UV protection for tires. Still important, and the facts haven't changed in 7 years

 This is a reprint of a post I did in 2014. The facts and data have not changed.

For some time I have been reading posts and advertisements about tire covers and UV protection. As an engineer I prefer FACTS over sales PR.

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.

As you can see the UV of 6 years here in Ohio,  has pretty much destroyed the cheap vinyl used by Coachmen for the side decoration. Anyway the front tire has my normal white vinyl tire cover and there is a standard blue tarp, a roll of window screen and some black cloth backed vinyl similar to what is used in black tire covers.

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.

Under the white cover the reading is zero

 and even under the black cover the reading is zero

.

  but the screen only reduced the UVI to level 5

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.

BOTTOM LINE
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.

##RVT1006

Was your "Blowout" caused by parking at Quartzsite two years ago?

This is a bit of a continuation on the topic of "tire Dressing" from last week's post.

I do wonder how many that complain of sidewall cracking or less than desirable tire durability makes the effort to protect their tires from the heat and UV degradation from direct sun exposure.

While there might be some benefit and shielding from applying such as "Dressing" or "Shine" or other "stuff" to the tire sidewall for UV shielding. No dressing will protect a tire from the accelerated aging process due to being "baked" by the sun's heat.

There is no standard SPF for tire dressings as there is for sun-tan lotion, It would not be that difficult to measure the level of UV shielding by measuring the UV going through some clear plastic sheeting and then applying the tire dressing to the sheeting and measuring the level of reduction if any in UV rays.

In many cases, the rubbing of the tire sidewall when applying a dressing can remove the special anti-oxidants and UV protection provided by the chemicals the tire companies use in all tires.

All rubber, natural or synthetic, loses strength and gets stiff over time. The rate of degradation is also temperature-dependent with the rate effectively doubling with each increase of 18° F. As I have shown in my blog on the use of tire covers sunlight can easily accelerate the rubber degradation by 4 times with 8 times not unreasonable in Southern states. This loss of strength and flexibility can eventually lead to a belt separation, which many sometimes call a "blowout". Maybe that unexplained "blowout" in June was brought about by the eight months of direct sun exposure in Quartzsite, AZ, over the last two winters.

I have confirmed, with temperature measurements, the significant temperature drop with the use of white vinyl covers on Class-B, Class-C and RV Trailer sizes, and the use of a flat mesh "Tire Shades" on Class-A motorhomes. I would recommend against the use of black or dark color solid vinyl covers as they would act more like an oven by both transferring the sun's heat to the tire and preventing cooling air circulation around the tire.

##RVT948

Do you need an external spare tire cover?

Reading a forum where the owners of one specific brand of trailers were complaining about the $21 the RV company wanted to charge for a spare tire cover.

I have previously covered, in detail the advantages and the "why" we should be storing our tires inside or under our RV or under light colored covers. It is the HEAT that kills tires and the aging effect on tires is exponential with an increase in temperature (doubles each 18°F) you could end up with a tire failure with ZERO miles as seen in this example.

 I pointed out, with temperature data, in my blog post on why white tire covers are good and much better than black covers.
This shot shows what can happen with a black cover that effectively places the spare in an "oven" where cooling air can't offset any of the Sun's heat.

You will note that in both the above examples the top side of the tire (location with most direct Sun heating) is the location of the failure.

These folks do it right.

I know of no tire shine or protectant spray that provided protection from heat.

Can Black tire "Covers" be used without causing damage?

Back in June 2011 I did a post that asked the question  "Tire Covers - Do they do any good?"  In that post I showed the numbers from a test I had run where I collected tire temperatures showing the effects of shielding my tires with white vinyl covers vs the tire temperature when exposed to direct sunlight for just a couple hours.

 I also covered the science of the damage that excess heat can do to our tires. The bottom line of that post was that white vinyl can help extend the life of tires by protecting them from both the affects of UV and the IMO more serious damage done to the internal structure of tires from excess heat.

I also did a rough check using dark trash bag covering a tire and in that case I found that the black cover actually resulted in a tire being hotter than when it was just in the Sun with no cover. Based on that limited data I have recommended against the use of Black or dark color vinyl tire covers.

On more than one occasion I have observed some Class-A RVs with what appears to be a mesh shield than hangs down off the side of the RV. This is different than the vinyl "bag" that hangs directly over the outside of my tires. I was able to collect a few data points while in Redmond , OR in 2014 at a large RV Convention, and that data suggested it might be possible to use this mesh material and not increase the temperature of the tires. Finally this Summer while at another RV Convention I struck up a conversation with a representative of ShadePro Inc who offered to send me a Tire Shade to test. In Aug & Sept i had some health issues and then I ran into difficulty with clouds here in NE Ohio but I was finally able to collect the data I felt comfortable with that would allow me to reach a conclusion of if this black mesh material could be used.
 

Here is a shot of my test set-up with a white vinyl on front, control sidewall in center and the black mesh shielding the rear. After 2 hours in the full sun 

In the shade a tire gave 92°F

In the sun the white cover was 126°F

The reference tire sidewall registered at 147°F

and the black mesh shade showed 136°F

Under the cover the front tire was at 114°

While behind the mesh shade the rear tire was only 101°F

Conclusion:
The data shows that in this test the black mesh did a better job of keeping the tire cool than the white vinyl.

I can think of a couple of reasons for this.
1. The vinyl cover was in direct contact with the front tire so heat was being directly transferred to the tire.
2. The mesh allowed better air circulation around the rear tire.
3. The fact that the black plastic was also in direct contact with the tire probably contributed to the poor results.

Observation:
I was wrong to suggest that all black shields were worse than white covers, as this test shows that data is better than opinion when it comes to facts. This is one of the wonderful things about Science. 

Quick Summary here

I have been following a number of RV forums and want to do a bit of a summary for those that don't have the time or interest to read a number of posts on this Blog: Remember more than half of the thousands of RVs that have been checked have been found to have one or more tire and/or axle in overload. So nect time you camp you can be pretty sure that one or both of the RVs parked next to you are overloading a component.

- You should have a Digital tire gauge. I have posted the results of my tests of dozens of gauges that RVrs were using and the bottom line is that about 15% were off by more than 5 psi which  IMO makes that tire gauge a good door stop or tent peg. I have provided information on how to do your own gauge "Calibration Check" to confirm the accuracy of the gauge you use daily and how to maintain your "Master Gauge"

- If you follow the advice from the two Tire Engineers on this thread you will be setting the pressure based on the appropriate method here:
     - On your TV inflate to pressure based on the Door sticker and Owner's manual for "Fully Loaded" operation. BUT get on a scale at least once to confirm you are not overloaded.
     - If you have a multi-Axle trailer you should be running the pressure on the tire sidewall. I have written in my Blog and provided the technical justification and need to follow this advice. You should still go across a scale and calculate the actual tire loads to confirm you are not overloading one or more tires
      - If you have Motorhome you need to confirm your unit's "corner weights". Use one of the worksheets I have provided links to. Use Load/Inflation chart from your tire manufacturer, to confirm you are not overloaded and identify the heavier loaded tire on each axle. Using the pressure for that load add 10% (without exceeding the wheel max) and that is your Cold set pressure for all tires on that axle.
      - If you follow the above there should be no reason to be chasing your tire inflation around unless you have a major change in Morning temperature ( More than say 30°F ) as you would only need to "Top Off" the air once a month at most.

- Don't be too anal about inflation. Variations of 1 to 3 psi day to day are normal. You should not need to make adjustments unless the Cold pressure is 4 or 5 psi away from your goal. (Multi-axle trailers might try and get no lower than 3 psi below tire sidewall pressure)

- TPMS are a WARNING device and like Insurance we should all be using them. Also just like Insurance they cannot "Prevent" bad stuff from happening but with luck they may give sufficient advance warning to lessen the impact of the bad stuff that does happen.

- If you are parked for more than a day you need to cover your tires that will be in direct sunlight with WHITE tire covers. This protects against both UV and higher temperature damage which can shorten tire life.

What is the Best Trailer Tire?

I frequently get asked "What is the Best tire for my trailer?

I don't want another blowout"

My answer:

 I previously did a post on "Best Tire".


Sorry there is not enough data to provide a more focused answer.  I am sure some are hoping I would provide the one size and one brand that will solve all their tire problems.
I would point everyone back to this link from an RV forum with data from NHTSA. As you can see the numbers of RV owners that make the minimal effort to file a complaint sends the message to NHTSA that there are no significant problems with RV tires. I also know from looking at some of the complaints the quality of the information is spotty even if a complaint was filed.

Examples include wrong size, wrong tire brand, missing or incomplete DOT serial. Expecting information on actual load, speed etc is unrealistic and expecting an accurate description of the real failure is just a dream.

Engineers react to and work with facts. I have been trying to educate a few folks on another forum that melted body ply cord, as seen in tires with a Run Low Flex Failure


is physical evidence of a tire having been run under-inflated at highway speed. The discussion ended with one poster accusing me of hiding the facts and lying to keep my job. Of course he had no idea why the body cord melted but was certain I didn't know either. That ended my participation on that thread.

I know of no data to indicate that anyone is intentionally making "bad" tires. I do know of data that confirms the majority of RVs have tires in overload and that a significant percentage of tires on the highway are under-inflated. I share with others the  personal observations that a good number of trailers are exceeding the speed limit of their tires.

Multi-axle trailers place unique and high side loading on tires. This cause internal forces that contribute to the short life for tires in this application. This is a fact based on engineering and all tires are subjected to this type of structural load. It is just a fact that multi axle trailers are worse than single axle RVs.

Bottom Line
If you want to minimize the probability of having a tire failure on your multi-axle trailer, all I can suggest is you read my post on "Best tire", inflate your tires to the sidewall inflation 100% of the time, at least once confirm your side to side and axle to axle unbalance is not giving you an overloaded tire, use TPMS w/metal valve stems and do a free spin inspection at least once a year.

 and cover your tires with WHITE cover whenever parked in the sun for more than a day. You will probably still only get 4-5 years out of your tires because of the internal stress load but hopefully they will be 5 years with no problems.


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Question on UV & Ozone tire damage.

Got this question and thought I would share my answer
"Tireman,
First of all, thanks for all your informative comments here, and also for the mounds of useful information in your blogs.
Have a question though... I've always thought that damage to sidewalls from ozone (which is always in the atmosphere) is going to cause sidewall damage more quickly than UV rays. Therefore, unless your motorhome spends a significant amount of its life in direct sunlight (as it might if you were full-timing or even half-timing), it really doesn't matter much if you cover the tires, since you are going to be replacing them in 7 or 8 years anyway. Is this faulty thinking?"

Yes Ozone can do real damage to tires. I have seen sets destroy because they were parked in a garage that had a leaking Ozonator.  BUT Heat is the primary killer of tires.
Ozone and UV can only attack the rubber surface but heat damages the internal components and structure in addition to the surface rubber.
The UV protection test in the link above shows how almost anything can stop the UV damage to tires.

The stuff sold that promises UV protection is like suntan lotion in that it may extend the time you can be in the sun without getting burned but I know of no spray on protection that cuts UV to zero.

 Heat accelerates the degradation of the molecular bonds which can lead to belt and tread separations.

I did a test on covers

that shows the significant increase in tire temperature. Since the affect of heat DOUBLES with each increase in temperature of 18F this translates to an effective doubling of the "aging rate" of tires (or reducing the tire life).

I cover my tires whenever parked for more than an overnight stay where the tires can be exposed to direct sunlight. The WHITE covers block all the UV and keep the tires at about ambient temperature rather than baking the life out of them.

With proper care:
Washing with same cleaners and cloths I would use on the RV body.
Having the tires "under-loaded" by about 20% (a 20% Safety Factor if you like) when setting cold inflation.
Never getting lower that 5% above the inflation needed to carry the load.
Multi-axle trailers should run the tire "max" inflation unless they have significantly upgraded their tires with higher Load Range and larger size, but they still need to run a much larger "Safety Factor" due to the unique loading caused my their tandem axles.
Always running TPMS and checking pressure every AM and after each stop.
Using digital gauges that have been shown accurate to +/- 1psi.

I am hoping for 9-10 year life on my Motorhome. If I had a multi axle trailer and took the same precautions I would hope for 5 to 7 year life due to unique loading from suspension design.

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UV Tire protection. The FACTS

For some time I have been reading posts and advertisements about tire covers and UV protection. As an engineer I prefer FACTS over sales PR.

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 today April 16 2014. 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.

As you can see the UV of 6 years here in Ohio,  has pretty much destroyed the cheap vinyl used by Coachmen for the side decoration. Anyway the front tire has my normal white vinyl tire cover and there is a standard blue tarp, a roll of window screen and some black cloth backed vinyl similar to what is used in black tire covers.

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.

Under the white cover the reading is zero

 and even under the black cover the reading is zero

.

  but the screen only reduced the UVI to level 5

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.

BOTTOM LINE
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.

Should I jack up my RV?

I see this question come up each year when some people are parking their RV for the Winter. There is a quick and simple answer and a more involved answer,

Quick Answer:
I do not jack up my Class-C RV over the winter but I do inflate the tires to 80 psi (the pressure on the tire sidewall). I do cover the tires with white covers over the winter (and whenever I camp at a location for more than 1 day).

There are other things you can do such as keeping the tires out of contact with wet sand and dirt. I covered this with pictures in my post on “Winterizing” 

More involved answer:
Jacking up the RV and removing the tire is one of those things that in a perfect world would be easy to do but in reality it isn't as many RVs don't have good jacking points or are so heavy you need very HD jacks so it may just not be safe to do..
I do understand the theoretical damage done from long term parking in one spot but again theory and reality clash. Lots of actions can theoretically prevent microscopic problems but if you extend the life of a tire by 1 month if you were to jack it up every time you were planning to park for more than 3 months, would it be worth the effort? Probably not.

There are actions that are easy to do and relatively inexpensive that can provide real "bang for the buck". I have covered these in various posts on my blog but will touch the big ones here.

1. Your actual static load should not exceed 85% of the max load capacity on any individual tire for the inflation you run..
2. You need to weigh and learn the actual load, when fully loaded and not simply take the total axle load and divide by the number of tires. You will NOT get the correct tire load by doing the simple division. You can download a worksheet on how to do the math HERE Or HERE

3. Get a TPMS so you will get a warning when (not if) you start to loose air due to puncture or leaking valve
4. Cover your tires with WHITE tire covers if they will be in the sun for better part of the day. A couple of hours in full sun does about same damage as a full day in the shade in Phoenix.
5. Replace the snap-in valves or rubber parts of your bolt in tire valves whenever you buy a new tire.
6. Get and use a digital hand held gauge at least once a month, even if you have a TPMS. You will probably be adding 1 to 3 psi each month anyway to maintain the tire inflation. This will also serve as a check on the TPMS.
7 NEVER drive on a tire that has lost 20% or more of its air. Structural damage will be done. Such damage is cumulative and this damage does not repair itself. (See post on Potato Salad)

8 Do not believe everything you read on RV Forums. Ask the poster for their actual training in failed tire analysis. Simply having owned tires from company XYZ does not make that person a knowledgeable source.
9. If you have a multi axle trailer your cold inflation should be the inflation on the tire sidewall

10 You might put on your To-Do list to read the posts in my blog (including the ones where I later point out my errors), then you could subscribe so you get a notice when I do a new post. I do about 3 a month so you will not be overloaded.
11.If you have a multi-axle trailer, learn how to do a rotating tire inspection and do your tires at least once a year. Watch this VIDEO  read the background in this POST to see what a failed tire looks like before it comes apart.

Why do tires fail?

There are basically two reasons that explain the vast majority of tire failures.

1. Over-load / under-inflation which are almost the same thing since it is the inflation air that carries the load not the tire.
Under-inflation: A tire operating at less than 80% of the inflation needed to carry the load, is considered to have been run flat and there is a good chance that there has been permanent internal structural done to the tire if driven on in that condition. Related to this is having the tire inflated to a level that just barely is rated for the actual load on the tire. Obviously you can be under-inflated because of cut or puncture or a valve leak or if you use an inaccurate gauge. If you run sufficiently low in pressure at highway speeds for a just a few miles you can have a Run Low Flex Failure or more commonly a "Blowout". Steel body tires can have "Zipper" failures due to fatigue of the steel body ply.

Over-loaded: Few people realize that by design, most passenger vehicles have 13% to 20% or more "Reserve Load". That means that they are actually under-loaded by that much for a vast majority of the time. Most RV trailers on the other hand have tires selected that are at the tire max load and can just barely carry the actual load while motorhomes seem to have some reserve load but not as much as passenger cars.
Data on actual loads measured shows that over half of RVs measured (out of many thousands) have one or more tires overloaded based on actual inspection.
While at a campground last week I got into a discussion with the guy parked next to me with a 5 week old RV.  I bet him a beer that at least one of his tires was at least 10% low. We found all his tires were between 18% and 21% below spec. I did enjoy the beer. :-)

2. Heat. Heat damage occurs at the molecular level and degrade the ability of rubber to flex and stretch and not break the chemical bonds. Once cracks form the rubber does not repair itself, the cracks just continue to grow. If they grow enough eventually you may have components come apart. Heat comes from a few different sources. This heat is generated by the flexing of the tire with the hottest region being at the belt edges (edge of the tread) in radials, not the sidewall if the tire is properly loaded and inflated. Increased speed generates more heat. Sometimes the heat is generated faster than it can be transferred to the surrounding air. Over-loading generates more heat. Under-inflation generates more heat. Having 0% reserve load generates more heat than having 10% reserve load which generates more heat than being 15%  under-loaded etc.  This heat can soak into the structure of the tire and actually accelerate the aging of the rubber in the tire. As rubber ages, it looses it's flexibility so this contributes to the breakdown of the rubber at the molecular level mentioned above.



Part of Organic Chemistry is chemical reaction rate.

For every 18F increase in temperature the rate of aging doubles. Heat also comes from being in the sun when parked. So if the RV is parked with tires in direct sunlight you can see the tire achieve 36F increase or more which means it is aging at more than four times the rate it would have if in full shade.
If you want to understand the technology behind this accelerated aging due to heat I suggest you can read some of these sources if you have a few hours.
http://en.wikipedia.org/wiki/Reaction_rate

http://www.chm.davidson.edu/vce/kine...tionRates.html

http://www.chm.davidson.edu/vce/kine...fReaction.html

http://chemistry.about.com/od/stoich...actionrate.htm

Here are some specific references on tires
http://www.rubberchemtechnol.org/doi...5254/1.3547913

I provided temperature data in my post on  white tire covers which protect tires almost completely from this heat damage. Many times the cumulative damage from excess heat can result in a separation of the belts and tread from the rest of the tire. Remember aging of rubber makes it less able to tolerate flexing.

Hope this helps others understand the causes of the vast majority of tire failures.

Long Term Parking - Winterizing

Now is the time many RV owners are "winterizing" their RV. Even if you are in Arizona, you might be getting it ready to be parked for many weeks or months. There are a few things you need to do to help preserve your tires.

1. When you wash your RV prior to storage be sure to clean the tires. The easiest thing to do is to treat your tires just as you would the side of your RV. Wash the tires with the same soap & water you use on the RV body. You wouldn't use SOS pad on the bodywork so don't use coarse scrubbing material on the tire.

2. Inflate to the pressure shown on the tire sidewall. This will decrease the tendency to flat-spot and make the tire flat on one side.

When I was checking the inflation I discovered one tire was almost 30 psi low. I knew the tire had not lost air when it was being driven so I immediately suspected that when I removed my external TPMS sensor the valve core must not have properly seated. This was confirmed with a shot of household cleaner. Here you can see the small bubbles that confirmed the 3.5 psi per week air loss past the valve.

3. If you are not parking on a concrete floor or pad it is suggested you not park on asphalt as the oils in the tar can attack the tread rubber. It is also suggested that you not park on dirt or sand as the moisture can migrate into the tire and possibly cause corrosion of the steel.

I have some pressure-treated boards that are large enough to completely support the contact footprint.


Here you can see the board and the reference footprint for a front tire.








You always need to completely support the entire footprint. Both in length and width. These pictures show what NOT TO DO.
                                                                                Too narrow










Off center



                                                                                             Just Right











 Be sure the support is wide enough for both duals.









Finally, be sure to cover the tires to protect them from direct sunlight, which can cause UV damage and overheat the tires.

If you haven't read my series on Tire Covers simply check "Tire Covers" on the label list to the left.

A little bit of preventive care can help avoid future problems and extend the life of your tires.


P.S. Don't forget that even when parked you should check the air pressure once a month. If I hadn't checked the air in the tire with the leaking valve it probably would have been flat by next spring and might even have been damaged and unsuitable for highway use.

Are Black Tire covers bad? part 2

June 11 I posted on black tire covers possibly doing more harm than good. There were a number of comments on this topic and I wanted to more than post quick comment replies so here are my responses.

Gareth said "Black VS. White is a no brainer". We all know that black absorbs heat, white tends to reflect heat" and that he hoped that there had been UV resistance testing done. He also wasn't impressed with my use of a dark color trash bag.

Well Gareth I agree that a plastic trash bag isn't the same as a vinyl (plastic) tire cover but I don't have a budget to go and buy products and do testing so I just made a quick comparison. I have learned that even with Apples vs Apples data some people will still question test results.   RE: UV testing. I have never seen tire cover mfg make any claims or provide data so I would not be surprised if they never bothered to pay a lab to do any testing. If anyone knows of such data please let me know.


Bob asked if he was better off with no cover or a black cover until he buys white covers. While I have no data, my opinion would be to use no cover but spray your tires with a protectant that claims to offer UV protection. High heat can damage the tire internals while UV will only attack the surface.


Al said his "shields" are black but since they attach to the side of the RV and not the tire they prevent a temperature increase of more than 2 degrees F.  I would really like to test his product.


Pennierich suggested using Mylar covers and Bill suggested trying "space blankets".
Well the problem is I haven't found tire covers that use the mylar material. I did look at the mylar sheets which are inexpensive but would need some R&D to make into tire covers as a simple sheet of this material would not stay on tires very well.


General comment on UV
A few weeks ago I asked a manager of a lab at a major tire company about UV testing and wondered if I could purchase the special light bulbs needed. To test for UV resistance I would need UV-C bulb and a simple 40w bulb would cost me $1,000 so I will not be setting up a test lab anytime soon.

Anyone thinking they have a better product please feel free to email me at Tireman9   at   Gmail  dot   com   and lets see what can be worked out. I will be happy to conduct a controlled test and publish the results. If there is something better and less expensive than the basic white covers I would like to know about the product.

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.

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.








KEY POINT
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.