195/45R15 tires have a diameter of 21.9", a section width of 7.7", and a wheel diameter of 15". The circumference is 68.8" and they have 921 revolutions per mile. Generally they are approved to be mounted on 6-7.5" wide wheels.
Can I use 195 tires instead of 225?
Yes it will be even smaller in diameter, which will help in acceleration (slightly), but the sidewalls will be better supported.Jun 10, 2004
Is it okay to go up a tire size?
As a general rule of thumb, it's safe to fit a tire up to 20 millimeters wider than stock on the original rim. The actual width of the tire will vary depending on the width of the rim: The tire will expand 5 millimeters for every half inch (12.5 millimeters) increase in rim width.