90 degree tire valve direction?

Duporth said:
It seems a neater solution, less losable (!) and 'permanent'
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yes,yes and yes. The biggest drawback to an internal sensor is that if you have issues with the sensor, mainly the battery, The tire has to be removed, or at least broke down to access and replace the sensor. If you do your own tire work and this isnt a big deal then great. If you need to pay someone to do the tire work, then you have to consider the cost and aggravation and the external sensors start make more sense. I dont have TPMS, but I have been watching the TPMS threads with the intention of getting a system and would like the internal sensors myself. TPMS systems make a LOT of sense to me... YMMV
 
dduelin said:
I disagree... The sensors weigh just .3 oz and technically could cause an out-of-balance wheel but I've not been able to notice this to unmentionable speeds.
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Hi Dave:

No problem with the disagreement, disagreements here in our forum usually promote more thorough investigation, and everyone wins when that happens.

Before I retired, I wanted to fit TPMS as standard equipment to a new production aircraft that I was responsible for. Highly sophisticated aircraft TPMS systems cost tens of thousands of dollars, and I was trying to advocate a less expensive solution - valve-stem sensors such as what we use on motorcycles. I figured that a valve stem sensor would be adequate because there was no imperative or regulatory reason to have TPMS, hence, we didn't need a $20,000 super-reliable aviation-spec system.

The engineering department put the nix on my idea, and they gave the following reasons:

1) The valve stem was not mounted perpendicular to axis of rotation of the wheels, in other words, the stem stuck out at an angle, and they had concerns about repeated stress imposed in the same direction on the stem.

2) Centrifugal force arising only from rotation speed was not a concern - this because touchdown speeds did not exceed 125 MPH. What concerned the engineers was the bending moment imposed on the (angled) valve stem if the wheel hit a surface imperfection, such as a tar strip, concrete irregularity, or a bump/hole on an unimproved runway.

That experience is why I suggested that it may be unwise to fit the sensors on angled stems. If sensors are fitted on straight stems, neither of the above concerns are valid.

Michael
 
FWIW, I’ve got about 90k miles using valve stem sensors on angled metal valve stems, with zero issues. And there are many other riders doing the same. Theory doesn’t match reality in this case because the valve stems are strong enough and sensors light enough to not exceed the fatigue limit of the metal. My .02.

And, both mine point to the right. ;)
 
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CYYJ said:
Hi Dave:

No problem with the disagreement, disagreements here in our forum usually promote more thorough investigation, and everyone wins when that happens.

Before I retired, I wanted to fit TPMS as standard equipment to a new production aircraft that I was responsible for. Highly sophisticated aircraft TPMS systems cost tens of thousands of dollars, and I was trying to advocate a less expensive solution - valve-stem sensors such as what we use on motorcycles. I figured that a valve stem sensor would be adequate because there was no imperative or regulatory reason to have TPMS, hence, we didn't need a $20,000 super-reliable aviation-spec system.

The engineering department put the nix on my idea, and they gave the following reasons:

1) The valve stem was not mounted perpendicular to axis of rotation of the wheels, in other words, the stem stuck out at an angle, and they had concerns about repeated stress imposed in the same direction on the stem.

2) Centrifugal force arising only from rotation speed was not a concern - this because touchdown speeds did not exceed 125 MPH. What concerned the engineers was the bending moment imposed on the (angled) valve stem if the wheel hit a surface imperfection, such as a tar strip, concrete irregularity, or a bump/hole on an unimproved runway.

That experience is why I suggested that it may be unwise to fit the sensors on angled stems. If sensors are fitted on straight stems, neither of the above concerns are valid.

Michael
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If the stems were vertical they likely wouldn’t sign off on the suggestion because the sensor, always holding the Shrader valve open, could fail allowing loss of tire pressure. Aircraft tires can require upward of 200 psi and a crack in the pavement unfelt at 45 psi might be a jolt at 200.

No engineer would have signed off on an unapproved $150 unit unless the manufacturer would, hence the $20,000 price tag for the FAA approved one.

You raise valid points though. I’m taking a risk.
 
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