Actually, diametor on 195/55-15 is23.3 with 892 revs/mi. There is no sutch thing as 215/40-15. And 215/45-16 has a diam of 23.7 with 874 revs per mi. 205/45-16 has diam 23.3 with 893 revs per mile(difference is because of rounding.) The 215 is approx. 0.5 inches wider.