The tyre is Michelin TRX as you can see on the photo. Michelin in the eighties had an experiment with wheel diameters in millimeters in stead of standard 15", 16" , 17". The Michelin metric wheels were not such a success and soon dissapeared. Specially the BMW´s that time came with Michelin metric wheels. So the wheel on this car could be metric and therefore very scarce, but I have not seen them before and cannot tell for sure.
If you look at this page you will see that the TRX tires were in mm instead of inches, like HR 340, HR 365, Hr 390 etc. So I am pretty sure that the wheel on the GTV is a special metric TRX-wheel.
http://www.longstonetires.com/trx.php