stupid aerodynamic bicycle helmet
- Thread starter fenster
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Doubt
Philosopher
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Terry said:
It just makes me wonder about the rest of their assumptions.
And I still find it hard to believe that 11 mph is the break even point. Makes me want to look for the source that I had for 22 mph. But that was long before most of us heard of the interent.
Doubt said:
143 lbs isn't so far out for rider weight. Many climbers are around that weight. It would be light for a triathlete who has to run and swim also, I guess.
Bicycling Science (ISBN 0-262-73060-x) states that at 10 mph air drag and mechanical drag are similar. pp 158, chapter 7. I've sometimes heard 12 mph as the crossover point in casual cyclists conversation - of course the exact number depends on how aero your position is. I'm highly skeptical of the 22 mph number - please do post the source, if you find it.
--Terry.
davefoc
Philosopher
Cool idea but i think that would fall under the idea of a fairing which the rules prevent.
Before the rules controlled hemet size some of the them got quite long with the idea of accomplishing something like you are suggesting. The rules eventually were changed to limit helmet size to prevent that sort of thing.
Before the rules controlled hemet size some of the them got quite long with the idea of accomplishing something like you are suggesting. The rules eventually were changed to limit helmet size to prevent that sort of thing.
Deetee said:
Well, as davefoc pointed out, there are rules which prohibit this. But even if there weren't, there are practical limitations. Actually the best way to get a full-body aero advantage is to go to a recumbent machine. But considering a regular bicycle outfitted for a time trial.
The head we've already talked about.
The arms are held together and horizontal on the aero-bars. Maybe you could add a small fairing to the front of the bars for the hands to hide behind. But otherwise that's already pretty good.
The torso is held as close to horizontal as possible. Nothing to do there except control the boundary layer as best as possible - which is already done with tight-fitting skin suits with special textures.
It is possible that a pointy butt-fairing might be of some assistance. However, you'd have to study whether the flow was already separated way before there. And there would be the practical problem of what happens to this cone when the cyclist stands up to climb a short grade. It has to clear his legs and the back wheel.
The legs do cause a substantial amount of drag. However, any restriction of movement of the legs is likely to be unacceptable to a racing cyclist. I imagine that small calf-fairings as sometimes seen on downhill skiers might provide some benefit.
The feet are typically already covered by a fabric fairing (over the cycling shoe). This is likely close to optimal, given the dirty flow the feet are embedded in, and the constantly changing angle of attack due to rotation.
Another factor to consider is that aerodynamic fairings typically have a bad effect when there is a crosswind. Not only do they not reduce drag anywhere near as much if the flow isn't in the designed head-on direction, but also they can apply unwanted sideways forces to the rider. This is why you rarely see people ride outdoors with a disk wheel on the front any more.
Disclaimer: this is somewhat off-the-cuff. I do have a degree in aeronautical engineering, but I haven't used it for 15 years or more.
--Terry.
Bikewer
Penultimate Amazing
It's generally felt that Greg LeMond's 1989 Tour victory over Laurent Fignon in the final time-trial (a mere 25Km) was due to his use of a semi-aero clip-on handlebar and his use of the just-approved aero helmet.
As the guys note, the differences apply only to the top riders in a racing environment. If you watch the Tour, you'll generally see that during the time trials the top riders (the ones who are shooting to win) are going as "aero" as possible, including little booties over their shoes and so forth. The specialty time-trial bikes are likewise the product of wind-tunnel testing, and feature even "bladed" spokes to cut turbulence. It's only in non-windy conditions that you'll see the "solid" (carbon-fiber spoke covers) wheels, as crosswinds can put you on your ear.
The Peloton riders disregard these items, and cruise on through the time trial as best they may.
As the guys note, the differences apply only to the top riders in a racing environment. If you watch the Tour, you'll generally see that during the time trials the top riders (the ones who are shooting to win) are going as "aero" as possible, including little booties over their shoes and so forth. The specialty time-trial bikes are likewise the product of wind-tunnel testing, and feature even "bladed" spokes to cut turbulence. It's only in non-windy conditions that you'll see the "solid" (carbon-fiber spoke covers) wheels, as crosswinds can put you on your ear.
The Peloton riders disregard these items, and cruise on through the time trial as best they may.
shecky
Master Poster
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TeaBag420 said:
Hold on big boy. I said BMX helmets have a thicker, more durable shell. Compare that with the sometimes paper-thin shell typically used on road helmets. This translates to a longer lasting helmet even when it never has a crash related (or any serious) impact, just from suffering typical handling wear.
TeaBag420 said:
Whether BMX riders skimp on safety, I can't say for sure. My observation is that some not only skimp on safety, but disregard safety altogether, performing wild stunts without helmets at all. Or even without brakes.
Nevertheless, all helmets I've seen, BMX and road, since the days of "hairnets", seem to meet or exceed industry standards, regardless of price. The BMX market is youth oriented. This dictates a market that generally will not (and can't) spend big bucks on a expensive helmet. This is not a compromise on safety given safety standards. The manufacturers simply charges what the market will bear. The often jobless teenage male generally having less discretionary $$ than the adult road bike enthusiast.
TeaBag420 said:
Why make yourself out to be a a$$hole? Seems there are many things you're not sure of. Tell us more about your knowledge of the bicycle world.
I can't believe you've done this. I am even cradling my forehead in my left hand (that's the one you don't use for, you know...)shecky said:
Jobless teenage males with BMX bikes typically have effectively unlimited discretionary "$$" where I live.
Ah, the profanity. I could tell you more, but I'm sure yours would be bigger than mine. You could have said "azzhole". It's not clever to get around the profanity guidelines. You could have simply called me an anus, but I imagine that's a sore spot for you.
As I sit here in my French cut t-shirt with my bulging pecs and six-pack abs, I have to say that yours is the most amatuerish performance I have ever had to endure. Moreover, you were pitchy. You get zero points for style, and I picture you returning to your parents' knotty pine panelled basement/rec-room with the telephone company wire spool forced into service as a table (who spilled the bloody bong?!!!) Thank god your dad's Playboys are just outside in the garage. You need at least a year of refining your craft.
shecky said:
I'm sorry, you didn't understand what I meant by "send-off". I meant that after you made it personal and used bad la$nguage, I was done with you. Your money, as the Chairman used to say, is on the dresser. I shall not be eating Eggs Benedict off your chest in the morning; I am done with you.
Minus one for not being able to spell "different".