Earlier MC18's have got a narrower rear rim. I had two mc18's and couldn't figure out why i couldn't get to the edge of the tyre, even on the track (both bikes had 150 bridgestone bt90's). Took me ages before i noticed the rim was narrower As for the handling, riding the bikes back to back i couldn't notice the difference round Brands hatch.
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If only i knew then what i know now.