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| visits | member for | 1 year, 9 months |
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| stats | profile views | 67 |
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Jan 26 |
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Does gear ratio affect Power? @StephenTouset That cadence/force band isn't constant -- it varies according to conditions. See here or here for a discussion of cadence, pedal force, and "optimal" power. |
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Jan 26 |
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How accurate are the power numbers from a Tacx Flow? Ah, yes. There is no simple way to connect the Flow to a computer. In order to get the power readings at different speeds I used a small voice recorder and then transcribed the data. It's much easier with a Power Tap. |
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Jan 26 |
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How accurate are the power numbers from a Tacx Flow? I used to own a Flow. I bought the Flow first, which is when I collected the data for the first plot that shows the Flow to be consistent. Then a year or so later I bought a Power Tap, and saw how far off the Flow had been. I had both for about a year but then sold the Flow and have kept the Power Tap. |
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Jan 25 |
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How do I calculate the power required to climb a hill at a given cadence? Yes, very close to that. I think I actually get 3.44 m/s and 12.4 km/h, so the rule of thumb for climbing a 10% hill would be about 286 watts. I did an exact calculation taking into account the 10% slope and also rolling and aerodynamic forces and I got 281 watts so in this case the rule of thumb got within 2%. Not bad for a rule of thumb. |
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Jan 24 |
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How do I calculate the power required to climb a hill at a given cadence? Right, so a watt is a joule/sec. So, if you had a very good estimate of food calories (= kilocalories) spent, you could use the "rule of thumb conversion" to say that was equivalent to the number of kilojoules spent, and divide by the time elapsed in seconds to get average power in watts. In practice, good estimates of Calories spent are hard to come by but, especially on a bicycle, one can occasionally get a good estimate of power (such as for hill climbs). This gives a good estimate of kilojoules and you can then convert that into food calories spent. |
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Jan 24 |
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How do I calculate the power required to climb a hill at a given cadence? Rick: Yes, but you also need to account for your gross metabolic efficiency in converting between calories burnt and power. In general, GME ranges between about 20% and 25%. As it happens, 1 calorie = 4.184 joules, or 1 joule = .239 calories, so a common rule of thumb is to assume a GME of 23.9%, in which case the number of food calories (= Calorie, = 1000 calories = 1 kilocalorie) is roughly equivalent to 1 kilojoule. Typically it's easier to estimate work in joules (or kilojoules) than it is to estimate Calorie expenditure so the conversion is usually in the opposite direction: power -> Cal. |
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Jan 24 |
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How do I calculate the power required to climb a hill at a given cadence? I'm not sure which "first formula" you're referring to. Rick Ant's question specified power on a 10% hill, not on the flat, and we know his speed had to have been the speed implied by 50 rpm in a 39/23 -- thus, if the bike used a standard 700c wheel with a circumference of 2.1 meters, we know what his speed would be. It is as I showed: 50 rpm * 60 minutes per hour * 39/23 * 2.1 meters = 10700 meters/hr = 10.7 km/h, or 6.6 mph. |
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Sep 7 |
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practical pro and contra for Nuvinci CVT especially for hilly terrain Nice answer. Three things: Spicer, in an article here measured drive train efficiency and found that (for usual chain stay lengths) lateral chain angle did not contribute much to losses -- on the other hand, he found that losses were very related to chain tension. Others' measurements have verified this. Second, Nuvinci's manufacturer refuses to disclose their hub's efficiency, even in comparison to the Rohloff. Third, usually derailleur efficiency includes chain losses while IGH systems exclude it and only count hub losses. |
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Sep 7 |
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Food costs compared to Gasoline riding cross country USA Here's a nice graph on efficiency of self-propelled methods of transportation you may want to include in your answer (self-propelled excludes sailboats and railway freight cars). Conversion from efficiency to cost depends, of course, on fuel cost. |
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Sep 6 |
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How to significantly lower HR[avg] while improving performance output The simplest way is to use an online calculator such as this one, which gives an estimate of around 215 watts or so. If you weigh 67kg, your average output was around 3.2 watts/kg. A quick alternative is to note that you climbed roughly 800m in ~3000 seconds, so the quick estimate is 75kg * 9.8 m/sec^2 * 800 m / 3000 secs which is right around 200 watts for the potential energy component. |
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Aug 31 |
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Why am I slow on flat surfaces? Do you mostly ride alone or with others? When you say you're "very fast" up hills or in strong head winds but "can't seem to keep up" on the flat, does that mean relative to the same other riders, or do you mean that you're faster than "average" when on hills and in the wind but not so on the flat? |
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Aug 27 |
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How much friction arise from the tires? As I mentioned above, the old Continental tests were performed on a single (homogeneous) surface. You can see some examples (but with no detailed results) of contemporary test rigs here: bikeradar.com/news/article/… In addition, there are ways that interested amateurs can measure rolling resistance at home or in the field, on a variety of road surfaces. |
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Aug 27 |
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How much friction arise from the tires? That's a good chart but I didn't mention it earlier because it's both dated and incomplete. That chart is based on tests done about 20 years ago at the Continental Tire facility using a large diameter asphalt-surface driven drum; no other surfaces were checked and it is known that road, tire, tube, tire-rim attachment, and additional suspension characteristics can affect total rolling drag. In particular, inflection or "break" points in rolling drag have been observed in some tests on other types of surfaces with increasing pressure. |
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Aug 26 |
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How much friction arise from the tires? If all you're looking for is a source, then the best source is Chapter 6 of Wilson's Bicycling Science. However, wouldn't a better question be something like, "which factors influence bicycle tire rolling resistance and how are they measured?" |
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Aug 24 |
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How do bicycle power meters work? Although I refer to the SRM, Quarq, and Power2Max as "crank-based", they actually fit on or replace the spider. They're called "crank-based" because the spider usually goes with the right crank. I think one company may have tried to measure deflection forces on the chainstays. I don't know if anyone has tried spoke-based measurement; the spokes are a kind of "noisy" environment since they naturally change tension with every wheel revolution. |
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Aug 23 |
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Safety vests: Yellow vs. Orange? Mathew: Good point. I'll edit my answer and add some references. Thanks. |
