Hunter if you use the 25.4 figure, then the P205/50R/16 is only 3.6 milimeters different than a P195/60R/15?

Answer 1

Yes, you are correct, but it is actually 4 mm difference.

The first number is the width of the tread and the second number is the percentage of the first number that is the height of the face of the tire.

So 205 is 205mm width of the tread and height would be 50% of that number which would be 102.5mm.

The other tire would be 195mm width of tread and 60% of that for height or 117mm.

Also the 3rd number is the diameter in inches of the rim it is on. 1 inch is approx 2.5cm or 25mm times 16 inches is a 400 mm rim and 25mm times 15 inches is a 375mm rim.

Adding up these figgures makes the following totals...........

P205/50r/16 would be 205mm wide x (50% of width x 2 for top and bottom faces or 205mm + 400mm for rim) 605mm high.

P195/60r/15 would be 195mm wide x (50% of width x 2 for top and bottom faces or 234mm + 375mm for rim) 609mm high.

Difference is 4mm.