Ask your local tyre firm. THey should have a chart.
Lets put it this way though, applying a little common, if the rim is more than 10mm wider than the tread then the widest point on the wheel will always be the rim width.
"Rule of thumb" is tread is effectively 5mm wider (or narrower) per
1/2inch rim width diff from nominal (but it goes to pot when you stretch it more than 1.5").
Nominal rim width should be about 80% of tyre section for modern lower aspect 70/60/50% tyres (70% on old cars, trucks, vans, 4x4, suv's etc with 82% tyre profile).
The 165/65 should be on a 5J and will be slightly "stretched" thus giving a contact patch like a 170. The 185/60 should be on a 6J and will have a contact patch like a narrower 180.
Very low profile tyres need wider rims, for 45% the ratio is 85% and for 40% it is over 90%.
So for your 195/45 the nominal rim is 195*0.85 = 165.75 = 6.5". On the 6J it will be about 5mm narrower and on a 7J 5mm wider, 190 and
200 respectively. All are so close as to be considered normal it only becomes really noticeable when rim is 1" or more oversize.
The "issue" with such dinky arches and poor clearance is that fitting suitable alloys in the space isn't easy.
Oh and keeping low wheel weight too.
If I can find some TSW Quads in the right size, great, but from the above the difference between a 6J 15" wearing 195/45s or a 7J rim with the same tyres isn't great. Still, 10 mm may be enough to put it over the edge... :-(
OZ Superleggeras are available _from_ 7J 15". :-/ They're about the most stylish, lightweight wheel we can find.
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