Use a tire size calculator for diameter. +/- 2% is usually OK. What car did your uncle have? Since it includes the rims, you'll need to check the offset, as well as the interior brake caliper clearance.
I'm going to have to agree and disagree with ejw2011. Yes, changing the tire size from OE will change the speedometer. In this case, though, the change is tiny. So I think a 235/55R-17 should work fine.
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