We have also been told by BRP techs that they got a bad batch of tires.
I have burned through many tires in my 75,000 miles on three spyders, a few of the OEM Kenda, some of the Kumhos, a couple of the Maxxis Vectras, and am now using the Toyo Proxes, which is also discontinued like the Kumho. The Kumhos were OK, the Maxxis was better, the Toyo Proxes was the best for traction and performance. I bought six of them when I learned they were discontinued. BajaRon likes this one as well, comes in the OEM size. I would not hesitate to again run the Maxxis Vectra, that is what I have on my original 2008 #006 Spyder right now.
It all depends on what your criteria is - longevity, cost, traction, wet pavement performance, speed rating, sidewall flex, what do YOU want? I know that I want a tire that is going to hold together at 100+ MPH, one that is going to grip the road when it is wet, one that lasts longer than the latest POS Kenda, one that isn't going to pop me $150 each time it is bald. The Kumho is getting tough to find, I know riders like this one but it is only fair at best. It IS perfectly OK to run a different size, preferably as close to stock diameter as possible. I have made many posts on what is acceptable size-wize, as have many others. I run my spyders long and hard, limit seeker for sure, and I know my nanny well, with stock and non-stock tires.
Bottom line, the latest Kenda rear tires are not lasting as long as the previous ones, and I REFUSE to replace the rear tire every time the oil is changed!