Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 26

Thread: Drafting

  1. #1
    Senior Member Cadillac's Avatar
    Join Date
    Jan 2003
    Location
    Chilliwack, BC
    My Bikes
    Trek 2000, Catrike, Gitane tandem, no-name mountain bike
    Posts
    224
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)

    Drafting

    A couple years ago on this forum I asked the following question about drafting and now I am having some doubts about the answers I got.

    When two riders (or more) are drafting each other, it is acknowleged that those who draft behind a front rider have cycling advantage. We all know that.
    However, how does drafting affect the rider in front?

    The answer I got was that the rider in front can also go faster if there are others drafting behind him/her.

    Yet I hear expressions like, "I was in front pulling the others." It was as though the person in front was not getting any benefit from those behind. He/she did all the work.

    I realize that in a paceline each rider should take his/her turn at the front (that's not the issue here). But if a rider stays in front, does he/she get any advantage over riding solo? Why?
    "Weary with toil, I haste me to my bed,
    The dear repose for limbs with travel tired;
    But then begins a journey in my head,
    To work my mind, when body's work's expired"
    -- Shakespeare Sonnet XXVII
    Click here to visit Motorera.com

  2. #2
    Tom (ex)Builder twahl's Avatar
    Join Date
    Jul 2004
    Location
    Manassas, VA
    My Bikes
    Specialized Allez
    Posts
    2,814
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I tend to be out front riding with the family most of the time, and have a couple of friends that I ride with, usually in front with them as well.

    My impression is that I do benefit a little from having a rider tucked behind me. On a larger scale, with cars, both the front and rear benefit, but the speeds and the size of the hole being made through the air are larger. However it would make sense that there is some benefit for cyclists as well. A lot of the drag comes from the tail end of the object moving through the air, so if that drag is assigned to the rear rider, that's taking a little bit of the load away from the front rider.

    It's not as great a benefit to the front guy as the rear guy, but it's my belief that there is some benefit to the front guy.
    Tom

    "It hurts so good..."

  3. #3
    Tom (ex)Builder twahl's Avatar
    Join Date
    Jul 2004
    Location
    Manassas, VA
    My Bikes
    Specialized Allez
    Posts
    2,814
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    A slightly more direct answer as to why...there is a lot of turbulance created when an object moves through the air. A good portion of that happens when the air closes back in around the rear of the object, so by having a rear drafting partner, that turbulance is created around that person rather than the lead, so that portion of the total drag is applied to them. They get a greater benefit from not having to create the hole in front, so they don't realize it...look at it as a total drag of 100%. Maybe 70% comes from the front, 20% from the sides, and 10% from the air closing around. So they get probably 50 of 70, keep the 20 from the sides, and get the 10. Sum total is they gain 20%, and the front guy gains the 10, making them 30% more efficient overall. Just rough numbers mind you, I'd have to get a slide rule to be accurate!
    Tom

    "It hurts so good..."

  4. #4
    Senior Member
    Join Date
    Dec 2005
    Location
    Auld Blighty
    My Bikes
    Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
    Posts
    2,187
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    There is no advantage to the person in front. The gap to the drafting rider is too large and the speed is too small for the viscosity of air. The stoker on a tandem is another matter...

  5. #5
    Senior Member DanielS's Avatar
    Join Date
    Sep 2006
    Location
    Adelaide, Australia
    My Bikes
    Surly Pacer, Hillbrick Pista, Avanti Sprint, Commencal Combi Deluxe
    Posts
    458
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    There is not benefit in being the person in front. The stuff about turbulence above is well.... a little misinformed to say the least.

    Aerodynamic drag is either created by friction between the air and your body and also by a pressure difference that exists between the front of the rider and the back of the rider.

    The pressure difference exists because there is a "wake" region behind you where the the air is swirling around and creating a low pressure zone. There is no way that this wake region would be big enough that the rider behind you is taking it up, and somehow reducing the drag.

  6. #6
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Cadillac
    A couple years ago on this forum I asked the following question about drafting and now I am having some doubts about the answers I got.

    When two riders (or more) are drafting each other, it is acknowleged that those who draft behind a front rider have cycling advantage. We all know that.
    However, how does drafting affect the rider in front?

    The answer I got was that the rider in front can also go faster if there are others drafting behind him/her.

    Yet I hear expressions like, "I was in front pulling the others." It was as though the person in front was not getting any benefit from those behind. He/she did all the work.

    I realize that in a paceline each rider should take his/her turn at the front (that's not the issue here). But if a rider stays in front, does he/she get any advantage over riding solo? Why?

    Air is a fluid just like water. Just as a displacement boat hull will have a higher maximum hull speed the longer it is, so will a row of drafting bikes. There is a slight benefit to the lead rider, some will notice it, and others will not It depends on the total environment too, the same rider may notice it once and not another time. The lead rider is still doing most of the work but there is a little less work. This leads to a lot of confusion, what the rider feels is not the indicator of how well it works. Many riders assume if they can, or can't feel a change, it is or is not, happening. Wrong! We all feel things differently, and things happen that we can't feel.

    A good place to read and learn about this is boat displacement hull design and theory. Forget about what people say they feel.

    Do you draft d/frame bikes with your trike? Do they draft your trike?
    [SIGPIC][/SIGPIC]

  7. #7
    Senior Member Richard Cranium's Avatar
    Join Date
    Jun 2002
    Location
    Deep in the Shawnee Forest
    My Bikes
    LeMond - Gunnar
    Posts
    2,786
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    But if a rider stays in front, does he/she get any advantage over riding solo? Why?
    It depends on what you mean by advantage. You can forget, the theoretical crap already posted regarding air pressure and drag. The nature and proximity of any trailing riders' "drag or pressure effects" is neither constant nor measurable. [a Mac truck at a constant 50kph might help]

    So no, there is no "energy" advantage over having no one draft. Drafting a cyclist is dynamic process, aerodynamic theory cannot be applied as simply as one might think.

  8. #8
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Richard Cranium
    It depends on what you mean by advantage. You can forget, the theoretical crap already posted regarding air pressure and drag. The nature and proximity of any trailing riders' "drag or pressure effects" is neither constant nor measurable. [a Mac truck at a constant 50kph might help]

    So no, there is no "energy" advantage over having no one draft. Drafting a cyclist is dynamic process, aerodynamic theory cannot be applied as simply as one might think.
    The result is ever changing when riding as opposed to a wind tunnel. That means it's different not gone.
    The amount is small, that means it is small, not gone.
    Of course there is an energy advantage.

    Not constant and not easily measurable is not gone. It does not even mean it is not usefull.
    [SIGPIC][/SIGPIC]

  9. #9
    Senior Member howsteepisit's Avatar
    Join Date
    Oct 2005
    Location
    Eugene, OR
    My Bikes
    Mecian
    Posts
    2,934
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    This brings to mind one of my pet peeves, This topic, like many is subject to many opinions. But there never seems to be any quantifiable studies, testing or even calculations to back up the opinions. Still interesting, but I would love to see real data back up the endless theories and opinions that dominate cycling.
    Recycle, Reclaim, Reuse and Repair
    The 4 Rs to save the planet

    "Toes"

  10. #10
    Professional Fuss-Budget Bacciagalupe's Avatar
    Join Date
    Aug 2005
    Posts
    6,362
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Cadillac
    When two riders (or more) are drafting each other, it is acknowleged that those who draft behind a front rider have cycling advantage.... But if a rider stays in front, does he/she get any advantage over riding solo? Why?
    My understanding is that the rider in front does not gain any real / noticeable mechanical advantage when they are pulling. There may be a small boost, but iirc it's too small to reliably determine via ordinary subjective means (e.g. perceived effort).

    The overall advantage of the paceline is that the riders who are drafting are expending less energy to ride at a higher speed. Since in theory you are all taking turns up front, the individuals can ride a little harder when you're pulling, and then rest while drafting.

    If you have one person pulling the entire time, then that individual gains none of the mechanical advantages to riding in a paceline.

    However, there are numerous psychological issues involved as well. Some people might get a mental boost by pulling the whole time, either because they're showing off, or enjoy "lending a hand," or just ride at that pace normally anyway. Conversely, if only one person pulls, that rider may dislike the idea that someone is benefitting from their effort without contributing. Mental conditions like these can easily alter one's perceptions and subjective experiences of taking a long pull at the front.

    Does that make sense?

  11. #11
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by howsteepisit
    This brings to mind one of my pet peeves, This topic, like many is subject to many opinions. But there never seems to be any quantifiable studies, testing or even calculations to back up the opinions. Still interesting, but I would love to see real data back up the endless theories and opinions that dominate cycling.
    Try and google "Laws of Physics" "fluid dynamics" "aerodynamics" etc. Go to the library. Get some college books, it's all over the place. It's not just a bicycling thing. If you really care you can find more than you need. Boats, planes, cars, etc. all use this.
    [SIGPIC][/SIGPIC]

  12. #12
    Seņor Member USAZorro's Avatar
    Join Date
    Oct 2004
    Location
    Carlisle, PA
    My Bikes
    1954 Hetchins M.O., 1959 Viking Severn Valley, 1970 Raleigh Pro, 1972 Fuji "The Finest", 1974 Raleigh Superbe&Comp, 1976 Raleigh Team Pro, 1994 Trek 830 MTB, 2000 Bob Jackson Arrowhead, Unicycle
    Posts
    13,034
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    The advantage that the lead rider gets is better training.
    The search for inner peace continues...

  13. #13
    Tom (ex)Builder twahl's Avatar
    Join Date
    Jul 2004
    Location
    Manassas, VA
    My Bikes
    Specialized Allez
    Posts
    2,814
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by DanielS
    There is not benefit in being the person in front. The stuff about turbulence above is well.... a little misinformed to say the least.

    Aerodynamic drag is either created by friction between the air and your body and also by a pressure difference that exists between the front of the rider and the back of the rider.

    The pressure difference exists because there is a "wake" region behind you where the the air is swirling around and creating a low pressure zone. There is no way that this wake region would be big enough that the rider behind you is taking it up, and somehow reducing the drag.
    Yeah I apologize. Pardon my background in aircraft and rocketry.

    I don't know about you, but I'm a fairly large object, and moving through the air at 20 MPH or greater, the "wake region" is both large enough and far enough behind me that it does make a difference if that load is taken by someone else.

    Oh, and studies have been done. Tell these people that they are misinformed. And those pesky scientists at NASA Langley that have helped several NASCAR teams.

    Another thought on the subject: "...if you have ever watched a Dolphin effortlessly ride the pressure wave created by the bow of a boat as it slices through the water you can see how this might work for the rider at the front of the pelton. The group is large enough that some of the air hitting them is pushed back in front of them and tends to give the front riders a bit of a push. Not so much drafting as reverse drafting "

    Have you ever watched a bicycle race?
    Tom

    "It hurts so good..."

  14. #14
    I eat carbide. Psimet2001's Avatar
    Join Date
    Jan 2006
    Location
    Elgin, IL
    My Bikes
    Lots. Current sponsors - Giant and Specialized
    Posts
    19,301
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    When people talk about laminar flow and boundary layers...it gets me turbulent.

  15. #15
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by twahl
    Yeah I apologize. Pardon my background in aircraft and rocketry.

    I don't know about you, but I'm a fairly large object, and moving through the air at 20 MPH or greater, the "wake region" is both large enough and far enough behind me that it does make a difference if that load is taken by someone else.

    Oh, and studies have been done. Tell these people that they are misinformed. And those pesky scientists at NASA Langley that have helped several NASCAR teams.

    Another thought on the subject: "...if you have ever watched a Dolphin effortlessly ride the pressure wave created by the bow of a boat as it slices through the water you can see how this might work for the rider at the front of the pelton. The group is large enough that some of the air hitting them is pushed back in front of them and tends to give the front riders a bit of a push. Not so much drafting as reverse drafting "

    Have you ever watched a bicycle race?

    nice
    [SIGPIC][/SIGPIC]

  16. #16
    Senior Member
    Join Date
    Dec 2005
    Location
    Auld Blighty
    My Bikes
    Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
    Posts
    2,187
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by twahl
    Oh, and studies have been done. Tell these people that they are misinformed. And those pesky scientists at NASA Langley that have helped several NASCAR teams.
    Those people are misinformed. At sub-40 mph speeds, there is no advantage. They even think that mildly ovalised tubes reduce wind resistance Run the calcs yourself with the correct Reynolds number.

    NASCAR is a different matter, not many cyclists can ride at over 150 mph.

  17. #17
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by LWaB
    Those people are misinformed. At sub-40 mph speeds, there is no advantage. They even think that mildly ovalised tubes reduce wind resistance Run the calcs yourself with the correct Reynolds number.

    NASCAR is a different matter, not many cyclists can ride at over 150 mph.
    Why do the laws of physics stop working below 40 mph? Did they get revised?
    [SIGPIC][/SIGPIC]

  18. #18
    Senior Member
    Join Date
    Dec 2005
    Location
    Auld Blighty
    My Bikes
    Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
    Posts
    2,187
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Do the calculations, get the right answer. Consider both viscosity and speed. Let me know what you come up with...

  19. #19
    Tom (ex)Builder twahl's Avatar
    Join Date
    Jul 2004
    Location
    Manassas, VA
    My Bikes
    Specialized Allez
    Posts
    2,814
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Use your brain. If the closing vortex is far enough behind me that a rider behind me can benefit from the draft, than it is far enough behind me that the rider behind me is moving that closing vortex to the rear of him rather than to the rear of me. He is taking that load away from me, it doesn't exist for me. I do not feel that drag. It is a small piece of the overall drag pie, but it is a piece of it, and it's no longer on my plate if there's a rider drafting behind me.

    All that aside, since we're obviously not going to agree here, in a drafting situation, the rider in the front should not always be in the front, even if they are a a stronger rider, they should still get a chance to get a break, so the measurable benefit is in a rotating pace line, even if it's not a race situation where a rider may only spend 30 seconds or a minute at a time in front.
    Tom

    "It hurts so good..."

  20. #20
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by LWaB
    Do the calculations, get the right answer. Consider both viscosity and speed. Let me know what you come up with...

    You first, prove that it does not happen. Let me know what you come up with.
    [SIGPIC][/SIGPIC]

  21. #21
    Has opinion, will express
    Join Date
    Jun 2003
    Posts
    12,994
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I am always fascinated how the TdF peloton can move along so rapidly (45-50km/h) with sometimes only one or two riders taking the pulls, and how that peloton can make up so much time on a breakaway duo working together. Maybe this explains it! A ship (the peloton) 150 metres long will move faster that a 3-metre non-planing dinghy (the breakaway duo). I suppose it's a matter of whether you can visualise a bunch of riders as constituting a solid mass

    The air displacement from a peloton is quite remarkable if you have the chance to stand alongside one as it speeds past.
    Dream. Dare. Do.

  22. #22
    Dog is my co-pilot 2manybikes's Avatar
    Join Date
    Jun 2003
    My Bikes
    2 many
    Posts
    13,783
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Rowan
    Maybe this explains it! A ship (the peloton) 150 metres long will move faster that a 3-metre non-planing dinghy (the breakaway duo). I suppose it's a matter of whether you can visualise a bunch of riders as constituting a solid mass
    [SIGPIC][/SIGPIC]

  23. #23
    Has opinion, will express
    Join Date
    Jun 2003
    Posts
    12,994
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    John Schubert is one of America's sagely cyclists and cycling author. He possibly has forgotten more than most people who contribute to BFs know. I was browsing through one of his books, "Richards' Cycling for Fitness", published by Ballentine Books. Richard Ballentine is an English author who ranks with Schubert in knowledge. Now I've established the credentials, I'll quote the following:

    "Drafting saves about one-third of the following rider's energy. What's less well known is that it also saves a tiny amount -- say, five percent -- of the lead rider's energy, the result of the way the air closes in behind".

    I am happy enough with evidence for the prosecution.
    Dream. Dare. Do.

  24. #24
    Senior Member
    Join Date
    Dec 2005
    Location
    Auld Blighty
    My Bikes
    Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
    Posts
    2,187
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 2manybikes
    You first, prove that it does not happen. Let me know what you come up with.
    Sorry about the delay. I couldn't find my calcs from nearly 20 years ago and had to redo them.

    I'll show you mine if you show me yours After all, I asked first

  25. #25
    Elite Fred mollusk's Avatar
    Join Date
    Aug 2005
    Location
    Edge City
    My Bikes
    2009 Spooky (cracked frame), 2006 Curtlo, 2002 Lemond (current race bike) Zurich, 1987 Serotta Colorado, 1986 Cannondale for commuting, a 1984 Cannondale on loan to my son
    Posts
    10,632
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    There should be a small effect on the lead rider. The presence of the second rider changes the flow around the first, especially the flow behind the lead rider, and this should decreases the adverse pressure gradient acting on the boundary layer on the lead rider. This will delay the separation of the boundary layer on the lead rider and hence decrease his pressure drag. My "feel" is that the drag decrease on the first rider is pretty small, though . I have done any modeling or calcs, but I wouldn't be surprised if it the effect is as large as a few percent of the total drag.
    I'm the world's forgotten boy. The one who's searchin', searchin' to destroy.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •