|
Post by Radchenister on Jun 16, 2014 9:59:06 GMT
Hang on, electric assist - nothing against that of course as an idea but it's not about unassisted sport riding; yes it keeps people moving when less fit / able / old etc. and is far better than driving a car but this is a road bike forum here (it says it across the top banner). We're into similar territory to comparing the efficiency of buses and sports cars now; I'd like to see how you manage to calculate the difference when sitting upright v tuck and what in fact constitutes a tuck on that bike. As for the holy grail of aerodynamics, perhaps there's mileage on relatively heavy and wide profiled 'bikes' like in your picture but probably not for track and road bikes, there will be mass and profile disadvantages, cross winds are an issue, particularly on light road bikes, despite what you say and I don't see what benefit they would have over disk wheels / deep section rims, with minimal spoke depth and slick air slicing rim profiles that take the friction out of the outer radius of the wheels, where the spinning speed is greatest and the deeper rims work best (cross wind conditions permitting - the racers put lower profile on in cross winds). Without data, this is of course conjecture but I don't believe that road bike developers would miss this trick, they are just tackling the issues differently (as explained above); I know for a fact that the big teams and bike developers do test their road and TT bikes to the nth degree via both computer and wind tunnel. In fact, watch the new Dogma clip below, where the bike manufacturer's worked with Jaguar's young bright aerodynamic computer modellers, followed up by wind tunnel tests. Pay note to all the factors, from frame design / profile, geometry, rider position, wheel rim depth / section and spoke numbers / profile, spinning weight, balancing cross wind forces etc. then consider how the fairings work in comparison.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 16, 2014 10:35:35 GMT
How about a picture of your bike with them fitted please? I'm always on the quest for more speed. As you can see, my bike is electric assist , anywhere from 10% to 100%. Since I used to pedal ultramarathons in my younger days I am always looking for ways to extend my battery range. These upper wheel fairings may be the single most effective aero mod possible. When I first found the Null Winds website I decided to test the technology and I was amazed how well it works. They are extremely difficult to set up properly however; that is why the inventor charges so much for his, they have infinite adjustments to tune them perfectly. Mine are by no means perfect but they give me 5% increased top speed and 20% increase in battery range. The front and back each seem to have the same effectiveness, ie they are twice as good when both used together. I estimate these will become the holy grail of aerodynamics once people get to know about them and try them. I have no affiliation with the company which sells them; I am both excited and enthusiastic because I have experienced how well they work. They may be just as effective as disk wheels but they actually improve stability in crosswinds. I have had mine on and off dozens of times to test the differences and I am at the point where I do not want to take them off. THEY ARE THAT GOOD ok, now I'm sure we will see it on TdF!
|
|
|
Post by chas on Jun 16, 2014 11:09:06 GMT
I'm inclined to be more open minded about these, the fact that they're not seen in the pro peloton has nothing to to with their effectiveness and everything to do with restrictive UCI regulations. When I saw the original post I thought they would make more sense combined with mudguards and may be a sensible addition to a fast audax bike, possibly just on the back wheel?
|
|
|
Post by Radchenister on Jun 16, 2014 11:29:17 GMT
I'm not saying they're a no no but the science doesn't add up to me. What are they actually doing? It's only a solution if considering friction / air resistance in isolation. If you have an aero rim and reduced spoke drag, then you get the same deal without the proportionally higher sail effect, you choose the depth to balance this. To claim that on the one hand they assist in reducing resistance (they will of course) and not be affected by cross winds or other factors is simply unscientific and emotive. There's the mass to carry here, relatively little on a heavy bike, relatively high on a light one - not so much of a deal on a flat road but when it's undulating and upward bound, then the disadvantage is magnified - not such a big deal if electric assisted, with easy wattage at hand but more of a deal with fickle and finite human power. As I said, we need to see an actual study, with comparative back to back testing - not anecdote and opinion from someone on an electric cruiser.
|
|
|
Post by chas on Jun 16, 2014 11:48:17 GMT
I'd rather have some nice deep section wheels if I could afford them, wouldn't want to fit them to a 'race' bike, and they must have a negative effect in a cross wind, just saying there might be some advantage for minimal cost (Β£&lb) adding them to a bike that already has mudguards (if you're going fast enough and don't mind people laughing!)
|
|
|
Post by Radchenister on Jun 16, 2014 11:51:47 GMT
I don't see the point on a road bike - our man with the electric engine is perhaps demonstrating the main useful purpose; the idea of having those out in winter makes me wince, mudguards are a pain enough; tacking up and down the Severn basin with howling winds is hard enough as it is .
|
|
|
Post by captslog on Jun 16, 2014 13:26:44 GMT
It's not about spokes. Any disc that is spinning experiences air drag, even in still air.
I seem to recall that there is a turbine which uses this drag principle. It has a plain spinning disc or discs onto which a jet of compressed gas is directed. It has no fins and reaches fiendish speeds. I think it's called a Tesla turbine.
For the bike wheel of course, the drag on the base of the wheel is not noticed, because the air is moving backwards along the bike, and so in the direction of spin (obviously). However, the top of the wheel is moving against the airflow AND it's own drag, and this will be where the fairings come in.
Just take a wheel, an axle in each hand and spin it near your face, you can feel the air it's pushing out of the way just by spinning.
For disc wheels. I'm not sure why these work better than spokes (if they do), because from the above, they shouldn't! I suspect that because the "disc" of a disc wheel (the bit that replaces the spokes) is inside the plane of the rim that it has sort of benefit from the wash of the same (a bit like the dimples on a golf ball help reduce it's air resistance).
|
|
|
Post by Radchenister on Jun 16, 2014 13:34:54 GMT
Yep, got the drag bit, it's about resistance of all the moving parts though ... the tyres, spokes and aero section are all part of it - as I said previously, without actual back to back data taken on a road bike, done in controlled condition and somehow over varied terrain, including cross winds, we're working on pure conjecture. I suspect the claims for added efficiency are over stated, particularly when it comes to the dimensions of a ROAD BIKE set up ... but am happy and ready to be proven wrong of course.
|
|
|
Post by Radchenister on Jun 16, 2014 13:40:48 GMT
...and when I say road bike, compare a 23 slick tyre width to the one on that electric bike. If we were to put the bikes on floats, dipping the rear into water, I reckon you could get that electric one moving a bit more like a pedalo, whereas you'd be spinning away like a loony on a road wheel going nowhere fast.
|
|
|
Post by captslog on Jun 16, 2014 13:49:17 GMT
I've seen aero sections and deep rims mention a few times above, and I get the feeling that the drag considered in them is that where a wheel (or spoke) is considered as an object moving through the air as a projectile.
However much you minimise this, there will also be drag caused by air's viscosity and adhesion which is opposite to the rotation of the wheel. This still exists when the wheel is spinning but not moving forwards.
Having said this, I still think they look like a bag of "manure" (a Jewsons one tonne tote bag at that), and I'm not having them on my bike unless they halve the times on my Strava segments and double the times Mrs Slog and I have sex.
|
|
|
Post by chas on Jun 16, 2014 13:58:12 GMT
While I agree the benefits on the above bike may be more noticeable than on a road bike It's not the size of the tyres, they havn't changed (on his bike). On the electric bike, he already has mudguards, which give you all the disadvantages of the fairing without the aerodynamic benefit (quite the opposite!). He will also reach higher speeds more easily which magnify any advantage.
|
|
|
Post by Radchenister on Jun 16, 2014 14:09:32 GMT
I'm not saying they don't have drag, it's the actual force and effects within the overall picture of forces that we need to get to the bottom of - Boardman and others are always on about the few extra Watts they shave with the details, I think they're pretty hot on this stuff already. Instinctively I mistrust uber deep sections in terms of drag but mainly cross wind effects (lets face it most of us suffer from this in the UK), does feel like 'Emperor's new clothes' at times but could see why you'd use them on a flat TT course, in mid July, with 24 degrees, still air and a fast pro on top. I kind of also accept that if the spokes are hitting into the air at the outer radius, then they'll also cause drag and turbulence, hence thinking minimal number aero spokes and deeper rims might help, taking the rough spots further down the radius to a point where the spokes are not moving as fast, hence reducing resistance (you'd hope to a degree than was better in terms of returns than the increased drag on the deeper surface of the rim). I also buy into the principle of a smoother profiled aero surface / section cutting through the air better than a square edged rim and the air trail flowing into the spoke zone, which is at a slower moving point (no idea if this actually happens), how much the rim then drags through the air is something I currently imagine as 'not much' in the scheme of things. Probably reads like Greek that? It would be nice if we had a fluid dynamics / wheel design expert on the forum but they're probably not into bargain bikes that cost less than a single rim lol.
|
|
|
Post by Radchenister on Jun 16, 2014 14:15:50 GMT
While I agree the benefits on the above bike may be more noticeable than on a road bike It's not the size of the tyres, they havn't changed (on his bike). On the electric bike, he already has mudguards, which give you all the disadvantages of the fairing without the aerodynamic benefit (quite the opposite!). He will also reach higher speeds more easily which magnify any advantage. The width of the tyres must push against more air (or the mudguards if you wish) and the surface area must have more drag - the extents of the forces are the things we don't know.
|
|
|
Post by Radchenister on Jun 16, 2014 14:18:59 GMT
We also don't know if the claimed improvements are based on anything other than fortunate interpretation after unscientific testing, perhaps on runs when the wind is in opposite directions by the minute; you'd struggle to make any meaningful discoveries unless testing was done on a perfectly windless set of runs .
|
|
|
Post by captslog on Jun 16, 2014 15:10:33 GMT
My opinions are partly devils advocate and partly that I don't want to see them dismissed for the wrong reasons. But I doubt they work as well as said. It's easy to get caught up with something and 'see' benefits which are not really there. How many people thought these were a good idea at the time....
|
|