Tire valve cores are critical components to retain air in your tires.
Here are the components of a standard “snap-in” rubber valve. On the left is the rubber body of the valve stem. In the center is a standard valve core (I have a paper clip holding the valve open). On the right is the basic rubber valve cap.
Untold billions of these “snap-in” valves have been used for many decades in almost every passenger vehicle, light truck and RV trailer since the ’50s. They are cheap and usually work at holding the air in the tire. Normally, they were replaced whenever a new set of tires was applied to the vehicle, so the life span of this type of valve was only a few years.
Parts of the valve core
One feature of the valve core is visible in the above picture. The air is let in or out when the center pin is depressed and the “valve” portion, where the paper-clip is, is opened. The small red sieve is the gasket that sealed the valve core in the body of the stem. The valve core can leak, as seen in the below picture.
I read the questions in a number of RV forums, on what valve stem to use with an external TPMS sensor. This post will cover the “bolt-in” metal valve stem.
This picture shows two problems with cheap “snap-in” rubber stems. One problem is its flexibility, and the other is the fact that rubber gets old and can crack, which can lead to a leak. A standard 65 psi max “snap-in” rubber valve stem is very flexible. The weight of a tire pressure monitoring system (TPMS) sensor can cause vibration of the rubber stem and potentially a stem failure.
The addition of an external TPMS sensor can, in some cases, accelerate the cracking due to the extra weight out on the end of the stem.
Here is a rubber stem with a TPMS sensor. You can see the mark left on the wheel from the rubber stem bending.
Some people think the 80 psi max “high pressure” HP-600 rubber valve stem is OK to use with external TPMS sensors, but you can see the HP-600 is also flexible.
Rubber stem can fail with TPMS installed
Here is proof that an HP rubber stem can fail when a TPMS sensor is installed.
This valve stem failure resulted in a tire failure.
In my opinion, staying with any “snap-in” type rubber stem is false economy, given the metal bolt-in stems only cost $3 to $5 each. Not all tire stores will have the bolt-in metal valve stems in stock, so check first. If they don’t have them, you can get bolt-in stems at AutoZone, O’Reilly’s, Advance Auto Parts, NAPA, or most any auto parts store or even on Amazon.
They are easy to install, too. Don’t let the service center tell you installing metal stems is a lot of work. Watch and you will see. HERE
Rubber snap-in stems
On standard “rubber snap-in” stems, like the TR413, if you look down the hole you can see the end of the brass part of the stem.
These have been used for decades on hundreds of millions of tires. These can be installed by hand using a “puller” that stretches the rubber. That makes the diameter of the stem small enough to “snap” into place in the wheel hole. The “puller” in the picture is the tool with multiple notches that allows leverage to be used to generate the force to “pull” the rubber stem into the hole in the wheel.
Once installed, the wheel “pinches” the rubber part of the stem to seal
the air in.
High pressure stems
Next, we have the “high pressure” stems, such as the HP-500.
The Diameter shown in the picture is for the the standard hole of 0.453" This is an industry standard so don't try to find some at 0.500".
Bolt-in stem
Now, when we look at a “bolt-in” stem, like this TR416s, we see the location in the wheel hole at the arrows. We can also see the much larger brass body (nickel-plated in this piece) that goes inside the air chamber and expands to a broad base. This type of stem needs to be installed through the wheel hole with the rubber grommet sealing the air. An external washer is used and the nut is to be tightened to specification to prevent air loss.
Here is the metal part of the bolt-in stem without the rubber gasket. The arrows point to where the wheel would end up.
Here are a couple pages from the U.S. Tire & Rim Association yearbook, aka TRA, which publishes the “interchange and fitment” specs so all tire companies and valve manufacturers know what dimensions are required. This is the book where all the Load & Inflation tables come from and might be considered the Tire Engineer’s “Bible”. It is used by tire engineers around the world when they are making tires that are intended to be used in the U.S.
Here are the dimensional specifications used by valve manufacturers and some details on the smallest but potentially the most critical part on your RV, the valve core, that we covered previously.
They even include something as relatively insignificant as the height of the little pin that sticks out of the valve stem.
As you can see, there is a lot of engineering work involved in the valve stem system. If the proper stem is installed correctly, the system should operate with no problems for many tens of thousands of miles. But as with any system, if incorrect parts or improper method (torque) is used, you may have problems.
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