Is there ANY reason that I can't run 205/50x15s in place of my 185/60x15s?
 

Every car I've owned, I've basically went 20mm wider and 10 lower........all these tire sites say it won't "fit," although I'm quite confident it will fit just fine. Don't want new wheels, just fatter tires.....are they just covering their butts since it's not a stock size tire? I cry poppycock, or balderdash....or something..... SURELY my factory steelies aren't less than 5.5", from what I've seen. The time is getting near to replace with something better, just starting to freak out a little. Am seriously gonna just order them and have 'em installed, I think the fit will be fine.....20 mm ain't a whole lot

Stock wheels are 6” wide I believe. 205 is the largest width tire that is recommended to be installed on 6 inch wheels. If you’re using 6.5 or 7 inch wheels, that’s a lot safer.

Assuming you’re running 6 inch width wheels, you should be ok. But keep in mind it’s still a fairly large side wall. There’s less options for 205/50R15s too, so you’ll lose a bit of selection compared to sizing up to a 16x7 wheel for example.

It’s probably not recommended you do highly spirited driving as you’re increasing the lateral grip, while not reducing sidewall heigh significantly. You’re also at the limit of what’s recommended for a 6 inch wheel. For day to day driving you’re probably fine, you’ll take a hit in fuel economy.

In short, is it impossible to run 205/50R15s? No. Can you do it? Absolutely. Maybe look into a set of 15x6.5 wheels?