I know... and there's quite a bit of variation between those... To be honest I have no idea how you could even get a 50-60mm slack with the bike upright since that means the chain would need to go into the swingarm...

Since I had some problems with the first chain on the bike - a ride of about 800km in which i haven't checked it and it jumped off the rear sprocket locking the wheel - I'm trying to figure which is ideal to avoid both wear and incidents.

I think i'll go on too and check what happens if i use some ties to pull the wheel up until front sprocket, swing arm axle and rear sprocket are in the same line, adjust the chain at that point so is not too tight and then see what happens when the bike is in either options Yamaha gives in different manuals.