That's amazing, i'm so envious!
You probably saw Spotted Hyena as they are the least shy species of Hyena and the most common in that area, all other Hyena species don't live in groups larger than 5-6 animals so if there were more than that it would've definitely been the Spotted.
As for the tires they generally try to eat anything that they can partially fit in to their mouth, there's a lot of stories of them even trying to eat Aluminium cans and metal buckets!
There were definitely more than 5-6. More on the level of 10 I would say (but this was 1 year ago already and my memory is not perfect).
You can check the picture on the other post I shared with you on the chat. Dunno whether it helps ;)