.... the faster the wheel turns the bigger the wash, that horse has been beaten to death, they just wanted an easier wheel to turn
Kent

[A2WindTunnel]

totally wrong about bicycle wheels.... i did quite a bit of work with Aerospoke wheels several years ago, and they had a different agenda.... there is tons of data available about a spinning mass (wheel) there big concern was in lowering the inertia of the wheel with attention to aero so the rider didn't have to expend energy to turn the wheel..... easier for the rider less hp out.... the faster the wheel turns the bigger the wash, that horse has been beaten to death, they just wanted an easier wheel to turn
Kent

Inertia is very important to them, and with the composites of today weight and strength are not an issue, but aerodynamics are now at the forefront of bicycle industry in the past several years.  In the past people thought if it looked aero it must be.  Now that there are so many bikes/wheels that claim to be aero they have to back up the claim with wind tunnel data to show how they stack up to their competitors.  Bicycle wheel manufactures are spending many hours in A2 (and other tunnels) on wheel design/shape to optimize aero to save riders time.  I have had a poll on here about a motorcycle platform I have designed that would allow spinning wheels and yaw to test things as wheel design/shape, fenders and other configurations (that need a spinning wheel simulation), but I didn’t have much interest from the motorcycle comunity.  

Zipp wheels videos:
http://www.youtube.com/watch?v=jxtxWp7iPN8&feature=related
http://www.youtube.com/watch?v=P7zgznQhJN4&feature=related

D

[bak189]

Cross winds................back in the early 1970's on the record 125c.c. Can-Am bike......it had wheel
covers ......Yes, they made the bike go somewhat faster (the tunnel also showed this) .....had to take them off, made riding the bike flat out dangerous.  Weather has changed since the "old days" we have been getting more wind at Bonneville over the past couple of years.....we have been racing our sidecar without the dustbin fairing due to the wind problem......in 2007 and 2008 with the dustbin mounted
Larry C. and Warren R. had more then one "moment" that got their attention.  In all the years that I ran my sidecar back in the 1980's and 1990's (with dustbin) I only had one "moment" due to cross winds....
now there is a problem several times during a meet.   Times and weather are changing........................

[Stainless1]

Bak, they are getting older and less fearless.... 
All of us seem to realize our mortality when we get older, those little glitches and were no big deal, apply a little age and wisdom and you all the sudden become concerned. 

back to topic...

[Eric_Noyes]

I have always assumed that 25% of “nominal rim circle area” of a 17 wheel would be 25% of a 17” circle or 56.745 sq in. This would require 1156 1/4" holes.

[Old Scrambler]

Regarding the inertia of a spinning wheel............Just theory on my part, but I designed my modified Triumph Cub to roll on 21-inch wheels. The thoughts were to reduce tire width in the air and on the salt (less drag) and to help with the final gearing ratio. I found a narrow fender for the rear of a 26-inch bicycle and mounted it on the front to keep drag at a minimum without 'skirts'. Just theory.......no engineer here.........but it seems to work as the bike rolls very easily and it carried my 200 lbs. to a class record.

http://www.facebook.com/pages/Salt-Team-Advanced-Landspeed/222251137821263

[maj]

I have always assumed that 25% of “nominal rim circle area” of a 17 wheel would be 25% of a 17” circle or 56.745 sq in. This would require 1156 1/4" holes.

And the surface area of the edge of all those holes ?? would it contribute more to drag than the original wheel with 3 shaped spokes

[Rex Schimmer]

I think that we need to look at what the pro bicycle racers are doing to their wheels to get an idea of what to do with motor cycle wheels. If you look at the latest racing bicycle wheels you will see that they are adding fairing to the back side of the wheel rim into the spoke area and they are either running flat spokes or the big dollar guys have special aero shape spokes rolled for them, and they are greatly reducing the number of spokes in the wheels.

We need to remember that at the top of the wheel the relative velocity of the wheel to the air is twice the speed that the wheel is moving and at the bottom it is zero so any aero we can do on the top half of the wheel can pay off big time.

Rex