Hi, i will try my best to explain to you...here goes (may bore
the rest to death
)
185 or 195: The tyre section width (W) in millimetres
70: The aspect ratio in % (The height of the sidewall divided by
the tyre's width) [H/W x 100%] = Aspect Ration %
If you understand the above, say the 185/70 R14 vs a 195/70 R14
based on the above theory, you will realise the height-H will be
different for both, thus if the Rim size stays constant (i.e. 14")
the overall radius and circumference will change.
I hope I have answered and cleared your doubts.....