Aero Deep Dive in The Specialized Win Tunnel – Ask a Cycling a Coach 188

aerodynamics

#21

I totally agree! I was looking forward to them delving in to that subject.

Taking an average trained rider at maybe 3.5 w/kg what percentage difference would that make to them riding a venge over a tarmac. And if “#AeroIsEverything” why would I buy a tarmac?

Strengths and weaknesses would be interesting. Where one would beat the other for the Joe rider not pro.


#22

Watch any of the Win Tunnel video and I think the state the test speed, and that is used for most of their testing.

(I can’t remember for sure but it is quite fast IIRC, and not a speed common for the avg Joe.)


#23

I sometimes get the feeling that Specialized have to use "at 40kph’ because it gives some form of data. Drag is also a much higher force at those speeds.

If I am saving lets say 25watts at 40kph with this latest and greatest venge am I only saving just over half of that for half that speed, lets be honest we are not riding around at that speed for 4/5 hours.

I feel like there is a combination of some data and marketing disguise going on here.


#24

I just watched this video which was quite a revelation…


#25

The beard stays! I don’t mind shaving my legs, but have to draw the line somewhere! :grinning:

Another plus one on the answer for the question of venge v tarmac (and by extension aero v lightweight) for the average rider @Nate @Jonathan


#26

Yes, I got his answer and I’ll mention it on the podcast. Basically the tarmac is more compliant so for the every day person you need to take that into consideration.


#27

That’s drag force, not drag power. Aerodynamic drag power is cube of velocity.


#28

That totally sounds like a very corporate answer… “Officially, we aren’t allowed to say one is better than the other but you might want to consider the Tarmac, not that its better, but its better, but we didn’t tell you that” :smirk:


#29

I was wrong, but still right. The effect of CdA at a given velocity is linear.


#30

Gotta do it…


#31

Absolutely. It is linear and independent of speed. So a 1% reduction in CdA will save you 1% of the power you’re putting in to fighting drag.

I guess that’s a good metric for thinking about if it matters at slower speeds. On a flat, almost all of your power is going toward drag. So CdA reductions are proportional to the power you’re putting out. If a pro (or test subject) is doing 400 W and shaving legs saves 20 W, if you’re doing 200 W, it’ll save you about 10.


#32

Sorry I missed this one in the links mentioned! The Specialized Win Tunnel video about number placement can be found here: https://www.youtube.com/watch?v=HXwiWWXl1J8&index=27&t=0s&list=PLcmaLnqmqDnmn_bCR0RJ-soSCDKCKR97t


#33

Thank you for asking my hydration pack question!


#34

I was a bit thrown by the explanation that dimples and trip seams are meant to keep the air tighter around the rider (or whatever object is moving through the air). I seem to recall from fluid dynamics that the point is to induce turbulent flow sooner, because turbulent flow puts less drag on the object than laminar flow. Drag a stick through water and you feel the resistance from the water “release” at a certain speed, when the stick is chopping through the water (turbulent flow) rather than trying to quickly glide through it (laminar). But maybe I’ve had this wrong.


#35

Actually, power loss is scales with the cube of velocity.

Power = Force x Velocity

Drag Force = p/2 * Cd * A * v^2

So the power to overcome aerodynamic drag is Drag Force * velocity = (p/2 * Cd * A * v^2) * v = p/2 * Cd * A * v^3


#36

I’m totally wading into a topic I know very little about, but it was my understanding that dimples essentially create a pocket of air around the objection (turbulent boundary layer) that creates less of a wake (and less pressure) behind the object as velocity increases.


#37

Just use whatever Team Sky are using. :+1:


#38

Does that include TUEs?!?


#39

Trip strips are sort of like vortex generators on airplane wings. They delay the separation of boundary layer air delaying or reducing stall speed (reduce pressure drag). They make the “bubble” of stalled air say behind your calf or car etc…smaller Smaller bubble=less drag.


#40

Dimples/trips/texture are designed to introduce turbulence.
The downside to turbulence is that it makes the boundary layer slightly fatter and increases the drag on the wetted surface. If you’ve got a lot of surface, you want to keep the flow as laminar as possible to reduce this effect.
However, cyclists/golf balls are pretty much blunt bodies, so the problem isn’t the wetted surface, but the huge amount of wake behind the rider/ball. Because a turbulent boundary layer has more energy, it can stay attached around sharper corners, and the longer it stays attached behind the rider/ball, the smaller the wake that will appear when it does detatch.