19 tooth Sprockets are here!

[Dave Whittle Thorn Workshop]

Now in stock http://www.sjscycles.co.uk/thorn-sprocket-for-rohloff-hubs-prod28817/

[revelo]

Hi Dave:

I'm in the process of switching from 42/17 to either 40/19 or 36/17. What concerns me about the 19T sprocket is that Thorn previously made a 21T sprocket but no longer. What is to say you won't also discontinue the 19T at some point? Then I'd have to make another switch of the chainring.

Also, after 8000 km with the 42/17, neither the sprocket nor chainring (Thorn aluminum) are showing significant signs of wear. I run with a chain that is filthy with dust most of the time, but replace the chain as soon as it shows signs of stretching. So far I've replaced it twice with another replacement due soon, or about 2667 km/chain (8000/3=2667). So I'm not sure as to what I'm gaining with this 19T sprocket.

BTW, I was planning to send you an email, but maybe it is better that you reply here so everyone can see. In addition to switching the sprocket/chainring, I also want to experiment with one of those chain guards (either http://www.sjscycles.co.uk/thorn-high-quality-alloy-chainguard-for-110-pcd-rings-up-to-38t-black-prod11144/ or http://www.sjscycles.co.uk/thorn-high-quality-alloy-chainguard-for-110-pcd-rings-up-to-44t-black-prod11089/ depending on whether I go with the 19T sprocket or not, not sure why the description is PCD rather than BCD). Currently, I have a UN55 73 x 110mm bottom bracket and 110bcd crank. I believe I have to get a wider BB, and also new crank bolts and washers, in addition to the chain ring and chain guard. Could you thus specify:

1) new BB width I need to accommodate the chain guard
2) bolts and washers to accommodate a Thorn chain ring and chain guard with this new BB (and the old 110 bcd Thorn crank)
3) bolts and washers to accommodate a Thorn chain ring WITHOUT the chain guard with this new BB (this is in case I decide I don't like the chain guard but don't want to hassle with switching back to the old 73 x 110mm BB)
4) bolts I am currently using on my existing BB (the 73 x 110mm) so I can order a spare along with everything else (this is in case I ditch the chain guard and switch back to the old BB, because I don't have a spare bolt now)
5) finally, would crank bolts and washers be any different if I used a Surly steel chain ring rather than a Thorn aluminum chain ring? If so, then please answer questions 2,3,4 for the Surly chain ring, just for reference.

[Dave Whittle Thorn Workshop]

Hi,

The 19t sprockets will probably be a no cost option on the bikes in a min so uptake should be alot higher than the 21t we used to sell. Cruicialy we can get the 19t sprockets made in smaller batches and for not much more than the Rohloff sprockets so again we should sell enough to keep it rolling as a product, people just wern't prepared to pay the extra money that Rohloff wanted for us to order the 21t versions i'm afraid, the people that make our 19t cant make anything bigger at the moment.

In reply to your questions:

In production we use:

Thorn Cranks - http://www.sjscycles.co.uk/thorn-110-74-pcd-triple-solo-alloy-crankset-silver-prod1673/
Thorn Crank bolts - http://www.sjscycles.co.uk/thorn-m8-crankset-bolts-stainless-steel-pack-of-2-prod27430/
Thorn Chainring bolts - http://www.sjscycles.co.uk/thorn-m8-single-chainring-bolts-stainless-steel-pack-of-5-prod27429/
Thorn Chainring - http://www.sjscycles.co.uk/thorn-110-mm-5-arm-reversible-single-chainring-3-32-inch-black-prod11053/
Shimano UN55 Bottom bracket in 73 x 110mm - http://www.sjscycles.co.uk/shimano-un55-68-mm-shell-english-thread-sealed-cartridge-taper-bottom-bracket-prod26972/

With this setup the chainring sits on the outer position.

If you want a chainguard we use:

Thorn Cranks - http://www.sjscycles.co.uk/thorn-110-74-pcd-triple-solo-alloy-crankset-silver-prod1673/
Thorn Crank bolts - http://www.sjscycles.co.uk/thorn-m8-crankset-bolts-stainless-steel-pack-of-2-prod27430/
ID Chainring bolts - http://www.sjscycles.co.uk/id-stainless-steel-chainring-bolts-m8-x-075-double-85-mm-nuts-pack-of-5-prod18426/
Thorn Chainring - http://www.sjscycles.co.uk/thorn-110-mm-5-arm-reversible-single-chainring-3-32-inch-black-prod11053/
Thorn Chainguard - http://www.sjscycles.co.uk/thorn-high-quality-alloy-chainguard-for-110-pcd-rings-up-to-44t-black-prod11089/
Shimano UN55 Bottom bracket in 73 x 113mm - http://www.sjscycles.co.uk/shimano-un55-68-mm-shell-english-thread-sealed-cartridge-taper-bottom-bracket-prod26972/

With this setup the chainring sits on the middle position and the chainguard the outer position.

If you wanted to remove the outer chainring guard without changing the bottom bracket back you would need to leave it in the middle position and fit the single chainring bolts, or use some 4mm spacers and re-use the double bolts.

We have never fitted a Surly ring they should work as above but are slightly thinner so you may end up needing some thin chainring washers http://www.sjscycles.co.uk/wheels-manufacturing-chainring-spacer-each-prod17702/

Hope this covers all your questions.

[JimK]

Wow thanks Dave, that's a regular lesson in chain line management! Very useful information for me, too, in case I ever want to reconfigure one way or another.

[revelo]

Yes, thank you very much Dave.

[Slow Legs]

Is the new 19 tooth sprocket reversible?
Thanks
Alan

[Dave Whittle Thorn Workshop]

Is the new 19 tooth sprocket reversible?

It is indeed.