Heavy Bikes are better !
11-01-20, 11:01 AM
#226
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Thanks for this TC, now it makes sense. Putting myself in the two scenarios you mentioned, I could do the first for hours, but the second for only minutes. So obviously (to me) the latter does require more power than the former, not the same amount.
So cool, I would love to take this bike for a 'spin'!
So cool, I would love to take this bike for a 'spin'!
11-01-20, 11:09 AM
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11-01-20, 11:21 AM
#228
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I remember some years back weighting my old steel bike from 1970s that has newer aluminum components on it and 700x23 tires and it came to ~26 lbs or 12KG . I was actually surprised at the 'low weight', expected something along 30+ pounds. But trying out my sister's kids MTBs with those fat tires, even if they have quite light aluminum frame and weigh about the same as that road bike (and probably even less), the ride on them is slow, probably the biggest factor is the tire rolling resistance which is horrible. So a light vs heavy when talking about road bikes, the big factor is the tire size, which heavy bikes tend to have in 28+ to even 30+ range which makes them slower even on flats and really everywhere, given the riders are about equal abilities. But saying that is like carrying coal to New Castle LOL
Riding a bike in a sporting fashion (never mind racing) is all about the feeling of speed and the lighter the bike and less rolling and air resistance it has, the better it gets. Finding a sweet spot when balancing what a pound of a bike weight will cost you is the best guide to choosing how heavy your bike should be.
11-01-20, 01:05 PM
#229
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A couple of PHD's here. For me, not really, just a BS in Physics/Math combo. Though I like to think I was a cut above the usual Physics graduate.
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11-01-20, 01:11 PM
#230
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It occurred to me that some readers might be helped if we reviewed the concepts of force, work and power, because we will inevitably show why things are as we have described.
Think of a force as a push or tug. Something capable of being put on a force diagram and in some cases causing a body to accelerate. We experience lots of forces.
As cyclists, what we mostly care about in this topic is all that work we have to do against these forces. It’s critical to understand that useful work is a force acting through a distance. No distance, no work.
Power is the rate at which we do work. At any moment, our power will be the force we are pushing times the distance per unit time that we move (our speed).
This is the essential point to why the work we do against the big forces (air drag and gravity) and the resulting power calculation includes our ground speed as a part of the term: for our push against that force to require us to do work, it must act through a distance. The faster we do this, the more power we must supply.
Actually, despite all the noise in this thread, it really is pretty simple.
Otto
Think of a force as a push or tug. Something capable of being put on a force diagram and in some cases causing a body to accelerate. We experience lots of forces.
As cyclists, what we mostly care about in this topic is all that work we have to do against these forces. It’s critical to understand that useful work is a force acting through a distance. No distance, no work.
Power is the rate at which we do work. At any moment, our power will be the force we are pushing times the distance per unit time that we move (our speed).
This is the essential point to why the work we do against the big forces (air drag and gravity) and the resulting power calculation includes our ground speed as a part of the term: for our push against that force to require us to do work, it must act through a distance. The faster we do this, the more power we must supply.
Actually, despite all the noise in this thread, it really is pretty simple.
Otto
Also, on those charts, wind resistance would disappear, and rolling resistance would disappear as a discrete factor and be added to bearing and drivetrain friction, perhaps as a different number.
Last edited by rollagain; 11-01-20 at 01:23 PM.
11-01-20, 01:15 PM
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I do all of my training on my 'husky' fixie but use my 'anorexic' CF Trek on events. Works great for me.
11-01-20, 01:27 PM
#232
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This is misleading. The ground speed of a stationary trainer is zero, while force, work, and power are all in full play. The work still moves machinery against a resistive load; the machinery just stays in one place. So ground speed needs to be replaced by some other metric for those equations to be meaningful.
Also, on those charts, wind resistance would disappear, and rolling resistance would disappear as a discrete factor and be added to bearing and drivetrain friction, perhaps as a different number.
Also, on those charts, wind resistance would disappear, and rolling resistance would disappear as a discrete factor and be added to bearing and drivetrain friction, perhaps as a different number.
Edit. Personally I don’t like them and use them only as a last resort. 😊
Otto
Last edited by ofajen; 11-01-20 at 01:33 PM.
11-01-20, 01:31 PM
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This is misleading. The ground speed of a stationary trainer is zero, while force, work, and power are all in full play. The work still moves machinery against a resistive load; the machinery just stays in one place. So ground speed needs to be replaced by some other metric for those equations to be meaningful.
Also, on those charts, wind resistance would disappear, and rolling resistance would disappear as a discrete factor and be added to bearing and drivetrain friction, perhaps as a different number.
Also, on those charts, wind resistance would disappear, and rolling resistance would disappear as a discrete factor and be added to bearing and drivetrain friction, perhaps as a different number.
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11-01-20, 01:32 PM
#234
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So, what is the cost of extra weight when climbing?
One extra kilogram weighs 9.8 N. In my example of climbing at 5.26 m/sec up 5% incline, the extra kg would cost me 9.8 x 0.05 x 5.26 watts = 2.58 watts.
The weight of my MTB costs me perhaps 5 watts on that climb, but I suspect the tires cost me about 15 watts (all the time).
Otto
One extra kilogram weighs 9.8 N. In my example of climbing at 5.26 m/sec up 5% incline, the extra kg would cost me 9.8 x 0.05 x 5.26 watts = 2.58 watts.
The weight of my MTB costs me perhaps 5 watts on that climb, but I suspect the tires cost me about 15 watts (all the time).
Otto
Last edited by ofajen; 11-01-20 at 01:35 PM.
11-01-20, 02:23 PM
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So, what is the cost of extra weight when climbing?
One extra kilogram weighs 9.8 N. In my example of climbing at 5.26 m/sec up 5% incline, the extra kg would cost me 9.8 x 0.05 x 5.26 watts = 2.58 watts.
The weight of my MTB costs me perhaps 5 watts on that climb, but I suspect the tires cost me about 15 watts (all the time).
Otto
One extra kilogram weighs 9.8 N. In my example of climbing at 5.26 m/sec up 5% incline, the extra kg would cost me 9.8 x 0.05 x 5.26 watts = 2.58 watts.
The weight of my MTB costs me perhaps 5 watts on that climb, but I suspect the tires cost me about 15 watts (all the time).
Otto
Which assumes negligible drag (low speeds). Your example is a little faster up that hill so it's actually less than 1.1%, but for estimating on the fly it's a good rule of thumb.
11-01-20, 02:46 PM
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Easier way to look at it: at low speeds the percentage change in power is close to the percentage change in weight. 2.2 pounds/200 pounds, 1.1% more power needed for the same speed.
Which assumes negligible drag (low speeds). Your example is a little faster up that hill so it's actually less than 1.1%, but for estimating on the fly it's a good rule of thumb.
Which assumes negligible drag (low speeds). Your example is a little faster up that hill so it's actually less than 1.1%, but for estimating on the fly it's a good rule of thumb.
Otto
11-01-20, 02:51 PM
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Well yeah, what you did is objectively better - I was just throwing that out there to simplify it for anyone interested. I think of the rule of thumb as an upper bound on what you can expect from shedding a certain amount of weight.
11-01-20, 09:31 PM
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Thanks. I was a lot more proficient back then. These days it takes a while to unpack stuff I learned or did if I haven’t been thinking about or using it for a while.
When I get to step back from the policy work and retire in a few years, I may start a second “career” in gravitational theory. I had the privilege to have two semesters of gravitation class with Bahram Mashoon back then.
He retired recently and published an Oxford monograph of his work on nonlocal gravity studies. Fascinating that nonlocal memory like effects in gravitation over large distance scales may actually be what is causing the cosmological behavior that others have suggested implies there is “dark matter”. Personally I think cosmology today is a shambles and find Bahram’s work very encouraging. 😊
Otto
When I get to step back from the policy work and retire in a few years, I may start a second “career” in gravitational theory. I had the privilege to have two semesters of gravitation class with Bahram Mashoon back then.
He retired recently and published an Oxford monograph of his work on nonlocal gravity studies. Fascinating that nonlocal memory like effects in gravitation over large distance scales may actually be what is causing the cosmological behavior that others have suggested implies there is “dark matter”. Personally I think cosmology today is a shambles and find Bahram’s work very encouraging. 😊
Otto
11-02-20, 06:18 AM
#239
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QUOTE: "But that equation can only be equated to speed through the air if the air is still."
Maybe it will help to realize that there is no such thing as still air as movement is always relative. Consider that the earth is spinning so the air is moving at the speed of rotation, the earth is moving around the solar system, and the solar system is moving through the universe. So now you realize that the air is always moving regardless.
This should illustrate the concept "movement relativity." .
Maybe it will help to realize that there is no such thing as still air as movement is always relative. Consider that the earth is spinning so the air is moving at the speed of rotation, the earth is moving around the solar system, and the solar system is moving through the universe. So now you realize that the air is always moving regardless.
This should illustrate the concept "movement relativity." .
11-02-20, 06:29 AM
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QUOTE: "But that equation can only be equated to speed through the air if the air is still."
Maybe it will help to realize that there is no such thing as still air as movement is always relative. Consider that the earth is spinning so the air is moving at the speed of rotation, the earth is moving around the solar system, and the solar system is moving through the universe. So now you realize that the air is always moving regardless.
This should illustrate the concept "movement relativity." .
Maybe it will help to realize that there is no such thing as still air as movement is always relative. Consider that the earth is spinning so the air is moving at the speed of rotation, the earth is moving around the solar system, and the solar system is moving through the universe. So now you realize that the air is always moving regardless.
This should illustrate the concept "movement relativity." .
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11-02-20, 11:01 AM
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"Still air" just means it's a windless day. There's no reason to make it any more complicated that that.
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11-04-20, 11:05 AM
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