I had a flat on my Concours one day. It was almost impossible to put air in the rear tire and somebody told me about BMW's accessory 90-degree valve-stem extension. I went and got one and put it on the bike. It barely weighed anything, but one day as I pulled onto I-76, I had just set the cruise control and felt a twitch in the handlebars. The next thing I knew I was in a full-blown tankslapper. I had had a friend have a rear-tire blowout and she had used the brake to try to slow down before the bike flipped. I had told myself that I would pull in the clutch and not try to use the brakes if it ever happened to me. I managed to do what I had planned and got the bike stopped. When I started to figure out what had happened, it turned out that the featherweight brass 90-degree extension had flexed the straight rubber stem until it tore through.
But after I put metal 90-degree stems on the Concours, I had no more problem. I also have had metal 90-degree stems on the NT since it was new with no trouble. I've got Doran's TPMS and external sensors mounted on the end of those stems. The Doron tire sensor on the front is between the calipers and has plenty of clearance.