Lots on here about Chaingliders but I could not find a thread on fitting them to Thorn bikes, specifically the Raven Tour.
The problems:
There are two problems with fitting a CG to a Raven Tour:
1. If a Thorn alloy chainwheel is still fitted it will need to be replaced as it is 5mm wide and the CG spec says the max chainwheel width is 3mm.
2. The seat stays on Thorn bikes are closer to the chain than on some other bikes. This is compounded by the fact that over the years Rohloff have increased their recommended chainline and Thorn bike frames were designed at the time of the narrower chainline.
Different Rohloff sprocket carriers require different chainlines:
- threaded (chainline 54mm)
- splined (chainline 57mm)
- threaded converted to splined with the thinner adaptor (chainline 55mm)
A narrower chainline gives more clearance between the chain and stay so a Rohloff hub with the earlier threaded sprocket carrier is best.
Solutions
1. The chainring - simply replace with a thinner chainring.
I used a 4mm thick Shimano STYX 38T alloy ring with Narrow / Wide teeth for no better reason than I have had one on another bike for 7500 miles with a CG. Being 1mm wider than ideal, however, it does make a sound like a squarking chicken when wet but I know this will go with time as the CG wears in (the chainwheel on the other bike did not not wear, it was the CG that wore down to size).
2. On my Raven Tour (threaded sprocket carrier and 537L frame) the closeness of the chain to the stay meant that the rear section of the CG was being pushed slightly inwards. Long term this could result in paint damage to the stay and the risk of the CG rubbing on the soft but expensive alloy hub.
My solution was threefold:
1. File off about 1mm from the top corner of the rear section of the CG where it touched the stay.
2. Heat the rear section of the CG in the area where it touched the stay with a hot air gun and push the now flexible material inwards maybe 2mm with a rounded piece of wood. The plastic appears to be ABS so becomes hard again once cooled. The geometry of the rear section of the CG allows this inward bulge to clear the chain.
These tweaks gave about a 1mm gap between the stay and the rear part of the CG.
The final detail was to stick a piece of clear plastic Gorilla tape on the stay to protect the paint, which reduced the gap slightly.
Different combinations of Thorn bikes / frame sizes / rohloff sprocket carriers may need different solutions, for example cutting away part of the rear section of the CG so it clears the stay.
