Ah, I see now that I answered your questions on 20 September 2013 at
http://www.thorncycles.co.uk/forums/index.php?topic=6813.msg46901#msg46901 Never mind, I've written another reply and there are some additional links and information in this post.
Also, I note you say you fitted it to a 38/17 combo but the SJS page for the CG says 39/18-22.
Is there a guide from Hebie saying that 17 goes with 38?
I am thinking of going for the 38/18 combo.
But when I look on the SJS site, the rear rings are only 13 15 16 & 17 teeth!
What am I missing?
Matt, a Chainglider consists of two parts that may be mixed and matched to suit the bike and its gearbox, a front part consisting of the chainring cover with two integral arms to cover the chain, and a rear part to cover the sprocket. Within each of those two parts there are several different models available, and you must take care to order the right bits or to find a supplier who knows his oats.
At the front, you can get Chainglider front ends that fit 38, 42, and 44 tooth chainrings; these are three different Chainglider components; choose one; when you get a different tooth count on your chainring, buy another Chainglider front end.
At the back you can get different Chainglider sprocket covers that suit different hub gearboxes. There is only one that works with a Rohloff.
(I don't know where SJS got a Chainglider for a 39T chainring from -- perhaps you mistyped. But the 18-22 tooth sprockets you mention belong to the Shimano hub gearboxes and is covered by a Chainglider rear end that will not fit your Rohloff and is likely to damage it.)
What you need is the specific Chainglider rear end for the Rohloff. That one component takes the Rohloff sprockets that have 15, 16 or 17 teeth; nobody except the makers of little folding bikes wants to know the 13T sprocket and one gets the idea Herr Rohloff would rather not own up to paternity of it. Martin appears to be of the opinion that the higher tooth counts may lift the arms of the Chainglider higher on the chain, presumably making it run lighter and more silently. Makes sense to me. In any event, the higher tooth counts do not require the chain to bend so sharply and may improve chain life. (Obligatory on-topic remark!)
It would be smart for you to buy your Chainglider from Thorn or another dealer who knows what he is doing, and to specify it precisely as "for a 38T chainring and a Rohloff hub gearbox with 17T sprocket".
There is an additional complication. There is in addition to various Chainglider front ends for 38, 42 and 44T chainrings, two
lengths of front end. If your bike is particularly large, in particular if it is a long wheelbase bike with the chainstays scaled in proportion, you may need the Chainglider front end with the longer set of arms. I haven't actually heard of anyone on the forum having to order the longer-legged front end for a Thorn, but I got them for my Kranich, which is over two metres long and scaled in proportion with custom-made tubes by Columbus. The long front end is available for 38, 42, 44T chainrings.
Note that there is no 36T front end at present and apparently no intention by Hebie to introduce one.
Here is a pictorial reference:
Rohloff Chainglider rear end, the only one that will work with a Rohloff:
38T Chainglider front end standard length for a chainstay up to 455mm:
The long Chainglider front is for a chain stay up to 525mm. The measurement is centre to centre of bottom bracket axle to rear hub axle.
Either front end can have a bit chopped off each arm -- your wife's breadknife or a metal saw is good -- to suit the particular length of your chain stays, but this isn't critical as the arms slide into sockets on the rear end.
Here's a page with a video demonstrating how easy it is to fit a Chainglider, and particularly how the pieces fit together.
http://www.hebie.de/en/protection/chainguard/chainglider/350/Scroll down this page for all the available Chainglider parts, including some that will damage expensive bits on your bike, see above:
http://www.hebie.de/en/protection/filter-cg/All the part numbers you need are on the page above.
Hope this helps.
EDITED 21 August to remove reference to the Chainglider front end for 48T chainrings, which
does not fit the Rohloff rear end. Thanks to Macspud for spotting it!