I have 18" Dunlop SP Winter Sport 3D runflats. Last weekend, I (and a passenger) were headed to the airport when the FTM went off. Canadian cars don't have TPMS but they have the almost useless FTM. They do their job but only when the tire has no pressure.
Anyway, I was on the highway in heavy snow when it went off. I had no idea the tire was flat other than the back end was 'squirmy'. I continued to the airport, picked up two passengers and their luggage and drove home. The tire was definitely flat. There was no air pressure.
After the holiday weekend, I pumped up the car in my driveway but could hear air escaping. I drove to my trusted independent. The FTM did not go off because there was a small amount of air left by the time I got there. They were able to source a new, exact tire, replaced my dead one and sent me on my way. More than $410 + tax.
I was able to see the damage and three installers had a look at the inside. The inside looked the same as the new one but the more I drove on the old one I had noticed the car was getting lower and lower as the sidewalls were slowly bowing out. The actual hole was from a 3.5 inch tapcon screw right through the centre groove of the tire. It took two guys with pliers to remove it. The belts were showing on the inside. The tire was not repairable. I doubt a regular tire would have survived.
I drove about 60km (37mi) but was very careful and watched my speed. I do wonder what would happen if I had been on a road trip with no spare and a long way from home. The tire definitely did its job. Until the end of the trips I could not tell visually if the tire was totally flat. Snow on the tire and the road didn't help. Kicking it doesn't help either. LOL I had to test it with a gauge.
2012 BMW 535i X-drive; Space Grey/Black Dakota, Fineline; Executive (Auto trunk, NAV, HiFi Prof, Lumbar, Rear Cam, SIRIUS, Voice), Technology (Blind Spot, Hi-Beam Assist, Lane Departure, Surround View), APPS, Rear heated seats, Tint.
Retired: 78 300D, 81 300SD, 87 190E, 88 Porsche 924, 89 260E, 93 300E, 97 Volvo 850, 98 E320, 03 BMW 325iT, 02 C230 Sport Coupe, 08 BMW 535i