The idea being that you can put out x watts which gives a calculatable speed for a given system weight/hill. You then match that speed to a gear ratio/cadence to find the lowest gear you need.
In other words if you're going up a 5%/5 km hill, you weigh 80kg with 10kg bike, and for whatever reason you can only put out 100W (say on an ultra or touring or something), you need a ratio lower than 1:1 to have a cadence above 60 RPM. At 150W, same rider, you're doing 75 RPM on 34/32. If you only weigh 65kg with a 7kg bike, 150W you can manage 70 RPM on 39/28.
I would be interested to hear what kind of power ultracyclists like @hippy can afford to put out over a whole event and compare that with these calculations for gear ratios.
And I will assume from now on that anyone with a small cassette/non-compact chainset has the upper body of Chris Froome
Someone cleverer than me could probably explain how inertia means that 150w up a hill is not the same as 150w on the flat. Just like 150w on a cheap turbo isn't the same as outside.
Who wants to argue about climbing gear ratios?
Found this article very interesting: https://www.cyclingabout.com/hills-are-not-harder-than-cycling-on-the-flat/
The idea being that you can put out x watts which gives a calculatable speed for a given system weight/hill. You then match that speed to a gear ratio/cadence to find the lowest gear you need.
In other words if you're going up a 5%/5 km hill, you weigh 80kg with 10kg bike, and for whatever reason you can only put out 100W (say on an ultra or touring or something), you need a ratio lower than 1:1 to have a cadence above 60 RPM. At 150W, same rider, you're doing 75 RPM on 34/32. If you only weigh 65kg with a 7kg bike, 150W you can manage 70 RPM on 39/28.
I would be interested to hear what kind of power ultracyclists like @hippy can afford to put out over a whole event and compare that with these calculations for gear ratios.
And I will assume from now on that anyone with a small cassette/non-compact chainset has the upper body of Chris Froome