Originally Posted By: Dyusik
...I think the wet clutch has to be the culprit for shearing.
If it's in your R1, I'd expect it's the gearbox. That's what the experts here seem to say anyway, that constant mesh transmissions are a big cause of oil shearing out of grade.
No idea if the OP's Thunderbird is a shared sump bike or not, but if it were, I'd probably choose a different oil. I've used T6 in shared sump bikes, and it worked out OK. But there are likely better choices--depending on your oil change interval, budget, etc.