Makes sense...do I just measure the width at the outside of the rim at the outter diameter of the wheel?
If so, looks like it's 5 inches.

On the Coker site,
the 600 tires have recomended rim width of 4-4.5
the 650 tires all have recomended rim width of 4.5-5.0
(the 700x13 tires, which is says are station wagon only, it recomends 4.5-6 inch rim.)

So, seems like I'm best off with the 650?
How do you know all this stuff Nathan??