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Monday, June 11, 2012

Black tire covers may do damage.

Last June I published the results of a test I ran on tire covers. I used my white vinyl covers as samples in the test. I mentioned that I did see some companies advertising black tire covers. I do not think are a good idea but need data to offer an informed opinion, so here is my test simulating black tire covers.

Here is a shot of my test set-up.
I used a trash bag that was actually dark green to simulate a black tire cover. The tire is just covered by the bag not in it.
Here we see the reference white cover at 93.5°F which is 5 degrees cooler than in the original test but close enough for this test.
The old passenger tire I had registered 113.3°F in the part that was in direct sunlight. This tire was dirty and gray so it did not register as hot as a clean black tire would.

Here we can see that the black (dark green) plastic cover was at 136.4°F which is almost identical to the uncovered tire in the original test at 136.1°F so this dark cover is actual heating the tire in this test.

Here we see that black tires and black covers can run almost 40° hotter than when under a white cover. This means the rate of aging of this tire under the dark cover is 12 to 15 times as fast as when a tire kept is cooler under a white cover.

Some will ask if lowering the temperature for a few hours each day is worth the effort, so lets set up a hypothetical situation.
Assume you spend 6 months out of the year in sunny Florida or Arizona or similar location with lots of sunshine. You are parked so one side of the RV is in the full sunshine for 8 hours a day and the sun shines 25 out of each 30 days. Now to make the math easier let’s assume it is always 85°F ambient. Now based on the original test our tires in full sun would be at 132° but if shielded by white covers would only be 96°.
So the question is: How much “older” would the tires without covers or with black covers be than tires that were covered with white covers?
Tire A has a cover. So lets figure that as our control so there are 25 days times 6 months times 8 hours per day of solar heat exposure for a total of 1200 hours.
Tire B has no cover, so it’s temperature is two times 18° hotter. Remember the “aging” rate doubles (times 2) with each 18° increase so this tire spends 25 days times 6 months times 8 hours times 2 times 2 or 4,800 hours.
The difference is 3,600 hours which equals 150 days or almost a half year. In this example each year your uncovered tire “ages” almost one and a half years vs one year for the covered tires. This means that after 6 years of staying only 6 months in a sunny location your uncovered tires have rubber properties that are more like nine year old tires. If we consider tha additional damage done by UV light I think you can see that the uncovered tires will probably have serious sidewall cracking after only 6 years of real time aging.
Covering tires with dark or black covers may shield the UV but they do nothing for the heat and could make the heat worse through radiation.

Bottom Line. If you want to get the most out of your tires you should cover them with a white or light colored cover when the tire will be exposed to extended time in direct sunlight.

5 comments:

  1. Because I am just an old guy who thinks different than others, I have the following comment. Number one, Black VS. White is a no brainer. We all know that black absorbes heat, white tends to reflect heat. As for the test, using a white tire cover vs. a black garbage bag is apples and oranges. How about a white trash bag vs a black trash bag? We really do not know the make up of either, however I would hope the commercial white cover which costs considerably more than a garbage bag from Wal Mart has had a minor amount of testing for UV etc.

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  2. I have black tire covers for my 5th wheel. I bought them because black was a better match to my unit's color scheme than white. At the time I bought them, I was a novice and I was thinking about UV protection not temperature.

    Next time I will buy white regardless of the color scheme effect. However, how about this comparison:

    With black covers I decrease tire life due to temperature but increase tire life due to UV protection. So until I buy white tire covers, am I better off with black tire covers or no tire covers?

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  3. Our tire "shields" are black - but they don't cover the tire, rather snapping onto the outside of the wheel well. Made of the same type of material as the snap-on sun shades we use on windshields, they don't actually touch the tires at all, and allow for plenty of air circulation. I too wondered about heat load - on a sunny day last summer, I found the difference in temp between the sunny side and the the shady side to be less than 2 degrees F.

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  4. In building solar heat units, we have been using a deep forest green surface and have found that it does indeed gain a higher temp than black. If you can get the mylar type wheel cover it will reduce the temp on the rubber even more.

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  5. If you already have black covers and this bothers you now then consider buying some space blankets from your local hardware store, they are cheap and bright reflective silver. Wrap that over the black and you will probable even get better results than the white ones. My white covers are insulated...but that is just how they came.

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