Originally Posted by
79pmooney
Edit: "lightest tension that is pleasant to ride" meaning no "kick-back when you reverse pedaling direction? Too tight! Use the kick-back to teach yourself to pedal evenly. Go to slow down and feel that one nice "click" . That kick-back and learning to avoid it is one of the best smooth pedaling tools there is. (Go to the velodrome and you will see a whole lot of really skilled riders and very expensive fix gears all with a ton of chain slack. You want a touch less slack because you have road bumps and they do not but you want to be as close to what they do as you can while guaranteeing your chain stays on.
On my coaster brakes I have some slack for two reasons. The first is to avoid brake snatch on coasting (not relevant to a fixie), and the second because of the kick-back. Hiding the kick-back through chain tension is not the same as removing the forces that create it. On loose surfaces the tire can slide, but on tarmac those forces generated as the tire bumps down the road will be shared by your legs, your ass and your BB.