Re: ST 1300 Tire Recomendations...
Larry and I are going to have to disagree on this one. I'm going to make this my one comment on this subject to keep the thread hijack down to a minimum. If there's interest in discussing it further, I'll pull the valve-stem posts out into a separate thread.
But I would not allow a ERT diver whom I was going on a deep dive with to get in the water unless his equipment was serviced correctly and completely.
If you'd care to point me in the direction of what an aluminum valve stem manufacturer recommends as correct and complete service, I'll be more than happy to start following those directions. My stems came with an instruction sheet that didn't recommend any regular maintenance.
The stems I'm talking about here are the ones made by Bridgeport. They're aluminum, have an 83-degree angle, have a B stamped in a circle on the housing, are re-sold by Ariete and others and used as OEM parts by at least one European motorcycle manufacturer. There are knockoffs and other types that get most of their support from a rubber grommet that mounts in the hole in the wheel. The latter are worse than rubber stems. Not talking about either of those. If the Bridgeports had a high rate of failure (or
any significant rate of failure for that matter), they wouldn't be on my bike and I wouldn't be recommending them to others.
Since the topic is avoiding failure, let's look at where Bridgeport's design could go wrong from an engineering standpoint:
The primary egress for air is through the valve, which doesn't have centrifugal force trying to open it while the wheel is spinning because it's not installed radially. The valve seal is backed up by the rubber lining in the top of cap. The lining is backed up by the threads that mate the cap to the housing. If the valve fails, you're going to know it next time you remove the cap for a pressure check. If the valve
and the lining in the cap fail, the worst case is a very slow leak at the threads. That's the very worst case because the air in the tire will be exerting outward pressure on the cap, forcing the threads more tightly together. It would take a complete failure of all three to have a rapidly-deflating tire. If anything in that part of the stem is likely to fail and should be replaced regularly, it's the one part that gets removed and replaced regularly: the cap.
The other way for air to get out is through the joint between the valve and the wheel. The first line of defense is the nut on the inside of the wheel. Torqued properly, that's not going anywhere, and whatever could get past it would amount to a slow leak. There's also a tiny gap between the housing and the hole in the wheel. Again, slow leak at worst. That's backed up by the O ring in question which, in addition to the pull from the nut on the inside of the wheel, is pressed into place by centrifugal force when the wheel is spinning. The side of the ring that has to fend off air leaks isn't exposed to the elements at all and the other side, which is, isn't exposed very much at all. That leaves an awful lot of material to disappear before the seal would be compromised. Unless the ring completely disintegrates and disappears, we're still in slow leak territory, and that's at worst.
Having said all that, if you've got Bridgeport stems that failed after proper installation, I'd really like to see them and hear your opinion of the cause.
Why would you NOT replace something that you know is a possible failure point, and is so simple and cheap to replace?
Because if it ain't broke, doesn't have a track record of breaking and hasn't been declared a wear item by someone who spent a few hours slaving over a hot drawing board to make that recommendation, it gets left alone. I installed these stems in part because they lack the vulnerabilities that make rubber stems need regular replacement and can't find a good reason to disturb a joint with a known-good seal on it, especially if there's the risk of making a mistake selecting or installing the replacement.
The condition of the failure point you're concerned about is easily checked any time you want with the tire on the bike and under full pressure by giving it a squirt of soapy water.
--Mark
