it simply doesn't work like that, you cannot interpolate tred life vs depth of groove...
all of thes new tires are multi polymer compounds, and inconsistant based on available thickness' if the tire has less than half what it started with as far as depth, you will only get about another third more out of the remaining tread, or even more closer to 25% left as far as miles go...
I can say my BT's when half worn, at about 4k by tread groove, only bought me another 1200 miles in reality, befor they were unusable. and I pushed them to 5800, before buying new ones.. and not BT's..
been thru multiple PR2's, 3's, and I can't say I could push any more than 7500 out of any of them, without worrying... and then the tire all of a sudden eats itself overnight..
leaving the house riding 2 up for a 4-5 day trip of 2k miles, thinking I was good for at least 3k, and changing a tire out on day 3, at dealer cost... sukz..
just saying...