Above is the Carrera Crossfire fitted with a Sun Race 40T cassette. It was difficult to tell how satisfactory the set up would be without a derailer extender as it was all so out of adjustment and needed a new chain and cable. The chain geometry looked as though it would work after a fashion.
I fitted an extender. This needed some alteration which I did with an electric drill and a metal bit. The metal is soft and easily worked.
Both the cassette and the hanger extender were Amazon acquisitions. Bike shops are reluctant to sell non-standard parts, I think because of liability and potentially disappointed customers.
However, I had a good deal of help from Boneshaker Bikes and Powerbikes UK in Whitehaven. They know Carreras probably all too well and keep good stock of parts for them. I bought a torque sensor and bottom bracket and various other bits from them and they were happy to advise with the benefit of real experience. Both names are in my little black book.
I bought on their advice an eBike chain by KMC. These have a Bosch label nowadays. I expect that if Rommel had a push bike in the Western Desert, he would have chosen a KMC chain. I broke 2 cheap chain splitters in the process.
On chain length there was some compromise. I wondered if the extender would mean a longer chain - as when swapping a short for a long de-railer cage. In the end I went for the usual formula length - around the chain wheel and biggest cog and then add two links. You can see the result in the photos when 1 and 8 were selected. The chain might be tighter on the small cog but then there may be difficulty selecting the large.
The changing could be crisper but everything selects without delay. There is a lot of play in the jockey wheels and I am pondering whether to buy a new derailer and perhaps a longer one. For the moment, I am happy with the result and the bigger cog makes a difference on our lovely lakeland hills.
Anyway, that is enough from Mr Pooter's derailer diary but I thought someone might be interested in a straightforward improvement to a popular bike. Although unreliable and now more expensive, at the time this bike did a lot to democratize ebiking. So far it has done over 2K miles and I hope for similar before the battery packs in.
Thank you for the help from this great forum. A contrast to Halfords. I took it there as my first thought was that there would be no drama fitting a new torque sensor. They forgot about it for 3 weeks and then their child labourers attempted to tell porkies about how they had exhaustively tested it but, the computer said, "No." But from reading here, I see that we're used to that ...
