Post Master General
Join Date: Apr 2012
Location: Bowling Green, VA
I Ride: '09 ZX6R
The slack required to make sure the chain doesn't bind up when the distance between the sprockets is greatest is going to remain really similar. The distance between the swing arm pivot, and the top of the rear sprocket isn't changing by very much at all.
When the suspension is fully compressed, all the way to the bump stop, the chain is connecting both sprockets at their greatest distance apart. That's what determines how much slack you have to have available at all times. You don't want the chain to stop the suspension from reaching full stroke..... that would make the chain do the spring's job, and it doesn't compress or stretch worth a darn.
I always run my chains at the maximum or greater slack numbers. It's the teeth engaging on the sprocket that do the work.... as long as the rollers seat all the way in the 'valley' between teeth, it's tight enough.
In your case, with the -1 +2, I presume you are using the OEM length chain, and as a result have had to move the rear wheel almost all the way to the front of the adjustable range. I'd personally make sure that you can get the maximum allowed slack, and call it a day.
New chain, new sprockets, you'll need to check the slack again a few times before it wears in. If you have ti too tight, the chain will wear out much more quickly due to the strain of being stretched by the swing arm. Remember that thing is a pry bar, almost 3' long. Lots of leverage. The pins in the chain are stronger than you'd think, but the side plates will suffer, and their holes will elongate which will create looseness.
"Basic stuff fellas. Use your head for something other than to break your next fall."