Well logically yes you are correct half of 13 is 6.5. But when it comes to tires/wheels logic goes out the window. My 13" tires on 6" rims sit at about 5.75" to centerline @ 10 lbs of air drop to 4lbs and I have a wee bit less than 5". The brand and style of tire will make these measurements different too. Best thing to do is get them in hand, mounted and measure them. THEN build your frame.
Yup logic went out the window...I measured my 15" on my cub that I mow with It was around 6-1/2" center line. Then I measured a 15" on my bench and it measured 7-3/4 " @ 14lbs inflation.
So I will get 13" tires mounted then check my center line. Gonna run turf savers.
Ever feel like the more we try to go forward on a new build the more questions come up ? I think I find what not to do before I find what to do LOL.
Some say its fun I say its not.
Thanks for the input.
Zeus