Re: Rear tyre size
 

The same principal should hold true for vehicle application. I have somehow man aged to put non-oem size tires on several cars and I'm no rocket scientist. Certainty a company that specializes in wheels and tires should be qualified to make that determination.

Re: Rear tyre size
 

Certain approved independent laboratories (i.e. Tüv in Germany) can confirm fitment of a set of rims/tires for specific car models. Some wheel manufacturers does go through with these certifications, and those wheels can then be approved on your car.

Fitting non-oem sizes on cars and observing that they'll rotate isn't hard, no. But confirming that they still keep their distance to surrounding parts while at full opposite lock around the track (or evading a donkey crossing the street) is not as easy.

It might seem odd to have such rules to protect the driver. Just like it's odd that there has to be a law against driving without your seat belt, as one would imagine using such a safety feature would be obvious, but it's not.

If all stuck to minor changes it probably wouldn't be an issue, but there's always that one guy.
https://i.ytimg.com/vi/QsvXX218gbk/maxresdefault.jpg

Are there really no restrictions in the US?

Re: Rear tyre size
 

So what kind of deals are you making with President Trump!!!

Re: Rear tyre size
 

Only the greatest and best deals ever. And so easily done. You'll get sick from all these great deals!