A lot of it depends on your gearing. Bottom gear on most of my road bikes is around 43-45 gear-inches (45/28, 42/26, or 38/23)); on the mountain bike, the middle ring gets me down to 37 gear-inches (40/28). I lean toward spinning (90-120 RPM) most of the time, but end up mashing when the grade gets too steep or when I have to slow down and have run out of gears. The only downside I can see to using a low gear is that I can start to lift the front wheel if I gear too low on a steep climb.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069