Wheel fairings for bicycles

One of the interesting things I saw during the Sea Otter Classic last weekend was this set of wheel fairings for bicycles created by aerospace industry veteran Garth Magee.

Null Winds Technology

These look a whole lot like the skirt & coast guards used on some utility bikes. The prototypes Magee had on hand at Sea Otter were a little rough, but he told me he plans to offer up something a lot more attractive hopefully by this time next year.

In the meantime, these proofs of concept demonstrate dramatic speed gains. While testing this on a short hill at Sea Otter, there’s a 1.5 MPH difference in the the top speed (from 19 MPH to 20.5 MPH) after attaching these Null Winds Technology wheel fairings using the same bike and same rider.

Magee and his company hope to sell these to non-competing enthusiasts, knowing they can never be used in competition at the amateur or pro level. The UCI ban on wheel fairings, first implemented 100 years ago in 1913, continues to this day. The International Triathlon Union and Race Across America also ban the use of wheel fairings, which is why you see deep dish and disk wheels.

Magee believes his fairings over the top half of the wheel offer superior slipstreaming over disk wheels. I can picture a fender as part of the package as well, and perhaps even integrating a fairing into the design of the frame by stretching a membrane between each chainstay and the seat tube.

Everybody asked about crosswinds. While variable crosswinds do impact a faired bicycle’s stability, a steady crosswind is known to increase the speed of a bike. Although faired bikes can’t easily adjust their angle of travel relative to the wind, the benefit is similar to a sailboat reaching or running perpendicular to the wind. HPV records on oval tracks are broken on windy days due to this crosswind benefit.

Null Winds Technology lacks content for now, but you can keep an eye on them here.

13 Comments

  • April 23, 2013 - 4:41 pm | Permalink

    > a steady crosswind is known to increase the speed of a bike

    This statement requires a citation. Certainly, Jobst’s analysis at http://sheldonbrown.com/brandt/wind.html seems to show that a 90 degree crosswind *slows* a bike rather than speeding it up. (Unless we’re talking about crosswinds that are partially tail winds too?)

  • April 23, 2013 - 4:44 pm | Permalink

    I read it in Bicycling Science last night (and it included footnotes) so it must be true. :-)

    I’ll provide the citation after I get home later tonight.

    All due respect to Jobst, but he frequently confuses dialectic with hard science.

  • April 23, 2013 - 9:05 pm | Permalink

    Here’s the relevant text from Bicycling Science, 3rd Edition By David Gordon Wilson, p. 203

    Weaver (2000) showed that over a wide range of incidence, the wind acts on a bicycle fairing in much the same way as it does on a sailboat: it provides forward thrust. THe fairing can take flow at a considerable incidence angle and turn it almost to leave the fairing in the aft direction, which provides thrust.

    The net positive thrust that results from the action of wind on a bicycle’s fairing can occur even though the fairing has no “camber” or curvature, as does a sail or airplane wing.

    The “Weaver” reference is to a paper published in Human Power #49, pp 21-24. I think you can find it here http://www.ihpva.org/HParchive/PDF/hp49-1999.pdf

  • Andy
    April 24, 2013 - 8:39 am | Permalink

    Ride a bike with panniers on it in the wind and see if you still want wheel fairings. Sure, a constant wind at the right angle helps, but as a windsurfer I can assure you that winds here are never constant in speed or direction. Plus any slight-angle-tailwind will later be a headwind, so any loop ride negate the benefits.

  • April 24, 2013 - 11:01 am | Permalink

    Andy, I am afraid that conventional wisdom regarding drag forces on wheeled vehicles is simply insufficient. These fairings provide not only a minimal benefit in a tailwind, but more importantly also provide a dramatic benefit in a headwind. It has nothing to do with sailing. Panniers provide so much exposed frontal surface area, that shielding benefits are largely negated.

  • April 24, 2013 - 10:39 pm | Permalink

    Your quotation out of Bicycling Science really doesn’t support your statement of “a steady crosswind is known to increase the speed of a bike”.

    I certainly do believe that under certain conditions, a fairing could act as a sail and provide forward momentum to a bike in a crosswind. Especially considering that many fairings are shaped like an undercambered airfoil and airflow across them would cause lift towards the front.

    … however, the fairings on these wheels are not shaped and oriented like that. This is the sort of fairing I think they’re talking about — http://bikesiliconvalley.org/files/images/blogch/fairing-recumbent.jpg (the bike in the middle of the picture).

    I do believe that Jobst has it right (note that he’s not talking about fairings at all –yes, a fairing like in the picture I gave could change things), and he even has experimental data that shows the same effect.

  • April 25, 2013 - 8:42 am | Permalink

    Why would non-competition bicyclists care about adding 1.5 mph on a downhill run by adding wheel fairings? This is just another useless bicycle accessary that increases the cost of an otherwise inexpensive transportation option.

  • April 25, 2013 - 9:32 am | Permalink

    1.5 mph faster on a downhill run is a rather artificial benchmark, but if the fairings improve the aerodynamics of the bike and make it a little faster without screwing up the handling much in a crosswind, then even non competition-cyclists will care about it.

    I mean, if you’re going to spend hundreds of dollars shaving a few ounces off of the weight of your bicycle for the extremely small benefit that’ll give you (and most of that will only be visible when going up hill), adding fairings that will give you a much more significant benefit on flat ground should be an almost no-brainer as long as there’s no real downsides (like problems with handling in crosswinds.) And while most non-competition cyclists shouldn’t be weight-weenies, if something like this can give you 18 mph speeds for 17 mph effort (warning: made up figures, but possibly close to accurate) on flat ground — that’s pretty significant.

  • Andy
    April 25, 2013 - 9:44 am | Permalink

    Garth, my point about panniers and windsurfing is that cross winds are not steady, and change direction and speed constantly. A gust form the side will require adjusting your steering, and it’s nearly impossible to keep up your cadence efficiently in the wind because of this. Add your fairings and those gusts will only be felt stronger.

    Anyway, it’s yet another bike product with no market. People that “need” to go fast for racing can’t use it, and people that aren’t racing won’t care. If someone is racing where fairings are allowed, then they will be looking for enclosed velomobiles that reach over 80mph, not a clip on skirt guard that gets and extra mph or two.

    Seeing as though front fairings have existed for years, and yet almost no one uses them other than a few recumbent riders, I don’t see how the market for your fairings would be any different.

    But good luck!

  • August 4, 2013 - 8:57 pm | Permalink

    If man were meant to fly, he’d have been born with wings!

  • May 9, 2014 - 8:26 pm | Permalink

    One benefit of these fairings not yet discussed is the ability to extend battery range on electric bicycles. I used a very crude copy of this technology by duct taping coroplast to the sides of my fenders. I experienced as much as 20% improvement in range under identical conditions. My tests prove that wheel fairings are like gold to a huge e-bike market.

  • May 10, 2014 - 5:44 pm | Permalink

    @Bill Ah yes, indeed something to consider!

  • May 10, 2014 - 8:04 pm | Permalink

    I just did as scientific a test as possible to prove this point. When I read about this technology explained by Garth, I constructed crude wind fairings by duct taping coroplast to my front fender. Later, on Garth’s suggestion, I made one for the back as well. Coincidentally, I was asked to test a new 450 watt motor for my 350 watt e-bike at the same time. At level 5 assistance and an average speed of 22kph the 350 watt motor with stock bike wheels gave me 60km of range and I had one quarter battery capacity remaining(I have the means to measure).
    With the 450 watt motor physics dictate a 22% reduction in range with the same conditions. But, using the 450 watt motor with the fairings actually improved my range by 7%. This is a PHENOMENAL 29% improvement in battery range. Imagine what could be done with a set professionally built by Garth. The result will be E-BIKE HEAVEN. Bill

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