Chains and chainrings

[Sven23]

Hello everyone, I’m new here and new to Thorn.  I’ve just bought my first, a second hand Raven.  It has a Shimano Alfine 11 speed with a 37 tooth chainring.  I’d like to up the teeth to somewhere around 40-50 but, don’t know what chain will fit this.  The crank is a Shimano Deore and the current chain rig is 104BCD 4 post.  Can anyone suggest what length of chain I’ll need and what chain ring will best suit. 
Thanks in advance.

[PH]

Hello to you and congrats on the new bike.
Do the components need changing for any reason other than the gearing?  If not, depending on current sprocket it may be more economical to change that and you could possibly keep the same chain, £7 V's £40+ for a new chainring and chain. The 37 to 45T chainring difference is around 20%, about the same as an 18 to 15 sprocket.
If you do decide to change the chainring, something singlespeed and reversible will be the best long term value, though not the cheapest upfront option, I like the Thorn ones*, though I haven't experimented with many others (An expensive Surly and a cheap Stronglight) For chains, pretty much anything, for economy 8 speed seem to be the sweet spot, though there are specific single speed options, the KMC e1 EPT is IMO as good as it gets, though it's triple the price of some others and I'm sceptical it's three times as good.

I expect someone will be along shortly recommending you fit a chain glider... which would then restrict your options.

* https://www.sjscycles.co.uk/chainrings/32-thorn-104mm-bcd-4-arm-reversible-single-chainring-332-inch-black/

[mickeg]

As noted by Ph, changing the sprocket to a different size can be cheaper.  And, sprockets wear out faster than chainrings, if your sprocket lifespan is near the end, that may make more sense.

I assume that somewhere on Thorn website there is instructions on how to adjust a chain on a Raven, but I do not recall where, I have not looked for that type of info for about nine years. 

To put a new chain on, it needs to be cut to length.  Most good multitools come with a chain breaker that can be used to cut a chain.  And eight speed chains I think always come with a quick link to attach the ends together.

Youtube videos for cutting a chain may help, Park Tools has very good youtube videos for a lot of basic bike repairs and maintenance. 
https://www.youtube.com/@parktool

I assume that Thorn website can help figure out how many links you need in a chain if you change to a different size sprocket, chainring, or both, but I am not sure on that.  The Park Tools youtube channel I suspect only describes that for a derailleur bike.

How to remove a sprocket from a Shimano hub?  I am clueless on that.  I only have experience with Rohloff and older Sturmey Archer hubs.

[martinf]

How to remove a sprocket from a Shimano hub?  I am clueless on that.  I only have experience with Rohloff and older Sturmey Archer hubs.

Shimano Alfine 8 and 11 (and Nexus 7, Nexus have the same pattern of sprocket as the older Sturmey-Archer hubs. The circlip is slightly different, I find the Shimano one slightly more difficult to remove and refit, due to the section (square or rectangular IIRC rather than round) and (maybe) a slightly stronger spring action.

[UKTony]

To give you some idea, my Nomad Mk2 which I bought new from Thorn in 2013 has a 40/17 chainring/sprocket set-up. A new KMC chain of the type mentioned above by PH comes with 110 links.  When I replaced the original chain for the first time I didn’t try to find formulae to calculate the number of links, I simply reduced the new chain to 102 links (including the Quicklink) to match the number of links I counted in the old chain I was replacing. I figured that Thorn  would have put on a chain of the right length to give as much adjustment as possible of the eccentric for the ring/sprocket combination I specified and the chainstay length of the Mk2 Nomad frame.

The Mercury I bought last year came with the same KMC chain and a 44/17 set-up with 100 links. The gearing was too high for me so I lowered the gearing by replacing the 44T chainring with a 39T and removed 4 links to achieve the correct chain length (96 links) to get as much adjustment of the eccentric as possible.

The Nomad Mk2 has a longer chainstay (about 46.6cm c-c) compared with the Mercury (about 43cm). I’m guessing that the Raven chainstay length will be somewhere in between.