Measuring power output

Future-pro said:

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

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.

Weisse Luft said:

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.

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

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.

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

Future-pro said:

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

Cycle2max cycle2max.comcycle2max.comOpen ↗ 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

bikeguy2 said:

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

Also, for completeness sake, here's another great site that offers a power and speed computer for various conditions (i.e. climb grade, weight, wind, rider position, bicycle type, etc.):

Bicycle Speed And Power Calculator

Berend