Two thoughts on riding vintage with modern:
1. If you get heckled, just tell them to f*** off and go find somebody else to ride with. That kind of attitude is completely infantile and inexcusable.
2. Only having a five speed rear is not necessarily a disadvantage. In my collection, I've got one two fives, two sixes, and a nine. The best one of the bunch for riding in my area is the Rossin with the six speed freewheel - I've got it geared to the point that most of my shifting goes from the third cog (slight uphills) to the fourth cog (flats and slight downhills) and back. It works wonderfully. Odds are you've probably got an old standard 14-28 rear, which covers the first eight gears of the usual modern ten speed cassette - the gaps are just bigger. And most modern bikes, IMHO, are way overgeared for my riding style. On my 9-speed Fuji, I'm gathering additional low end cogs to beef up the low and middle, and get rid of three of the fourth top ones. If I gotta have all those gears, I'd rather have ones that I can actually use.
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Syke
“No one in this world, so far as I know — and I have searched the records for years, and employed agents to help me — has ever lost money by underestimating the intelligence of the great masses of the plain people. Nor has anyone ever lost public office thereby.”
H.L. Mencken, (1926)