Would a 10 speed shimano chainset work with 9speed chain /rear and front mech? I only ask this question because I can get one cheaper than the 9 speeed version. advice appreciated

Yes

As I understand it for Shimano the rear mechs and shifters (and cassettes obviously) have to match 9-to-9 or 10-to-10 because of different cable pull to change one sprocket. This is new for 10spd MTB stuff and is unlike the 7, 8 and 9 spd scenarios where you could get away with mixing shifters and mechs.

Everything else is interchangeable but may work a little better if arranged as Shimano saw fit.

As an aside, a 10spd MTB cassette and 10spd road shifter appear to require a 9spd rear mech to make them work – all Shimano parts that is. Bizzare.

I read somewhere that the internal dimensions of the chain are the same as 9sp.

a 10spd MTB cassette and 10spd road shifter appear to require a 9spd rear mech to make them work

I understand the pull ratio is changed for MTB 10sp, but maybe on road it’s the same as 9sp?

Its only limiter screws…… You could widen the limits of a 7 speed to work on a 9 speed cassette. But the shifter has to have same number of clicks as there are cogs at the back…..

I ran this for a few months before I completely went 10 speed. I did find a 10 speed chain ran slightly better as the 10 speed chainsets are designed for the externally narrower chains. As above 9 and 10 speed chainset have same internal width.

A 10 speed cassette requires a ten speed chain, a 10 speed rear mech requires a 10 speed shifter, a ten speed front mech will work with a nine speed shifter.
A ten speed cassette, chain, shifters, and mechs will run on a 9 speed crank and chainrings.

The internal measurements of a 9 and 10 speed chain are the same, the external measurements are different, thus a 9 speed chain can and does snag in the chainrings on a 10 speed cassette, this also means that a ten speed chain will run on a 9 speed crank and rings.

Think that covers it…
T

Except when you mix road and MTB parts…