TST TPMS 507 System and valve stem Question

We have the tire tracker and 6k miles later our rubber valve stems have been fine. Now, when I replace my tires I will put on metal valve stems since I will be replacing them anyways.

It's all a function of the rigidity of the valve stem. My original OEM stems were quite flimsy and sensor-rim contact was clearly evident. In the past 16 months I have since replaced all five tires and had high-pressure rubber stems put in. These are much more rigid, and have tolerated the 3lb force without complaint---so far at least.

Very good. Since the time of this post I made a 3780 mile journeyt to California and back to Houston and had no issues with my rubber valve stems flexing, breaking or contacting the rim. Simple rubber fuel line mod fixed that.

wmoses wrote:

Using this calculator, why does one need to put in the angular speed as a variable? With linear speed of the vehicle and radius of the wheel, angular speed is derived. It even says so (omega = speed/radius).

Correct. Before you use the calculator, you independently derive the angular velocity of a typical RV wheel of 14-inch radius rolling down the road at 65 mph. By my reckoning, that's 65*5280*12/60/3.1416/2/14 = 780 rpm.

Then you enter 7 inches for the radius at the valve stem, and 0.38 ounce for the mass, to get ~2.9 lbf for the effective weight of the sensor.

RCMAN46 wrote:
Suggest you do a calculation dugggg is right on. a 17 gram sensor on a 15 inch wheel and 225x75R15 tire at 65 miles per hour will require a force of 4.7 lbs.

Centrifugal Force Caliculator

Using this calculator, why does one need to put in the angular speed as a variable? With linear speed of the vehicle and radius of the wheel, angular speed is derived. It even says so (omega = speed/radius).

That said, if one still uses this calctool and puts in say 6" for a radius (assuming a 7.5" radius for a 15" wheel and the sensor is at say 1.5" closer to the axle; tire is immaterial) and 65 mph and mass at 17g and with nothing in the angular speed field, I get 21.2 lbf. If I now start inputting numbers for omega I can get any number I want for a force.

In my younger days when I was sharp I would have calculated this for you including the transverse force and hence the deflection of the valve stem but I am lazy now. On top of that I have to get back to work ... ;)

wmoses wrote:

dugggg wrote:
Why such concern over a tiny fraction of an ounce? Because at 65mph the centripetal force is nearly 3 pounds! That's quite a load on a rubber valve stem.

First of all I liked your technical response to this - nice to see some engineering in these here forums from time to time. :)

I have not done any calculations myself but I doubt that the centrifugal force on the sensor (centripetal at the rim) will be 3# at 65 mph on a 0.42 oz sensor. For one thing the centriXXXal forces are in an axis perpendicular to the axis of rotation while the valve stem is at some acute angle to that vertical axis. So the centrifugal force acting on the sensor needs to be resolved into stem-axial and stem-transverse components. It is the latter one that causes the relative outward deflection at the tip of the valve stem that could cause the sensor to contact the rim.

Naturally the deflection is a function of several things, length of the valve stem being one. That would explain why W.E.BGood has the problem shown in his pictures while other don't. :)

In other words rubber may be good for some and not so good for others.

Suggest you do a calculation dugggg is right on. a 17 gram sensor on a 15 inch wheel and 225x75R15 tire at 65 miles per hour will require a force of 4.7 lbs.

Centrifugal Force Caliculator

bshpilot wrote:
interesting - i don't have this issue on my Jeep Wrangler & I've got the OE valve stems on it, I'm approaching 3 yrs & at least 30k miles (combined towing & driving) w/ the sensors in place

...and you may never have a problem. I believe some stems are better than others and maybe "stouter". I would keep an eye on them though and check for cracks from time to time as it's a very slow process and not easy to spot.

dugggg wrote:
Why such concern over a tiny fraction of an ounce? Because at 65mph the centripetal force is nearly 3 pounds! That's quite a load on a rubber valve stem.

First of all I liked your technical response to this - nice to see some engineering in these here forums from time to time. :)

I have not done any calculations myself but I doubt that the centrifugal force on the sensor (centripetal at the rim) will be 3# at 65 mph on a 0.42 oz sensor. For one thing the centriXXXal forces are in an axis perpendicular to the axis of rotation while the valve stem is at some acute angle to that vertical axis. So the centrifugal force acting on the sensor needs to be resolved into stem-axial and stem-transverse components. It is the latter one that causes the relative outward deflection at the tip of the valve stem that could cause the sensor to contact the rim.

Naturally the deflection is a function of several things, length of the valve stem being one. That would explain why W.E.BGood has the problem shown in his pictures while other don't. :)

In other words rubber may be good for some and not so good for others.

I have read where it is recommended to keep the speeds below 65.

My TV is used for some travel without the trailer. Legal speed limit in Utah and possibley soon in Idaho is 80. If I am travelling with truck only I will be going 80 so metal valve stems is absolutely required in my opinion with TPMS sensors.

I have an 05 Duramax that had the pull through metal stems. Had new tires two years ago and the tire dealer said the pull through were the only ones that will work.

Last week I was getting ready to leave the camp ground and I checked tire pressures with my Pressure Pro system. All tires OK except left rear on truck. It was at 65 psi should be 80.

I decided to try and drive to a local Big O tire without the trailer about 15 miles and have the tire fixed. My thinking was a nail and if I watched the pressure should be OK it I did not let it go below 30 psi.

After less than 2 miles the pressure dropped to 25 so I stopped and put on the spare. Returned to campground and hitched the trailer and went home. Short trip as we were only 25 miles from home.

Next morning decided to take the truck in to have the tire fixed. Checked pressures with Pressure Pro as always before I drive the truck. Left front was at 20 psi. Now I had to use my Subaru Outback to take the tires to the tire shop for repair.

The pull through valve stems had failed on both tires. I could see marks on the rim where the pressure sensors had been hitting the rim.

My local small tire dealer found me a set of all metal stems.

All metal stems is the only way to go and get the shortest stem possible.