This tire is $141 for a 190/55/17 GT rear (yes, that's GT, or like a Pirelli A Spec) .  Then throw in a rebate of $60 on a debit card if you buy a set, that makes this tire $111. 

Tire
https://www.rockymountainatvmc.com/tires-and-wheels/bridgestone-battlax-sport-touring-t31-gt-rear-motorcycle-tire-p

Rebate
https://www.rockymountainatvmc.com/l/2019-Bridgestone-Mar-Apr-Rebate-Info?il_source=bridgestone-tires&il_medium=rebate-banner

I bought 2 rear T30's for about the same price.  I ended up with < 4000 miles.  As a frame of reference, I have put 17 rear tires on this bike and averaged 4370 miles per rear tire.  The traction was fine.  But I ended up paying $300 at a shop for a Pirelli Angel GT 190/55-17 reear because that 3700 miles ended in the middle of a trip to PA/WV/OH. I have 3 trips planned this year, so I could put a new set of these on at the beginning of one of the shorter trips and be OK if I got 4k out of the tires, as I would be home by then.

Reread the question. I thought I had tried a 31 but it was a 30 like you. I got more use out of the 23's than the 30. Didnt get many miles out of the 30.

Curious about the 31 too.

I had a bunch of Rocky Mountain cash.  Between that and the rebate, I got a set of tires, both GT, for $77 shipped!