Realy like the idea of an Alfine for the 456 but its not got the slide drop outs.
Can it be done without a chain tensioner?
Seem to remember someone talking about it can be done with a half link chain.

What about when the chain stretches?

My 456 (SS SS) has an ISCG mount. I use one of these to great effect. http://superstar.tibolts.co.uk/product_info.php?cPath=56&products_id=336

If you don’t have an ISCG mount you may still get away with the BB mount option. The tension is adjusted by sliding the roller up and down, but unfortunately I only get about 3/4 of a link worth of adjustment so need to be careful with sprocket sizes etc.

Use a Philcentric BB

I reckon you need a thingymabob… You know a whatd’yacallit. Purely due to chain stretch. I’ running an alfine on a slot inbred and have to occassionally re-tension.

Chains don’t stretch, they wear! I run two single speeds without tensioners and I have no problems. Chains wear fact. They should be changed at 0.75% wear in any case where it is a SS or geared. That is the wear point on a SS without tensioner that may start to cause slippage. So I do not see the problem. Every time a post appears about SS without tensioners there is always some who posts about “chain stretch”. I don’t to sound angry or rude but I feel I already have. There is a lot of misinfortation out there that does not chime with my experience of riding SS for quite some time.

Yes you can run a alfine without a tensioner or use one it is up to you. If a half link has to be used then use one but you can add or take two teeth total from the rear cog or chain ring to have the same effect. Take or add 6 teeth aand you will take or add 1 1/2 links total to the chain length. Doing this may allow you to keep the desired ratio.

Or use a tensioner it is up to you. There is no right or wrong way.

I’d go with a BB mount chainguide type tensioner and make use of a half link to get the chain as short as possible.

The 456 has vertical dropouts so I’m not sure how you’d manage chain length without some form of tensioner.

Whether you want to nitpick on the correct terms or not, the end result its the same, the chain gets longer and this makes getting a good chain length a bit hit or miss. No one wants a saggy chain, right?

You can if you pick the right cog sizes. I have two bikes with vertical dropout that I run single speed. Neither has a tensioner. With the right cogs you can have between 0- 1/4″ excess chain. More than 1/4″ would cause issues but a bit less is perfect. I can be done!

What bm0p700f said ^^^
You can get a single half-link to add into the chain to increase your options, but avoid it if you can. I tried it twice, both times the chain snapped at the link.
Aim for the “magic ratio” for chain length/sprocket size. Measure your chainstay length exactly then use this website calculator to help you find the nearest useful combination that’s a tiny bit bigger.

http://www.eehouse.org/fixin/formfmu.php?maxRing=36&minRing=32&maxCog=23&minCog=18&stayLen=16.35&wheelDiam=26.16&isMetric=0&display=png&useHalfLink=0&stretch=0.00&axleAdjust=vert&sortKey=Stay_length

Or you could fit a Philcentric Bottom Bracket.

BB is more expensive though. Magic gearing is cheaper in the long run.

I have used mostly used magic ratios over the years. Currently running an Alfine hub like this. So long as you have a good chainline and use proper SS cogs it won’t matter if you get a bit of wear in the chain. (I replace at 50%)

Nothing wrong with tensioners, but it’s a bit like procreation with a large rubber thingy removing the sensation…

I have no experience of running the perfect ratio talked about but you may find that this does not suit your Alfine set-up. I reckon it is easier to run a tensioner. I’m running the Alfine as a fit and forget set up and do not want to concern myself with chain wear hence my suggestion of a tensioner..