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Thursday, June 16, 2011

Tire Covers - Do they do any good?

I have seen some posts and comments about tire covers. One post caught my eye.

The owner was complaining about the cover degrading in the sun so he was of the opinion the cover wasn't worth the cost. I have to wonder how he failed to properly interpret the proof that the cover was protecting his tires. How would he answer the question: Which would you rather have degrade due to being in the sun? Your tires or the low cost cover?

As an Engineer I always prefer to have data rather than just someone's opinion. So I set up a quick test on my own RV.

As you can see I have covers for my tires. They were the second purchase after buying my rig. The first was a Tire Pressure Monitor System.

The Test
With one side of the RV in full shade I checked the temperature of the side of the unit.
You can see I recorded 85.1°F.

Then I took the temperature of the side of the RV in the full sun.

Here we see 107.9°F

Next the temperature of the white tire cover in full sun.

We get 98.6°F
I believe the cover is cooler than the side of the RV because air can circulate behind the cover.

I then removed the cover to see what the tire temperature was under it.

We see 99.5°F
Only 1 degree hotter than the cover.

I then waited 30 minutes to see how hot the black tire got while in full sun.

We see the black tire was at 136.1°F.

There are three things that can "kill" your tires. Ozone, UV and High Temperature. The Ozone & UV directly attack the surface of the tire making it crack when flexed. Temperature works no only on the surface but deep down inside the tire structure.
Increased temperature causes continued and accelerated chemical reaction which "ages" a tire faster than when the tire is cool. A rule of thumb would be that the rate a tire ages doubles with every 18°F increase in temperature. We can see the result of old rubber on the surface. What we don't see is the more brittle rubber of the internal tire structure. As rubber gets more brittle with age it also looses strength.

NOTE Overload and Underinflation can overheat a portion of a tire to the point the rubber and reinforcement materials loose all their strength.

Based on my simple test it would appear that by covering my tires I am significantly reducing the artificial aging for all the daylight hours my RV is parked and the sun is out. If I didn't have covers my tires would be "aging" FOUR times faster than with the covers in place.

I don't have black tire covers so can only guess at their temperature. While they may provide protection from UV I would be surprised if they can offer much temperature protection.

So I will let you answer the question of Tire Covers being a good investment or not.


  1. Hi, Roger. You certainly do a service with this blog!

    Question: do you ALWAYS cover your tires, or do you have a rule of thumb like... use the tire covers if you are going to be parked for 3 days or longer? Obviously, EVERY time would be better... but I wondered if even an expert trades off perfection for convenience. :)

    Thanks for all the info!

  2. Oh, one more question:

    Seems I heard in a tire safety class that if you are going to be parked on concrete for very long (a week or more??), you should put a barrier of some sort between your tire and the concrete. I don't remember the reasoning... seemed like the concrete interacted in a bad way with the rubber? Any truth to this, or am I "mis-remembering"? Thanks.

  3. Thanks for the timely post. I'm looking at some tire covers for our rig, and just wasn't sure if I wanted the white ones or not. Now all I have to do is find the white ones that are the easiest to put on and take off. That was always the hardest part with the others that we had on our old MH.
    Any good suggestions?

  4. Lets see if i can answer all three questions.
    I always have my tires covered when parked at home. If i am at a campground for two days or more I cover my tires unless it is heavy overcast and / or raining ( No Sun).

    Parking con concrete is probably OK unless it is seeping groundwater. You should not park on wet dirt or sand as moisture can leach through the rubber over weeks. Also don't park for weeks at a time on asphalt as the oil & tar can attack the rubber.

    You can find covers here
    If you order please tell them where you found the information to go to their site.

  5. Thanks, Roger. I'll check that site. Appreciate the information.

  6. So the answer to the question is a definitive maybe, it is up to your own good judgement?

  7. Very good article. I'm lucky, in that our RV is parked on the North side of the house, and in the shade, so I don't need the covers for the Sun/temperature, BUT, I wondered if they make any kind of difference for the Ozone?

    It would seem that it wouldn't matter, since we only cover the outside of the tire, and the Ozone will reach all of the tire, but I figured I'd ask the expert?

    Thanks again :-)

  8. When a tire is rolling down the road the temperature of the tire tread is typically arround 150 degrees for a passenger car at freeway speeds. In racing, the tire pressure, caster and camber are adjusted to make the tire run at about 190 degrees. Some race crews use higher temps. The temperature at which you start to worry is more like 300 degrees.

    I suspect that a temperature of 100 degrees has little effect on tire life. The tire cover is more for UV protection than temperature protection.

  9. invmartyc
    To me the answer is pretty obvious. I think I would rather have a much less expensive cover get old & die from heat & UV exposure rather than my tires.
    Was my example of the aging rate at high temperature confusing?

  10. PapPappy. No good way to protect from Ozone with a cover. If you don't park with tires in the sun days at a time probably not worth the effort for you.

  11. Diva
    Tires running down the highway normally run 30 to 60 degrees F hotter than ambient. Race tires have a life measured in minutes of use at racing speed or possibly months in controlled condition storage so their info doesn't translate to highway use for tires. I also believe their max temperature is closer to 215 than anywhere near 300 and would expect that a tire exposed to 300 will fail in just a few minutes. I do know that some tire materials can loose over 50% of their strength at much above 250 F.

    Tire "aging" and loss of properties (strength & elasticity) is cumulative and cannot be reversed. I will stand behind the chemistry and my belief that minimizing acellerated aging, exposure to high temperature, Ozone & UV effects are good polices when possible.

  12. Just to let everyone know. I am trying to collect samples of different materials to do additional testing of dark colors as well as to measure UV blocking.

  13. Thanks for the great info Tireman9. What do you know about a product called 303 Protectant. It is suppose to be a water based product, as opposed to a silacon based one, and is touted as having the ability to "replenish" the effects of sun/ozone to help extend the life of tires? Any truth to these claims? I your humble opinion.

  14. Bob Swift
    Sorry for slow reply but I had the "Notify" shut off.
    I would think if 303 really worked the magic as claimed tire companies would use it on the ultra expensive tires. Not saying it is of no value just questioning the level of protection claimed. I am trying to develop a test but no luck so far.

    1. Roger, were you able to complete a 303 test?

    2. Still no reliable data. Have to wonder why 303 doesn't publish some actual performance data.

  15. If you have dual tires in the back, do both tires need to be covered or just the one that is exposed to the outside.

  16. Good question Tim. I was guessing only the outer but I could be wrong. As for the 303 I have noticed over the years ALL additives and protectants claim to be miracle ingredients. Most were eventually proven useless.

  17. I have used 303 for over 20 years with great results. I even coat the inner side of the tires every time I change oil (~5000 miles) to protect the non-sun side from ozone. I started doing the inner side when I noticed cracking there, but none on the outer sun-side which had been protected with 303. Tire cracking has reduced dramatically.

    1. Glad the spray is working for you. The problem is, that no spray will result in lowering the temperature of the tire when exposed to sunlight. This was a key point of the post on the desirability of using white covers.


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