A while back I overnighted in Boston (not a bad place for a layover). We had a 6am show, and as I was walking to the plane in the pre-sunrise light, I noticed something seemed off. I performed my walk-around and came back to the #4 tire. It seemed low (see photo - can you even tell it's low?? It's the one on the left). It's not as easy as whipping out a tire gage so I called a mechanic over to take a reading. It was well below minimums. The tolerances on jet tires are tight - the pressure range on a Lear 60 main tire is 209-219psi. If pressure drops below 180psi on one tire you have to replace BOTH tires on that side. Why is this critical? Tires are prone to blow out at high speed if they're under inflated - causing catastrophic consequences. Let me tell you, changing tires ain't easy - or cheap. It's at least a 24 hour process where a mechanic "builds" up a tire and waits to test the pressure the next day. The Boston case turned out to be a fiasco because when the maintenance team went to jack up the plane to put on the new tires, the nose wheel jack jumped its cradle and dented the plane (see photo). What's a dent? Well, the Bombardier engineers said if the dent was less than 100 mils, we'd be OK. Of course it was 150 mils! After more days in Boston (now, not a bad place to be broken down), we had to ferry the plane to a Bombardier repair facility for manufacturer's repairs. Three months, yes, three months later I airlined up to pick up the repaired plane.