Wheels and tires play a vital role in your driving experience, that's why it is so important to make the right choice when you decide to replace them or upgrade to a different option. You may easily identify what type of tires you need based on your needs, but when it comes to the right size...
This is what I always use if I'm buying new tires and the rims are of a different size from the oem rims.
It's important to get the right numbers so your speedometer does not go out of wack. Hope it helps.