Still new at this, so I hope I'm posting the right subject in the right forum: ever seen those racing cyclists wearing those "teardrop" shaped helmets? I feel like taking it off their little heads and beating them with it! You see, I'm a little skeptical regarding their claims of aerodynamic advantages when these ridiculous-looking things are used. Okay...I shouldn't call them stupid without proof: can anyone corroborate or contradict me here- I'd be happy one way or the other. But to me, it's about as useful as putting a spoiler on the Titanic and is nothing more than bad science being used as justification for accessorizing and consuming....now I feel better- thanks.
stupid aerodynamic bicycle helmet
- Thread starter fenster
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- aerodynamic bicycle helmet
Bicycle helmets are routinely tested in wind tunnels. In competition it can be hundreths of a second that determine the winner. Wind resistance is a HUGE factor in cycling efficiency. If a helmet can gain a few seconds over 25 miles then it is well worth it. If you were a cyclist then you would know this instinctually. Wind is always a consideration on a time trial course. Position on the bike is the most important. Aerodynamic clothing is the next consideration. Us cyclists are not the dumb a$$es you think we are.
Mikie Callahan
Former Cat 1 Racer
Mikie Callahan
Former Cat 1 Racer
fenster said:
You feel like beating people because you don't know the answer to a question?
Welcome to the forum. Still, I'm glad you feel better.
If only the racers in the Tour de France used wind tunnels.
Oh, that's right... they do.
But to bring it back to your point, you have an objection to the shape of some bicycle helmets, not because they're worse, but because they're not better? You should have posted here before the moderators reined me in. It would have been great sport. But I suspect that you are looking very lovely today.
I've always heard these helmets have been tested, and I'm sure that at a certain speed over a certain distance with perhaps with a certain headwind these helmets MAY result in minimal resistance reduction. By minimal, I don't mean "cyclists need every thousandth of a second" minimal- I mean that unless you are among the top 100 in the world, you don't need one....and even then.... and you're right- I can't prove this: but I'd like to see a comprehensive wind tunnel test that shows a real advantage- a study not done by a manufacturer. And don't get me started on swimmers shaving their bodies....
The majority of the power expended by a cyclist going at a reasonable speed (15 mph or greater) is expended overcoming aerodynamic drag. Remember that power lost to drag goes like the cube of the speed, so even a small reduction in drag coefficient can be important. Having said that, the biggest aero advantage in a regular race is to ride in someone's draft. That's worth 20% or more reduction in expended energy. So that's why you typically don't see people wearing aero helmets except in an individual time trial (where you usually aren't riding near anyone else, and if you are, the rules say you may not draft).
--Terry.
--Terry.
Chris Haynes
Perfectly Poisonous Person
I do not find aerodynamic helmets annoying. Here is an article about Lance Armstrong using a local wind tunnel... it even has video: http://uwnews.org/discoveruw/article.asp?app=discoveruw&articleID=5596
What I do find annoying are the people who wear them wrong. Like wearing them on the back of head with the forehead completely exposed... and recently on the local bike trail, I saw a woman not only wearing it so that it just covered the back of her head but she had it on BACKWARDS!
Editted to add: the above link came from here http://www.uwal.org/index.html ... which also has pictures of skiers and others in the wind tunnel:
http://www.uwal.org/multimedia/sports.htm
What I do find annoying are the people who wear them wrong. Like wearing them on the back of head with the forehead completely exposed... and recently on the local bike trail, I saw a woman not only wearing it so that it just covered the back of her head but she had it on BACKWARDS!
Editted to add: the above link came from here http://www.uwal.org/index.html ... which also has pictures of skiers and others in the wind tunnel:
http://www.uwal.org/multimedia/sports.htm
You might want to consider making more extensive use of the little button on your keyboard just to the right of the period.fenster said:
You seem to be saying "Because I don't know, other people must be wrong."
Once again, welcome to the forum.
I think someone already got you started. Dr. Drew and I are getting out our wallets right now. Where's Dad?
shecky
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The most aerodynamic are not terribly practical for riding on the road, being unvented. Ventilation seems a big consideration with most practical helmets.
The only annoying thing I find with helmets is how expensive they can be. They're just styrofoam and thin plastic, with very little difference between a $25 model and a $125 model. The most practical designed ones I've found are actually non-full-face BMX helmets, which usually have a thicker, more durable shell than road bike helmets. And the BMX market also tends to be less tolerant of expensive helmets.
The only annoying thing I find with helmets is how expensive they can be. They're just styrofoam and thin plastic, with very little difference between a $25 model and a $125 model. The most practical designed ones I've found are actually non-full-face BMX helmets, which usually have a thicker, more durable shell than road bike helmets. And the BMX market also tends to be less tolerant of expensive helmets.
I have to agree to your earlier statement, Terry: at higher speeds they do make a difference. Perhaps at 20mph with the body in position for min drag- yes...at the prof level without the opprotunity to draft. It's just that sometimes it seems to me that the onus is not on science to prove that it is a valuable piece of engineering; it is more a marketing tool and all you need is a helmet company to pay a Lance Armstrong some coin and the next day you see cyclists wearing these stormtrooper helmets....
crimresearch
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The aerodynamic properties of bicycle helmets are not there to make the cyclist go faster *on* the bike...they are there so that when the cyclist flies off the bike they will travel farther.
Since the draft behind someone is created by not allowing the streams of air which you seperated to come together agian. This creates an area of negative pressure behind you which drags on you and helps the other person.
When riding fast, every little thing counts, but if cycling helmets look wierd, look at ski-racing gear.
When riding fast, every little thing counts, but if cycling helmets look wierd, look at ski-racing gear.
shecky said:
"Durable"? When I rode motor, SOP was to replace the helmet after one impact. You seem to be saying BMX riders skimp on spending for safety and choose to use compromised gear. I'm sure that's not what you're saying. I'm equally sure you're still living with the 'rents.
fenster said:
What the heck are you talking about? Have you read anything you wrote? Why does it bother you that big boy grownups who are actually physically able to make a bicycle go 20 mph (sometimes uphill!) wear helmets that actually let them go faster, even though you don't understand it?
"at higher speeds they do make a difference. Perhaps at 20mph with the body in position for min drag- yes...at the prof level without the opprotunity to draft. "
How do you know? Your earlier argument was that you didn't know. Twenty miles per hour is hobbyist level. Serious rider, but not a pro. Minus one for spelling.
voodoochile
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Isn't the primary reason to wear a helmet for safety?
Starting with that premis, there are better and worse designs that will cost or save you time compared to other helmets.
I don't know if wearing a helmet makes you go faster than not wearing a helmet, but suspect the thinking stems from swimmers wearing caps - which actually does help, but obviously water causes more friction than air.
Starting with that premis, there are better and worse designs that will cost or save you time compared to other helmets.
I don't know if wearing a helmet makes you go faster than not wearing a helmet, but suspect the thinking stems from swimmers wearing caps - which actually does help, but obviously water causes more friction than air.
voodoochile said:
We are talking about two different things here. "Regular" bike helmets are (intended to be) safety devices. Aerodynamic drag is not the driving factor for these helmets. Ventilation, weight, and fashion (not necessarily in that order) are.
The OP was talking about special time-trial helmets.
In a time trial, wearing a head fairing most certainly does make you go faster. The head causes quite a lot of drag, due to the flow separating from it rather than recovering smoothly around the back side. The "teardrop" head fairings address this by making the pressure recovery behind the head much more gradual, allowing the flow to remain attached for longer. This vastly reduces the pressure drag due to the head, although it does increase the friction drag, due to the larger wetted area.
--Terry.
davefoc
Philosopher
I think this subject has been reasonably well covered including a few nicely crafted shots at the opening poster.
I just thought I might add that world class bicycle racers on flat ground are going about 30 mph and they go much faster on downhills. At these speeds wind resistance swamps out all other forms of drag and even tiny tweaks can make major changes.
As I understand it wind resistance goes up with the square of velocity. So at 30 mph a rider will need to overcome about 2.25 times the wind resistance at 20 mph. But the really bad news is that the power required (that is the energy per time) being expended goes up as the cube of velocity because the rider not only needs to overcome the higher wind resistance he needs to go faster through it. So the rider needs to expend 3.375 times the power to maintain 30 mph that hew would have to expend to maintain 20 mph.
While the principal trick that world class riders use to maintain these incredible speeds is to be incredibly well conditioned athletes they also do everything legal to reduce wind resistance and a tear drop helmet was found to have a value in reducing wind resistance. As I recall, (and i"m old enough to remember when riders wore those almost useless hairnet helmets) when the transition was being made to helmets that actually worked it was something of a surprise to the bicycle technologists to find out that they could actually reduce wind resistance. This, of course, led to some really extreme designs to squeeze every little bit of advantage possible out of the helmet. This eventually led to rule changes which restricted the size of the helmet.
I just thought I might add that world class bicycle racers on flat ground are going about 30 mph and they go much faster on downhills. At these speeds wind resistance swamps out all other forms of drag and even tiny tweaks can make major changes.
As I understand it wind resistance goes up with the square of velocity. So at 30 mph a rider will need to overcome about 2.25 times the wind resistance at 20 mph. But the really bad news is that the power required (that is the energy per time) being expended goes up as the cube of velocity because the rider not only needs to overcome the higher wind resistance he needs to go faster through it. So the rider needs to expend 3.375 times the power to maintain 30 mph that hew would have to expend to maintain 20 mph.
While the principal trick that world class riders use to maintain these incredible speeds is to be incredibly well conditioned athletes they also do everything legal to reduce wind resistance and a tear drop helmet was found to have a value in reducing wind resistance. As I recall, (and i"m old enough to remember when riders wore those almost useless hairnet helmets) when the transition was being made to helmets that actually worked it was something of a surprise to the bicycle technologists to find out that they could actually reduce wind resistance. This, of course, led to some really extreme designs to squeeze every little bit of advantage possible out of the helmet. This eventually led to rule changes which restricted the size of the helmet.
Doubt
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Time to chime in with the triathlete perspective.
I am an average tri-geek. Came into it from a swimming background.
Years ago somebody did a study of the energy output for wind resistance and speed on road bikes. For a normal rider on a typical road bike, a rider ends up spending equal amounts of energy on wind resistance and speed at around 22 mph. At any higher speeds, the energy needed to overcome wind resistance take an ever increasing toll on the rider. Daveoc already pointed out that the wind resistance increases at an exponential rate.
Those helmets make a big difference. Cyclists also shave their legs, but that is as much to keep down road rash problems when they crash as it is aerodynamics.
Swimmers shaving? Never read a study documenting the effect. Given the density of the water, it is kind of hard to imagine it not having an effect. Little variations in body position have a huge effect on drag. Hair is not irrelevant to resistance.
I did shave in high school. I don’t do it anymore, since I am not that competitive at either swimming or cycling. I was just happy to hit an average speed of 19.4 mph for 112 miles once on the bike.
I am an average tri-geek. Came into it from a swimming background.
Years ago somebody did a study of the energy output for wind resistance and speed on road bikes. For a normal rider on a typical road bike, a rider ends up spending equal amounts of energy on wind resistance and speed at around 22 mph. At any higher speeds, the energy needed to overcome wind resistance take an ever increasing toll on the rider. Daveoc already pointed out that the wind resistance increases at an exponential rate.
Those helmets make a big difference. Cyclists also shave their legs, but that is as much to keep down road rash problems when they crash as it is aerodynamics.
Swimmers shaving? Never read a study documenting the effect. Given the density of the water, it is kind of hard to imagine it not having an effect. Little variations in body position have a huge effect on drag. Hair is not irrelevant to resistance.
I did shave in high school. I don’t do it anymore, since I am not that competitive at either swimming or cycling. I was just happy to hit an average speed of 19.4 mph for 112 miles once on the bike.
Doubt said:
According to the reasonably detailed calculator at
http://www.analyticcycling.com/ForcesSource_Page.html
for sensible defaults, the speed at which aero drag becomes 50% of the resistance is around 11 mph (4.75 m/s).
Also, <pedantic_git> I've seen two people now say that power lost to drag increases exponentially with speed. Nope, it is a cube law. Exponential is by-end-points greater than any polynomial. A cube law is a polynomial expression. </pedantic_git>
--Terry.