90° rubber valve stems failed on my front tire at 80mph.not instantly flat, but scary, as the lower the pressure becomes, the harder it is to turn the bike. I believe it was caused by the back and fore movement when either checking or adding air into the tire. Rubber fatigue I guess. I immediately purchased a TPMS and tee valve stems and used them ever since. Probably the most sensible addition to my bike I've ever made.I strongly suggest changing to bolt-through metal valve stems or at least using compression tubes with rubber stems if the bike is capable of highway speeds.