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.
TPMS recommendations
- Thread starter Nitesail
- Start date
ST Gui
240Robert
This. The L-shape allows the stem to flex especially with added weight on the end. I noticed that on a 'Wing there was an additional support for the end of the L-shaped stem. Centrifugal forces an unsupported end of the stem to the rim at speed. When rotation slows down the stem returns to its normal position.
Short vertical stems won't have nearly as much flex with wheel rotation. Metal stems have none.
Uncle Phil
Site Supporter
On the rear, point away from the disc. On the front, not many options. 
If I can I like to point them to the right so the stem is more accessible with the bike on the side stand.
ST Gui
240Robert
Ditto. I'm generally not going to put the bike on the center stand to air up. It also allows for most any kind of air chuck to be used without extraordinary contortions of the hose.
- Joined
- Jun 21, 2011
- Messages
- 891
- Age
- 72
- Location
- Ada ( Grand Rapids ) Michigan
- Bike
- '07 ST 1300 & '91 GW
My " Sykik Rider SRTP-300 " TPMS brand has worked for me . I don't have 90° stems though on the ST .