Another single-speed newbie question: chain tension

[Louis]

How do I figure out how much is enough? (Single speed, but not fixed, if that makes a difference.)

(Other than setting it somewhere and seeing if I drop the chain?)

TIA

[gavingould]

tap up on the chain from below, under the chainstay - IMO you should have less than 3/4" up and down movement. also check (very carefully- you dont want a finger in the cog/chainring) for tight/loose spots while slowly spinning the cranks.
chainrings aren't usually super round, but it can also be the ring not "centered" on the spider.

[Louis]

Thanks Gavin, I'll do that.

[mokmu]

Ask any track racer. Loose is fast!

I like the old wrench test: If you can push the chain off by applying sideways pressure to the chain with a wrench, while pedaling, it's too loose. Otherwise, carry on. If your chainline is good, you will have no problems.

[Bob Loblaw]

Also, be aware that as the chain wears it will have tight and loose spots as it travels around the chainring and freewheel. When you set the tension, make sure it's at a place where the chain is tight.

BL

[11.4]

These days you shouldn't have to worry about eccentric cogs or chainrings. The old problems came when they were made partially on a lathe, partially on a mill, and it was too easy to lose precision. The mill was used in particular to drill the five holes for chainring bolts, and all too often they weren't concentric with the teeth. These days everything is done with CNC on a single machine and I frankly haven't seen a bad chainring made in the last five years. With a ring like (for this kind of fixie application) a Sugino Messenger, it won't be a problem. Nothing from Sugino, Dura Ace, etc. should be a problem. I haven't seen any problems with Omnium or Miche rings either. Even the cheap stuff like FSA and All City may not be particularly smooth but they are round.

As for looseness. You say you are using a freewheel. Assuming everything is 3/32" (ring, chain, cog), you can measure your chain tension as described above, by pushing it up and down and looking for how much play it has. You won't have problems until you are way over an inch of vertical play, so to have 3/4" to 1" of vertical play is comfortable and works well. Going tighter just wears things, makes more noise, and if it were a fixed gear would beat up your legs more.

Do be careful about your fingers. You may think you know how to keep your fingers out of the way because you work on road bikes, but until you have a chain that's moving and going to drag your finger into a chainring simply because the rear wheel has momentum, you don't appreciate how quickly you can mangle a finger. I've lost a couple fingernails in the past. I've seen plenty of bike mechanics who lost part or all of a finger.

One thing about single freewheels is that there are very few good ones around. Most of them do have an unsettling tendency to come apart unexpectedly -- and I do mean come apart completely with parts everywhere and damage to your frame. If you want to commit a whole hub, you can get a nice freewheel assembly as part of a Chris King hub. Otherwise, it's worth it to drop the money on a White Industries freewheel. And while you're at it, consider getting something like their Duo -- it has two cogs on one freewheel, like 16/18 or 17/19. It gives you two gears and a very simple way to adjust without having to finagle with fenders in most instances. Very nice product.

[PSC]

Agree, get a WI freewheel they are expensive but well worth it. SS are about simplicity and reliability.