I am looking for some "formal" information about which tyres I can put on my car rims. More generally speaking, I'd like to be able to find an optimal match between a tyre and rim width.
The question is triggered by the situation I found myself in now. My Volvo V70 came with 225/50-R17 tyres on 7Jx17-ET50 rims. Looking at www.tyresizecalculator.com, this is not an optimal combination, rather on the edge. It gives 195 mm as minimum, 205/215 as ideal and 225 as max allowed. Would Volvo build a poor combination wheel? A Volvo dealer, to whom I showed the linked table and whose competence I really doubt, said that 205 mm would be too narrow for these rims, not to mention 195 mm. On the other hand, another table I've found (in Russian) lists 7 inch as the optimal rim width for my tyres. So that Russian table (from an online tyre shop) seems to agree with the dealer and Volvo, but doesn't match TyreSizeCalculator.
I wonder where all this information is coming from, why a mismatch, and where I can find the "holly truth". Isn't there some sort of standard for this?