Aerodynamics, Dimples and hair/thorns

Opik

Opik

Well-Known Member
wathicng vidoes and reading about golf ball aerodynamics, like this

and a beard is more aerodynamic

I've been thinking, if a bike+rider clothing has dimples or hair/thorns, would it be more aerodynamic? would it create that thin layer of moving air which shields the surface directly brushing against wind?

so rather than a smooth area, we have a rather hairy/holy surface to create that thin air layer
 
Don1

Don1

Guru
cant remember which pro team it was that rubbed a cream with lumps in it over the riders exposed limps for a speed gain during a team tt. oh of course the uci banned it. besides there is a whole bunch of other stuff riders have to do before boundary layer and vortex generators concerns them. maybe larry can test sticking little triangles on his "trailing edges" and lumpy cream at his secret facility..
 
Opik

Opik

Well-Known Member
Mythbuster team did a dimple car test back in 2012? (CMIIW). and the gas mileage of the dimpled car was moe efficient (29 vs 26 mpg) . This got me thinking why hasn't this trickled down? Whre are the dimpled race cars? where are the dimple helmets, dimple suits, dimple frames, dimple fairing, etc.

and they can't believe the results themselves

 
billyk

billyk

Guru
Opik said:
Mythbuster team did a dimple car test back in 2012? (CMIIW). and the gas mileage of the dimpled car was moe efficient (29 vs 26 mpg) . This got me thinking why hasn't this trickled down? Whre are the dimpled race cars? where are the dimple helmets, dimple suits, dimple frames, dimple fairing, etc.

and they can't believe the results themselves

Click to expand...

So then a regular helmet (with air vents making a "dimpled" surface) must be more aerodynamic than those ridiculous military style spherical-shell helmets millennial consider fashionable, right?

Not to mention cooler (temperature, not fashion).

What's the relation between dimple size and speed for largest effect?
 
E

ed72

Zen MBB Master
Opik said:
wathicng vidoes and reading about golf ball aerodynamics, like this

and a beard is more aerodynamic

I've been thinking, if a bike+rider clothing has dimples or hair/thorns, would it be more aerodynamic? would it create that thin layer of moving air which shields the surface directly brushing against wind?

so rather than a smooth area, we have a rather hairy/holy surface to create that thin air layer
Click to expand...

So are sandals and ski parkas.

Beards are not faster, watch again and listen. Spesh aerodynamicists say beard vs no beard are equivelent at normal speeds based N = 1 sample.


I doubt either of these "tests" would apply to the recumbent position where anyone's guess is better than mine
 
E

ed72

Zen MBB Master
USGA's testing facility and museum in Far Hills, NJ is awesome.

I am not so sure dimples on bike gear would work due to the relative lack of speed. I haven't looked to see if anyone has studied.

I do know from golfing days that the number of dimples, the shape, and especially the dimple depth impacts ball flight and distance tremendously. Some balls work well for players with slower swing speeds of say 95-100 while others are good for 100-110 mph swings (driver of course). Compression of the core and the surface frictional characteristics effect spin rates causing more lift that also interplays with dimple design. The balls come off the club face of a driver at 140-200 mph as a very broad range. Tour players are usually in the 165-180 mph range and long distance champions can approach 220 mph ball speed. I just can't "see" little eddy currents coming off dimpled Zipp rims and the air remaining attached a little longer but they sure look cool.
 
E

ed72

Zen MBB Master
I forget the most important difference.

Golf balls rotate at 2000-10,000 rpm vs bicycle wheels at what a few hundred a minute.

Going out on a limb.....dimples anywhere on a bicycle would merely be lovely marketing for gullible.
 
ratz

ratz

Wielder of the Rubber Mallet
ed72 said:
I forget the most important difference.

Golf balls rotate at 2000-10,000 rpm vs bicycle wheels at what a few hundred a minute.

Going out on a limb.....dimples anywhere on a bicycle would merely be lovely marketing for gullible.
Click to expand...
Vortex reattachment works at any speed over 15-16 mph. Check out the marginal gains podcast
 
E

ed72

Zen MBB Master
ratz said:
Vortex reattachment works at any speed over 15-16 mph. Check out the marginal gains podcast
Click to expand...

I don't know what podcast you are referring to. Neither of the two videos linked would suggest that. Questioning the formation of eddy currents and minimization of detachment due to dimpling of bicycle part surfaces is not the same as saying there is no reattachment at 15-16 mph. I agree there is reattachment. Where and under what circumstances is the point. The trip socks work. Wind tunnel tests have shown fabric patterns also work. Dimples on Zipp wheels? Very, very doubtful. If so, why are they seemingly phasing them out on the newer wheels (fewer holes in number). They were originally marketing for speed and then crosswind stability on later models. I have looked in the past for any sort of scientific data to support either claim. I have a set of 404 wheels with dimples; I rarely use them. I do prefer my NACA profile rimmed front wheel. I thought long and hard about buying Zipp 858 wheels and frankly, I do not buy into their marketing hype and absent any real data, I wasn't forking out $4400.

Dimples and such.....gets interesting around 9-10 minutes in. He eventually calls Zipp dimples, "Marketing Crap" at the end.

 
ratz

ratz

Wielder of the Rubber Mallet
ed72 said:
I don't know what podcast you are referring to.
Click to expand...
Allow me to google that for you: https://marginalgainspodcast.cc/

Joking aside; it's an interesting listen with Josh Poertner who was the engineer at Zipp the brought most of the deep wheels into existence (if they could keep him on topic it would be more so). If you dig into the history behind all this, it's about the evolution of design. Before all the CFD software and the ability to run all the optimal pattern analysis the dimples probably had value or at least they did no harm. With todays software and compute power the value add is probably gone because the can test thousands of designs. With the cavet that as long a you ride the correct size tire. Through a 28c on that 17mm id rim and you might as well ride a 20mm deep box rim. 40mm rim help everyone, 65mm help a subset of everyone, 90mm help those that can and will adhere to rule 105.

Doesn't stop me from putting 28c on my 90mm flo rims. It's a training aid. As long as I know to put 23c on the front and a 25c on the back on event day; works for me. Just have to look fast because it will take them 30secs to figure out I'm out of shape and slow.
 
McWheels

McWheels

Off the long run
I couldn't find Rule 105, but I try to meditate on Rules #5 and #10 over the winter until the cricket season gets going again.

And just quietly, Rojo appears to be Rule #85 incarnate.
 
ratz

ratz

Wielder of the Rubber Mallet
Rule 105 = Max rim width must be 105% the width of the tire mounted on the RIM to maintain airflow in crosswinds greater than (I think) 8-10%.

That was the big breakthrough finding that the computer models produce over and over as a hard limit that can't yet be overcome.
 
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