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Discussion Starter #1
I was at the LBS last night and Kurt K has a new type of bike computer that says it measures wattage while on the traininer. It seems like a cook idea, but I can't figure out how it really works. (engineer, I aint.) Has anyone tired one, see it, or heard about it?<br><br>
It works by speed, but I guess I don't quite understand it as I thought power was measured by speed and gear. This does say it is not perfect and does not measure things exactly like a ture power meter, but woud it be a good comparison tool for the trainer or is a plain old bike computer and HRM good enough. While I'd love to get a powertap or something, if we are spending any money, it will be on a treadmill.<br><br>
here are a few links.<a href="http://www.kurtkinetic.com/kinetic-wired-power-computer-p-152-l-en.html" target="_blank">http://www.kurtkinetic.com/kinetic-w...-152-l-en.html</a> - this may not be the one I saw in the store, but..<br><br><a href="http://www.kurtkinetic.com/documents/PCManual.pdf" target="_blank">Manual</a>
 

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it's ok. If your tire is at the same pressure and the roller pressure is the same, you get numbers that are repeatable so you can apply a more precise load on your body. You can really improve with it if you do the work.
 

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Jr's right.<br><br>
So put your way-back hat on to last winter. If you remember, I post workouts according to my overall average wattage, or based on the wattage numbers I tried to hold. In the wattage numbers I am always laying down qualifiers such as, "these numbers are crude... I'm just looking at the relative scale." And the reason I do that is because I don't have a true power meter. I have pretty much exactly what the Kurt provides. It's a crude number, but since it is repeatable, the accuracy of the finer number isn't required. I try to make sure my workouts are stepping me forward, and that repeatable number is more than sufficient enough. I paid, like, $175 or less for my trainer. It's a sturdy Nashbar fluid trainer with wattage reading. I love it. And I've gotten my money's worth. The wattage reading is very powerful if you learn to use it properly.
 

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The Kurt trainers use a fluid that increases in viscosity as it moves faster. So the faster you spin the trainer drum, the more the fluid resists the movement. They devised a mathematical formula to calculate the power required to spin the drum at the speed ranges involved with a bicycle (0-40 mph). They claim it's fairly accurate, but it doesn't really matter as long as it's consistent. I use a Kurt trainer and it does seem to be consistent. That is, 20 mph today feels just as hard as 20 mph yesterday. The formula tells me that's 250 Watts (or whatever), but all I really care about is pushing 20.1 mph next week and 20.2 mph the week after that, and so on.
 

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I suppose this could work on the trainer, but it implies it would work off the trainer, and I would say it certainly would not, unless you are riding on a complete flat road with no wind resistance. But on a trainer I certainly see how this could help, I'd buy it if I were interested in power on the trainer and I had a Kurt.
 

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it works off the trainer, but only as a speedometer. A power meter has a strain guage so when I'm riding 6 mph up the ski hill it realizes that requires a lot of pedal torque, as compared to 6mph out to the mailbox<br><br>
the power measuring technology is expensive right now, about $600 for the entry level
 

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Yeah I meant power side of it. I guess there is cheaper power solutions (Polar, ibike?), but not sure how reliable they are.
 

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Discussion Starter #9
So, based on this, it seems that I can get basically they same kind of "quantifying" training results on the trainer using my HR and my Speed? Assuming all things are consistent, tire pressure, etc, I get the same power in or out? - the way this device works, not a true power meter. I mean if I had a power meter, and went into my hardest gear at a lower rpm, I'd have 1 power, vs the same thing in the small gear but faster.
 

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Right. Big gear, slow cadence generates the same amount of power as a small gear at high cadence. Think of it this way - it takes a certain amount of power to move the bike a certain speed, how you choose to achieve that power (i.e. gear choice) is up to you.<br><br>
The only real downside to the "trainer power meter" method is that it doesn't carry over to the road. So you have to really pay attention to what 180 Watts feels like on the trainer and then try to replicate that feeling when you're out riding. It's not easy, but you can get fairly close if you work at it.<br><br>
ETA: The reason you have to learn what various power levels feel like is because your "speed" on the trainer will not match your speed on the road. The Kurt trainers (and probably all of them, I presume) are designed to accurately simulate the power required to ride up a 1% grade. So 20 mph on the trainer is the same as 20 mph on the road <i>up a slight hill.</i>
 

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Yes. The speed you spin the drum is what matters, so you can use your gears to vary the resistance you are pushing against.<br><br>
Heart rate is worth observing, but it responds more slowly. Since I have power now on my bike I don't bother looking at heart rate.<br><br>
In your case it gives you some additional information. When you try to train during or after illness, it can be particularly telling.
 
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