Why does one bike climb better than another?
#26
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Assuming that all else is equal, it's not necessarily the total weights of each wheelset that matters. What counts most is the locations of the weight. If the 700c wheels have lighter hubs, but heavier rims+tires, than the 650b bike, all of those little accelerations will take more force to accomplish. If the 700c rims+tires weigh exactly the same as the 650b, but have a larger diameter, those little accelerations will take more force. If the 700c rims+tires weigh more than the 650b, and they have a larger diameter, they'll need even more force.
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There are about a hundred different factors as to why one bike would ride better than another for any stretch of ground. Pick one.
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Don’t be ridiculous. Everyone knows red bikes are faster.
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#31
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Assuming that all else is equal, it's not necessarily the total weights of each wheelset that matters. What counts most is the locations of the weight. If the 700c wheels have lighter hubs, but heavier rims+tires, than the 650b bike, all of those little accelerations will take more force to accomplish. If the 700c rims+tires weigh exactly the same as the 650b, but have a larger diameter, those little accelerations will take more force. If the 700c rims+tires weigh more than the 650b, and they have a larger diameter, they'll need even more force.
There may be some efficiency difference in the biomechanics, like how quickly it tires out the muscles to accelerate slowly on each pedal stroke, or perhaps differences in the flexing of the tire (and frictional losses from that, if the tire flexes more during more of the downstroke, like especially if the rider is out of the saddle), but in terms of rotation of the wheel itself, there is probably relatively little energy lost regardless of wheel weight or weight distribution.
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In this case, I expect it’s the tires. WTB Horizon is fairly fast rolling for its size and probably some fair number of watts less work to move than the Kenda K-1024 which looks to be a hefty touring tire. It’s the sort of thing that really gets noticed when you are climbing and have to also deal with the work against gravity.
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Has the OP stated what tires he is using? the post above indicates WTB Horizon vs Kenda K-1024. If that is the case, that alone would make a pretty big difference.
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Trying to answer the OPs question without knowing what tires he is running is like trying to figure out why a house is cold without checking to see if the windows are all open.
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In this case, I expect it’s the tires. WTB Horizon is fairly fast rolling for its size and probably some fair number of watts less work to move than the Kenda K-1024 which looks to be a hefty touring tire. It’s the sort of thing that really gets noticed when you are climbing and have to also deal with the work against gravity.
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Perhaps, but the 47c Horizons which came on my Doppler were 697g each (actual)! That’s heavy AF! Rode like the proverbial Cadillac, but was slow. I replaced them with Herse Switchback Hill 48c standards, claimed at 441g, dropping over a pound in rubber and bringing the ride alive. It’s still a heavy bike, though, so I dunno if it made any meaningful difference to climbing speed, but I find the bike a blast to ride, so I don’t care!
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Heavier rims/tires mean more inertia and it does require more force/torque to accelerate them, but that energy is not lost - it's stored in the wheel and assists the rider in between strokes.
There may be some efficiency difference in the biomechanics, like how quickly it tires out the muscles to accelerate slowly on each pedal stroke, or perhaps differences in the flexing of the tire (and frictional losses from that, if the tire flexes more during more of the downstroke, like especially if the rider is out of the saddle), but in terms of rotation of the wheel itself, there is probably relatively little energy lost regardless of wheel weight or weight distribution.
There may be some efficiency difference in the biomechanics, like how quickly it tires out the muscles to accelerate slowly on each pedal stroke, or perhaps differences in the flexing of the tire (and frictional losses from that, if the tire flexes more during more of the downstroke, like especially if the rider is out of the saddle), but in terms of rotation of the wheel itself, there is probably relatively little energy lost regardless of wheel weight or weight distribution.
Yes, there is some inertial energy/momentum which keep a bike in motion... (and let's just say, in this case, roll resist, 'drag' and overall mass is the same for flat & uphill)
so, once gravity is added in, things change.... quickly demonstrated - given an equal velocity, stopped pedaling will carry you further (momentum/inertia) on the flat as opposed to any level of uphill.
so, for any degree of upslope, you will have to add more energy (pedaling) to cover an equal distance.
Depending on the slope/gravity, that inertia will dissipate quite rapidly, so the 'work' you will need to do will be greatly increased.
'Work' over time is 'Power'...
Graviity creates 'Acceleration' - base jump w/o a chute and you will experience acceleration until you hit terminal velocity OR stop...
riding uphill, is the same in reverse, except is deceleration ...
every pedal stroke requires acceleration to counter the deceleration.
I'm not gonna go into the limitations of our human pedaling power, cadence, gear selection, mass, rolling resistance - we all know the real world of that....
so things we can improve/change for climbing...
POWER (tough, not a money thing, except what is spent to create more of it... LOL !!!)
overall mass of the object being accelerated
rolling resistance (tire, pressure AND road/riding surface)
rotating mass (which will add acceleration requirements)
the last three elements are what the OP is asking... most often a money thing...
so heavier rims/tires will require more force in acceleration.
Thx
Yuri
Last edited by cyclezen; 09-13-21 at 09:13 AM.
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I dunno anything about the Kenda at issue, only that a 697g tire is very heavy…to the point that I’d be surprised if the Kenda 700x40c were significantly heavier than that.
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Would be interesting to try and put the 650b wheelset onto the other bike and see how it feels then.
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Well we are talking about climbing, so I guess that would depend on how steep, how fast, and how far we’re measuring. In any case, a 650b tire weighing nearly 700g is not constructed for low rolling resistance; it’s probably a coarse, stiff, low thread count casing with a lot of rubber making it it even less supple.
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Well we are talking about climbing, so I guess that would depend on how steep, how fast, and how far we’re measuring. In any case, a 650b tire weighing nearly 700g is not constructed for low rolling resistance; it’s probably a coarse, stiff, low thread count casing with a lot of rubber making it it even less supple.
WTB Horizon is 60 or 120 tpi, depending on the model. Kenda in question is 30tpi.
There are many reasons why a tire can be heavy, some correlate to rolling resistance, others do not. The WTB in question costs ~4x what the Kenda does. It is reasonable to assume that in addition to the higher tpi casing, it may also use higher quality (more supple) casing material. Also, it matters a lot WHERE the extra casing material and stiffness is. It matters less in the middle of the tread than in the sidewalls.
I am curious about the nearly 700g weight you are claiming. BikeRumor, Gravel Cyclist, Riding Gravel all show actual weights around 510-520g a tire.
Last edited by Kapusta; 09-13-21 at 11:47 AM.
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OK, let's put this to rest quickly...
Yes, there is some inertial energy/momentum which keep a bike in motion... (and let's just say, in this case, roll resist, 'drag' and overall mass is the same for flat & uphill)
so, once gravity is added in, things change.... quickly demonstrated - given an equal velocity, stopped pedaling will carry you further (momentum/inertia) on the flat as opposed to any level of uphill.
so, for any degree of upslope, you will have to add more energy (pedaling) to cover an equal distance.
Depending on the slope/gravity, that inertia will dissipate quite rapidly, so the 'work' you will need to do will be greatly increased.
'Work' over time is 'Power'...
Graviity creates 'Acceleration' - base jump w/o a chute and you will experience acceleration until you hit terminal velocity OR stop...
riding uphill, is the same in reverse, except is deceleration ...
every pedal stroke requires acceleration to counter the deceleration.
I'm not gonna go into the limitations of our human pedaling power, cadence, gear selection, mass, rolling resistance - we all know the real world of that....
so things we can improve/change for climbing...
POWER (tough, not a money thing, except what is spent to create more of it... LOL !!!)
overall mass of the object being accelerated
rolling resistance (tire, pressure AND road/riding surface)
rotating mass (which will add acceleration requirements)
the last three elements are what the OP is asking... most often a money thing...
so heavier rims/tires will require more force in acceleration.
Thx
Yuri
Yes, there is some inertial energy/momentum which keep a bike in motion... (and let's just say, in this case, roll resist, 'drag' and overall mass is the same for flat & uphill)
so, once gravity is added in, things change.... quickly demonstrated - given an equal velocity, stopped pedaling will carry you further (momentum/inertia) on the flat as opposed to any level of uphill.
so, for any degree of upslope, you will have to add more energy (pedaling) to cover an equal distance.
Depending on the slope/gravity, that inertia will dissipate quite rapidly, so the 'work' you will need to do will be greatly increased.
'Work' over time is 'Power'...
Graviity creates 'Acceleration' - base jump w/o a chute and you will experience acceleration until you hit terminal velocity OR stop...
riding uphill, is the same in reverse, except is deceleration ...
every pedal stroke requires acceleration to counter the deceleration.
I'm not gonna go into the limitations of our human pedaling power, cadence, gear selection, mass, rolling resistance - we all know the real world of that....
so things we can improve/change for climbing...
POWER (tough, not a money thing, except what is spent to create more of it... LOL !!!)
overall mass of the object being accelerated
rolling resistance (tire, pressure AND road/riding surface)
rotating mass (which will add acceleration requirements)
the last three elements are what the OP is asking... most often a money thing...
so heavier rims/tires will require more force in acceleration.
Thx
Yuri
If you are riding at a constant speed up the hill then the inertial energy stored in the wheels is also a constant (since they are spinning at a constant speed). So it's all really just about the total mass and gravity acting on it vs the pedal force. Lighter wheels help climbing simply because they are lighter, regardless of their rotational inertia.
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You are making a lot of assumptions, here, based solely on weight.
WTB Horizon is 60 or 120 tpi, depending on the model. Kenda in question is 30tpi.
There are many reasons why a tire can be heavy, some correlate to rolling resistance, others do not. The WTB in question costs ~4x what the Kenda does. It is reasonable to assume that in addition to the higher tpi casing, it may also use higher quality (more supple) casing material. Also, it matters a lot WHERE the extra casing material and stiffness is. It matters less in the middle of the tread than in the sidewalls.
I am curious about the nearly 700g weight you are claiming. BikeRumor, Gravel Cyclist, Riding Gravel all show actual weights around 510-520g a tire.
WTB Horizon is 60 or 120 tpi, depending on the model. Kenda in question is 30tpi.
There are many reasons why a tire can be heavy, some correlate to rolling resistance, others do not. The WTB in question costs ~4x what the Kenda does. It is reasonable to assume that in addition to the higher tpi casing, it may also use higher quality (more supple) casing material. Also, it matters a lot WHERE the extra casing material and stiffness is. It matters less in the middle of the tread than in the sidewalls.
I am curious about the nearly 700g weight you are claiming. BikeRumor, Gravel Cyclist, Riding Gravel all show actual weights around 510-520g a tire.
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yeah, I’m making assumptions precisely for the reason that it seems to be a special OE Horizon that’s not sold retail, based on the weight. They’re hanging in my garage, wire bead, and very rigid sidewalls. I don’t think this OE Horizon has much in common with commercial options, but I don’t anything about it other than what I can observe; casing, compound, and stuff like that are unknowns, suggested only by weight and texture.
Considering the OP has not even bothered to say what tires he has, I think we have already invested way too much time in this corner of the discussion.
Last edited by Kapusta; 09-14-21 at 06:56 AM.
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The fact that some of the mass is rotating is not even worth talking about in respect of climbing performance. Only the total mass makes any real difference on a slope, governed by trivial Newtonian physics. Whether or not it is rotating is almost irrelevant in this respect.
If you are riding at a constant speed up the hill then the inertial energy stored in the wheels is also a constant (since they are spinning at a constant speed). So it's all really just about the total mass and gravity acting on it vs the pedal force. Lighter wheels help climbing simply because they are lighter, regardless of their rotational inertia.
If you are riding at a constant speed up the hill then the inertial energy stored in the wheels is also a constant (since they are spinning at a constant speed). So it's all really just about the total mass and gravity acting on it vs the pedal force. Lighter wheels help climbing simply because they are lighter, regardless of their rotational inertia.
why ? By Definition 'climbing' is a change in vector, hence 'Acceleration'
Mind Experiment (which could be done in 'reality).
So, maintaining same air and rolling resistance, same equipment/rider, you ride to a set velocity (speed) , on 'flat', stop pedaling, you will coast a certain time/distance...
same air and rolling resistance, same equipment/rider, you go on an up-slope and stop pedaling at the same velocity, you will coast a shorter time/distance...
going upslope is 'acceleration' - the inertial energy is dissipated/used faster, over a shorter time, which also determines distance... Gravitational acceleration.
The pull (acceleration) of gravity is a 'Constant' during all this, but when you 'climb' you are changing the 'vector' and now needing to overcome the 'acceleration of gravity'.
an example of calculation of this - lifting a 35kg object 1/2 meter... I'm lazy and the calculations are all done here:
How much work does it take to lift a 35 kg weight 1/2 m ?
I expect measurement or calculation of inertial stored energy will be spectacularly well below what is needed to climb 1 meter of road elevation.
rotational mass... is then also affected by gravity, - "the rotational inertia of an object depends on its mass. It also depends on the distribution of that mass relative to the axis of rotation." more on this here: What is rotational inertia?
Anyway, differences in rotating masses are also involved in the gravitational effect.
Th
Yuri
Last edited by cyclezen; 09-13-21 at 10:32 PM.
#48
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Yes, Inertial energy is determined by the velocity (and mass) of the entire mass, but not a 'constant'...
why ? By Definition 'climbing' is a change in vector, hence 'Acceleration'
Mind Experiment (which could be done in 'reality).
So, maintaining same air and rolling resistance, same equipment/rider, you ride to a set velocity (speed) , on 'flat', stop pedaling, you will coast a certain time/distance...
same air and rolling resistance, same equipment/rider, you go on an up-slope and stop pedaling at the same velocity, you will coast a shorter time/distance...
going upslope is 'acceleration' - the inertial energy is dissipated/used faster, over a shorter time, which also determines distance... Gravitational acceleration.
The pull (acceleration) of gravity is a 'Constant' during all this, but when you 'climb' you are changing the 'vector' and now needing to overcome the 'acceleration of gravity'.
an example of calculation of this - lifting a 35kg object 1/2 meter... I'm lazy and the calculations are all done here:
How much work does it take to lift a 35 kg weight 1/2 m ?
I expect measurement or calculation of inertial stored energy will be spectacularly well below what is needed to climb 1 meter of road elevation.
rotational mass... is then also affected by gravity, - "the rotational inertia of an object depends on its mass. It also depends on the distribution of that mass relative to the axis of rotation." more on this here: What is rotational inertia?
Anyway, differences in rotating masses are also involved in the gravitational effect.
Th
Yuri
why ? By Definition 'climbing' is a change in vector, hence 'Acceleration'
Mind Experiment (which could be done in 'reality).
So, maintaining same air and rolling resistance, same equipment/rider, you ride to a set velocity (speed) , on 'flat', stop pedaling, you will coast a certain time/distance...
same air and rolling resistance, same equipment/rider, you go on an up-slope and stop pedaling at the same velocity, you will coast a shorter time/distance...
going upslope is 'acceleration' - the inertial energy is dissipated/used faster, over a shorter time, which also determines distance... Gravitational acceleration.
The pull (acceleration) of gravity is a 'Constant' during all this, but when you 'climb' you are changing the 'vector' and now needing to overcome the 'acceleration of gravity'.
an example of calculation of this - lifting a 35kg object 1/2 meter... I'm lazy and the calculations are all done here:
How much work does it take to lift a 35 kg weight 1/2 m ?
I expect measurement or calculation of inertial stored energy will be spectacularly well below what is needed to climb 1 meter of road elevation.
rotational mass... is then also affected by gravity, - "the rotational inertia of an object depends on its mass. It also depends on the distribution of that mass relative to the axis of rotation." more on this here: What is rotational inertia?
Anyway, differences in rotating masses are also involved in the gravitational effect.
Th
Yuri
If you want to accurately predict how fast a rider will climb up a hill, all you need to know is:-
1. Total mass of the bike + rider
2. Gradient of the hill
3. Rolling resistance of the tyres
4. Aerodynamic drag
5. Rider power output
The distribution of wheel mass is, to all intents and purposes, irrelevant to the result. I can't think of a model that even includes it as a parameter in such a calculation. Can you?
I'm not questioning the concept of rotational inertia and being an engineering grad I'm well aware of how to calculate it, but it is simply not relevant to your climbing speed. Lightweight wheels with low inertia feel nimble, accelerate more easily etc, etc. but none of this matters (except their overall weight) when you are plodding at a steady 5 mph up a steep hill.
Last edited by PeteHski; 09-14-21 at 03:09 AM.
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This is incorrect. When you are climbing up a constant slope (eg. 10% gradient) the only thing that changes compared to riding on the flat is the direction (vector) in which the Force of Gravity is acting relative to the body and ground. Whether or not you accelerate depends entirely on how much force you apply in the opposite direction. When you are climbing at a constant speed your mass is not accelerating. It is moving through space at a constant speed, just in a different direction i.e. forward and upward.
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Graviity creates 'Acceleration' - base jump w/o a chute and you will experience acceleration until you hit terminal velocity OR stop...
riding uphill, is the same in reverse, except is deceleration ...
every pedal stroke requires acceleration to counter the deceleration.
riding uphill, is the same in reverse, except is deceleration ...
every pedal stroke requires acceleration to counter the deceleration.
This gets a lot easier to understand if you think in terms of applied forces rather than accelerations. Every pedal stroke requires a force. In physics/engineering we don't talk about applying accelerations do we? Accelerations are the result of net forces acting on bodies.