Belt tension on ground versus hanging

[Jetfixer]

I managed to get a hold of a new Gates 508C Sonic Belt Tension Meter at an online auction for a very nice price! I decided to check my 15 RTL belt tension both "by the book" and sitting on the ground. With the rear wheel jacked off the ground at the frame, and using the book method of lining up the wheel spokes with the swingarm, my belt tension averages 630N. With the bike on the ground it averages 1020N. To me that is a huge difference. I didn't adjust it because it rides fine and only gives a slight vibration between 72 & 75 mph. Has anyone else been able to compare the in the air and the on the ground tensions?

 

[IdahoMtnSpyder]

I managed to get a hold of a new Gates 508C Sonic Belt Tension Meter at an online auction for a very nice price! I decided to check my 15 RTL belt tension both "by the book" and sitting on the ground. With the rear wheel jacked off the ground at the frame, and using the book method of lining up the wheel spokes with the swingarm, my belt tension averages 630N. With the bike on the ground it averages 1020N. To me that is a huge difference. I didn't adjust it because it rides fine and only gives a slight vibration between 72 & 75 mph. Has anyone else been able to compare the in the air and the on the ground tensions?

The pivot point of the swing arm does not coincide with the axis of the front sprocket, therefore the center to center distance of the sprockets changes as the tire (swing arm) moves up and down. What your numbers tell me is that it takes very, very, little change in the center to center distance to cause a huge difference in belt tension. That stands to reason, in my mind anyway, because the belt is essentially non-stretchable.

The reason for the book method is that is the most reproducible condition, both from one time to the next, and from Spyder to Spyder.