Late last year while traveling home from a rally in Kamiah, Idaho, I had an issue with some 90* valve stems on my wheels. I tried to check my tire pressure, because the rear tire looked low. When I connected the tire pressure gauge to the stem and pulled away, the valve core remained open and emptied the air from the tire. We tried several different cores and finally found one that held. Filled the tire and rode home. Fast forward to this year, having to install new tires, I figured I'd put on some new 90* stems, after all, what are the chances I could get another set that would bind up and not hold pressure? Apparently very good. We were on a ride, and I decided to check the tire pressure only to have the tire dump all the air through another stuck valve core. We finally got it to hold, but now I have zero confidence in these particular stems and cores. Having way too many rides and rallies to attend this year, I got online with Revzilla and ordered a pair of the machined aluminum stems. Since the bore for the valve cores is straight with no bend to interfere with the cores, I'm hoping they will be the answer.