I ride some pretty steep hills with a compact double and so there is no way I can maintain my cadence at the rate I use on flats going up a steep hill, since I usually end up in my lowest possible gear combination. 75% seems about right to me, though I do try to maintain my normal cadence as long as possible.
I shift down as the hill gets steeper but then as the pitch levels out I shift back up, sometimes standing a little first to get my speed back up. So on a steep hill I will generally drop to my small chainring and shift up a few gears in the back. So a flat->steep hill for me might look like:
9-8-7-6-5-4-3-2-1-4-(stand)-3-4-5
This is my normal pattern on a hill I ride almost every day, about 1/2 mile and 8-10% grade. At the top it levels out to 5 or 6%. Though lately I've been trying to avoid my lowest gear and stand more just because I am a masochist.
It really depends a lot on the hill, though. On a less-steep hill I'll stay in the mid range as long as I can keep my normal cadence up. When I was new to riding I stayed in my lowest gear a lot. As I've gotten stronger my gear choices have increased.
I think the thing that confused me most about gears when I was really new to cycling was that the shifting seems opposite in the front and back...but with good reason. Dropping to a smaller chainring in the front makes it easier to pedal, while shifting to a smaller cog in the rear makes it harder.
On a triple, I am usually in the middle chainring on flats, large going downhill and small uphill. On my compact double I am usually in the large chainring unless I am on a steepish hill or heading into a bad headwind. I have no idea if this is 'good' or 'right'...it just works for me.
Anne



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