S-Works Shiv 2019. Bike or Yacht? Aerodynamics discussed.

[@sodalitia]

You know what else this bike has in common with a yacht? Pricing.

[@AB-fh9zh]

That was my first thought when I saw the title.

[@phoenixaroui8712]

@@AB-fh9zh me too

[@Hambini]

Whilst I don't want to urinate on your fire... When an aerofoil generates lift you get a lift squared term added to the drag. It's called the drag polar, here's awikipedia article on it en.wikipedia.org/wiki/Drag_polar Basically you can never generate more lift as a forward vector compared to the drag generated from the lift. Nevertheless, the video is good and I give it a thumbsup.

[@PeakTorque]

Cheers @Hambini, agreed and at 8:00 I mention that. The perp L and parallel D components will always be up and backwards, with respect to the apparent wind axes. However with respect to the direction of travel axes the final vector can be forward, just like a yacht. Morphing the wings into wind would improve this even more, just like the land yacht with its wind vane. Maybe I should have made this clearer in the video. As I also mentioned the bike foils more likely than not are just lowering pressure drag more than anything, what do you think?

[@mathman0101]

Just wanted to say to you guys thanks for raising the technical discussion and content on bike tolerances and aerodynamics. Both the modeling work and comparison of different bike manufacturers products is likely no doubt to get you some letters which let’s say put you under pressure to stop. While I do like that specialized have done more technical work in improving aerodynamics of their bikes. I do feel they then let themselves down by using poor tolerances when it comes to bottom brackets. Btw when specialized released their new s-works venge last year they had all their technical team sit down and discuss over the hour the aerodynamics and modeling process, not sure you saw it, I did think this was interesting up to a point but at times you are left wondering and trusting their analysis. I wanted more peer review of that work. Why is that important for me? As a consumer. If I am going to drop 13-14k on an aero bike it better have verifiable aero numbers and the bike should work like a dream. Keep up the good work. You know I think a state of the art of bike aerodynamics/tolerance textbook is in order. You can both combine to write, I will check your math.👌🏾

[@brandonhicks7549]

@Hambini, typically drag is stated with the reference plane aligned with the apparent wind. So lift is perpendicular to the wind, and drag aligned with it. On a bike we are more interested in the axial “thrust” and the normal “toppling” forces. It’s a simple vector rotation by the yaw angle, and yes you can generate thrust, as shown by fact that sailboats work.

[@renebaretta]

@@PeakTorque First off, love your engineering vids. Keep up the debunking, it is very refreshing. But this comparison with the sail boat just doesn't sit right with me. I have agree with Hambini and Ken Webster on this. First of all, the sail is not an airfoil. The sail is a concave shape only. You have an enormous wind 'force' pushing on the airfoil, which is directed 'into' the concave shape of the sail. Big difference. You left those 'frontal' flows behind when you compared the sail with the Shiv airfoils. Ken and Hambini are obviously much more into aerodynamics than me (I'm just an aero-enthusiast and anti-BS engineer ;]), but if I just imagine an airfoil, or a disc wheel (like Zipp claimed), or any symmetrical shape, placed on a no-friction roller, I just don't see it moving into the wind, at any angle. But, like I said at the beginning. Keep doing what you do! ....and maybe I am wrong 🙈....I hope to learn more either way!

[@gregnichols9363]

here is a fun video kzbin.info/www/bejne/r3TWmKKCmMSZsKs

[@robenright2647]

What a superb informative, technical video. Really enjoy your content and presentation.

[@PeakTorque]

Thank you, appreciate the comment.

[@MozzySails]

The toppling force is not opposed by the centreboards (although it is by weight of the keel of a yacht). Righting moment here is created by the weight of the boat to windward of the centreboard and to some extent by the windward rudder. The centreboard opposes the sideways forces (not toppling) and provide lift to stop the boat slipping sideways in the water (leeway). On a bike, in a cross wind, you oppose toppling forces by leaning in to the wind (like a dinghy crew learns out to windward). The tyres friction would oppose the lateral forces (to stop the bike from skidding sideways) and (in a cross wind) the aerofoil shapes could definitely create lift... BUT it is rare to have extreme apparent wind (once bikes speed is taken in to account) angles on a bike unless it is very windy. The air we cycle in is often very turbulent. We are low to the ground, and the ground is not smooth like wat, instead we have lots of hedges and buildings. So the apparent wind angle, even on a windy day would not be that stable. This leads to the feeling of being 'pushed' about with these deep section frames and wheels.

[@jonnythelegs2597]

You could probably reduce the low pressure drag on the trailling edge with pivoting tails on the air foils but the extra weight involved may well negate the savings on anything other than a super flat course but there's always a way. Maybe Mr Bambini could do some cfd modelling to test the theory, it would certainly be interesting to see.

[@Alan_Hans__]

I could see those profiles working an absolute treat at a 180 degree yaw angle. Anything under 90 degree yaw angle I can't see it working but the effect will ramp up significantly as you approach 180 degrees.

[@kenwebster5053]

OK, so lift is a function of dynamically created pressure and pressure exerts a force to right angles (90 deg to a surface. This means that the force at any point on a sail is at 90 deg to the surface at that point. There is also a small rearward skin friction drag force. The total lift is the sum of all those force vectors from all over the surface and this is about 90 deg to the straight chord line between leading and trailing edges. In order for this to produce thrust, the sail must be angled somewhat across the vehicle so that the whole lift vector rotates forward producing thrust. Your diagrams ignore this very vital and significant detail until near the very end. This is what a sail boat does to sail from 40 - 45 degrees against true wind. In effect, this means that the wing foil on the TT bike must be articulated (free to rotate) somewhat across the apparent wind to effectively produce thrust. If it does not rotate, it cannot produce meaningful forward thrust. I have had thoughts about putting a sail inside the frame triangle with a shock cord in the upper rear corner to allow the sail trailing edge (leech) to fall away automatically and produce thrust in a crosswind. So my take on it is that without articulating the foils it seems exceedingly unlikely that forward thrust from lift could overcome drag. Do the math and prove me wrong. (L = 1/2 . p V^2 . S . Cl ) (Df = 1/2 . p V^2 . S . Cd ) (M = 1/2 . p V^2 . S . MAC . Cmo ) (Drag = Df + Dp + Di)

[@renebaretta]

Excellent

[@adamconquest6045]

Great insight...thanks for sharing :) Ive just picked up my Shiv Disc & rides amazingly!!!

[@PeakTorque]

Cheers

[@waynosfotos]

Very interesting, People never talk about the lift (or as I call it “sail affect”) only how the bike heads into the wind, they also forget to mention spokes create drag, but for some reason, everyone remains quiet about this stuff.

[@gourami7]

Is that why tri spoke front wheel is sometimes used in TTs ?

[@waynosfotos]

@@gourami7 it is because normal spokes cause a lot of drag, tri spokes are far more aero but are heavier and are affected by cross winds more. As to the sail affect, if a force hits a wheel at right angles, due the the resistance of the wheels on the ground, some of the force is transferred into forward motion, this is the same with a sail boat. the problem is due to the lightness of the bike it can also cause instability, which people don't like. So they design the foil section of the wheel (rounded back) to turbulate to reduce the sail affect.

[@simonalexandercritchley439]

Interesting idea with the forks. This would require a central vertical pivot connected to steering and separately adjustable fork blades or foils and some way to have the rear foil follow this. Perhaps on low friction bearings(needle?) that can change with the wind. I wonder about cross wind stability though,deep rims are tricky in side winds without disc. Of course a lower rim profile for the front,or tri spoke.

[@jrcp87]

so...the cliff notes? is this yacht of a bike fast by design or does that wing is more of a hinderance? for a disc brake triathlon bike would you consider this one the best option out there or a different one?

[@kc3718]

there's a chap who tt's , has his own engineering business down south ( Raltech, which used to make carbon disc covers) and he turns his aero helmet to catch the prevailing wind and thus provide thrust as sail. Always struck me as an 'obvious' thing that none else had ever eluded to and led me to get one of those early 2000 'Lance' type helmets with the massive tail.

[@bjma654651651]

To counter the toppling moment while maintaining balance on two wheels, surely the bike needs to be ridden slightly at an angle into the force? I wonder what effect this has on effective drag/rolling resistance. The benefits of the more straightforward aerodynamics in the fore/aft axis seem clearer (developed by maintaining laminar flow for longer along the extended foil.)

[@michelbesedin7081]

Did Spes guys get in contact with you ? I bet they had no intention for it. A lot of "fresh tech" from Specialized ended up just selling flufs . It is more like "marketing tech" that benefits mainly sellers, not customers. I remember their zertz inserts.

[@gauterh]

You are probably mostly right, but you don’t mention the two rotating «flywheels» (also called wheels) that help counter the “toppling”?

[@PeakTorque]

Good point, Gaute.

[@jonnythelegs2597]

@@PeakTorque the trail/rake on the forks contributes far more to the stability or self righting ability of a moving bike than the flywheel effect coming from the wheels. The weight and leverage or the frame alone bearing down on the axis point of the spinning mass easily overcomes any flywheel effect.

[@qibble455]

Very interesting. 10/10

[@ttmallard]

Windcheetah, the Lotus bike was a cutaway frame, some steel bikes for polo put the downtube ABOVE the front derailleur & chainrings, this geometry is worth about a 1mph over distance by the reduction in drag over having it to the bb. Track bikes were banned, keeping the dt attached to the bb is stupid if you want more velocity per watt, the UCI is revenue for aerospace tech, having the dt-to-bb rule killed steel in the peloton, frames way less cash for average riders to use. Your turbulent wake volume is the deal, the more volume in turbulence created the slower you go, structurally having the tube above is just move the jig & new lugs on the assembly line saves about a mile in 11 times bicycle commuters globally per day in food & physical effort. I've never gotten replies to emails over the years to allow the above-chainring geometry for that reason into the peloton so cheap bikes would be made that way & gave up. Ymmv 🍺

[@tacituskilgore8379]

It would be great to see some more The Truth episodes. It’s so refreshing to hear from someone with obvious intelligence and not have to listen to sales blurb, or utter shite read straight from a brochure by mugs who lack any common.

[@samuellambert8919]

just randomly clicked on this video on my feed. Video starts... voice comes in..... wooh shit its "CYCGNR" Better set my ears open for an interesting vid. damn you're so random with your uploads… but haha doesn't matter, i'll stick around and stay subbed anyway.

[@sasha371]

I think it can, I can actually feel how my 60mm wheels are catching side wind and go faster, comparing with my 50mm in same conditions. By seeing that big field - 100% it will add few watts savings here and there. We also need to remember that wind often is deflected by hedge, walls, cars and on some streets creates much more preferable angles, i.e. it's not constant for the duration of the course

[@GregTheGuitarist]

I genuinely thought it was a photoshopped meme from thumbnail!

[@plantfuelled8912]

It may help at wind front angles and side/yaw angles. However with a direct side wind on a real road it's gonna be a pig, and TBH it looks dangerous on a real road.

[@noellaukkanen84]

If you go fast enought it will be more from the front

[@yourrightiamwrong9643]

dont know whether you familiar with velomibiles, this sail effect has been proven.

[@magicmatrix9216]

New shiv is over 20 pounds

[@Sills71]

Ugly, greatly over priced, completely unnecessary for the unsponsored athletes... BUT it it visually unique so those that have too much money and want to "be seen" will waste money on it...