I'm off on a 600 mile round trip this weekend and I've just noticed the Guzzi is down to 1.5mm on the rear Bridgestone. Given I get 4000 miles to a tyre (on average) how many miles will I get out of the 1.5mm left? How much from the 0.5? Likelihood of getting a 120/90-18 Bridgestone tomorrow for 5pm?