Basics of Tires, Inflation Pressure, Overinflate, Overloading Tires, Tire Essentials, tire pressure, tire safety, Travel Safety, Underinflate
It’s National Tire Safety Week, so this is a good time to discuss the topic of RV tires. Although I am a professional engineer, my area of expertise is not specifically in materials or road safety. I leave the topic of tire theory to Walter Cannon, executive director of the RV Safety Education Foundation (http://www.rvsafety.com). Walter has written many articles and produced many videos on RV tires and safety, and I highly recommend them to anybody who wishes to further educate themselves. This two-part article serves as a general overview of the basics of tires in order that RV owners may understand tire types, inflation pressure, and general use. In part one of this series, I will discuss the important topics of inflation pressure and loading.
Many RV drivers believe that it is appropriate to simply air the tires to the inflation pressure shown on the tire or vehicle ID plate. This is a dodgy oversimplification, as the listed pressure is the maximum design inflation pressure for the tire, and may not be a safe pressure for the RV load. The correct way to determine proper air pressure is to weigh the RV at each tire position and note the highest weight borne by each axle. Most tire manufacturers post recommended inflation pressures based on weight on their websites. Use your data to determine the correct inflation pressure for each axle as determined from the manufacturer tables.
Check the air pressure in each tire at least once a month, before each trip, and each morning before you drive. Tire pressure should be checked cold, as pressure ratings have been determined with typical running heat/pressure build-up in mind. Remember to check the air pressures of the inside tires on dual wheels and inflate all duallies on the same axle to the same pressure. Ensure the valves and caps are free of dirt and moisture.
Most people recognize the risks of overinflation, such as chance of blowout and poor tread wear. However, underinflation also carries significant hazards. Underinflation presents a higher chance of damage due to road hazards, reduces casing durability and fuel economy, and results in uneven or irregular tire wear. Additionally, Severe or prolonged underinflation brings about an increased risk of tread separation.
RV owners sometimes lower tire pressure in an attempt to create a smoother ride. This is not only dangerous, it’s relatively ineffective, as the difference in ride quality is not significant. When minimum recommended inflation pressures are not maintained, durability and optimum operating conditions for the tires are compromised. Therefore, tire inflation pressure should always meet at least the minimum guidelines for vehicle weight. It’s important to note that if the pressure in any tire drops by more than 20% of recommended inflation pressure, the tire should be professionally inspected before air is added. Personal injury may result from the tire separating from the rim while under pressure. A professional tire shop will use a cage to inflate the tire.
Overloading tires can have serious consequences for passengers and the RV. Too much weight causes stress on the suspension system, brake failure, shock absorber damage, handling and steering problems, irregular tire wear, and possible tire failure. Excessive load or underinflation can lead to an excessive amount of heat buildup, possibly resulting in tire failure. If you find that your tires cannot handle the load, lighten the load or install tires with a higher carrying capacity. Remember to consult your owner’s manual, tire retailer, or RV manufacturer for information concerning selection and installation of new tires.
In next week’s article, I will discuss RV tire types.
About the Author:
Steve Froese, an avid RV owner, traveler, and Coach-Net member since 2013, is the principal of “A Word to the Wise Technical Communications”, a published RV author, certified RV technician, and licensed Professional Engineer. He frequently collaborates with the “RV Doctor”, Gary Bunzer, and has worked with the RVIA/RVDA as a technical and training writer and consultant. Professionally, he works as a quality engineer and musician. Watch for more of Steve’s work in upcoming Coach-Net publications.
Karl P. UT~ “Kurt from Quality Tire was exceptional. He came and pulled both sets of back tires. The inside tires on both sides of our motor home had 0 pressure. Both Valve stems had been damaged for some reason. He replaced the valve stems on both tires, checked and filled all 6 tires to correct pressure. He was a pleasant and pleasurable person to work with. We were called by Coach-Net several times to make sure everything went as it was supposed to. Thank you to all the Coach-Net Representatives and to Kurt from Quality tire. It took something that was a pain and made it a pleasure.”
For trailers especially, using max sidewall isn’t going to increase risk of blowout. It is lower pressures that cause heat buildup and that is what increases risk of blowout. Higher pressures mean cooler tires. Use an IR thermometer to keep any eye on tire temperatures. If they run hot, you need more air in the tires (or less load) . See http://sierranevadaairstreams.org/snuze/?p=1836
Where can you get your tires for each postion weight that won’t break the bank.
If you use VTR Double Seal Inflate Through Valve Caps on your valve stems for convenience, be sure not to tighten them too much. I have had those caps leak-down my RV tires. I removed them.
Kurt from Quality Tire may have been exceptional but he was not doing anyone a favor. With two tires having been run an unknown number of miles when flat we also have a situation of the other two tires being run with 100% overload at the same time.
Re-inflating tires that have been run flat has potential safety consequences that could result in serious personal injury or even fatality when steel body tires are involved. Continuing to run tires that have been damaged from running in overload means that Karl P. from UT is riding on a set of time bombs that could fail at any moment.
All to often the tire service tech is the one with the least experience and as a result the RV owner needs to be proactive and knowledgeable on proper tire service procedures even if he doesn’t have the tools or physical strength to change a large truck tire.
Proper tire inflation for trailers is different than proper inflation for motorized vehicles such as tow vehicles or motorhomes. This is because towed vehicles such as trailers do not have their tires rotating about a center-line that passes through the center of a turn radius. This results in large amounts of slip on the trailer tires. This slip generates “Interply Shear” which is a technical term for the forces in the tire structure that are trying to tear the tire belts off the body of the tire. The best way to lower, but not eliminate, the Interply Shear is for trailers to use the max inflation molded on the tire sidewall as the cold tire inflation. Trailer owners should also confirm that they have a minimum margin of 15% more load capacity than the measures load on any tire.
Motorhomes do not have the same level of excess shear force so they can select a cold inflation that is sufficient to support the measured load on their tires. I suggest that the cold inflation pressure be at least 10% above the minimum needed to support the measured load.
It should be pointed out that most stick trailer tires are borderline junk. I couldn’t even find the tire specs on the Internet in my 2015 Coachmen. Between the axle ratings and tires, I’m at 85% load limit just pulling it off the lot because they were class C tires.
I upgraded to class D which increased by weight capacity greater than what my axles can carry, which isnt what I’m trying to do. I’m trying to make them run cooler by not running close to the limit, which I was doing with class C. Also, most trailer tires are only rated for 65 mph. My new ones are rated for 81mph. Not that I’ll be traveling that fast, but again, the more margin you have, the better they will handle going down the road. At least theoretically!
Long story short, your stock travel trailer tires are most likely no name, marginal, and the bare minimum the chassis manufacturer put in order to sell it to your trailer manufacturer. That’s basically how this business runs.
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