Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Folding Bikes Discuss the unique features and issues of folding bikes. Also a great place to learn what folding bike will work best for your needs.

Reply
 
Thread Tools Search this Thread
Old 05-30-12, 05:58 PM   #1
Micheal Blue
Senior Member
Thread Starter
 
Join Date: Dec 2010
Location: Toronto, Canada
Bikes: Dahon Mu P24, Trek 7300
Posts: 135
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.
Micheal Blue is offline   Reply With Quote
Old 05-30-12, 07:16 PM   #2
ratdog
Senior Member
 
Join Date: Mar 2005
Location: New York City
Bikes:
Posts: 874
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.
ratdog is offline   Reply With Quote
Old 05-30-12, 10:05 PM   #3
jur
Senior Member
 
Join Date: May 2005
Bikes:
Posts: 6,792
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.
jur is online now   Reply With Quote
Old 05-30-12, 10:29 PM   #4
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Bikes: 7
Posts: 18,086
It does not matter.. to me.. have to carry the stuff, off my back..
fietsbob is offline   Reply With Quote
Old 05-31-12, 06:12 AM   #5
Micheal Blue
Senior Member
Thread Starter
 
Join Date: Dec 2010
Location: Toronto, Canada
Bikes: Dahon Mu P24, Trek 7300
Posts: 135
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...
Micheal Blue is offline   Reply With Quote
Old 05-31-12, 09:24 AM   #6
kamtsa
Senior Member
 
kamtsa's Avatar
 
Join Date: Dec 2008
Bikes:
Posts: 1,815
Quote:
Originally Posted by Micheal Blue View Post
Sorry Ratdog, but your answer lacks intelligence.
-1
kamtsa is offline   Reply With Quote
Old 05-31-12, 09:29 AM   #7
bmac.to
Member
 
Join Date: Mar 2011
Bikes:
Posts: 34
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.
bmac.to is offline   Reply With Quote
Old 05-31-12, 10:14 AM   #8
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Bikes: 7
Posts: 18,086
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..
fietsbob is offline   Reply With Quote
Old 05-31-12, 06:36 PM   #9
ratdog
Senior Member
 
Join Date: Mar 2005
Location: New York City
Bikes:
Posts: 874
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.
ratdog is offline   Reply With Quote
Old 05-31-12, 07:12 PM   #10
jur
Senior Member
 
Join Date: May 2005
Bikes:
Posts: 6,792
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.
jur is online now   Reply With Quote
Old 05-31-12, 07:57 PM   #11
feijai
Senior Member
 
Join Date: May 2007
Location: Washington, DC
Bikes:
Posts: 893
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.
feijai is offline   Reply With Quote
Old 05-31-12, 08:37 PM   #12
BassNotBass
lowlife bottom feeder
 
BassNotBass's Avatar
 
Join Date: Apr 2008
Location: Lou-evil, Canned-Yucky USA
Bikes:
Posts: 1,993
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.
BassNotBass is offline   Reply With Quote
Old 05-31-12, 09:48 PM   #13
ratdog
Senior Member
 
Join Date: Mar 2005
Location: New York City
Bikes:
Posts: 874
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.
ratdog is offline   Reply With Quote
Old 05-31-12, 11:02 PM   #14
pacificcyclist
Senior Member
 
Join Date: Dec 2007
Location: Canada
Bikes: 2012 Masi Speciale CX : 2013 Ghost 29er EBS
Posts: 918
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.
pacificcyclist is offline   Reply With Quote
Old 06-01-12, 04:00 AM   #15
badmother
Senior Member
 
badmother's Avatar
 
Join Date: Nov 2007
Bikes:
Posts: 3,085
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
badmother is offline   Reply With Quote
Old 06-01-12, 05:44 AM   #16
Micheal Blue
Senior Member
Thread Starter
 
Join Date: Dec 2010
Location: Toronto, Canada
Bikes: Dahon Mu P24, Trek 7300
Posts: 135
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.
Micheal Blue is offline   Reply With Quote
Old 06-01-12, 05:58 AM   #17
Micheal Blue
Senior Member
Thread Starter
 
Join Date: Dec 2010
Location: Toronto, Canada
Bikes: Dahon Mu P24, Trek 7300
Posts: 135
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.

Quote:
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.
Micheal Blue is offline   Reply With Quote
Old 06-01-12, 06:06 AM   #18
Micheal Blue
Senior Member
Thread Starter
 
Join Date: Dec 2010
Location: Toronto, Canada
Bikes: Dahon Mu P24, Trek 7300
Posts: 135
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.
Micheal Blue is offline   Reply With Quote
Old 06-01-12, 07:49 AM   #19
pacificcyclist
Senior Member
 
Join Date: Dec 2007
Location: Canada
Bikes: 2012 Masi Speciale CX : 2013 Ghost 29er EBS
Posts: 918
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.
pacificcyclist is offline   Reply With Quote
Old 06-01-12, 08:20 AM   #20
LeviPounds
Levi
 
LeviPounds's Avatar
 
Join Date: Mar 2005
Location: Toronto
Bikes:
Posts: 98
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.
LeviPounds is offline   Reply With Quote
Old 06-01-12, 09:52 AM   #21
pacificcyclist
Senior Member
 
Join Date: Dec 2007
Location: Canada
Bikes: 2012 Masi Speciale CX : 2013 Ghost 29er EBS
Posts: 918
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.
pacificcyclist is offline   Reply With Quote
Old 06-01-12, 10:17 AM   #22
pacificcyclist
Senior Member
 
Join Date: Dec 2007
Location: Canada
Bikes: 2012 Masi Speciale CX : 2013 Ghost 29er EBS
Posts: 918
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!
pacificcyclist is offline   Reply With Quote
Old 06-01-12, 11:00 AM   #23
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Bikes: 7
Posts: 18,086
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.
fietsbob is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 06:26 PM.