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Stupid power, gearing AND cadence question
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If two bikes are side by side, in same gear (and gearing) at same cadence (all other things being equal; tyres, crank length, rim diameter) does power have to be the same?

If one cyclist was on tyres with very low rolling resistance and very aero and the other high resistance and low aero coukd they still be in same gear at same cadence but have different power outputs?
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Re: Stupid power, gearing AND cadence question [Andrewmc] [ In reply to ]
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Assuming by "side by side" you mean they're going at the same speed, then power doesn't need to be the same. The power needed to generate a speed of x is determined by wind resistance, rolling resistance, drive chain efficiency and if there's any gradient involved then also by weight.

To turn your example around, if 2 bikes are going the same speed and have identical weight, rolling resistance and aero, then the power is the same regardless of what gear or cadence they're using. (Actually that's not quite true as using larger cogs makes the drive train slightly more efficient, but if we ignored that it would be true)
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Re: Stupid power, gearing AND cadence question [cartsman] [ In reply to ]
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cartsman wrote:
Assuming by "side by side" you mean they're going at the same speed, then power doesn't need to be the same. The power needed to generate a speed of x is determined by wind resistance, rolling resistance, drive chain efficiency and if there's any gradient involved then also by weight.

To turn your example around, if 2 bikes are going the same speed and have identical weight, rolling resistance and aero, then the power is the same regardless of what gear or cadence they're using. (Actually that's not quite true as using larger cogs makes the drive train slightly more efficient, but if we ignored that it would be true)

So...yes, the bikes mentioned above are at the same power, they just aren’t going the same speed...or of going the same speed, the one with less aero, and slower tires is putting out out more watts (in a different gear or peddling faster).
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Re: Stupid power, gearing AND cadence question [Andrewmc] [ In reply to ]
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It would appear the power would have to be the same if you have the cranks hooked up to motors, and the motors are spinning at the same RPM but we are dealing with humans. The same cadence and gear does not necessary mean that two riders turning the pedals over at the same RPM are applying the same force/watts over the course of each revolution of the cranks. So, it would come down to how the power meter is actually measuring watts over time to give you the number you see. I'm not sure, but I think there is a way to game the system so to speak with different pedaling styles at the same RPM.
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Re: Stupid power, gearing AND cadence question [Andrewmc] [ In reply to ]
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Andrewmc wrote:
If one cyclist was on tyres with very low rolling resistance and very aero and the other high resistance and low aero coukd they still be in same gear at same cadence but have different power outputs?

Of course. The high resistance rider will be applying greater force to the pedals.

Power = Force x speed.
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Re: Stupid power, gearing AND cadence question [STP] [ In reply to ]
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That's what I think but it's quite difficult to explain
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Re: Stupid power, gearing AND cadence question [Andrewmc] [ In reply to ]
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Cartsman has it right.

Gear-inches x pedal-rpm = speed (inches per minute). So, two bikes in the same gear at the same cadence means the two bikes are going the same speed. Nothing more or less. It says NOTHING about the power required to go that speed.

Make the example silly....one rider puts on a drogue chute, or clamps on the front brake. Who's working harder to maintain speed?
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Re: Stupid power, gearing AND cadence question [Andrewmc] [ In reply to ]
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When thinking about this question, I conceptualize a different hypothetical... Consider a fixed gear bike going over a hill at a constant speed. The fixed gear bike removes cadence as a variable if you are holding speed constant. On the way up the hill, in order to maintain a constant speed, power must increase. On the way down, in order to maintain a constant speed, power must decrease. The change in power to overcome the resistance force of gravity comes from increased force applied to the pedals as speed (and therefore cadence) are constant.

The same applies to overcoming other forms of resistance, such as rolling resistance and aerodynamics. If one rider faces greater resistance, they must be applying more power to overcome that resistance. If cadence is constant, they must be applying more force to the pedals.
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