Miata Turbo Forum - Boost cars, acquire cats.

Someone is selling WORK RSB 15'' rims for a Miata in my area for a good price, with RS3s on them. I have searched the internet for the specifications on that rim, and cannot find much information. Looks like it has been discontinued a while ago. To make matters worse, the seller does not even know their width or offset. The tires mounted on it now are 225/45/15. Has anyone used these rims in the past? I want to find out if they are forged, and how much they weigh. I don't think he will let me take it to the tire shop, dismount the tire, and weigh the rim. Any factual input is much appreciated!