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Does the location of the weight on a bike matter?
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 2013-06-14 12:56 PM |
Member 143   Plano, TX |  Subject: Does the location of the weight on a bike matter?Another question for you numbers guys/gals out there. Does the location of the weight (lets assume between total body, frame of bike, and wheels are the 3 things I'm evaluating) matter? I.e. if one set of wheels weighs 1 lb more than another set (think flos versus zipps), but I personally have a pound I could lose, does that make them equivalent? Or is the weight of the wheels more important than that of the rider making those lbs being considered unequal? (forget the fact that if you lose a pound of body weight it would apply to both sets of wheels...just trying to understand the concept of all of this). Or if deciding between a frame that weighs 16lbs versus 15 lbs but could have a 1lb lighter set of wheels with the 16lb frame, is that equivalent? Hopefully you get the idea... Hopefully this question makes some sense....if it doesn't I'm sure someone will let me know or maybe no one will respond anyway!  |
| 2013-06-14 2:15 PM in reply to: jte463 |
Champion 10668  Tacoma, Washington | Subject: RE: Does the location of the weight on a bike matter? Rotating weight is much more impactful than stationary weight, and the farther away from its axis it lies makes it doubly so (two wheels could weigh the same, but the one with the weight at the rim/tire vs the hub would fare worse for energy cost). For that reason, lightweight rims, tires and tubes, and pedals, can make a considerable difference, as long as you're not increasing aerodynamic drag to do so. Once you've got THOSE things covered, however, it's a wash whether the weight comes from the body or the bike. |
| 2013-06-14 2:24 PM in reply to: jte463 |
Champion 9407 Montague Gold Mines, Nova Scotia | Subject: RE: Does the location of the weight on a bike matter? |
| 2013-06-14 2:33 PM in reply to: briderdt |
Extreme Veteran 410 Northern Illinois | Subject: RE: Does the location of the weight on a bike matter? Originally posted by briderdt Rotating weight is much more impactful than stationary weight, and the farther away from its axis it lies makes it doubly so (two wheels could weigh the same, but the one with the weight at the rim/tire vs the hub would fare worse for energy cost). For that reason, lightweight rims, tires and tubes, and pedals, can make a considerable difference, as long as you're not increasing aerodynamic drag to do so. Once you've got THOSE things covered, however, it's a wash whether the weight comes from the body or the bike. +1 We could dive into some physics if you want... |
| 2013-06-14 2:51 PM in reply to: runninirish |
Expert 1168 Vancouver (not Canada) Washington (not D.C.) | Subject: RE: Does the location of the weight on a bike matter? Agree with your +1 The area where moving weight really matters is acceleration. So if you are doing a flat course and holding steady speed, once you are up to speed, it really doesn't matter or if you are theoretically able to climb a hill at constant speed then it doesn't matter either. However, in the real world there are courses whether rolling or crowded that require acceleration. Also, few of us can climb hills, especially those steep ones in which each pedal stroke surges the bike, without acceleration playing a substantial role. So, I think lighter rims, tires and pedals for riders like me feel faster. |
| 2013-06-14 3:01 PM in reply to: runninirish |
Champion 9407 Montague Gold Mines, Nova Scotia | Subject: RE: Does the location of the weight on a bike matter? Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane |
| 2013-06-14 3:39 PM in reply to: gsmacleod |
| Member 143 Plano, TX | Subject: RE: Does the location of the weight on a bike matter? Thank you all for the responses....always very interesting and I love learning about this stuff even though the reality is that I have much work I can do on the engine ...so great to have so many willing and knowledgable people to contribute! |
| 2013-06-14 3:51 PM in reply to: gsmacleod |
| Subject: RE: Does the location of the weight on a bike matter? Originally posted by gsmacleod Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane Hard to argue with Shane here. It's important to remember also that whatever advantages you gain in being able to accelerate lighter wheels, they also deccelerate with less resistance as well. If you're riding a course where you're constantly on your brakes to get through turns and re-accelerating, then lighter wheels (assuming aerodynamics are the same) will work in your favor because deccleration won't matter as much (since you're using your brakes anyway). Most tri/TT courses aren't like that though. |
| 2013-06-14 4:33 PM in reply to: gsmacleod |
| Master 10208 Northern IL | Subject: RE: Does the location of the weight on a bike matter? Originally posted by gsmacleod Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane And do note the use of "appreciable" in said posting. |
| 2013-06-14 10:15 PM in reply to: brigby1 |
Veteran 186 | Subject: RE: Does the location of the weight on a bike matter? Originally posted by brigby1 Originally posted by gsmacleod Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane And do note the use of "appreciable" in said posting. http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_... Total mass matters, location does not matter appreciably. -J |
| 2013-06-15 1:26 AM in reply to: karlaj |
| Master 5557 , California | Subject: RE: Does the location of the weight on a bike matter? Originally posted by karlaj Originally posted by brigby1 http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_... Total mass matters, location does not matter appreciably. -J Originally posted by gsmacleod Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane And do note the use of "appreciable" in said posting. Read that with some careful attention to his testing at 25-30mph. It's no surprise that he found the increase in mass to be insignificant compared to his drag at that speed. |
| 2013-06-15 5:13 AM in reply to: spudone |
Elite 7783 PEI, Canada | Subject: RE: Does the location of the weight on a bike matter? Originally posted by spudone Originally posted by karlaj Originally posted by brigby1 http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_... Total mass matters, location does not matter appreciably. -J Originally posted by gsmacleod Originally posted by runninirish +1 We could dive into some physics if you want... By all means - and you will see that it supports that what I posted above. Shane And do note the use of "appreciable" in said posting. Read that with some careful attention to his testing at 25-30mph. It's no surprise that he found the increase in mass to be insignificant compared to his drag at that speed. I've got nothing to add except that the Facebook discussion after the article between Tom, Tim and Jack was entertaining. |
| 2013-06-15 1:30 PM in reply to: gsmacleod |
Extreme Veteran 410 Northern Illinois | Subject: RE: Does the location of the weight on a bike matter? Originally posted by gsmacleod For tri/TT, no appreciable difference in where the weight is reduced. Shane Fair enough... Hard to argue with "appreciable"...you are correct. More rotating mass away from axis of rotation will give you a larger moment of inertia. Basically, making it more difficult to accelerate. Or perhaps a better way to say it, requires more force/torque to make the same acceleration. How much? Hardly not enough to notice. As someone else pointed out, it also works the other way. That extra force you applied to accelerate is will come back to help you (conservation of energy) and will help keep the bike moving that speed due to increased inertia (again, hardly enough to notice). You will also be losing some of this energy to friction from the ground (which you would lose anyway). Rotating mass vs mass should make NO difference what-so-ever when considering climbing. |
| 2013-06-16 12:27 AM in reply to: jte463 |
Champion 10668 Tacoma, Washington | Subject: RE: Does the location of the weight on a bike matter? Let's separate the physics of moment of inertia from the actual physical cost of the difference in that moment of inertia. Does it take more force to accelerate that rotating mass? Yes. Where does that force come from? Muscles. In an endurance race where you don't have the draft to recover without actually slowing down, once you dig into that well of higher muscle tension you don't recover from it. So even if it doesn't take more energy/force to keep that heavier object moving, you still don't recover from GETTING it moving. Also, the fact that it doesn't slow down as easily is really only relevant when you DO need to slow down, in which case you're needing to brake harder, again, costing you energy. You don't get it back as if it were some generator feeding back into your muscles. I will concede gladly that aerodynamics trumps weight. But for equal aerodynamic drag, the total energy cost of the lighter weight (lower moment of inertia) rotating object is lower. You have to decide whether that "lower" is enough to justify the expense of the lighter weight. |
| 2013-06-16 6:35 AM in reply to: jte463 |
| 287 | Subject: RE: Does the location of the weight on a bike matter? One item that has not been "touched"- too much weight distributed on the front end of the bicycle will effect handling. I don't believe this thread is about this issue and will thus end my post. |
| 2013-06-17 8:44 AM in reply to: runninirish |
Champion 9407 Montague Gold Mines, Nova Scotia | Subject: RE: Does the location of the weight on a bike matter? Originally posted by runninirish Hard to argue with "appreciable"...you are correct. More rotating mass away from axis of rotation will give you a larger moment of inertia. Basically, making it more difficult to accelerate. Or perhaps a better way to say it, requires more force/torque to make the same acceleration. How much? Hardly not enough to notice. Exactly - this is the point that is missed that while it does take more energy to spin up a heavier wheel than a lighter wheel, even if we take this example to absurd lengths, say a 1.0kg wheel versus a 2.0kg wheel, the actual differences are minute compared to the energies involved in moving the bicycle forward. As someone else pointed out, it also works the other way. That extra force you applied to accelerate is will come back to help you (conservation of energy) and will help keep the bike moving that speed due to increased inertia (again, hardly enough to notice). You will also be losing some of this energy to friction from the ground (which you would lose anyway). Also an important point that is often missed; the energy used to spin the wheel up to speed also needs to be dissipated when slowing; obviously when braking this will be through friction with the brakes but if slowing due to a hill, the rider with heavier wheels is actually carrying slightly more energy into the base of the climb (both linear and rotational kinetic energy). The bottom line is that within the scope of modern cycling components, weight savings are so small as to be inconsequential in almost all triathlon applications. All else being equal, go with the lighter components if you can afford them but it is rare that all else is equal. Instead of worrying about weight, worry about aerodynamics and forget about the weight of the bike and its components completely. Shane |
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