This link (when translated by Google Chrome) seems to suggest that the MC18 R2J has a 4.00" x 18" rear rim and a 3" x 17" front rim. This suits a 140/18 rear and a 110/17 front. Let me know if I am wrong here.

I have an MC18 R6k which differs in that it has a half inch wider rear rim at 4.5" wide.

I just bought a set of Bridgestone BattleAxe BT-090's for mine (110/70/17 and 150/60/18 )
However, assuming you have a 4" wide rear then you would ideally want the 140/60/18 rear although the 150 will probably be OK?
To get a 140/60/18 you would need to go for the Bridgestone BattleAxe BT-092 which might not be quite as sporty as you were hoping? I am guessing that they are available in the UK?

I haven't investigated other brands, so maybe there is a better option out there.
Anyway, I hope this was helpful.
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