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Discussion Starter · #1 ·
how to calculate a rider's power in watt? i found some formula like 1 Watt = 1 joule/1 second, but those like 1 joule how to get it from cycling? do we need any heart rate monitor ? or trainer?
 

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To calculate absolute value of power takes some effort.

www.analyticcycling.com has some formulas for estimating power, using a bunch of simple variables (go to "static forces", then "power given speed"). This method takes the least amount of investment.

Other than that, you need a power measuring device that estimates Force using either strain gauges (power hub, or crankset), or wind/altitude change, piezoelectric devices, or by powering an electric motor (computrainer). There's also other resistance trainers that have power estimates charts using wheel speed (Krietler rollers, Kurt Kinetic, or 1Up trainer, etc.), which were created using a power measuring device.

All those devices are expensive.

The important formula for power, that most reflects cycling (mechanical power) is:

Power = (T*2*pi*rpm)/60

where T=Torque, pi=3.14, rpm = pedal rpm

Torque has to be in Newton meters. Rpm is pedal revs per minutes. RPM is easy to measure, the trick is getting torque.
 

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Discussion Starter · #3 ·
i have bike trainer with adjustable for the roller tension, heart rate monitor(polar). DO u think i can calculate the power using these devices?

Energy is expressed in joules. Using joules or kilojoules, we currently calculate that one calorie equals 4.19 joules. Joules can be abbreviated using the capital letter 'J'. We also often see the expression KJ (1000 joules).

Power = energy per unit of time and is expressed in Watts (W). This unit corresponds to the amount of energy delivered by 1 joule in a unit of time of 1 second. Therefore, 1 Watt = 1 joule/1 second.

i found these 2 statement from TACX web site. is it mean get the calory value first.?
 

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daytona said:
i have bike trainer with adjustable for the roller tension, heart rate monitor(polar). DO u think i can calculate the power using these devices?

Check your trainers' website. The only way really is if they provide a speed vs. power chart.

Energy is expressed in joules. Using joules or kilojoules, we currently calculate that one calorie equals 4.19 joules. Joules can be abbreviated using the capital letter 'J'. We also often see the expression KJ (1000 joules).

Power = energy per unit of time and is expressed in Watts (W). This unit corresponds to the amount of energy delivered by 1 joule in a unit of time of 1 second. Therefore, 1 Watt = 1 joule/1 second.

i found these 2 statement from TACX web site. is it mean get the calory value first.?
I think it is difficult to estimate power from calories burned. I think they present that information just as "gee whiz" type info. I see what you're getting at though:

Power = Energy/time = Calories*K/second, where K is a conversion factor of some type. Where calories are estimated from the polar HR monitor. Those estimates are notoriously inaccurate I believe (using HR and weight to estimate calories).

Some of the caloric energy goes to the pedals, but a lot is released as body heat. So there is another source of uncertainty (which changes with ambient conditions). Don't know what fraction actually went to the pedals, which is the power we care about.

Even caloric values from a powermeter is just an estimate. Saris just says to take the pedal KJs and just call it calories. Can't get it exact because can't capture the body heat loss.

But the beauty of strain gauge based power devices is their ability to capture stochastic and instantaneous events, which the "caloric back calculation method" would be pretty weak at.
 

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daytona said:
how to calculate a rider's power in watt? i found some formula like 1 Watt = 1 joule/1 second, but those like 1 joule how to get it from cycling? do we need any heart rate monitor ? or trainer?
You could get a rough estimate based on a long sustained road climb where speed was always low, so air resistance and rolling resistance would be small compared with work performed against gravity. You'd need to know the vertical distance of the climb.
 
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