12/43 How big in rear w/o changing chain?

I know if I looked hard enough I'd find the answer somewhere on another thread, but like the title says, how big can I go in the rear without having to change the chain? And would a 12/45 or 46 be good for the dirt? Not caring too much about top speed.

As long as you have a 12-tooth front sprocket on there, you can go up to a 45-tooth rear.
The chain adjusters will be fully forward in order to get enough chain slack, but it will work, and I did this for a while with my 2008 WR-250R.

In my opinion, even 12/45 or 12/46 still isn't low enough even for mixed street and dirt usage.
Most of my milage on my WR-250R was with 12/47, and that was good on the street and still a bit tall for the dirt.
For concentrating on dirt riding, something like 12/48 or 13/51 would be more like it.
The bike is geared so tall to start with, you could use 12/48 and still have plenty of speed for the street. :)

I recently changed Tyres to michelin comp enduro 90/90x21 up front and 120/90x18 on the rear. Fantastic Tyres for the dirt. Then dropped to a 12t on the front to compensate and the difference was very noticeable. I now want lower gearing but on a budget! If I fit a 45t on the rear with stock chain will I still have clearance in the swingarm for my oversized tyre? Any one tried this ?

Thanks

Lee. UK.