Back in 2003 Ron Fraiser sent this to the list:
>>>Good Question about the original tires. I don't know the real answer; I
>>>can only reverse engineer the size of the tire from the printed facts in
manual and on hand.
Original Tire = 5.90 x 13 - not much help here.
1-From the Tiger Manual - 23.92mph @ 1000 rpm Calculate tire size using 2.88
gears Tire circumference = 72.75" - Diam. = 23.15"
2-Let's calculate again using the speedometer gear ratios. Speedo cal# = 980
rev/mi, speedo cable gear = 15 teeth,
trans drive gear # B7C-17285-A = 6 teeth, 2.88 gears
This gives you 24.49mph @ 1000rpm
Tire circumference = 74.48" - Diam = 23.71"<<<
A number of years ago (6 years to be more accurate) Jim Boynton sent me the
circumference of his original, barely used spare tire. It was 74.875".
So, for those that want to be "factory accurate" take your pick. 72.25",
74.48", or 74.875 as each has its merits. In closing his post Ron wrote, "I
hope this helps and doesn't confuse people too much." I would agree.