Adjusting Single Speed Chain
 

Servicing a friend's Bikes Direct Dawes single speed.

I'm really unimpressed with Bikes Direct. The Formula hubs seem to have had very little grease, and were adjusted way too tight. I replaced the balls. The headset was similarly almost grease free and extremely tight, I thought it was brinelled. Grease and adjustment fixed it. The brake cable housing ends weren't seated in the lever bodies, and routed with sharp bends and lots of friction. I fixed that and replaced the cables, so now her brakes actually work. The wheels were fairly true, but the rear has an intractable bulge - that might be damage from a pothole or something, though. I don't have the appropriate tool for the bottom bracket so that will remain as is, I figure it is probably a cartridge anyway. The freewheel on the flip flop rear hub sounds bad, noisy and scrapey, but a bunch of oil helped a little. The dropouts are not parallel. The seatpost is ridiculously long. It is a small bike and she is a short woman, there is enough post for a six footer.

Yeah, it only cost her $300 and has served as basic transportation for 2.5 years, but $300 would have bought a far nicer used bike that would have been much nicer transportation.

Anyway, it is almost done, just needs new bar tape, but I have a question because I don't know single speed bikes. How loose or tight is the chain supposed to be? I have it just loose enough to avoid a noisy spot when pedaling. With light finger pressure on the middle of the upper run of chain, it sags about 1/2". Does that seem okay?

With freewheel it's pretty forgiving. Just make sure that it sags somewhat at all times. Chainrings can be eccentric so the amount of sag may vary, so you want some at the tightest. W

On a fixed gear it's a bit more critical, since you also want to minimize backlash when applying back pedal pressure. So you'd try to get the chain ring to run as round as possible, and adjust the chain slack to be at an absolute minimum at the tightest place.

Either way the key is simple, there should never be tension on the chain except (of course) what you put into it to drive the bike.

Thanks, FB.