I know that some riders around here ride SS or even Fixies, but seriously - my midweek rides that I think of as fairly flat? They still have 1000 feet of climbing in 24 miles, including some pitches over 8%. So, my flirtation with the idea of a single speed bike was really brief.
So, it depends on where you live. Florida? Yeah, get a SS bike. What do you need gears for anyway? Overpasses? But here? Not for MY aging joints!
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"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles