What’s the recommended tire size (13”) for my 1980 (Gen 1) Brat? And what are some other sizes that have worked for people. I’m looking for a quality set of tires for my brat and would prefer to put on the original size, 

From memory 185/75r13 is the factory tyre size. It should be in your owners manual if you’ve still got it! 

Cheers 

Bennie

Could also check the door jam Vin tag. Sometimes that info will be there

At this point in the vehicle's life, whatever 13-in. tire you can find close to ~22-23-in. diameter is the right size tire.  There's only a handful of decent handling, safe options out there (I'm looking at you, re-treaded tires...)