Screw-on 90 Degree Valve Stem Adapter - K-Bikes.com - Excellence in Motion
 
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post #1 of 5 (permalink) Old Jul 27th, 2009, 11:11 pm Thread Starter
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Screw-on 90 Degree Valve Stem Adapter

I carry one of these in my glovebox to make it easy to fill the rear tire at service stations:



You can find them everywhere. I bought mine for $10 at the local BMW dealer. Here is the source for the photo above: http://www.ascycles.com/detail.aspx?ID=2123

The problem is that I hate the fuss of losing air pressure while trying to screw and unscrew this little adapter. You can't leave them attached, or you will damage your valve stems. I have TPM, so I can't install a nice metal angled valve stem. I am looking for a very small accessory with a quick release, so I don't lose air after I get the pressure set.

Does anyone make a "clip-on" version of this adapter? Do you have a better, very portable solution that works with TPM-equipped rear wheels?
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post #2 of 5 (permalink) Old Jul 28th, 2009, 3:18 am
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My on board compressor has a 90 air chuck on it. That avoids those gas station hoses and searching for quarters. Plus it's always with me, no matter where I am.

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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post #3 of 5 (permalink) Old Jul 28th, 2009, 10:42 am Thread Starter
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Quote:
Originally Posted by Meese
My on board compressor has a 90 air chuck on it. That avoids those gas station hoses and searching for quarters. Plus it's always with me, no matter where I am.
Good point. I have one exactly like it (thank you!), but I have been reserving it for emergencies only, and assumed that you did too. The clip-on 90 degree stem does the job well. I don't carry it with me around town, but always have it for longer trips.

I once read a convincing paper about air, nitrogen, and water vapor in motorcycle tires. It was well-written, with an explanation of the physics involved. I have been searching for it to share with everyone here, but no luck so far. Here is my takeaway from the article (from memory):

* Nitrogen in motorcycle tires is better than air, but not worth the extra cost. Nitrogen does not leak through tire rubber as quickly as oxygen, so a nitrogen filled tire will hold its pressure longer.

* Because oxygen leaks out of the tire at a faster rate than nitrogen, your tire will evolve to a nearly pure nitrogen content over time as you add small amounts of air. The added air is 80% nitrogen, so very few oxygen atoms get in. Why pay for nitrogen when you tire will evolve to it anyway?

* Water vapor in your tire is bad. It will cause a greater variance in tire pressure with changes in temperature. It has corrosive effects on metal parts in your wheel. (I realize that alloy wheels won't corrode, but what about the affect on the TPM?)

* Compressors with reserve tanks introduce far less water vapor into your tires compared with the mini compressors that have no reserve tanks. This is due to the physics of the reserve tank and its size compared with the air capacity of a motorcycle tire, not special moisture filters and draining. A mini compressor on a very dry day will be close to what a reserve tank compressor does even when the relative humidity is much higher.

That last bullet is why I have been using gas station compressors rather than my own very nice mini compressor, perhaps erroneously. I assume that the gas station compressors have reserve tanks built in, leading to drier air in my tires. Maybe I need to re-think my approach, especially in the summer when the air is very dry here.

Of course, one of these days I should go out and buy a decent air compressor, but I have no room to put it in my garage, even the ones that fold up.
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post #4 of 5 (permalink) Old Jul 28th, 2009, 12:07 pm
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Good points, except maybe that last one. The assumption there is that the gas station compressor has a properly fitted and working air/water filtering system. I've sprayed gas station hoses into the air and seen actual water come spraying out. So you can't always assume that those systems are working properly.

Another point is that I hardly ever top off my tires. On tire installation, I'll clean the rim bead very well and also the tire bead, then mount them as normal. That minimizes random leakage. Plus I don't fret over a pound or so change registering on the TPM. That's just normal. If it gets 3-4 psi low then maybe I'll top up, but honestly, that may happen once per tire lifetime, or not at all.

So yes, I do pay attention to pressure, but I'm just not that anal about it. Hell, I go through tires way too fast to worry that much.

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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post #5 of 5 (permalink) Old Jul 28th, 2009, 8:14 pm Thread Starter
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Quote:
Originally Posted by Meese
Good points, except maybe that last one. The assumption there is that the gas station compressor has a properly fitted and working air/water filtering system. I've sprayed gas station hoses into the air and seen actual water come spraying out. So you can't always assume that those systems are working properly.

Another point is that I hardly ever top off my tires. On tire installation, I'll clean the rim bead very well and also the tire bead, then mount them as normal. That minimizes random leakage. Plus I don't fret over a pound or so change registering on the TPM. That's just normal. If it gets 3-4 psi low then maybe I'll top up, but honestly, that may happen once per tire lifetime, or not at all.

So yes, I do pay attention to pressure, but I'm just not that anal about it. Hell, I go through tires way too fast to worry that much.
Fair enough. I don't obsess over tire pressure either. I normally fill my tires to 37/43 (one psi high) on the TPM, and refill them when the TPM consistently reads 2 psi low. The typical interval is six to ten weeks, which matches your tire changing cycle.
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