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Friday, December 31, 2021

Valve Extensions come in two 'Flavors"

 Valve stem extensions come in two "flavors". One being a longer metal stem the other is some sort of "extender" that screws onto the end of a standard stem.

If you chose the long metal stem route, you probably should have them installed by a tire shop that services Heavy trucks as they have the experience and should know how to install properly. The stem for the inner tire can be straight or almost straight but needs to be long enough to come through the outer wheel "hand hole".  The long stem may look like this one.

The outer stem can be a regular brass stem like this one.

it will help if you have a "dual foot" inflator tool. Like this.

  If you have short metal stems as shown above and a "Dual-Foot" inflation adapter you should be able to get to both the inner and outer short stems. One end you Push on the inner tire. The other end you Pull onto the valve for the outer tire.

The above doesn't answer the question for those that use TPMS or want easy access to allow measurement of tire pressure. You can use the "other flavor of extender", a flexible "Hose" extenders BUT you REALLY need to pay attention to the following:

1. Be sure to tighten the hose properly. That means no leaks (test with some soapy water) and not over-tighten.  I screw the hose on till the air stops leaking then tighten about 3/4 to 1 additional turn. I then check and confirm no air leak.

2. The outer end needs to be SOLIDLY attached.  I use pop-rivets and the small 'L" bracket that comes with the Wheel Master stainless steel hose kit (#8001 or #8005 depending on wheel diameter). Like this. (shown with TPMS sensor)

3. When adding air you should hold the hose so you are not loosening the attachment point as pushing an air chuck or pressure gauge on an extender can generate a lot of force which can bend or loosen the attachment.

4. Do Not over-tighten the hose extenders. There are small rubber "O" ring gasket seals that can be torn resulting in a slow leak.

5 As with all rubber parts, I had one of my hose seals failed after 9 years.  The rubber is any seal can eventually fail due to "old-age". This applies to hoses, rubber valve stems and any other rubber part in your car, truck or RV. One advantage of my using a TPMS I was able to see the slow ( 2 - 3 psi per hour) and after a close inspection of the hose extender confirmed.

 Some people have used a stiff extender instead of the flexible hose. The downside of these extenders is that it is hard to "attach" the outer end to stabilize the extender. This might allow the extender  to vibrate  or unscrew which can develop into a leak. I think that these "extenders" potential to leak is what has led to the negative opinions of extenders..



Friday, December 17, 2021

“The Rest of the Story” - Attention to details.

 Many of us have heard that phrase used as a preface to additional facts that sometimes do not make it into a story as widely published, but once the additional information is explained we learn that we do not always get all the important information  the first time around.

What brings this up was an item in an RV magazine I stumbled upon when cleaning out some old boxes of stuff. This is from Nov 2008 but the facts and information are still important today. The author is one of that small group of RV “experts” that make a living providing information on the Internet on just about all things RV. Sometimes they are answering questions about refrigerators, then they might be answering a question on holding tanks or plumbing. From my point of view it seems that they are quite knowledgeable about most topics but sometimes there are important details related to tires that don't always make it into their posts on tires.

The owner of a 5th wheel trailer had purchased a set of tires and offered that the tire store inflated the tires to 85 psi which was the “maximum” as molded onto the tire sidewall. The owner said he had heard that using the maximum inflation from the tire as the standard pressure was advisable and wanted to know the “rule of thumb” for the proper inflation.

He also wanted to know if he needed to reduce the tire pressure when he traveled to 8,000 ft elevations.

The “expert” correctly replied that the inflation on the tire was the minimum required to carry the load on the tire, he continued with the recommendation that tire loads be measured on a truck scale and then the inflation set based on Load & Inflation tables. There was no mention of ensuring that there was at least a 10% margin between the tire Load Capacity and the actual load on the tire. This recommendation to a trailer owner would address some of the unique side loading
(Interply Shear) seen on multi-axle trailers which is significantly different than that seen on motorized RVs.

While I advocate that trailer owners get their rig weighed so they can confirm they are not overloading any individual tire, as it is not unusual for one tire or axle to be 500 to 1,000Ibs away from a theoretical 50/50 weight balance. I do strongly suggest that all multi-axle trailers run the inflation shown on the tire, which in most cases is the inflation shown on the RV placard as provided by the RV manufacturer. This will help reduce the side force  overload seen by trailers but not by motorhomes.

The expert did correctly advise that while the tire pressure will change with elevation, but said that unless the owner was checking his inflation daily, "as recommended", it was not necessary to adjust inflation when traveling to high elevations.

When I originally read this reply I was concerned and did send a letter to the expert pointing out the missed opportunity to educate RV owners about the importance of setting proper inflation, and that a stronger statement on more frequent or constant inflation checks by using a tire pressure monitoring system ( TPMS) was needed.

I do not consider daily inflation checks sufficient, especially for towables as too often the driver of the tow vehicle has no idea a tire is loosing air till it is too late to save the tire and there has been a "blowout" from a puncture or leaking valve which could cause thousands of dollars worth of damage to the RV. I also would not imply that when traveling to high elevations it isn't necessary to adjust your inflation whenever the inflation is checked.

As you can see the general RV expert provided mostly correct information, but he left out some considerations that I, as a tire engineer, do believe to be very important.



Friday, December 10, 2021

DOT Tire Safety Regulations

 Occasionally I will get questions about some specific feature in a tire or asked why tire engineers didn't design tires to perform in a different manner. Sometimes some even want to question why I didn't design a tire to perform some task such as supporting more load so the RV owner wasn't forced to buy a more expensive tire. The primary reason is that there are numerous federal Safety regulations that all tires sold in the US for highway use must pass or face fines that could be as high as $1,000 per tire.  For those that think they can do a better job of designing tires I can save them some time when they do the research themselves so they can ignore people such as myself who do have experience on the subject.

For those interested in the various safety regulations as they pertain to vehicles you can start HERE:

Then start digging down to the appropriate specific standard.

 For my 40 year career, I had to live every day under Chapter V National Highway Traffic Safety Administration, Department of Transportation and most of the time focus on section 571 ( but occasionally confirm others sections such as 569, 573, 574 and a few others.

I found myself most concerned with Sub Part B and 571.109, 571.119 and of course 571.139. Our focus would of course change depending on the type and size tire we might be tasked with developing or evaluation.

I doubt that you want to have to learn all the appropriate sections but if you don't want to accept my experience and expertise you are welcome to read and research all of 571 and then contact the appropriate department in DOT to get a clarification on some of the apparent contradictions.

Good luck with your research and education.

Friday, December 3, 2021

"65 psi is too much"

 "65 psi is too much" was the opinion posted by Tom when he said 

"Ok, I can’t find any info here so one last time. The tire pressure says 65psi cold on the side wall of the tires on my travel trailer. That sounds like a lot to me. What tire pressure do you run your camper at?" on an RVTips FB page. 

I'm not sure where he did his search. On the FB page, he did get some answers such as "60"  and "110" and "80".

 I responded:

 As an actual Tire Design Engineer, with 40 years of experience including decades of trailer ownership, I can explain why you need to follow the Science of proper tire loading and inflation. You have a Certification sticker or label on your TT that was applied by the RV company based on safety regulations. The sticker tells you the correct information for tire size, type, and Load Range. It also tells you the GAWR. You should not exceed the GAWR because you can break wheels, bolts, axles, hubs, springs, and related parts. Known strength limits of these parts were used to establish the maximum load you should put on your axles. The tire industry has tables that cover the dimensions and load limits for tires for different levels of inflation. These tables have been around since the 70's and all tires sold for highway use, in the US, are required to be capable of passing a number of different strength and durability tests. The test conditions specify both load and inflation levels for the different tests. The RV company has the responsibility to provide the information on the certification sticker such that the specified tires are rated to support at least 110% of GAWR when they are inflated to the stated inflation when the tires are at Ambient Temperature, i.e. "cold". You didn't offer what tire engineering experience you bring to this discussion so I don't know how you arrived at your conclusion that 65 psi cold (ambient) was "too much" but I sincerely doubt that the RV company would select LR-D tires if that level of load capacity was not needed. You can learn more about tires by reading some of the 500+ posts on my blog       www.RVTireSafety.Net