I have a 1989 NSR 250 MC18-race bike! Currently I have two sets of wheels-one set up with slicks for the dry and another set set up with wets for damp conditions.
However with the original MC18 '89 she came with a wheel size of 18 at the back and 17 at the front.
Someone has got a 17" for the back-I was told so they could put slicks on.

Presumably having different size wheels must change steering/ handling of hte bike although I see on the next model they actually went to 17 front/ rear anyway.
I would prefer to have an intermediate tyre for racing so don't have to change wheels if track wet-would I be better to get intermediates for original 18" back or put on 17" back? What tyres best as intermediate for racing?
Currrent tyres are Metzeler slicks-racetec made in germany and wets are Bridgestone!

I would tend to go for a slick for both 17 and 18 and take a tyre cutter. If you feel the need for an inter you can then just cut the amount of tread you think is right for the conditions.
_________________
If I have to take the carbs off once more...