Tires: rolling circumference comparison, 17 wheels, winter tyres

Question
Hi - I live in England & due to recent bad snow I want to change my 17" wheels for 16" with taller profile winter tyres. The current tyres are 225/45/17, will 225/55/16 offer the same rolling circumference? I have checked stud centres/wheel offset & brake clearances.
Many thanks,
Colin

Answer
Colin,

First, there are no regulations that say a particular tire size has to be a certain diameter.  However, most tire manufacturers make tires at about the target dimensions, so usually changing tire sizes is pretty straight forward.

Here's a calculator that answers the question that you have.  But you should be aware that it assumes that the 2 tires are designed in the same way - diameterwise.

What this calculator says is that the tires are NOT within 3% of the same rolling circumference - and that creates a whole series of issues - rubbing being the most obvious one.

Opps!  I forgot to post the link:

http://www.1010tires.com/TireSizeCalculator.asp