I’m suprised you guys have got time to post on here. Shouldn’t you be googling tractor tyres or something?
You should know mate
Bear Grylls Survival Race Training
We split into three groups to carry a big tractor tyre, a log, two ammunition boxes and a sandbag around the outside of the grass area. I am nothing if not keen, and against all better judgement took an ammunition box, knowing that I would find it hard enough to just run, let alone while carrying something. And it turned out to be as heavy as I had imagined a Royal Marines ammunition box would be. The tractor tyre was well oversized, so this weight came as no surprise, and at around half way round I was more than happy to let someone else take it off me, but what I was not planning on was immediately replacing it by becoming part of the tyre team. I filed in at the front on the left, with the tyre on my right shoulder, and immediately felt that the tyre was as heavy as it looked. We pushed along before slowing to a speed march for a count of 5, then ran for a count of 10, and continued with those intervals until we finally reached the finish line, shattered. We were not finished yet, though, as we were told to stay in our teams and line up in the press up position to form a caterpillar, so that the person at one end could crawl below us, with the next person going once they had reached the other end. We had no set finish line and would keep going until we were told to stop. It seemed to go on forever and I am sure I must have crawled through at least 5 times.
http://jamesablog.starjump.org/?p=6984
and its free by the way
. Something about swapping parts and having issues and being off of the trainer 
