I voted 16,000-19,999. The first time I replaced my belt was to change to the Mitshubishi belt at the same time I installed the J. Costa variator. The OEM belt was still in great shape and I kept it.
I changed the belt again after 16,000 miles with another Mitshubishi belt and it was also in great shape. I only changed it out the first time at 12,000 since I wanted to install the J. Costa and I just thought I would do it so I didn't have to take things apart so quick. I was putting a bunch of miles on the bike at that time and I knew I would have to change it in a couple of months anyway.
I change my belts and tires before they probably need replacing just so something doesn't break down and I have to walk. When I was younger I would ride the bike until it did break down, but then I was young, and dumb, and broke. lol
I will probably put my OEM belt on after my current belt has 16,000 miles since the OEM should have at least another 4,000 miles on it.
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Ride safe,
JeffR
2007 Silver Wing (30,000 miles)
2005 Majesty 400 (sold 12,500 miles)
2004 Reflex (sold 3,500 miles)
Givi Windshield, top case, vista cruise, power commander, dr pulley sliders, air hawk seat pad, (J. Costa not installed now), kevlar belt