Cycling UK Forum

I'm trying to resolve a driveline issue with a 2x10 Boardman Comp. On the 38T front ring when using the smallest 11T cog the chain brushes the adjacent 13T cog. This results in some vibration through the driveline and an occasional skipping sensation on the flat. After repeatedly trying to adjust this out without success, I though there may have been a wear issue but I'm not sure this is the case. I fitted a new x10 KMC chain (the same as the one fitted from new) and comparing old to new there's just 0.35mm difference over 106 links. I also checked the teeth for hooking and other wear and tested the new chain for engagement.

If the chain is slightly deflected outwards on the top run the drive is very smooth. The bike changes and indexes really nicely in every gear and the RD is not bent. The adjustment is started with cable slack to ensure the RD is not being limited in movement. I've tried experimenting with adjustment but there's no position between where the chain stops rubbing and where the RD is so far out the chain comes off or hunts.

The bike has always felt rough in the highest gear and I can now see why. No spacers are fitted to the rear cassette, but the largest 36T cog has an inbuilt spacer 1mm thick. While I was at it I serviced the hub and freewheel. I checked the spacing and all the cogs are spaced 2.4mm except the smallest, which is 2.1mm from its neighbour. This has an inbuilt spacer but no shim. The front chainwheel runs true to within 0.3mm.

What steps should I take to further diagnose and remedy the problem?

Thanks for the info. I checked and the chainrings fitted are the same size as the ones in the link you posted. Ours is maybe an earlier version (I think it's an XCM-AX) with a Hollowtech II crank. I've now found plenty of rings of the correct size.

The Suntour 38T outer has a particular pattern of machining in the teeth and a number of ramps and studs to assist with changing. Is it necessary to buy a specific ring for an outer that has the same features? (assuming that it's intended for a 10-speed setup)

I'm looking for a pair of chain rings (24T and 38T) for my wife's 2017 Boardman Comp but have been unable to find them. The crankset is a Suntour XCM. Can anyone advise where I can get them from? I've also tried searching on the individual part numbers, but nothing.