Thanks all. I went over to see fellow club member Chris near York and bought 4 gorgeous Compomotive CXRs with 175 55 r13 on the front and 205 55 r13 CR500s on the back. We "measured" ( by offering up a couple of planks of wood ) the clearance under the sump, then changed the wheels over and re-measured. The sump was indeed lower by approx 1cm ( 2.0L wet sump Duratec SupersportR ). Although I'm no racing driver, the lower ride height was immediately apparent, as was the brisker acceleration but the increase in grip was just astounding. The ride was also transformed. Far less jiggly - presumably the combination of bigger sidewalls and considerably lighter wheel & tyre combo. I knew the tyres would make a difference but wasn't prepared for the amount of difference. I am now more nervous about grounding it out so will be saving for a dry sump and chatting to other club members about fettling the ride height. Now though, I'll be able to "just" buy ZZSs albeit 185 55 r13 and 215 55 r13. Also need to re-calibrate the speedo, find some centre caps and no doubt a pile of other things... Have to say, Chris near York, lovely chap, lovely R400, great coffee and now I'm jealous of the Stack dash!