BullSh*t Science...

[Gumpole]

There has been a lot of this lately on the Hub, with some people with matric level Physics shooting down the salespeople (who are without), but here is a little more BS from Zipp.....

 

a Wheel with negative drag!! so it actually helps push you forward and I also imagine that the faster you gi the harder the push!!

 

 

http://www.cyclingnews.com/tech/2007/shows/eurobike07/?id=results/eurobike072

 

Zipp probably meant to refer specifically to other manufacturer's disc wheels, though, as it also says its new Sub-9 disc achieves a negative drag figure when equipped with its updated Tangente2 dimpled tubular tire. According to Zipp, the Sub-9 produces -80g of drag at a 15? yaw angle, effectively yielding 11 watts of forward power. Shapewise, the Sub-9 almost looks to be an 808 toroidal rim blended with a small-diameter flat disc in the middle. Naturally, just about every surface on the Sub-9 is graced with Zipp's ABLC dimples.

[Red Zone]

I dont think Zipp meant that their wheel produced negative drag compared to other wheels. But actualy mean that the wheel produces negative drag. I believe it, call me a sucker, Unfortunatly I probably will never put that specific wheel to the test as I am too poor.

Apparently when the wind hits the wheel at a certain angle it will produce negative drag i.e propel it forward, much like a sail can propel a boat forward when the wind hits it at a small angle (ie 15 degrees).

[JasonW]

So all you need to do is ride the whole race leaning over at 15 degrees and you will be at an advantage!

 

Of course you will probably go round in circles and/or crash...

[Bikalot]

So all you need to do is ride the whole race leaning over at 15 degrees and you will be at an advantage!

 

Of course you will probably go round in circles and/or crash...

 

ha ha ha ha ha ha

 

so doesnt really help then?

[Racing Hart]

no its impossible to get a wind from behind while riding on a bike unless you are riding in a 70km/h tailwind... there would always be drag on a wheel its impossible to create a wheel thas has a negative drag!!

[lowracer]

possibly the sailwind effect when you get negative drag if the wind is coming from lets say 15 degrees from the front instead of straight on?

sme wheels have been known to do this

[Racing Hart]

no that is impossible that over writing the newtons laws of physics

[Racing Hart]

a wheel can only create less drag than another wheel manufacturer but never can the drag become zero or less

[Christie]

I also think the term "negative drag" sounds a bit funny - something a marketer came up with, perhaps?

As to what it means, I would guess it generates a small thrust component like a sail if the resultant wind direction is from 15 degrees?

I may be wrong (physics guys please correct), I figure this means for a rider doing 40km/h this means a 10.7km/h component perpendicular to the direction of motion? Perhaps not too bad, but when is the wind too strong to ride a disc?

 

Secondly, what would the UCI think of "negative drag" designs?

[Racing Hart]

they wind is only to strong for a disc when the resultant wind is from about 85-95 degrees...in other cases a disc is always better...(eg allmost all cases)

[Racing Hart]

"I figure this means for a rider doing 40km/h this means a 10.7km/h component perpendicular to the direction of motion?''

nope because the you have a resultant wind that still thrusts backwards!! eg 165 degress in the direction of motion

[The Guy in Pink]

It is possible to get "lift" from an aerofoil , like a yacht sail or a subject that I am looking at at present, wind Turbines.

This site site explains the concept a bit http://club.cycom.co.uk/vertAxis.html .

However it would be impossible to get "Lift" from a symetrical object like a bike wheel.

[Racing Hart]

lift is totally something different to drag...lift actaully uses the drag to lift off

[The Guy in Pink]

Not in the case of a Vertical axis turbine, Lift or more correctly Torque is generated throughout the rotation of the aerofoil 

[Racing Hart]

okay I've worked it out...if you are travelling 40km/h and get a crosswind from 15 degrees in the direction of movement.. you get a resultant wind of 38.8km/h a hour 176.15 degrees in the direction of movement... thus is still impossible for a negative drag... It only becomes possible for a short while if you ride at 40km/h and you suddenly get a wind straight from behind thats travelling at 41km/h..but you will then pick up speed just until your above 41km/h and the resultant wind becomes zero

Racing Hart2007-09-03 14:29:21

[Racing Hart]

haha phen miskien kan jy dit kontroleer...