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Cadence & coast ratio...?

Old 07-02-10, 12:15 AM
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Cadence & coast ratio...?

If you ride a fixie, your coast ratio is about 0 %, but if you have gears, it's probably more. Apparently I made this concept up, which is shocking to me. I just got a cadence sensor that talks to my GPS, and I was very disappointed to learn that a glide ratio is just horizontal vs vertical distance. ( Imagine how useful this is to sea kayakers. )

I never thought bikes were that much exercise, because I used to coast a lot, and still do sometimes. If you climb the biggest hill in Seattle, you earn yourself a nice reward going down the other side. Anyway, would this be a more accurate way to guess how many calories you've burned during a ride, by using pedal time instead of saddle time? Or are you still working pretty hard when you coast on a bike, moving your weight around to control it, etc?

I'm guessing there's no such thing as a target to shoot for here, but higher is better for exercise. On the other hand, I'm comfortable at around 70 rpm, and feel like it's time to shift when I hit about 80, so I might be better off concentrating on spinning faster, and not spinning more/longer?

If anybody is interested (I was before I got my HRM!), this is what the files look like out of a Garmin with the cadence sensor. I was expecting to see speed measured at the wheel in the data ... even though I haven't figured out how to set the wheel size. That would be convenient, even if it'd also be redundant.

<trkpt lat="47.645524" lon="-122.325807">
<ele>21.29</ele>
<time>2010-07-02T02:06:08Z</time>
<extensions>
<gpxtpx:TrackPointExtension>
<gpxtpx:hr>115</gpxtpx:hr>
<gpxtpx:cad>68</gpxtpx:cad>
</gpxtpx:TrackPointExtension>
</extensions>
</trkpt>
<trkpt lat="47.645744" lon="-122.325713">
<ele>20.32</ele>
<time>2010-07-02T02:06:12Z</time>
<extensions>
<gpxtpx:TrackPointExtension>
<gpxtpx:hr>115</gpxtpx:hr>
<gpxtpx:cad>69</gpxtpx:cad>
</gpxtpx:TrackPointExtension>
</extensions>
</trkpt>
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Old 07-02-10, 08:47 AM
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I think that you are WAY over-thinking this I've never even considered a ratio of time spent coasting vs time spent pedaling.

As for the Garmin, I'm not sure which one you've got, but to set wheel size on a 705, push the "menu" button then use the thumb stick to scroll down to "settings". Push down on the stick, then scroll down to profiles and push down on the stick then scroll to bike profiles. At the very bottom of that screen is a menu for "wheel size". I'm pretty sure that it defaults to "automatic": the GPS will calculate your wheel size based on how far you've gone comapred to how many revolutions it took to go that far.
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Old 07-02-10, 10:04 AM
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I've got an Oregon 550t; it's not a cycling unit, but I do a lot of hiking and kayaking, too, so it's been pretty good for me. In the setup menu, there's an area for "fitness," which lets you turn the HRM and CAD sensor on or off, and to pair new ones to the unit. But those are the only options I've found related to wheel size. But it doesn't really matter if it's not going to write the speed ( or even the rpm at the wheels ) into the xml. I've already got the GPS-inferred speed, and I can infer it again from the time and lat/lon data, but it'd be nice to have in there for quick-and-dirty Excel stuff. I know the sensor is picking up the spoke magnet, though.
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Old 08-08-10, 02:39 PM
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I was told that coasting allows the lactic acid to build up in your legs and that you should keep pedaling even if it is just to keep your legs moving. Going down hill you should always be able to find a gear that adds minimal effort.

Also it will keep you close to your needed gear to put in an effort when you decide to pedal hard again.
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Old 08-08-10, 04:41 PM
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The only time that you should coast, is when you are going downhill. But it takes lots of riding hours to be able to do that. In a big ride (like TOSRV) you can tell the poorly conditioned riders, they peddle, coast, peddle and coast.
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