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I am at my wits end with trying to figure out the chain on the singlespeed I am building so any advice would be brilliant!
The correct length seems to have two “inner” pieces of chain meeting, I purchased some connector links but adding that makes it too long and slack, am I missing something obvious? I have been messing with it all week now and ready to throw it over the garden fence!
Get a half link (or rather, or rather link and a half I suppose). This will allow you to adjust the chain length in 1/2 inch increments.
Obviously you can’t do this if you are using a narrow/wide chainring.
what are you using to create chain tension, or is it just standard frame and you're looking for the magic ratio?
Get a half link
Yep, that would allow you to join the chain at exactly the length you have the two inner pieces meeting.
It is a narrow wide chainring, it’s a standard frame and using nothing to create tension.
Is it just the case that with this ratio of gears it will never work?
Nothing to create the tension is a non-starter on a standard mountain bike - you need a chain tensioning device or it will be skipping left right and centre. They're v easy to set up.
If you just want to ride the bike to the pub you can look for the magic ratio, no tensioner, as it'll be on smooth surfaces and you'll never be putting much torque through the drivetrain.
You might get it to work tension wise with a half link but that'll also mean you can't use a NW chainring, and then as the chain wears / stretches the tension will gradually fade again to the point where it might become a problem.
I know some people can do magic ratio singlespeeding but needs to be able to swap in F/R cogs to get the length right while also having the right ratio.
Really you need some sort of tensioning device; you could look at an eccentric BB but cheaper and a good way to see if SS'ing is for you (I'm assuming it's a first go here) would be to get a tensioner, or bodge one out of an old mech.
http://forums.mtbr.com/singlespeed/how-use-old-rear-derailleur-chain-tensioner-82061.html
Oh, didn't realise you were trying a magic gear. No such thing, it never works to a satisfactory level unless you get it to work with a brand new chain and change your chain every few weeks...
This is a calculator that will work out possible magic ratio for you.
http://eehouse.org/fixin/fixmeup.php
It’s a mountain bike but with slick tyres to be used for commuting so not rough terrain! So best option is buy than chain tensioner from the link above, get the chain as close as possible and use that?
Appreciate all the help
yes - get the chain as close as possible and use a tensioner. Personally I prefer a sprung tensioner as chainrings are always ever so slightly eccentric and chains can wear unevenly.
https://www.charliethebikemonger.com/4jeri-tensioner-29-p.asp
yeh, that's what I'd do. I ran a SS for a couple of years with a tensioner before going to a SS specific frame and it only rarely shipped the chain on rough stuff. On flat stuff, and with a NW too, I reckon should be fine*
* just know, on the 1/100,000 times it isn't, you'll be thrutching up a hill when it decides to skip, and you <span style="text-decoration: underline;">will</span> hit your nuts on the stem and swear profusely into your beard. Unless you're a lady SS'er, in which case you'll whack your ladyparts on the stem and swear profusely into your beard.
The chain tensioner was delivered today but I am a little to confused to how it fits to the frame?
Do do I use the old derailer hanger?
Yeah, it's basically a derailleur sans the deraill-ey stuff.
Depends what sort you have -
If you've got one of the style in TJ's link, then you fit to the mech hanger and run the chain under the jockey wheel, you then adjust the reach of the jockey wheel to match the chainline. If you got a one as per my link then the topnut replaces the nut on the end of your QR skewer and the other goes in your mech hanger hole and you adjust the tension by hand, with the wheel being a bit wider than a chain to account for varying chainlines.
How is your rear cog spaced - with a spacer kit, or is it a proper SS wheel with screw on freewheel?
An ISCG chain doofer with a bottom roller makes a good tensioner for SS and there's less chance of the chain coming off as the chain's wrapped around the front cog more than it would be with a sprung tensioner on the back 🙂
An ISCG chain doofer with a bottom roller makes a good tensioner for SS and there’s less chance of the chain coming off as the chain’s wrapped around the front cog more than it would be with a sprung tensioner on the back
It depends how close you are to a magic ratio, if you have to add almost a whole inner/outer set of links then the tensioner has to work at quite an angle to take up the slack. That's why push-up tensioners only work on some frames and only in some ratios.
I suppose you could always use a blackspire stinger style devie pushing down, it would still give more wrap at the sprocket.
It's only really an issue months/years/thousands of miles down the line, a proper SS frame with EBB or track ends lets you wear out a chain and sprocket to the point the teeth fall off, any sort of tensioner can't deal with the forces involved.
@theotherjohnv yes it’s the one of Tj’s link, I have thrown the mech hanger away so will order a replacement!
The rear cog is spaced with a spacer kit.
an iscg device does also have the advantage that the dropout can be used just like a regular dropout, so if you need to pull the wheel it's simple. you may need to use a half link to make it work, but it's a good solution for a frame with no other built in tensioning mechanisms. i used one for a couple of years.
an iscg device does also have the advantage that the dropout can be used just like a regular dropout, so if you need to pull the wheel it’s simple. you may need to use a half link to make it work, but it’s a good solution for a frame with no other built in tensioning mechanisms. i used one for a couple of years.
That's what I like about it, you don't have to re-tension the chain every time the wheel comes out. Here's my Switchback yesterday, with an ISCG doofer-
[img] 
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It works fine despite looking like it'll be as draggy as a draggy thing, as long as the bottom roller/cog spins freely.
edit- I've got a full chain thinger on because that's just what I had spare, the Stinger I had went on my niece's bike.