Force distribution on pedals...

[Rocket69]

Hi all... looking for a website or an answer to this question.

If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the pedals? (in pounds or kilos)?

Thanks to anyone who helps or gives direction...

Rocket69

 

[Andy Coggan]

"Rocket69" <[email protected]> wrote in message
news:[email protected]...
> Hi all... looking for a website or an answer to this question.
>
> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
> pedals? (in pounds or kilos)?

Power (in W, or Nm/s) = torque (in Nm) x angular velocity (in rad/s)

Therefore:

300 Nm/s * 1/(90 rev/min * 6.18 rad/rev * 1 min/60 s) = 32.4 Nm

Assuming a crank length of 170 mm, this means an average (around 360 degrees) effective (tangential
to the crank) force on the pedal of:

32.4 Nm * 1/0.17 m = 190 N, or 19.4 kg.

Note that the actual force will vary in essentially a sinusoidal manner from close to zero when the
cranks are vertical to close to twice the average when the cranks are horizontal.

The following web page may provide you with some additional insight:

http://home.earthlink.net/~acoggan/quadrant_analysis.html

Andy Coggan

 

[Dave Lehnen]

Rocket69 wrote:
> Hi all... looking for a website or an answer to this question.
>
> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
> pedals? (in pounds or kilos)?
>
> Thanks to anyone who helps or gives direction...
>
> Rocket69
>
>
>
> --
>
>

Do you mean the magnitude and direction of pedal force during one complete cycle? The average
tangential force, for a crank throw of 170 mm, at 300W and 90 RPM, is 42.09 lb or 187.2 N or
19.09 KgF. There is no unique answer for how the force is distributed through the cycle. Studies
have been done with instrumented pedals to determine how force varies through the cycle with
various riders and conditions. The book "High-Tech Cycling", 2nd Ed., has quite a bit on this in
chapter 5. There is usually some downforce even on the upgoing pedal. As you would expect, the
highest forces are from the downgoing leg, somewhat past mid-stroke. There are probably websites
with similar information, which you can search for as well as I can.

Dave Lehnen

 

[Peter Cole]

"Rocket69" <[email protected]> wrote in message
news:[email protected]...
> Hi all... looking for a website or an answer to this question.
>
> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
> pedals? (in pounds or kilos)?
>
> Thanks to anyone who helps or gives direction...

There's a pedaling vector model at www.analyticcycling.com.

 

[Ted Bennett]

Rocket69 <[email protected]> wrote:

> Hi all... looking for a website or an answer to this question.

If a rider
> pedals at 90RPM and is generating 300 watts, what is the
force distribution
> on the pedals? (in pounds or kilos)?

Thanks to anyone who helps or gives
> direction...

Rocket69

First get your units right. Force = mass x acceleration, so a kilo can't be a measure of force.

--
Ted Bennett Portland OR

 

[Zog The Undenia]

Rocket69 wrote:

> Hi all... looking for a website or an answer to this question.
>
> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
> pedals? (in pounds or kilos)?
>
> Thanks to anyone who helps or gives direction...
>
> Rocket69

Depends on the size of the pedal circle, but for 170mm cranks it would be an average of 93N (9.5kgf)
on each pedal, assuming the rider can produce a perfect couple. The pedals are travelling a distance
of 1.6 metres per second. You can scale the force up for shorter cranks developing the same power.

Of course, for most riders the peak force on each pedal will be much greater than this and there
will be very little force at the top and bottom dead centres. For a highly trained rider using
clipless pedals it will be closer to the average.

 

[Robert Chung]

Andy Coggan wrote:
> "Rocket69" <[email protected]> wrote
>> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
>> pedals? (in pounds or kilos)?
>
> Note that the actual force will vary in essentially a sinusoidal manner from close to zero when
> the cranks are vertical to close to twice the average when the cranks are horizontal.

Rocket69 can plot the data available at http://www.isbweb.org/data/kautz to see the sine and to see
that the max force is roughly twice the average.

 

[Andrew Bradley]

Zog The Undeniable <[email protected]> wrote:

> Of course, for most riders the peak force on each pedal will be much greater than this and there
> will be very little force at the top and bottom dead centres. For a highly trained rider using
> clipless pedals it will be closer to the average.

That doesn't seem to be the case in practice though.

Andrew Bradley