technically, every time you turn a corner, all four wheels travel slightly different distances. How do the clutch packs deal with that? Sounds wierd that seeing as theyre going different speeds anyway that a difference in diameter would cause cornering issues...
For long term issues tho, i nutted this out - this is my reasoning as to why something that seems so inconsequential can cause dramas -
A difference of 10mm in rolling diameter (Say 660mm front and a 650mm) rolling diameter rear tyre is a different of 31.42mm difference in distance travelled per rotation. Given that each rotation of a 650mm diameter tyre is about 2050mm, your larger tyre would rotate about 65 times every time your smaller one does 66times. So your larger tyre will have rotated one less time than your smaller one every 133 metres. If you do 1000 km a month, so 12,000km a year, then its a matter of your clutch packs coping with a difference of 90225 rotation difference every year. Thats a lot of wear and tear on your clutch packs, from a difference of 10mm.
if you have 225 tyres with 40 section, and 225s with 45 section, your difference in diameter will be 22.5mm (45% of 225 - 40% of 225, then multipliy it by two as we're dealing with diameter, not radius), so double the above figure. More than 180,000 times is what ur gonna get.
Hope that A) that makes sense and that B) it is correct!!
Bobbeh