Spoke with a BRP rep during the demo ride and this question came up. First, these are 1 off tires, can't get them just any old place. They are specifically made for the Spyder. We were also told that their cost would be comparable to any standard motorcycle tire.
From what I understand, they were designed specifically for the Spyder. They're a unique size and tire pressure, 6lbs. I don't know the rim size but an ATV rim would be the closest match as is the tire pressure.
I doubt the back tire will make it to 35000 miles on my Spyder! I am surprised to hear that Michelin has tires available and thought Kenda was the only one making tires for the Spyder in the first year.
if you google the tires sizes (without the "KR21") there seems to be a fair amout of companies making those tire sizes for the rim size. i'm assuming they wont change tire tire/rim size from the spec sheet on BRP's website .
i dont know what the kr21 means though . any thoughts ? i'm not that familiar with speed ratings of tires but i looked that up too and couldn't find a KR rating anywhere