After many hours of looting various industrial buildings I have concluded one of the following regarding car loot:

1. Car loot spawning is dependent on how many present items exist per server.

or

2. Olga hoods are common, doors and backs occasionally exist, and wheels are very rare (AMONG rare car loot). Making wheels extremely rare.

I've played this game for 19.7 hours the past two weeks and have found 1 tire. My suggestions are the following:

1. Increase tire/car loot spawn and reduce motorcycle helmets/hardhats/clothing.
2. Make wheels universally applicable to all in-game cars.