This is a reprint of a post I did in 2014. The facts and data have not changed.
This investigation has taken more time than I originally wanted as I needed a reasonable way to measure UV and a day with full Sun.
- Not something easy to find in NE Ohio-
As they say it all came together one day in April. While it was cold 24°F last night and we had an inch of snow yesterday, it is bright and sunny today with only a little haze in the sky.
The test uses a Hawk2 UV meter. This unit is intended to help you judge how much sun you are getting while at the beach but I felt it would serve my purposes as we are not trying to measure an absolute value in milliwatts per square centimeter but a gross relative level of shielding of different materials used to cover tires.
If interested you can learn more about UV HERE and more about the UV Index HERE
I set up a test using my RV.
I will show the meter readings for each "shield".
Full Sun gives a reading of 9 which is considered "HIGH"
while in full shade the reading in zero.
I interpret these results to indicate that anything that is not in direct sun or that shields all direct sunlight will provide adequate protection from UV damage for tires.
I would not be worried about reflected light going under the RV to the back side of the tires as this is full shade. After all, tires are designed to be outdoors and we are not trying to protect tires for 20 years but only to get past a normal vehicle usage of 4 to 5 years to the 8 to 10 year range for many RVs. I would not consider open mesh as used in some "tire covers" complete protection but it is probably better than nothing.
NOTE I did not address the effects of heat on tires in this post. I did cover in THIS post and that clearly shows that white covers are the ones to use if you want to keep your tires cooler so they age more slowly.
If you want to protect your tires to give you the longest life possible you need to cover them with white solid covers such as cloth backed vinyl being a most reasonable option.