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  1. #1
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    Brompton T-bag - a big sail in headwind...or not a big deal?

    Do the Brompton bags (the luggage system) present a challenge in headwind? This luggage system seems brilliant, but OTOH having a large rectangle facing the wind... While the Tikit doesn't have such a handy and large bag (the T-bag), it can carry panniers and they seem more aerodynamic. Thanks for the answers.

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    How fast do you think you'll be going on a Brompton? Fast enough that wind resistance is going to be a major impact?

    The upright riding position probably is more of a factor.

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    jur
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    I have a front basket for my Brommie; I can feel it's drag once the speed gets to about 50km/h or so. Going downhill it has a fair old impact; but the Brommie isn't exactly a speed machine so the overall impact is modest enough that I don't worry about it too much.

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    coprolite fietsbob's Avatar
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    It does not matter.. to me.. have to carry the stuff, off my back..

  5. #5
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    Quote Originally Posted by ratdog View Post
    How fast do you think you'll be going on a Brompton? Fast enough that wind resistance is going to be a major impact?

    The upright riding position probably is more of a factor.
    Sorry Ratdog, but your answer lacks intelligence. Or perhaps I'm wrong and you live in a deep valley with no winds. Many are the days here in Toronto when my afternoon commute from work means biking against some fairly strong winds along the lakeshore. The winds can easily blow at 40 km/h. Add to it your speed and...

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    Senior Member kamtsa's Avatar
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    Quote Originally Posted by Micheal Blue View Post
    Sorry Ratdog, but your answer lacks intelligence.
    -1
    Happier than a camel on wednesday.

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    I have an S-bag and I havent noticed a big deal - in a strong headwind, it is hard to bike with or without the S-bag attached. However, the T-bag is bigger ... I do thing the bike handles a bit better with a bit of weight on the front than without.

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    coprolite fietsbob's Avatar
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    time for the pedal-electric kit for the up wind leg?

    I ride into the wind into town in the summer ,
    Then into it on the way home in the winter.

    I just compensate, add time of travel , myself..

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    Quote Originally Posted by Micheal Blue View Post
    Sorry Ratdog, but your answer lacks intelligence. Or perhaps I'm wrong and you live in a deep valley with no winds. Many are the days here in Toronto when my afternoon commute from work means biking against some fairly strong winds along the lakeshore. The winds can easily blow at 40 km/h. Add to it your speed and...
    Michael,

    I've biked in plenty of windy conditions. Usually around the edges of hurricanes since I like to vacation in Delaware during late August and early September which happens to be the season. The upright riding position is more of a factor as far as your aerodynamics.

    And by the way, there's no need to be insulting since aerodynamics as it relates to a headwind and and going faster are pretty much the same since the faster you go on a windless day the more headwind there is.

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    jur
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    Seems to me a 40km/h headwind is going to bring you to a near-standstill, because riding in windless conditions, maintaining 40km/h is very hard. Add the Brompton front sail, and yes that is going to have quite an impact.

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    Quote Originally Posted by ratdog View Post
    How fast do you think you'll be going on a Brompton? Fast enough that wind resistance is going to be a major impact?
    One would hope so. Even at quite slow speeds, aerodynamic drag is a huge, if not primary, factor in performance. At any rate, I presume that if the poster is worried about drag, then he's not going 5 miles an hour.

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    lowlife bottom feeder BassNotBass's Avatar
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    Unless you're extremely thin/small or ride with your torso sideways to the wind your arms and torso are about as aerodynamically inefficient as a large bag on the front of the bike or panniers sticking out from the sides. I suggest you just enjoy the ride for what it is and what you're accomplishing regardless of whether or not you can maintain the same speeds as if you were on a training ride or racing.
    I plan on living forever... so far so good.

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    Quote Originally Posted by feijai View Post
    One would hope so. Even at quite slow speeds, aerodynamic drag is a huge, if not primary, factor in performance. At any rate, I presume that if the poster is worried about drag, then he's not going 5 miles an hour.
    The point I was making was that the OP needed to ask himself if he was going to go fast enough to have wind resistance become a factor or in his case which was only clarified in post #5, ride into enough headwind for the wind resistance to be a factor. If so, my opinion is that the wind resistance from the upright seating position was going to be more of a factor than the profile of the bag. The question(s) were not meant to be facetious even though some readers have taken it to be.

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    Quote Originally Posted by Micheal Blue View Post
    Do the Brompton bags (the luggage system) present a challenge in headwind? This luggage system seems brilliant, but OTOH having a large rectangle facing the wind... While the Tikit doesn't have such a handy and large bag (the T-bag), it can carry panniers and they seem more aerodynamic. Thanks for the answers.
    About 90% of cycling energy is used to drag you and your bike through air. A drag coefficient is determined by the objects frontal area and the Brompton Bags as well as the Dahon bags or modified luggage truss system does not "add" any additional frontal area. In effect, the Brompton Bag itself does not add any additional frontal area because part of your body is in the "shadow" of the bubble of turbulent air behind the bag. It's akin to a racer who tucks behind the leader to save energy. So basically, part of your stomach is "drafting" behind the brompton bag. However, adding bike panniers will provide a noticeable increase in drag because it increases the frontal area of the bike causing more drag.

    So to answer your question. Yes, the Brompton bag is aerodynamic friendly than panniers.
    Last edited by pacificcyclist; 05-31-12 at 11:14 PM.
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    Senior Member badmother's Avatar
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    This has been discussed in the Yahoo Brompton group. I remember it was discussed if it was worth it to DIY a bag (and the frame to fit it) to a more "narrow but pregnant" shape, a bit like a backpack. Maybe the solution is to just use the Rixen Kaul backpack wit a sort of adaptor to the luggageblock. Look up the Yahoo group to read the discussion.
    Last edited by badmother; 07-09-12 at 03:32 PM. Reason: zPelLinG
    °Empty drums make a lot of noice... (Old Hungarian proverb).

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    Quote Originally Posted by jur View Post
    Seems to me a 40km/h headwind is going to bring you to a near-standstill, because riding in windless conditions, maintaining 40km/h is very hard. Add the Brompton front sail, and yes that is going to have quite an impact.
    From your reply it seems that you don't experience much wind where you ride. Fortunate you! I've expereienced stronger headwinds than 40 km/h. While it's not fun and I have to gear down and creep along at, say, 13 km/h, or perhaps even slower.

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    Quote Originally Posted by ratdog View Post
    Michael,

    I've biked in plenty of windy conditions. Usually around the edges of hurricanes since I like to vacation in Delaware during late August and early September which happens to be the season. The upright riding position is more of a factor as far as your aerodynamics.
    Thank you, Ratdog, that's helpful info. It may seem obvious to some, but I have no personal experience
    with this bike + T-bag.

    And by the way, there's no need to be insulting since aerodynamics as it relates to a headwind and and going faster are pretty much the same since the faster you go on a windless day the more headwind there is.
    Ratdog, saying that an answer is not intelligent - how can it be insulting...to whom or what? I made no statement about you, only about the answer. Perhaps the answer could be insulted. You were talking
    off topic. I asked about the challenge the T-bag presents in a headwind and you were answering about
    upright riding positions and how fast I was going, which are not the same scenarios. I'm not trying to nitpick words, I'm trying to understand the situation of how it is riding a Brompton with a loaded T-bag against a headwind, so I appreciate answers for that subject. From the answers so far, it seems it's not a big deal. Great.

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    Quote Originally Posted by pacificcyclist View Post
    In effect, the Brompton Bag itself does not add any additional frontal area because part of your body is in the "shadow" of the bubble of turbulent air behind the bag. It's akin to a racer who tucks behind the leader to save energy. So basically, part of your stomach is "drafting" behind the brompton bag. However, adding bike panniers will provide a noticeable increase in drag because it increases the frontal area of the bike causing more drag.
    That's an interesting way of looking at it, though it's really the legs that are behind the bag, not the body.
    Turbulent air is not very desirable though, from what I've seen so far. When designing fast machines, engineers look for parts that create turbulences and try to eliminate them for smooth air flow.

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    Quote Originally Posted by Micheal Blue View Post
    That's an interesting way of looking at it, though it's really the legs that are behind the bag, not the body.
    Turbulent air is not very desirable though, from what I've seen so far. When designing fast machines, engineers look for parts that create turbulences and try to eliminate them for smooth air flow.
    Yes, but that's only relevant if your forward speeds exceeds 20mph or 32km/h; anything under that will not be as relevant as other factors like bike and rider weight, frame flex, rolling resistance and aerodynamic riding positioning which play an important role in robbing watts power away which can be put towards forward propulsion in multiple varied terrain! Aerodynamic drag starts to become a significant player in higher speeds and engineers look for ways to reduce it because cars and planes can easily travel faster than 32km/h for sure. Even a recumbent with fairings can easily travel faster. What you may not realize is that, reducing aerodynamic drag is a kin to becoming more fuel efficient. Which means that if the car is more aerodynamic, it requires less energy to move forward as it would being so boxy. This is the same with the bike, but you would realize it until you reach or exceeds 20mph. If you consistently ride faster than 20mph which you alluded you could (53km/h of riding speed to combat a 40km/h head wind), then I think you are riding the "wrong" bike to begin with. With 53 km/h average speed, you should be riding a Cervelo S5, skin suit and aerodynamic helmet and then tow a carryfreedom or Burley Travoy trailer in which the trailer tucks behind you creating little aero drag to make the ultimate commute machine! Not!

    Don't waste your time analyzing this. It's insignificant. Rather, train yourself to become an efficient and strong rider! However, there are a lot of people who make a huge industry out of selling aerodynamic toys to triathletes at insane prices making them believe that even below 20mph, you can still ride like the pros. In the USA cycling coaching manual and even in Canada, good coaches emphasize mainly on building cycling power and efficiency if you're riding below 20mph first rather trying to cheat wind.
    Last edited by pacificcyclist; 06-01-12 at 07:53 AM.
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  20. #20
    Levi LeviPounds's Avatar
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    Michael Blue, I think have the same commute as you; riding west on Lakeshore path to work and east on the way home. I also own the T-bag and have noticed it slowing me down significantly i headwinds. I usually switch to Queen St. or Eastern ave. on these days. Slightly less windy, but still red lights to contend with, mind you.

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    Quote Originally Posted by LeviPounds View Post
    Michael Blue, I think have the same commute as you; riding west on Lakeshore path to work and east on the way home. I also own the T-bag and have noticed it slowing me down significantly i headwinds. I usually switch to Queen St. or Eastern ave. on these days. Slightly less windy, but still red lights to contend with, mind you.
    While I don't ride in Toronto, in Vancouver BC along River Dr in Richmond my front MEC bag which is almost exactly like the Brompton T-Bag that is in front of my Speed Uno presents negligible wind drag in heavy head wind conditions (just today is nasty in the early morning commute) compared to say a pair of touring size bags hanging on the sides. I've done some scientific tests and I have concluded that unless you are cycling faster than 20mph, then other things on the bike and your riding posture are slowing you down. Although I realized my MEC cycling rain cape presents the most aerodrag when worn.

    The Brompton is not exactly a speed machine per se, not as stiff as a Tern Verge or my Mu SL. Even the Speed Uno is slighter stiffer than the M6L and there is a reason for this. I think what you are experiencing is frame flexing as you are putting more power to the pedals to combat the head wind. You can't help it as the upright riding is conducive to a poor drag coefficient -- more front area exposed as opposed to a time trialist on a Cervelo S5. As you are putting more effort on the pedals, the frame needs to be stiff enough around the BB and rear triangle area to allow the transfer of pedal power directed towards forward propulsion. Unfortunately, the Brompton has a suspension thingy on the rear and while it helps cushion the blows from rough roads, unfortunately the suspension robs some of your pedaling power in a form of "frame flex" and suspension movement from pedal induced motion (bobbing) -- it's essentially a URT design (Unified Rear Triangle) like the infamous Trek Y bike of the past. In fact, you can improve the stiffness of your Brompton by replacing the soft suspension block with a much firmer version to try and lock it out. Peter at NYCEwheels commented exactly that as some one commented why riders on the demo video is putting a lot more effort moving the bike forward even in an isolated bike path under the bridge than need be! Peter commented that it was the suspension block that is robbing some of the pedal power flexing the frame. I concur as I rode the B and noticed the flex under stress. This is also the very same reason why some touring cyclists mistakenly assumed that it was wind drag at 10mph that had caused them to cycle with more effort with panniers when in fact it was frame flex that make the panniers wiggle (most cyclists wiggle side to side to a varying degree) that some of that pedal power went to move the bags rather than mainly moving the bike forward. Which is also the reason why a correctly designed loaded touring frame is equally stiff and heavy to combat frame flex from the movement of the heavy panniers so it allow the rider pedal power to get to where it needs the most -- move the rear wheel!
    Last edited by pacificcyclist; 06-01-12 at 10:14 AM.
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  22. #22
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    Quote Originally Posted by LeviPounds View Post
    Michael Blue, I think have the same commute as you; riding west on Lakeshore path to work and east on the way home. I also own the T-bag and have noticed it slowing me down significantly i headwinds. I usually switch to Queen St. or Eastern ave. on these days. Slightly less windy, but still red lights to contend with, mind you.
    While I don't ride in Toronto, in Vancouver BC along River Dr in Richmond my front MEC bag which is almost exactly like the Brompton T-Bag that is in front of my Speed Uno presents negligible wind drag compared to say a pair of touring size bags hanging hanging on the sides. I've done some scientific tests (heart rate monitor, power meter and with a GPS ANT sensors etc..) and I have concluded that unless you are cycling faster than 20mph, then other things on the bike and your riding posture are slowing you down.

    The Brompton is not exactly a speed machine per se, not as stiff as a Tern Verge or my Mu SL. Even the Speed Uno is slighter stiffer than the M6L and there is a reason for this. I think what you are experiencing is frame flexing as you are putting more power to the pedals to combat the head wind. You can't help it as the upright riding is conducive to a poor drag coefficient -- more front area exposed as opposed to a time trialist on a Cervelo S5. As you are putting more effort on the pedals, the frame needs to be stiff enough around the BB and rear triangle area to allow the transfer of pedal power directed towards forward propulsion. Unfortunately, the Brompton has a suspension thingy on the rear and while it helps cushion the blows from rough road services unfortunately robs some of your pedaling power in a form of "frame flex". In fact, you can improve the stiffness of your Brompton by replacing the soft suspension block with a much firmer version. Peter at NYCEwheels commented exactly that as some one commented why riders on the demo video is putting a lot more effort moving the bike forward even in an isolated bike path under the bridge than need be! Peter commented that it was the suspension block that is robbing some of the pedal power flexing the frame. I concur as I rode the B and noticed the flex under stress. This is also the very same reason why some touring cyclists mistakenly assumed that it was wind drag at 10mph that had caused them to cycle with more effort with panniers when in fact it was frame flex that make the panniers wiggle (most cyclists wiggle side to side to a varying degree) that some of that pedal power went to move the bags rather than moving the bike forward. Which is also the reason why a loaded touring frame is equally stiff and heavy to combat frame flex from the movement of the heavy panniers so it allow the rider pedal power to get to where it needs the most -- move the rear wheel!
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  23. #23
    coprolite fietsbob's Avatar
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    Would be a job making it, rather than just buying from stock.
    but .. a front bag with one of Zzipper company's road fairings
    in front of the Bag (or sewing a bag with one of their Bubbles
    as a front stiffner shape, would be an aerodynamic shape as a frontal area..

    I rode one of the Moultons a friend had, with a Zzipper front rack/fairing kit.
    it was great.. a bit taller fairing, further ahead so bars/steering,
    rotated behind it ,

    .. rather than over the Bag, as Bromptons must.

    same friend gave me one of his other Zzipper fairings ,
    I fitted to my bike [700c wheels] there is a small % of gain
    thru air flow around a smooth curved front.
    Last edited by fietsbob; 06-01-12 at 11:09 AM.

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