chain rub

Done about 1000 miles on new Bridgestone BT45 (this is my second rear after 4.5k miles on the first one). Bike is close to 12k miles on original stock chain & sprockets. There is some noticeable wear on the chain - links look a bit worn on the inside, but when chain is pulled at back of rear sprocket, everything seems tight. Plenty of space left on indicator blocks. Chain slack around 40mm as per manual. about 5mm clearance between tyre & chain.
Sooooo: why are there a few chunks of tyre ground away by the chain? If I push chain side to side, it will touch tyre, but the rubbing seems excessive. Anyone else had this problem? Should I be worried?? BT45 is 140 width, but measures at 148mm.....

chain should not be hitting a 140.
40mm sounds a bit much, 1.57 inches, I do about an inch slack.

Yep. My chain was a little to loose and was making a nice design in the side of my 140. Tightened it up and now it's good.

f3joel wrote:

chain should not be hitting a 140.
40mm sounds a bit much, 1.57 inches, I do about an inch slack.

Hmmmm.... manual says 40 to 50mm slack at mid-point of chain, with bike on side stand, no weight. If I go down to 1 inch/25mm, are there any implications if I take any big jumps??
Thanks!

I measure 8-13mm between chain and swing arm, half way-sidestand-no weight.

Yamaha released an updated method from the manual.

mash100 wrote:

Chain slack around 40mm as per manual.

There was a technical service bulletin released with revised chain slack : Chain Slack Thread

f3joel wrote:

Yamaha released an updated method from the manual.

Yeah - I adjusted everything at lunch time. Chain is some 10mm from swing arm, but it was fairly close to that anyway. I do not have a tension gauge, but used my incredibly strong index finger to push up on chain!
Thanks for all replies. One theory I have is that I commute maybe 1/2 mile up a concrete farm road. It is badly cracked, & has a really rough, uneven/textured surface, causing suspension chatter. In fact there is a stretch of some 100 yards where the wheel will bounce if giving it full throttle even in 3rd... I can bearly manage more than 30mph without requiring dental surgery . So - I think the chain must get bounced all over the place, sometimes sideways, which would explain the occasional rub. Not much I can do about it apart from taking it easy over this road. Its a bit of a surprise, though, as I thought these bukes were specifically designed for this type of abuse....

Any other theories welcomed!!