Originally Posted by
sfrider
I almost always spin out a 50x12 on descents, keeping up with traffic. No big deal - bikes are faster in tight corners, cars on straight sections. Hwy 1 descending from the coast towards Sausalito CA is one example. But I don't think it matters much, I'd always spin out whatever I have on the bike anyway. 40 or 37mph... doesn't terribly matter.
Bigger large chain rings make sense for people who do a lot of climbing. They tend to use their top and bottom gears a lot.
But most recreational cyclists spend more time in flatter areas. They often can't really use their top gears, so when they're in the big ring, they only use the bottom part of their cassette.
In any case, when spinning out requires a steep descent, aerodynamics rather than pedal power is the limiting factor.