morning

i have recently purchased a P100 tipper and i need new tyres, now the question;

the tyre guy offered me a whole set of 196/60/14 for a very good price.
Is the stepp from 185/80/14 to much? i have got no idea about that the only thing is that all these tyre size calulator pages tell me they are 60mm smaler in diameter and that is about 10% less than the originals. by the way my speedo is way out with the original tyres anyway reads 45mph when doing 30mph, got no idea why.

thanks for all your help

Team Fragglerock