For those who want the fundamental things that bike design is based upon, check this presentation out:
http://www.bakker.org/dartmouth06/engs150/11-bl.pdf
You want to look at pages 9-25 (lots of pics and not many words!)
Page 20 explains the theory behind the dimples on zipp wheels.
Because I’m not starting another one post only thread:
Aerodynamic work from Felt (I’m shocked no one else has posted this yet).
I thought I was the first to use poser style mannequins, but they released this pic back in Jan 2008 so they beat me to it by 3 or so months!
Something to note - the concentrated stream of airflow under the saddle. Ever wondered why good TT frames have the seat stays join low?
I am bringing that picture to Biomechanics on Tuesday! We are discussing fluid dynamics.
so what are the conclusions for under the air saddle? is that a hot spot that needs smoothed out and if so what if anything canwe do to improve it?
so what are the conclusions for under the air saddle? is that a hot spot that needs smoothed out and if so what if anything canwe do to improve it?
I’ve got a rear bottle holder in that spot but I’m stuck with it because I’m still riding my softride rocketwing. Moving to the downtube would cut me to 1 bottle and I’m a water hog that can burn 2 bottles an hour on a hot day.
JJ
Most rear carriers sit just below the saddle (the air in the Felt image is being channelled much further down, just above the rear wheel). This issue is also much smaller on a Softride, since the air is not being squeezed between the rider’s legs and a seattube. Per John Cobb, the best rear position for bottles is just below the saddle, behind the upper legs.
The tops of the bottles only sit about an inch or so above the seat so they’re pretty well shielded but it’s hard to say what kind of turbulence you get back there.
JJ
I notice that the rider is barefoot … and not obviously wearing shorts. Have you cropped the image to shield his computer-generated modesty?
That’s probably pretty good. The key is not to have them so high up that they sit in the flow coming off of your back (like the old x-labs used to). It’s hard to have them down by the rear wheel (unless you ride a very small frame).
Good:
Bad:
Disclaimer: Both athletes shown above are in the process of winning the Ironman.
cool post, thanks!
It’s the image Felt released. They used a method similar to mine where an artistic mannequin is used. You can switch on and off his features and I guess that they’ve got them switched off!
Here’s one that I did a year back; less detail in the model, but you can see more streamlines and so get a better general idea of flow (plus, my model is available in 3D and can be spun and stuff!):
http://www.biketechreview.com/aerodynamics/CFD.htm
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Gorgeous. Thank you.
Professor is at a conference today so we have a SUBSTITUTE. omg not fair, doesn’t he know he’s just supposed to cancel class.
The link from my original post btw - it explains dimples. I am surprised that no one is overly worried about this considering the number of people who spend their time commenting on dimples!
How about with the wheels turning? I am assuming they aren’t in these models because the streamlines are uniform from the ground to the top of the front wheel/tire.
Here’s one that I did a year back; less detail in the model, but you can see more streamlines and so get a better general idea of flow (plus, my model is available in 3D and can be spun and stuff!):
His seat is too high! (or, is it “too low” these days?) 
Seriously though, if you start playing around with this stuff again, I’d like to see a model where the torso is a bit more “horizontal” 
Yes, this suggests that dimples are dumb!
According to this:
The Re for a bike wheel would be about 100K (=1x10^5)
-this assumes a 5" deep rim/tire combo
-going 25mph
This has some interesting implications
-suggests dimples are moronic- looking at slide 20, suggets dimples matter at around 5x10^5, vs a front wheel at Re 1x10^5- in other words for bikes that go 125 mph not 25mph
-alternatively they would matter for something like a disc (25" long surface) but not for a front wheel (5" surface). But once you get to the back wheel there is almost no laminar flow- the seat tube is a huge tripwire- so dimples dont matter back there
-the otehr dumb thing about dimples- its not like a the transition from tire to rim is smooth- id say its about the definition of a “tripwire”- according to slide 20 that tripwire has already done its job
-ANOTHER dumb thing is that half hte dimples are under stifckers- if they are that important, why are we putting stickers on them?
-the last dumb thing about dimples- they are in the wrong part of the wheel- you would wnat dimples at the front of the shape, but these are at the back of the shape (towards the inside of hte wheel)
I just realized that the cyclist on the pink bike needs shoes
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It looks like if you had a fairing in the back of your shorts like a helmet does, it would help the air flow off your back.