Originally Posted by
quester
I've seen this alluded to a couple times, but I don't get it. Why does the dropout angle matter?
The chain has to be tight otherwise it will skip, in addition to wearing out the chainring, chain and sprockets prematurely. Because vertical dropouts do not allow you to take up the slack in the chain, you need to use an eccentric BB or to install a chain tensioner (similar to how the rear derailleur mechanism works).
If you have an older bike that has more horizontal style dropouts, slack in the chain can probably be taken in by moving the rear wheel back and forth.