I have a 2015 zx14r with a 12in stretched swing arm and was wondering if you still follow the book and adjust the slack to 1.0-1.2in or not. I've tried searching other forums but couldn't find any answers.

When the swingarm is at its squat, meaning the top of the rear tire is hitting or scrubbing the rear fender, that shortens the chain or tightens up. So you make it so that chain does not tighten up, there is where you loosen it to and in inch or so of slack.

seems to me he longer the bike is stretched, the more that swing arm is going to swing. You know, 3 inches of movement at stock wheel base, now move that wheel base out another foot...the swingarm still has to travel the same distance but you have a longer lever which means the end of the lever is moving more than it would at stock wheelbase. I have seen drive chain spring tensioners with a roller on stretched bikes and I imagine for the reason I just mentioned.

My first thought was adjust by percentage.

If stock swing arm is 24" and extended is 36" and sproket
is moved back by 12" that's a 50% increase in length.

So 1.0-1.2" +50% becomes 1.5-1.7"

Not sure if x length increase = y swing travel distance.

but it's a thought.

I'd call the manufacture.

What really matters is how far will that rear suspension ever travel at max. If you can find reliable info about the stroke of the shock you have, you could disconnect the tie rods and raise the swing arm as high as the shock should let it go. There's where your chain should be tight as a bow.

One of those yellow tie-downs, the one where you can put your hand in the handle to crank it down. Bottom wrap the swingarm, around the tail section [seat off] squat it as far as you can, check chain.

I'd more have it tight but moves some, then unload the swingarm see how much slack you have. You, ever bottom out, you'll know how to adjust either way.

I'll give bottoming out the suspension (or at least almost all the way) a try and see how tight the chain gets and go from there then. I didn't even think about increasing the length of the swing arm effecting the chain tightness as the suspension moves but it makes sense.

For what it's worth... a somewhat looser chain causes les missed shifts.