I mentioned in an earlier post that 4x4's were pretty common in Iceland, but that wasn't the whole story.
Not only are 4x4;s popular but fitting extreme wheels and tyres seemed to be the norm. Given that it was summer time presumably these are for getting off road where the surface is soft, maybe the lava fields or can you drive on a glacier?
And what about this one, it was one of the tour companies that go up into the interior. I guess the trailer was for camping equipment or maybe it just had to be that big to carry the spare tyre.