Results of Tire Cover Temperature Study

[tireman9]

I have added detailed info on the results of my study on RV tire Temperatures to my "Tire Basics for RV Owners" seminar. This was first presented last week at Gypsy Journal Rally in Elkhart, Indiana, but I thought you would find this interesting.

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It is well known that heat is one of the major killers of tires. It is a little less well known that one of the reasons tires seem to age at different rates is their different temperature history and tires are basically always "curing". Ever seen how hard a 40 or 50 year old tire is?

It is known that chemical reaction rates (1), in general, double every 10°C (18°F) so the more hours we keep our tires at higher temperature the more cumulative "accelerated aging" we are doing to our tires.

While keeping the proper inflation pressure in our tires can keep the operating temperatures relatively under control ( +20°F to +50°F) above ambient while driving down the highway. One area I have not seen any data on is the temperature of a tire just sitting in the Sun.

The attached shows the temperature using an inexpensive IR Thermometer. Pictures are:

Of side of RV in the shade

Of side of RV in the sun

Of a tire in full sun for an hour

Overview of my white tire cover

Temperature of the cover

Temperature of the tire under the cover.

I think it could be argued that your tire "ages" between two and four times faster if you do not use a white tire cover than when your tires are in full sun when parked.

Another way to think of this could be that 6 months of full exposure to bright sunlight does as much heat damage to a tire as two years under a white tire cover.

I will have to leave it up to someone else to do a test on black tire covers.

How "old" are your tires?

(1.) http://chemistry.about.com/od/stoichiometr...eactionrate.htm

[tbutler]

Hello Tireman9,

Can you give me the model of IR thermometer and information about where I can obtain one?

I'll try your test on black tire covers.

[StellersJay]

The non-contact laser thermometer looks very much like a unit sold by Harbor Freight for $25.99 (sale price).

Interesting study! Thanks for posting.

Sam

[susan.charles@windstream.net]

Thanks for the info Tireman9. I'll be anxiously waiting for your findings on the black ones Tom. Our motorhome sits in our backyard and black ones would look better than white ones. While we're on this subject ours is setting on dirt. I've been thinking about pouring concrete pads for it but I don't know if it is worth the effort. We're unable to travel much right now but we do take it out every few weeks for 30 or 40 miles on the interstate. What are your thoughts on dirt versus concrete? Thanks for your thoughts, ccmsm

[Guest BillAdams]

I think it could be argued that your tire "ages" between two and four times faster if you do not use a white tire cover than when your tires are in full sun when parked.

Another way to think of this could be that 6 months of full exposure to bright sunlight does as much heat damage to a tire as two years under a white tire cover.

"I think it could be argued" and "6 months...is as much damage to a tire as two years....." are very interesting statements but I was curious if this information is based on any particular science or your own personal speculation.

I do suspect that covering tires if you park the coach for months at a time is likely beneficial since the tire is designed to be driven and designed to work best while warm.

[tireman9]

Some answers:

IR Thermometer - Harbor Freight $26 - $30 when on sale. Be careful. It is doing some averaging over a 1" to 3" diameter circle so it will NOT give accurate max temp of a tire tread. This is based on my experience with $20k Thermograph video camera which shows that different areas of a tread can have a temperature range of over 50 degrees for over small distances. I have seen this range over as little as 0.10". This hand held unit is OK for approximate temperatures but you need to have a consistent surface temp over the entire area being scanned.

Looks vs Results.

Ya, I understand that the nice flat black mesh covers that hang down from the side of a Class-A might look better than a white vinyl "bag" over the tires. But if you want to get longer life from your tires while parked you may have to make the choice of "Looking Marvelous" as Billy Chrystal said or or actually maximizing the protection of your tires. Maybe if people started asking for a White or Light Grey or possibly even a IR reflective material for their tire cover then some manufacturer might start making such. Color along does not dictate a material's ability to reflect IR or to insulate.

Dirt vs Concrete vs Asphalt

You want to not park on a surface that can "wick" oil or moisture to the tire. So Concrete would be first choice but you can also just park on the plastic pads they sell at RV stores or you could get some pieces of 2x12 or plywood and cut to a little larger than the contact patch of your tires. These could be covered with some sheet aluminum or plastic that you can get from local home supply store. You might even look at using floor tile to cover the wood. The aluminum or plastic sheet doesn't need to be thick as the wood will distribute the load. Cheaper than concrete and you can move around as needed. Cheep enough to be replaced every couple of years if needed.

Opinion or Science?

Well the science of rubber chemistry indicates that tires are always "curing" it is just the rate that changes with temperature. See the link on Chemical Reaction rate vs Temperature in my post.

The longer tires "cure" the harder they become, which can lead to microscopic cracks which once started can grow. Rubber does not "heal" like your skin so once cracks start, they just get bigger.

So given that "curing effect is cumulative and not reversible, every day your tire spends at 135 degrees is about like two days at 115 or four days at 95.

You can think of a tire as having a finite amount of "life". It is always leaking "life" out. Once the "life" is gone the tire is not able to resist serious damage as well as it can when full of "life".

So the question is, Do you think it is worth the effort to keep your tire "full of life" as long as possible?

The question of operating warm is related to the migration of wax and UV protectant chemicals that are part of the tire's compound. These chemicals are "consumed" by exposure to UV and flexing a tire allows these chemicals to migrate to the surface easier than when parked. It is not just the tire temperature that allows the protectants to migrate.

Normal vehicle operation is in the 10,000 to 50,000 miles a year depending on type of tire and application. With tires good for 30,000 to 100,000 miles total, you can see that "normal" tire life is five years or less with most tires coming out of service at four years. RV applications might see only 5,000 to 10,000 miles a year. Class-A tires are basically the same as used on Heavy truck tires. Heavy truck tires are generally worn out in two to four years and then replaced but RV owners want their tires to last two to five times as long as "normal" tires do so RV owners need to make extra effort to maximize the life of their tires.

[tbutler]

Thanks for the information. As soon as I can get to Harbor Freight to pick up an IR thermometer

I'll give this a try and report back on my findings.

[Guest BillAdams]

So based upon Tireman's link I will have to assume that this is personal speculation since none of it specifically applies to tires. Additionally, the link states:

The rate of a chemical reaction depends on the medium in which the reaction occurs. It may make a difference whether a medium is aqueous or organic; polar or nonpolar; or liquid, solid, or gaseous.

So there's really no way to know if the tires life expectancy is shorten by the amount of he is speculating. My guess is that a tire exposed to the air (ozone degradation) as well as the simple fact that tires live shorter lives due to lack of movement has much to do with the life or lack thereof.

[mikev]

Thanks for the info Tireman9. I like your premise and am glad that I have white tire covers. I have to admit I bought them because my MH is predominantly white, however I did think that white would be cooler. The reality is that heat and sunlight damages most things quicker than cool and dark. I already utilize plywood under my tires for any long periods of inactivity, as well as taking some of the weight off them using my jacks. Following the advice of this forum last winter I also increased the pressure to their rated maximum covered them and put the MH in a dry dark hanger. I'm not looking to increase the lifespan too far, mainly trying to keep them in as good condition possible for their lifetime.

I like to walk a more middle ground than some and feel that every little bit helps. That and I don't want to spend $2-3k too often....

All this info is great, I hope to attend one of your seminars some day.

Cheers

[tireman9]

So based upon Tireman's link I will have to assume that this is personal speculation since none of it specifically applies to tires. Additionally, the link states:

The rate of a chemical reaction depends on the medium in which the reaction occurs. It may make a difference whether a medium is aqueous or organic; polar or nonpolar; or liquid, solid, or gaseous.

So there's really no way to know if the tires life expectancy is shorten by the amount of he is speculating. My guess is that a tire exposed to the air (ozone degradation) as well as the simple fact that tires live shorter lives due to lack of movement has much to do with the life or lack thereof.

Sorry Bill but not just my "personal speculation" but based on 40 years of extensive work with tire compound chemists and research scientists in the tire industry. I have seen data on cross link density which is a good predictor of rubber properties and ultimate tire performance and durability.

The math does hold up as I personally did an experiment on "cure equivalents" which took 35 years to complete as time is one thing we can't accelerate in the lab.

Link was just to give simple background info. Actual cross-link density numbers for individual compounds are proprietery unless you want to spend the $$$$ to have an analysis done.