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Strain on valve stems with air pressure monitors [message #342416]

Wed, 10 April 2019 06:30

RF_Burns

Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

So I installed air pressure monitors on my tires last year. TST unit with 6 monitors included for $199 which seemed to be a good deal. So far has worked excellent.

Then I read the monitors should be installed on all steel valve stems. Mine are rubber with a metal sleeve which seem to be rated for our use up to 80psi (I believe). So I Googled a site with a centrifugal force calculator to measure this. The sensor weights 0.77 oz according to the TST site and the distance from the center of the wheel to the center of the sensor is 6.5". So at 700rpm (approx for 65MPH on my LT225/75R16 tires) the calculator indicates 4.4Lb-force.

That seems like alot! maybe I'm using the calculator wrong, but I then tried several others with the same result. It works out to be a 100 times increase in weight force.

Has anyone had issues with the sensors causing issues? Have you changed to all metal valve stems?

Thanks,

Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

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Re: Strain on valve stems with air pressure monitors [message #342417 is a reply to message #342416]

Wed, 10 April 2019 07:12

Jp Benson

Messages: 649
Registered: October 2011
Location: Fla

Karma: 2

Senior Member

That force is opposed by air pressure in the tire. The real concern should be side torque on the rubber valve stem as the tire rotates.

JP

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Re: Strain on valve stems with air pressure monitors [message #342418 is a reply to message #342416]

Wed, 10 April 2019 07:32

RF_Burns

Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

JP,
Its the force on the valve stem that I am worried about. It didn't occur to me that o.77oz could become 4.4lbs at 700rpm. Not to mention that in the linear direction, the circumference of the tire goes from Stop, accelerates to 120mph at the top of the rotation, then decelerates to zero mph again when the rubber meets the road... 700 times per minute.

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Re: Strain on valve stems with air pressure monitors [message #342419 is a reply to message #342418]

Wed, 10 April 2019 08:21

Jp Benson

Messages: 649
Registered: October 2011
Location: Fla

Karma: 2

Senior Member

Thanks for the info and analysis. I've wondered what the TPMS dongle weighed and what risk it posed to the valve stem. Enough so that I didn't consider installing them on my vehicles. Years ago I bought a small aluminum bat that truckers used to for rough gauging tire pressure. It kind of works.

Probably most of us have seen rubber valve stems break off when pushed sideways too hard. Tires are essentially flywheels. Angular momentum generated by a rotating tire is significant and constant as the tire rotates. Consider what happens when a tire tread separates. I would be inclined to heed the manufacturers instructions on this one.

JP

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Re: Strain on valve stems with air pressure monitors [message #342420 is a reply to message #342416]

Wed, 10 April 2019 08:23

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

Are these the add on screw on type? Realize that those have the schraeder depressed so it can't do it's job and you are relying on the threads and the seal there to retain air. Not a fan of add on's that can cause faults.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: Strain on valve stems with air pressure monitors [message #342421 is a reply to message #342416]

Wed, 10 April 2019 08:55

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

RF_Burns wrote on Wed, 10 April 2019 07:30

So I installed air pressure monitors on my tires last year. TST unit with 6 monitors included for $199 which seemed to be a good deal. So far has worked excellent.

Then I read the monitors should be installed on all steel valve stems. Mine are rubber with a metal sleeve which seem to be rated for our use up to 80psi (I believe). So I Googled a site with a centrifugal force calculator to measure this. The sensor weights 0.77 oz according to the TST site and the distance from the center of the wheel to the center of the sensor is 6.5". So at 700rpm (approx for 65MPH on my LT225/75R16 tires) the calculator indicates 4.4Lb-force.

That seems like alot! maybe I'm using the calculator wrong, but I then tried several others with the same result. It works out to be a 100 times increase in weight force.

Has anyone had issues with the sensors causing issues? Have you changed to all metal valve stems?

Thanks,

I have a TST TPMS with flow through monitors (sensors). I have Alcoa wheels and metal valve stems. The sensors are a fairly tight fit in the wheels which probably help to keep them from moving around.

I installed them in July 2013. It's been over 40,000 miles and almost 6 years and the only issue I had was at random intervals, some of the sensors would drop off and not display. The solution was to add a repeater. That fixed the problem and I have no issues.

The system works great. I would not want to be without TPMS.

Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com

Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water heaters.

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Re: Strain on valve stems with air pressure monitors [message #342526 is a reply to message #342416]

Mon, 15 April 2019 08:03

jhbridges

Messages: 8412
Registered: May 2011
Location: Braselton ga

Karma: -74

Senior Member

Bruce, the tire doesn't start and stop each rotation - it rotates at a constant speed. The motion of any spot on the tire accelerates and decelerates >relative to the ground<. Thus at the top of the spot's rotation it is traveling faster than the coach while at the bottom it is traveling slower than the coach >relative to the coach<. Its rotational speed is unchanged. It will induce a bit of a Doppler shift in the signal transmitted by pressure sensor relative to the receiving antenna on the coach. So far, I've not seen this to be a problem.

--johnny

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell

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