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  1. #1
    Disco Infiltrator Darth Lefty's Avatar
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    Everyday Aerodynamics

    I started this essay after learning of the kitty litter panniers and thinking, gosh, I wouldn't want to be riding that when a UPS truck goes by on a country road with no shoulder.

    When you are cruising along on a bicycle, the force of drag is the main thing on which you are spending power. If your intent is to get a workout, this is not really a problem. But if your intent is transportation, you'd probably like to go faster and get there sooner. You probably would also like to carry enough stuff and be comfortable. To reduce aerodynamic drag, you want to make a smaller wake. There are two basic approaches. First is to clean up the shape, second is to make the shape smaller. The ideal shape is generally that of a fish, a bomb, a bird in a dive with its wings folded. You cannot get there from here with a normal bike. But you can avoid making it worse.

    Bikes are not particularly aerodynamic and it's mostly your fault. When you look at the front profile of a bike, the rider is most of it. You want to look as small as possible. Road bikes really are better in this regard. Drop bars lean you down and bring in your elbows. So if you can stand it, do it. Don't wear floppy clothing if style does not demand it. Not only does it make you bigger but the fluttering also saps power. If you can feel anything flapping in the breeze, correct it.

    Even without you, bikes are still not particularly aerodynamic. Bikes are made up of many cylinders sticking upright in the breeze like flagpoles - dozens if you count the spokes. There are excellent structural and monetary reasons for this. Solutions generally involve making things smaller, fewer, or sculpted. Hence 23mm tires on deep V rims with 18 flat carbon spokes, egg shaped down tubes, smooth webs between the tubes. You can take this as far as you like - people have preferences that should be respected. Some of these things reduce weight, some add it.

    You don't want to add anything to the bike that further increases its drag. Since you are already creating a big messy wake with your body, the best place to put stuff is in that wake. In that light a big saddlebag or rack-top bag is better than panniers, although admittedly less useful, and as long as it's not wider than you. Backpacks are good in this regard too. Unloaded wire baskets cause less drag than panniers (just imagine holding either one against a river current). Folding baskets or fold-out panniers are a great idea - keep them out of the breeze unless needed. Directly ahead of you is also a good spot, since it isn't going to make the wake much bigger, so a small handlebar bag is ok. A big wicker basket is probably not great. Accessories like lights and bells add drag too. They are small enough and dead ahead of you so they probably don't have too bad an effect.

    Once you have folded out your chosen cargo container you are going to be carrying a lot of weight and going slower and the aerodynamics won't matter as much. But still, the same idea applies to your load. Keep it shipshape. Tie plastic bags shut so they don't flutter. Zip it all closed. If the load is light and small enough, just use one side of your folding bags, or don't unzip the expanding section, or whichever.

    Do I practice what I preach? Somewhat. My commuter bike is a mountain bike with slicks. I'm sort of stuck with it for now due to saving money, but its replacement will have drop bars. I do have a road bike but I'm not commuting on it because it's not modern. Its gears aren't low enough and I don't believe it will be reliable enough, and it's classic enough to keep it original. In this season I often wear normal pants to ride to work since it's cool enough to want legs covered, and I tie up the cuffs with a velcro strap. For the ride home I wear cycling shorts. I haven't ever switched from tee shirts to jerseys, mainly because I don't think I'm slim enough to look good in them. I have an expanding rack-top bag.

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    Quote Originally Posted by Darth Lefty View Post
    Do I practice what I preach? Somewhat. My commuter bike is a mountain bike with slicks. I'm sort of stuck with it for now due to saving money, but its replacement will have drop bars. I do have a road bike but I'm not commuting on it because it's not modern. Its gears aren't low enough and I don't believe it will be reliable enough, and it's classic enough to keep it original. In this season I often wear normal pants to ride to work since it's cool enough to want legs covered, and I tie up the cuffs with a velcro strap. For the ride home I wear cycling shorts. I haven't ever switched from tee shirts to jerseys, mainly because I don't think I'm slim enough to look good in them. I have an expanding rack-top bag.
    I'm feeling you bro, but, just saying... I got serious push-back in this forum when I advised a poster to opt for a cargo trailer over a kiddie trailer to haul groceries. Even Burley Travoys do not frighten these good folk. I'd look for the thread for you but the memory is just too painful. When I told them that at 12mph, 90% of your effort goes to fighting aero drag, I was soundly rebuked. The figure cannot be more than 50% I am told. So be it. I've heard that independent corroboration of a truth creates something... factual?

    H

  3. #3
    Disco Infiltrator Darth Lefty's Avatar
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    That's why I put it in the commuter forum.

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    I also commute on a mountain bike (Full-suspension Kona), and frankly don't concern myself with aero effect; yes, MTB commuting takes longer than a skinny-tire roadie or touring bike -- so what? It's just more time ON THE BIKE! I'm not all that concerned about getting there sooner or faster, I know approximately how long each of my multiple routes in/back home take; the whole POINT is ride time, the best time of the day!

    Not trying to down you, Darth, but your post comes across as having taken the driver's mentality about the commute, and applied it to the ride. Commuting by car SUCKS (hell, IMO, DRIVING sucks!), and most people (somewhat subconsciously) try to get it over with as soon as they can. Commuting by bike can, and SHOULD, be one of the highlights of the day!

    I personally have NO interest in a bike commute that involves the least amount of effort manageable. What people say about jobs ("do what you LOVE, and you'll never work a day in your life!") also applies to commuting by bike (and riding a bike PERIOD!); I happen to LOVE riding the bike.

    With all that said, I generally carry my daily load in a backpack, and when carrying home large/bulky items, they are in poly bags hanging from the bar. I won't pay what OldManMountain wants for a full-suss pannier rack.

    (NOTE: it was quite entertaining one day last year, when I was taking home a laundry tote for my nephew -- strapped to my back! I looked like a swollen turtle!)

  5. #5
    Passista Reynolds's Avatar
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    What you say is true , but at the speeds I commute (15-25 kph) the aero advantage is minimal IMO. Above 35 kph is another story though.

  6. #6
    7-speed doomsday prepper ThermionicScott's Avatar
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    Great post, Darth. Even though I enjoy spending time on the bike, I like being able to zip along when I have/want to. So all of my regularly-used bikes have drop bars, set no higher (but not much lower) than the saddle. It really makes a difference.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
    RUSA #7498

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    Senior Member tjspiel's Avatar
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    I think what a lot of people have found is that often times getting lucky with traffic lights saves more time than worrying too much about aerodynamics. It's not that aerodynamics don't matter, it's just over the course of a 30 minute or shorter commute with lots of stops and starts, using a trunk bag instead of panniers isn't going to get you there much earlier.

    Now, an hour or more on an open road is a different matter entirely.

    I guess it depends on how you look at it. I can maybe save 2 or 3 minutes on a 25 minute commute using my road bike vs my mountain bike (with semi-slick tires). On the one hand, that's a 10% improvement which is really pretty good. On the other hand, it's still only 2 or 3 minutes.
    If you're not riding with a psychedelic gecko on your shirt, you ARE having a substandard experience.

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    The only time that I really care about aerodynamics while commuting is on windy days.

  9. #9
    imi
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    Quote Originally Posted by itsthewoo View Post
    The only time that I really care about aerodynamics while commuting is on windy days.
    Me too... Getting into the drops really helps

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    I only commute 18 miles round trip so you would think it matters little how fast I go. But I find it does: it is just more motivating to be fast. I also commute on a slick shod MTB (with an air front fork) and I think it would be more comfortable with a riser bar, but I can't bring myself to buy one because it will make me even less aero.

    I carry everything in a backpack, but my clothing is usually flappy since I don't change upon arrival; I wear on the bike what I wear at work (casual gear).

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    In flat, windy areas, headwinds are a serious problem. In northern parts of Netherlands, many granny bikes come complete with clip-on aerobars and old ladies use them. The big advantage of aerobars is in reducing width, not height. You can close off the chest area from acting as a parachute. On my drops, I usually ride on the tops rather than the drops for the most effective aerodynamics.
    For racers, the usual figure is that 90% of aerodrag is caused by the rider and 10% by the bike. For load-carrying commuters, that figure would change but no-one has done any wind-tunnel tests of luggage (yet...)

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    Quote Originally Posted by MichaelW View Post
    ...no-one has done any wind-tunnel tests of luggage (yet...)
    See Bicycle Quarterly vols. 1 and 6 from 2007 for some such wind tunnel tests of panniers, handlebar bags, and seat bags.

    http://janheine.wordpress.com/2012/0...orld-bicycles/

    I wish they'd tested a Xooter Crossrack setup, which feels to my legs as the most aero high volume cargo carrier going. It is not wider than my hips and thighs.
    Last edited by chaadster; 05-28-13 at 06:58 AM.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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    Certified Bike Brat Burton's Avatar
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    Have had a few particularly stormy and windy days here lately including a couple days with pretty steady 20 to 30kph headwinds. The guys that seemed to be affected the most were BIG guys. BIG meaning both large and tall and was regardless of weither they were driving a road bike with aerobars or a city bike. It was probably just all that frontal area.

    No one was breaking any speed records but I did manage to creep by a dozen other riders on my commute home and was passed by no-one. Interesting because I was the only guy on the MUP that day running panniers out front. That may not sound particularly aerodynamic but SOMETHINGS got to break the wind - either the luggage or the rider. I run Ergon GP5's on cut down bars and a low stem position which pretty much puts me in a low forward position anyway.

    In this case I just happened to be in the dead space behind the luggage so net losses or gains were propably negligable since I'm only 5'7". But the added stability offered by having the panniers in the front was a really big plus under windy conditions.

    Other than that - if it was so windy aerodynamics on a touring or commuting rig was an issue - I'd stay home because crosswinds would be a serious issue anyway. . Otherwise I'd say just drive slower and hope the wind hasn't changed directions on the return trip.
    Last edited by Burton; 05-28-13 at 07:17 AM.

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    Burton: yes, frontal area, but also re-accelerating all the mass of us big guys after getting hit with a gust of wind takes a lot of watts!
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

  15. #15
    johnliu@earthlink.net jyl's Avatar
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    I switched from commuting on MTB w/ slicks to road bike, mostly for aero reasons.
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    What is the biggest source of drag in this picture?


    It's the rider. You can make the bike as aero as you can, but the rider will still be the biggest wind drag by far.

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    ^^ the road surface.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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    Quote Originally Posted by chaadster View Post
    See Bicycle Quarterly vols. 1 and 6 from 2007 for some such wind tunnel tests of panniers, handlebar bags, and seat bags.

    http://janheine.wordpress.com/2012/0...orld-bicycles/

    I wish they'd tested a Xooter Crossrack setup, which feels to my legs as the most aero high volume cargo carrier going. It is not wider than my hips and thighs.
    Sweet rig.

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    coprolite fietsbob's Avatar
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    Got a Zzipper 'thriller' Fairing for a bike setup i was doing a 12 mile commute.
    the aerodynamics was the airflow around a smooth frontal ..
    It wasn't really a Low crouch..
    a benefit I didnt have to dress so warmly, since the airflow was less through my clothing..

    It was a river bottom road so pretty flat.. the Fairing also made the audio on my Books on tape
    hearing easier to fill the hour..

  20. #20
    ouate de phoque dramiscram's Avatar
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    I have a kitty litter bucket on my winter bike and I don't really feel a big difference in the aerodynamic. When the roads are clear of snow I could manage a decent average speed.
    Originally Posted by Leebo
    Headwind is like a hill without a soul. Just gear down and suffer.
    Quote Originally Posted by jrickards View Post
    Headwinds are hills dipped in evil!
    Tabarnac de vent!!!

  21. #21
    johnliu@earthlink.net jyl's Avatar
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    Quote Originally Posted by spivonious View Post
    What is the biggest source of drag in this picture?


    It's the rider. You can make the bike as aero as you can, but the rider will still be the biggest wind drag by far.
    Completely true, but the bike affects how aero the rider can be.

    On an upright bike with wide handlebars, you can't get your torso very low, can't comfortably remain in that position for long, and your arms are still wide like a parachute. On a bike with drop bars, just placing your hands in the drops brings your torso low and your arms tucked in, you can even have a flat back if you are flexible enough, and you can ride that way for hours.

    At 13 mph it doesn't make much difference. At 18+ mph it makes a big and increasing difference.

    Here's a somewhat extreme example. I went on a 40 mile ride on my mountain bike w/ slick tires, with some guys who were all riding long-wheelbase recumbents with fairings and full body socks. So I was at a huge aero disadvantage. On the flats, I could keep up but I was clearly working harder than they were. On the downhills - not steep slopes, just rolling hills - I had to tuck low and pedal my highest gear as hard as I could, panting, to keep up as they pedaled casually and enjoyed their vastly superior aero. Thank goodness every downhill was followed by an uphill where I could rest. Odd experience, relaxing on the uphills and busting my lungs on the downhills.
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  22. #22
    coprolite fietsbob's Avatar
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    Velomobile.

  23. #23
    Senior Member Notso_fastLane's Avatar
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    Velo is the way to go! I was going to suggest a recumbent lowracer, but Velo even has those beat for great Aero.

  24. #24
    Disco Infiltrator Darth Lefty's Avatar
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    Thanks for the kind words, everyone. The first response had me worried I had waded into an old flame war! I tried to keep it general and light on the math, figuring that would be more useful. You can't make a lot of power with your body, and I have even further limits due to health, so every little bit helps. On my own commute going to work it's downhill and I can shave a good five minutes off the half hour by using the Paramount instead of the Hardrock. Multiply by a week or a month or a lifetime, that's not peanuts. Coming home it's uphill, and the efficiency of the bike is probably more important, but the road bike does help there too.

    Just about everything mentioned will also help on a recumbent, since the physics are no different.

    I've only seen one windshield on a bicycle around here and it was the kind that goes along with a child seat just behind the handlebars. It seems like the payoff would not be drag but comfort.

    The highest payoff thing to do, that is nearly impossible on a conventional bicycle, is to close the wake behind you. A hard full fairing is the way to take this to its natural conclusion, as with a velomobile. This is true of motorcycles too - Craig Vetter, who was famous for designing the original Windjammer fairing that turned Honda Gold Wings from absurd hotrods into touring bikes, has been working for years on full fairings but they're too confining for most people. There are also stability issues from crosswinds and weight distribution that keep you from making the tail as long as you'd like. http://craigvetter.com/ The Mythbusters tried it not too long ago, though they didn't go to real world use.

  25. #25
    Senior Member alan s's Avatar
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    Quote Originally Posted by jyl View Post
    At 13 mph it doesn't make much difference. At 18+ mph it makes a big and increasing difference.
    When you are commuting to and from work, the difference is less important compared to other factors, such as comfort, safety and reliability. Sure, you don't want extra windage that can easily be eliminated, thereby saving time and energy, but aerodynamics for commuters ranks pretty low on the scale.

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