Hay Plate,
First positively identify. Then a couple of things - Wear light colored clothing as their natural defensive reaction is against dark predators (bears, skunks). You mentioned that they have been there a few years. When the nest becomes crowded (maybe the tire is full?), they will become agitated and very defensive - and you may soon see a swarm. Interesting is that the swarm is very docile, even though it looks like total chaos! Like Rafe said, call a local beekeeper. They will gladly take the nest, if accessible, off your hands. If it's hidden in a tire, maybe you can let them have it! They will cover the opening and take it away. Even better, have a local keeper show you how to transfer them to a hive for yourself. It's a great hobby!
My Grandpa and Dad kept bees. My Grandpa was immune to stings and never wore gloves or a hood. My Dad had the normal reaction to stings. My sister has to carry an epi pen because she is deathly allergic to them. After one or two stings in the spring, I have no reaction for the rest of the year - like my Grandpa. I used to help my Dad all the time without protection and my Mom would always be freaking out - because of the scary situation my sister went through. I have kicked around setting up a couple of hives, but there are always things more pressing... Nothing better than honey!
Jim