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Power - relationship between gearing and cadence

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Power - relationship between gearing and cadence

Old 01-18-23, 06:53 AM
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RoverInAz
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Power - relationship between gearing and cadence

Hi all, as a new Zwifter this last year I am starting to learn about power (watts).
All other mechanical things being equal (ie smooth deraileur alignment, well waxed chain etc) is power a direct function of the cadence and the gearing ratios used? Ie if two people cycle at the same cadence and with the same gearing ratio will their power be identical or do other factors come into play (pedal technique etc). If so what are those factors? Thanks in advance.
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Old 01-18-23, 08:20 AM
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Not sure if this an answer.
I notice on the hardest workouts and tough climbs in Zwift; when my leg strength feels like it's giving out, quite often I'm just mashing, pedaling square and not sweeping through the bottom. By re-focusing on pedal technique I can maintain the power goal and cadence with less overall muscle strain.
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Old 01-18-23, 08:58 AM
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Originally Posted by RoverInAz
Hi all, as a new Zwifter this last year I am starting to learn about power (watts).
All other mechanical things being equal (ie smooth deraileur alignment, well waxed chain etc) is power a direct function of the cadence and the gearing ratios used? Ie if two people cycle at the same cadence and with the same gearing ratio will their power be identical or do other factors come into play (pedal technique etc). If so what are those factors? Thanks in advance.
First the basic physics:-

Power = Pedal Force x Cadence (slightly simplified as technically it should be Power = Crank Torque x Cadence but it amounts to the same thing for the user i.e. how much pedal force you apply x cadence)

It gets a little more tricky when you compare two people pedalling at the same cadence with the same gearing because the resistance (i.e. pedal loading for a given cadence and gearing) will depend on several other factors i.e. aerodynamic drag, road gradient, rider/bike weight and rolling resistance. So the answer to your question is actually no, unless the riders, bikes, road and weather conditions are all identical. In Zwift all these other factors are simulated to provide a realistic pedal resistance. So when climbing a hill the pedal resistance increases and you will need to produce more power to maintain cadence (if you are using a Smart trainer)

In the power equation above, a lower(easier) gear has the effect of reducing your pedal force and increasing your cadence at any given power output. Your power output (along with the simulated rider/road parameters I mentioned earlier) is the only thing that determines how fast you go in Zwift. Zwift doesn't care about your choice of gearing, only the power you are producing i.e. Pedal Force x Cadence.

Last edited by PeteHski; 01-18-23 at 09:02 AM.
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Old 01-18-23, 09:23 AM
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RoverInAz
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Originally Posted by PeteHski
First the basic physics:-

Power = Pedal Force x Cadence (slightly simplified as technically it should be Power = Crank Torque x Cadence but it amounts to the same thing for the user i.e. how much pedal force you apply x cadence)

It gets a little more tricky when you compare two people pedalling at the same cadence with the same gearing because the resistance (i.e. pedal loading for a given cadence and gearing) will depend on several other factors i.e. aerodynamic drag, road gradient, rider/bike weight and rolling resistance. So the answer to your question is actually no, unless the riders, bikes, road and weather conditions are all identical. In Zwift all these other factors are simulated to provide a realistic pedal resistance. So when climbing a hill the pedal resistance increases and you will need to produce more power to maintain cadence (if you are using a Smart trainer)

In the power equation above, a lower(easier) gear has the effect of reducing your pedal force and increasing your cadence at any given power output. Your power output (along with the simulated rider/road parameters I mentioned earlier) is the only thing that determines how fast you go in Zwift. Zwift doesn't care about your choice of gearing, only the power you are producing i.e. Pedal Force x Cadence.
Thanks Pete. I thought i must be missing something (!) as heavier riders can generally produce more pedal force thus generate more watts. Presumably, however more pedal force also provides a faster cadence as force will drive the speed of the pedal rotation (or at least the downward movements).
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Old 01-18-23, 10:25 AM
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Originally Posted by RoverInAz
Thanks Pete. I thought i must be missing something (!) as heavier riders can generally produce more pedal force thus generate more watts. Presumably, however more pedal force also provides a faster cadence as force will drive the speed of the pedal rotation (or at least the downward movements).
You are welcome! More pedal force will tend to increase your cadence, but the resultant cadence (and hence road speed) depends on the resistance. The same pedal force/torque applied on the flat will lead to a higher cadence (in the same gear) than it would on a hill with higher resistance. So in that case you may choose to drop into an easier gear to reduce pedal force for a given cadence. The easier gear means you would ride slower at that same cadence.

Your road speed all comes back to how much power you are producing (pedal force x cadence) against a resistance. It doesn't matter what gear you use to produce that power, gearing only affects the balance between pedal force and resultant cadence. So you can produce the same power with a high pedal force and low cadence or low pedal force and high cadence.

I hope that makes sense to you as it can be a bit difficult to explain.
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Old 01-19-23, 11:17 AM
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Originally Posted by RoverInAz
Hi all, as a new Zwifter this last year I am starting to learn about power (watts).
All other mechanical things being equal (ie smooth deraileur alignment, well waxed chain etc) is power a direct function of the cadence and the gearing ratios used? Ie if two people cycle at the same cadence and with the same gearing ratio will their power be identical or do other factors come into play (pedal technique etc). If so what are those factors? Thanks in advance.
RoverInAz
Welcome to bike forums.

If everything is equal and both riders create the same rear wheel RPM, the power at the wheel is the same.
(For a wheel -on trainer, the rider weight must also be the same.)

However what you asked only skims the top when it comes to cycling.
Cycling is about getting the best performance and efficiency from an imperfect engine, you!

Mix this engine with poor cadence and/or poor pedal stroke and your perceived effort goes up causing you to tire.
I've spent a lot of time indoors and out working to better my cadence and pedal stroke.

All the best

Barry
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Old 01-20-23, 06:58 AM
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Originally Posted by Barry2
RoverInAz
Welcome to bike forums.

If everything is equal and both riders create the same rear wheel RPM, the power at the wheel is the same .
(For a wheel -on trainer, the rider weight must also be the same.)


Barry
That boils down to having equal trainer resistance. Power is only generated against that trainer resistance. So at a lower resistance you need to pedal faster to generate the same power.

You have actually created a zero sum equation there in bold
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