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TECH NEWS
Spoke Fins 2Introducing Spoke Fins: swivelling fairings for your spokes
US company Null Winds Technology is seeking Kickstarter funding for its swivelling Spoke Fins: nylon plastic fairings that are designed to cut spoke drag in both headwinds and crosswinds.
Fairings for your spokes? Uh-huh!
“Optimally streamlined Spoke Fins reduce the spoke drag coefficient by more than 50% in the critical, faster-moving, drag-inducing region located nearest the wheel rim,” says Null Winds Technology. “Since round spokes have relatively high drag coefficients — thereby becoming the major contributor to overall wheel drag — reducing critical spoke drag also reduces total wheel drag. Spoke Fins are also tapered lengthwise to reduce drag principally on the critical uppermost spokes, where wheel drag most retards vehicle propulsion.
That’s not all.
“As the wheel rotates, Spoke Fins automatically adjust their streamlined alignment for the changing orientation of the effective wind vector impinging on the spoke. Spoke Fins swivel to reduce pedalling effort under any wind condition, becoming especially effective on typical recreational bicycles with higher spoke-counts.”
So, that’s it in a nutshell. There are enough wheels about with bladed spokes; why not just go for a set of those?
“Bicycle racers know that bladed aero-spokes quickly become ineffective in crosswinds,” says Null Winds Technology. “Spoke drag quickly increases when impinging winds are directed crosswise across the flat blades. In a direct headwind, the common round spoke develops more wind drag than does a bladed spoke. However, against a crosswind the bladed spoke can actually produce much more drag than a round spoke.”
Null Winds Technology doesn’t present any wind tunnel data relating to Spoke Fin-equipped wheels. To be fair, that’s understandable because wind tunnel time is very expensive.
The Spoke Fins do, though, seem to fall foul of the UCI’s technical regulations. Article 1.3.011 says, “Any device, added or blended into the structure, that [is] destined to decrease resistance to air penetration or artificially to accelerate propulsion, such as a protective screen, fuselage form of fairing or the like, shall be prohibited.”
Null Winds Technology are seeking US$30,450 (£19,908) to buy the eight-cavity polished steel injection mould it needs to produce Spoke Fins.
Assuming the target is met, a set of Spoke Fins will cost you from US$20 through Kickstarter, although they’ll ship to the US only via this campaign.
For more info go to Kickstarter or www.nullwinds.com
Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now over 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.
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41 comments
Centripital force. Centrifugal force doesn't exist. You're not pushed outwards, you're actually pushed inwards. Anyway. ...
All sailors know of somrthing called apparent wind. It's the combined vector of your vehicle's speed and any additional environmental winds.
I agree that the rotation of a spoke (esp over the top) is a much higher velocity than any other vector, except if you live in Holland or Norfolk I suppose
could be useful for a RTW, lejog or RAAM rider?
Maybe this is what Liz Dimmock was waiting for to start her RTW ride?
Thanks for the correction, I've not heard of centripital force before!
Well at least I've learnt something today!
Just to play devil's advocate...
That Mr Newton taught us that every force has an equal and opposite, so if centripetal force exists, so too must it's opposite...
Centrifugal force is a perfectly good concept. If you make the legitimate choice to look at something from a rotating viewpoint, then you will see a centrifugal force that pushes everything outwards. If you choose a non-rotating viewpoint then there is no centrifugal force. It's a 'fictional force' like the G-force that pushes you back into your seat in an accelerating car, or the coriolis force that changes how things move on the rotating earth.
Simply construct newton's laws in a rotating system...
Null Winds are the idiots who were trying (apparently still trying) to sell the "un-fender" wheel farings, optimized for making crappy bikes more aero while keeping no amount of water off of you and probably rubbing against your wheel/tire regularly. http://www.nullwinds.com/products-fairings.html
I can't imagine how the blades will point sideways in a crosswind with the centrifugal forces and air flow that the revolving wheel will generate, what this means is that the crosswind will have to be faster than the speed that the spokes slice through the air.
Also the picture shows that the blades trail behind each spoke, so if you picture the top of the wheel to start with, as the wheel rotates in the direction of travel the fin is behind the spoke but as this spoke approaches the bottom of the wheel towards the ground, the air flow is now coming from the opposite direction in relation to the fin, so as the fins are free to move they will then be pushed by the air and rotate to point back towards the bike frame, and as this particular spoke approaches the vertical position again it will have to spin round again to its first position.
I wonder how noisy that will be?
The airflow is always in a positive direction (i.e. only acts head on to the spoke). When you say it is in an opposite direction, it is in fact actually at 0.
As the bike moves over the ground at, let's say 20 mph, the circumference of the wheel travels at 20mph. So, at the top of the wheel's rotation the velocity is +40 mph (speed of bike, 20mph+speed of wheel relative to bikes movement, 20mph) and at the bottom of the rotation the airspeed is 0 (speed of bike, 20mph+relative speed of wheel, -20mph).
You have then got to think about when the spokes are horizontal, but in this case the airflow is acting at a tangent; when it moves from horizontal into the downwards position, the incident tangential airflow should be negligible (so the fairings would be unlikely to rotate the opposite way).
A cross wind is often only 10mph @ 50/60 degrees, so the relative airflow at the top of the wheel is near enough head on. This means the only time that these spoke fairings are useful is when the wheel is nearing the bottom of it's rotation (i.e. the slowest) as this is the only time the crosswind component is overly significant.
It's a lot of hassle for such a small gain. I'd chose aero spokes over fairings (regardless of their poorer x-wind performance).
But into a stiff headwind... say 15+mph at say 30º? Do you think there'd be any chance of them turning to the point of causing a negative effect?
I'm especially wondering what happens if you're on a 5%+ climb into the wind and these things effectively start flapping back and forth.
This is an idea that has popped into my mind a lot recently, but I'd need to see wind tunnel test data to show that adding to something with such a small cross-section actually reduces drag (significantly)... especially compared to bladed spokes. That said, they would be cheap, could give them a go and bin them if they don't seem to help.
I'd be more interested in a similar thing for tyre valves, it could even simply screw onto the valve shaft?
spokey dokeys
Have had a makeover........
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