[raayn]

what's the best sized spacers to use with 17x7 +45 offset wheels with 215/45 tires?

 

[Chris]

don't use spacers unless you intend to install longer studs too!

 

[raayn]

That's the plan.

 

[slimlou]

3/16" (5mm) in the rear is all you need/fit because you're going 215 wide. I've got 205/50/17 on the same sized rim size with a 1.5" drop and it's got a nice wheel gap.

 

[gailgill]

You can measure the distance between wheels and fenders to determine what thickness of wheel spacers to install.

I had BONOSS wheel spacers 20mm on my car for almost 21,000 miles, with no issues whatsoever.
Maybe you can try what I installed.

They can customize the thickness and data that I want, so that I can install new tires with different data, and the customization time is very fast, just 1~3 days. If you need it in the future, this is their case article.