Correct spacer for a Shimano 9sp cassette on an 11sp road hub?

[rogerzilla]

There are various thicknesses on the Bay Of Thieves but they can't all be right.  Also, anything that claims to be for 8/9/10 speed cassettes is bollix because 10sp is narrower than 9sp.

Anyone actually done it?  My guess is it needs to be 1mm, or just under.

[Hot Flatus]

1.85mm*

10sd needs 1.85 plus a 1mm.

*1.75mm if hub is Mavic

[grams]

AIUI 10 speed cassettes are usually bundled with their own spacer to make them the same width as 8/9, although I’ve never bought one.

[rogerzilla]

Thanks all.  The rear rim was worn out so I thought I might as well future-proof the new wheel, although moving to 11sp at this time is pointlessly expensive.

Moultons don't accommodate long rear mechs, so gearing is always a problem (especially as triples are dying out).  The best I can do is 11-32 with a short cage 105 mech.  Even that is outside spec.  Usually, I wouldn't care about low gears on an unladen bike, but a Moulton can't be honked uphill without wasting a whole load of effort making the fork pogo up and down.