Why and how to take care of your tire valve cores

 

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.

Leasking HP stem  video

 

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.

How to select a tire for your RV

 

If you want to know what tires to get for your RV, I can tell you that as a Tire Design and Forensic Engineer, the most important feature is that is it rated to support the weight you are placing on the tire when the tire is inflated to the level you set it for. 

The Max load is spelled out on your certification label affixed to your RV and is stated as "GAWR" which is the max load ever allowed on an axle. BUT it is important to remember that the tire load capacity depends on the "cold inflation" you set the tires to. If you do not have at least that level of inflation when you drive down the highway you will be doing damage to your tire. 

The MINIMUM inflation you need to achieve that load capacity is also clearly stated on the label. 

These inflations are the "cold" inflation you set your tires to BEFORE you start driving and you should never bleed down the psi after you start driving each day.

I hope this helps answer some of the questions I see in many RV forums.

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Do I need to balance my RV tires?

 I was recently asked about tire balancing.

Reasonable question but as always the answer starts off wit "It Depends"

Vibration can be because of a tire/wheel suspension component is out of balance. Vibration can also occur because the tire or tire and wheel assy is not "round". On a small (14' to 16") tire you can see and measure out of round when the tire & wheel are placed on a spin balancer.   I have shown that you can "balance" a square cement block

  so you need to be sure your tire & wheel assy is "round within at least 0.030"

The person asking the question, said that they had done some research and learned there were three methods. They wanted to understand the advantages of each and which they should use for their Class-A RV.

The basic method is static or "bubble balance". as seen in this  video   https://youtu.be/hp3ShyNzK84

The mounted tire is placed on a balance and the heavy spot is counter balanced with weights.

This static balancing is lower cost but does not provide the best balance. This method is not usually done any more by full service tire stores as it only affects the "static" imbalance and with today's light weight cars the driver is more likely to feel even a minor imbalance. I once had a car with one front tire 1/4 oz out of balance and on a very smooth portion of the interstate on my way home from work I would occasionally got steering wheel movement. A re-check at the store solved the problem. The car was a small light weight sports car and it just happened to be sensitive at that level. My one-ton dually pickup was not sensitive at the two ounce level on the rear axle.


The next best method would be with the mounted tire on a "spin balancer", This rotates the wheel and tire at speed and electronically calculates where to place the weights.
When you buy a new passenger or pick-up truck tire, this is the method they are normally talking about.

But truck/bus size tires can also be balanced using a heavy duty version of this type of machine.

Spin balancers measures the up-down imbalance and the side to side balance and tells the operator how much weight to place on both the inside and the outside of the wheel to counteract forces in both directions.

 Finally there would be "On-Vehicle" spin balance this would give the balance for the tire, wheel and the brake drum and hub of the vehicle so if the drum was slightly out of balance it would be included and weights would counter balance all the spinning components. If you get this type of balancing done it is important to mark the wheel position on the hub if you ever remove the wheel to check brakes and to re-mount the wheel in the exact same orientation. A downside to this method is that it can't be done to tires on drive axles.

Many drivers of Class-A do not balance their tires as they do not feel the imbalance. Some others always balance the fronts because the driver & co-pilot are sitting almost on top of the tires. On-vehicle spin would probably give the best results but this would be for the front only. Here is a video showing the process on a Corvette
 but RV tires would be the same process but with HD bigger equipment.

I see little reason to balance the rear duals on a Class-A as you will not feel the balance problem unless something was very out of balance.

Some additional info in another post.

https://www.rvtiresafety.net/2011/11/do-you-need-to-balance-your-motor-home.html

BOTTOM LINE
For Class-A I think you can just take the RV out for a quick test drive on a nice section of smooth Interstate. If you feel shaking either through the steering wheel or floorboards then you would go and have the front tires "on-vehicle spin balanced".

For Class-C and smaller vehicles using 16" diameter LT type tires I would spin balance all six assemblies.

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How much air pressure do my motorhome tires need?

 

Tire loads and proper inflation for motorhomes

Today’s key points: Know the minimum tire inflation based on tire industry guidelines. The basic instruction for your minimum RV tire maintenance is to check your inflation with a good gauge at least monthly and every morning before travel.

Tire inflation seems to be a topic that confuses some and has others believing in misleading or just plain incorrect information. Tire inflation is one item that directly affects the safety of your RV, truck, or car as you travel down the highway. Many of my posts have outlined information that you really should know and understand. The intent of these posts is to give you a better foundation of understanding more about tires. But if you only pay attention to one series of posts, this is it.

Tires do not carry the load

Some people have been led to believe that the load is carried by just the tire sidewall. This is not correct. Tires are just a container of air. It is the inflation air that does the work. Think for a moment of an impact wrench. It can’t do the work of loosening or tightening nuts on your wheels without the air. A tire can’t do the work of carrying the load or providing the traction needed to turn, start or stop if it doesn’t have air. The load a tire can carry is based on the air volume in the tire and the pressure of that air inside the tire. You can see this if you look at any Load & Inflation chart, as found HERE.

 it is important to understand that these tables are essentially identical across all tire companies that are making the same size tire.

Load Range vs. Ply Rating

Some people believe that tires with a higher Load Range can carry more load at the same inflation. This is just not correct. Don’t forget that the term Load Range replaced Ply Rating with the introduction of radial tires to replace bias tires. You would be hard-pressed to measure the uninflated load capability difference between a Load Range D and E tire or between a G or H Load Range tire.

If you still think the load is supported by the tire construction, I would challenge you to find a Load vs. Construction table. Here is an example of a Load & Inflation table for a 255/70R22.5 and it covers both LR-G and LR-H tires in that size.

 

 

 Sidewall stamping examples

Here are sidewall stamping aka “marking” examples from a large P-type tire showing the dimensions, along with Load Index and Speed Rating. An LT-type tire would look similar except that LT-type tires and Commercial Truck/Bus (22.5″) can be applied as single or dual (side by side). So they would have two sets of numbers for the Load Index (single and dual application). Commercial truck tires are not speed rated, but Michelin and Goodyear and others indicate a 75 mph Max operating speed in RV applications no matter what the tire rating is.

 

 Here are the tire reinforcement materials, both type and quantity.

 

 

Next, we see the Load and Inflation ratings for this standard load P-type tire.

 

 

Nowhere do we see a statement on construction or Load Range for various inflations and different load capacities for different constructions.

 The Load Range is marked on the sidewall of your tires except for Passenger-type tires, which are considered to have “Standard Load.” If you don’t see the words “Load Range,” look for “LR” followed by a letter, usually between C and G.

“Load Range” may not be in large letters, but you should be able to find them on your tires. “P”-type aka passenger-type tires are actually “B” or some are “XL” or Extra Load. Light truck, commercial, and bus tires all have a Load Range letter.

“Load Range” replaced “Ply-Rating” in the late 1970s with the introduction of radial construction. People really need to try and stop using the old nomenclature.

How much air is needed

The simple answer to how much air you need is on your data sheet. Depending on the year your RV was made, this information is on a label near the driver’s seat in your Class A or glued to the wall inside a cabinet or on the inside of your entry door if your RV is older than 2009. Class B and Class C will have the label on the driver’s door jamb, which is where it is in your car, too.

Wherever it is, you should also have the information in the stack of owner’s manuals you received when you bought the RV. Find this data sheet and write down the information for loads, minimum inflation, tire size, and load range, and place this info where you can easily find it. This inflation is the minimum based on what the RV manufacturer says is the maximum you can load on each axle.

Motorhomes have much lower Interply Shear forces, so that is why tire life on motorhomes, in general, is much longer, i.e., 6 to 10 years versus 2 to 5 years on trailers.

 

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