Drag slick dilation?

I recently score a pair of 28 10.5 15 drag slick for a really sharp price. They're a little close to the front and rear of the arches, but not so close that I can't get my had, (or at least my fingers) between them. But it's got me thinking, how much will the tires dilate? I know I don't exactly have a rail, (Those boys get some serious dilation happening!) but being such big soft ballons, I don't want the tire to contact the body.

What are your experiences?