Measuring power output

Future-pro

Does anyone know a formula which can be used to calculate the amount of watts produced on the bike

Weisse Luft

Chain tension in Newtons multiplied by chain speed in meters per second yields power in Watts.

Likewise, crank torque in Newton*meters multiplied by crank rotational speed in radians per second (revolutions per second multiplied by 2 pi) yields power in Watts.

And finally, wheel torque in Newton*meters multiplied by wheel speed in radians per second is power in Watts.

This is how Polar, SRM and Power Tap measure respectively.

ric_stern/RST

of course you'll need a power meter to actually measure that data. however, if the OP was trying to find another way (i.e., not purchase a power meter) then www.analyticcycling.com is very good.

ric

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bikeguy2

For cycling at constant speed the power required is roughly equal to the following and doesn't include frictional losses from the chain drive system:

P (watts)= VaVaVg*0.5*fa*Cd*airdensity+Vg*Crr*mass(kg)*9.8N/kg

Va is air velocity meters/sec, Vg is ground velocity meters/sec, Fa is frontal area in meters squared, Cd is drag coefficient, a typical value is 0.5, Crr is coefficient of rolling resistance, a typical value is 0.005 on a paved road. Air density is typically about 1.2 kg/cubic meter but varies with temperature.

Also see the excellent site analyticcycling.com to get this stuff figured out automatically.

bikeguy2

Whoops, I forgot the term for going up/down a hill Vg*mass*9.8 N/kg*sin((tan-1 (Gr))

steve

Cycle2max http://www.cycle2max.com/ is a pretty cool site that allows you to workout your power output on a given climb. If you do a search in their forum you should be able find the formula they use to do the calculation.

cheers

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Steve

CyclingForums.com