My road 10spd (double) chainset running with 9spd everywhere else does have a niggling issue. in little little the chain rubs against the outer ring and occasionally tries to upshift when the shifting pins catch it. I presume 10spd chains are narrower so the rings aren’t as “offset” as 9spd and closer to the centreline. (I got the chainset a while ago and ran my old 9spd rings on it for a while till that drivechain died, no probs, swapped to 10spd rings and the issues started)
On an mtb I’ve got a 10spd middle ring on an otherwise 9spd system, seems a bit more fiddly to setup the front mech – dunno why tho as shirley a middle ring should be smack bang on the centreline anyway.
Anyway they work well enough if the 10spd is at a good price but if there’s no difference in cost I’d go for proper 9spd.
