Power output on Taxc , at 25km/h

[lyot]

To make a bike (and yourself) of some weight, go at a specific speed on a particular grade will always take the same amount of power, whether you're mashing a large gear with low cadence or spinning a low gear with high cadence

I read this statement from Berend in another thread. I had a discussion with someone yesterday. he said that cadence does matter to know what power output you get.. My initial question was : if you do 25km/h on a Tacx, what is your power output in that case. He said it depended on the cadence.. But that ain't true, right ?

 

[ric_stern/RST]

To make a bike (and yourself) of some weight, go at a specific speed on a particular grade will always take the same amount of power, whether you're mashing a large gear with low cadence or spinning a low gear with high cadence

I read this statement from Berend in another thread. I had a discussion with someone yesterday. he said that cadence does matter to know what power output you get.. My initial question was : if you do 25km/h on a Tacx, what is your power output in that case. He said it depended on the cadence.. But that ain't true, right ?

to ride at a specific velocity under specific conditions, requires exactly the same power output whether you cycle at 40 revs/min or 160 revs/min or any other cadence. cadence does not matter in this above scenario.

ric

 

[lyot]

to ride at a specific velocity under specific conditions, requires exactly the same power output whether you cycle at 40 revs/min or 160 revs/min or any other cadence. cadence does not matter in this above scenario.

ric

thanks Ric for your insights !
does this also mean that at an average 150 Watts of output , you will always have the same velocity on a Taxc, no matter what the cadence is ?

 

[Eldrack]

thanks Ric for your insights !
does this also mean that at an average 150 Watts of output , you will always have the same velocity on a Taxc, no matter what the cadence is ?

Power = force * velocity

For most Tacx trainers (except the one with progressive resistance) you have a series of different resitance settings with a different braking force for each one (15 newtons for the Tacx 1460 swing at lowest resistance level.)

Therefore if you keep your power output constant your velocity will be the same no matter what your cadence.

Cadence is the number of times you complete a full rotation with your cranks per minute. For a 1 to 1 gear ratio for each full rotation of the cranks you get one rotation of the back wheel. For a 2 to 1 gear ratio (front cog twice as many teeth as the rear) you get two full rotations of the rear wheel for each full rotation of the cranks.

Your speed at a cadence of 100rpm with a 1 to 1 gear ratio is the same as your speed at 50rpm candence with a 2 to 1 gear ratio. Increasing your cadence increases your speed provided you stay in the same gear. If you increase your speed you will be producing more power as the resistance of the trainer won't change.

To summarise: if you keep your velocity the same and the resistance setting the same your power output will stay constant. Increase your speed (by changing up a gear or by increasing cadence) you increase your power output. Putting the resistance setting up but still maintaining the same velocity also increases power output.

Hope that helps.

 

[lyot]

Power = force * velocity

For most Tacx trainers (except the one with progressive resistance) you have a series of different resitance settings with a different braking force for each one (15 newtons for the Tacx 1460 swing at lowest resistance level.)

Therefore if you keep your power output constant your velocity will be the same no matter what your cadence.

Cadence is the number of times you complete a full rotation with your cranks per minute. For a 1 to 1 gear ratio for each full rotation of the cranks you get one rotation of the back wheel. For a 2 to 1 gear ratio (front cog twice as many teeth as the rear) you get two full rotations of the rear wheel for each full rotation of the cranks.

Your speed at a cadence of 100rpm with a 1 to 1 gear ratio is the same as your speed at 50rpm candence with a 2 to 1 gear ratio. Increasing your cadence increases your speed provided you stay in the same gear. If you increase your speed you will be producing more power as the resistance of the trainer won't change.

To summarise: if you keep your velocity the same and the resistance setting the same your power output will stay constant. Increase your speed (by changing up a gear or by increasing cadence) you increase your power output. Putting the resistance setting up but still maintaining the same velocity also increases power output.

Hope that helps.

it does ! thanks a lot for your help !!

 

[closesupport]

mine says at about 15.5mph 76.0watts/77.0watts with 99/100rpm on a 0.0% slope