Modern Vespa

So about 3 weeks ago my front tire went flat after i came thru a really bad section of road (patches on top of patches). Had to be towed to my mechanics and the valve stem was sheared. Fast forward to last week when my rear tire went flat after doing the same section of road. My problem is i have to take that section of road unless i want to go around the island to get to honolulu. Only a couple of ways out of here. While i'm sitting awaiting the tow truck,who by now, has my phone number on his phones contact list. i think i figured out what was making the valve stems go bad. My TPMS Tire Pressure Monitoring System sensors . I put them on my scooter about 4-5yrs ago. Obviously our roads have really degraded over time. While the sensors aren't particularly heavy i think their just heavy enough to cause the valve stems to move enough, so that the valve stems cause the air to come out of the tire. The reason i put them on was because it's a real PIA to get to the rear tire to check the tire pressure. Front one no problem. I like to check my tire pressure weekly so this system was perfect (until it wasn't ). I always found it to be accurate, maybe 1-2 PSI off. So now their in the garbage. I hate it when good things go bad.

Yeah, I think you have it nailed. It is something that can (clearly) happen with the tpms setup. Glad you have it figured!

I had a similar problem with right angle metal valve stems. I suspect it was caused in much the same way. The large metal valve stems are heavy and the weight is off center.

Thanks S. I'm a slow learner. While i knew the roads bad news the fact that i had them on for years without any problems skewed my thinking that they could be the cause.

youre talking a few grams in weight difference at most. If you put right angle stems that arent threaded & properly gasketed on both sides... that is problematic as well.
Amazes me in 2018 bikes still come with cheapo rubber stems that make it impossible for a lay person to take pressure readings accurately.

I loved the idea of them too. Bought it and a month later I removed them because they intermittently lost air. bummer!

I tried telling you that can happen, no one listened to me. Told me I was full of it.

Web If one worried about what "could" happen we'd never get out of bed. I had 4 years of trouble free use out of them. It's the roads. But for them being so bad i'd still have them on. I have no choice i have to take that road to get to Honolulu. I also have 48,600 miles on the LX at the time i took them off. So "i told you so" doesn't cut it.

It is not what could happen, it happens all the time with these type of tire monitiring systems. Just like putting those HUGE valve stem caps on does the same thing.
I wasn't guessing, I have see it more than once.
That is why aftermarket companies are finily coming out with the in wheel valve stem sensors like OEMs use.

Sometimes generic tubeless valves which are fitted when tyres are replaced are too long for scooter wheels. In hot condition they are prone to bend sideways partly as a result of centrifugal force. I have had a broken one which destroyed itself by hitting the brake calliper like this. Special short stemmed valves are much better.

Would replacing right angle stems with short straight ones solve the problem?