Long rigid valve stems. They mount directly to the rim completely replacing the usual short valve stems. The one on the inner wheel is 8 or 9 inches long and extends through a support in the outer wheel opening. The one on the outer wheel is shorter but curved about 150 degrees. So both valves are rigid and 100% accessible - even with wheel simulators. It’s a nice setup. The only drawback really is the cost. 4 stems (both sides) ran me $110 plus another $100 to have a local tire shop install them. Since they replace the normal stems the tires must be dismounted and then remounted. Notwithstanding, I consider it an essential upgrade. Obviously it’d be a lot cheaper if you do it when replacing your tires!
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