How long can you park an RV without causing ‘flat-spotting’ on the tires?

Ted sent in this question: “How long can a trailer sit and you not have to worry about flat spots developing on the tires? I have seen some units sitting in lots for years.”

Good question and, as with many simple questions about tires, there is NOT a simple answer such as “You can park for up to 83 days with no problems.”

Here are the facts

Rubber has properties similar to “thermal plastics.” These materials can change their level of flexibility based on the temperature, and these materials can take a “set” when cooled off. After taking a “set,” the molecular bonds that make the material stiffer or less flexible will actually break at the molecular level when bent or flexed. These “breaks” or “cracks” do not re-form, but with additional flexing, the cracks will grow.

When you drive on a tire, it warms up and the material can more easily bend. However, as rubber is always “curing,” eventually a “more cured” or older rubber will get to the point of no longer bending and stretching the molecular bonds. Think about how stiff and even brittle a rubber band gets after years of sitting in the back of a desk drawer. Tires are the same. The longer they sit, the stiffer they become. Once they get stiff enough they can form microscopic cracks rather than bending and stretching when flexed. These cracks can grow until they get large enough and the result is a belt separation that can grow until the tire comes apart.

“Heat-set flat-spotting”

When I was designing and testing tires, I did some work on “heat-set flat spotting” in tires when certain compounds or types of rubber got warm and more flexible, and some would get stiffer than others. When driven and warmed up, and if then parked and allowed to cool, the materials in the portion of the tread that was “flat” from being pressed to the ground would take a set so the tire had a “flat spot.”

It was discovered that some types of rubber and some constructions were more susceptible than others to taking a “set” when cooled. In a laboratory setting we could measure this “set” after just a few hours of parking and cooling off.

The above is why I and others recommend that if you are parking your RV for more than a few weeks, you inflate the tires to the “MAX PSI” number on the tire sidewall. This will reduce, but not eliminate, the amount of “flat-spotting” the tire takes.

Suggestions to avoid flat-spotting

While I have not seen any hard data on long-term parking of RVs, I can offer a couple of suggestions:

1. When parking your RV for more than a couple of months, you need to drive the RV for a couple miles and park it with the tires that contact the ground being at a different spot of the tread.

In this case, you should also inflate the tires to the sidewall max, as this will decrease the level of deflection of the tire tread.

2. If you are parking for more than a year, you might want to consider either raising the RV so the tires are not touching the ground, or remove the tires and wheels from the RV to eliminate all deflection by storing the tires so the tread does not touch the ground.

3. If none of the above were done and you are looking at tires that have been parked for more than 3 years with the weight of the RV on the tires, and without being moved, I would suggest the tires be replaced as a precaution.

Roger Marble

MORE HELPFUL POSTS FROM ROGER

• How close to ‘Max Load’ is OK for RV tire inflation?
• What is the proper inflation for my tow vehicle and RV trailer tires?
• How to avoid tire failure
• RV Tire Types 101: Selecting the correct tire for your RV or other vehicle

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If you have tire questions, check out Roger’s Blog as well as his posts on RVtravel.com. There are hundreds of posts covering everything to do with tires.

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