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Old 04-30-2009, 02:22 PM   #1
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Post Some Facts about Rubber (Tires)

I've read a number of recent threads on tire aging, types, etc, and thought I'd put in my $0.02 worth. I should note that I've been designing critical fabric-reinforced elastomer parts (not tires) for about 25 years. I don't have an argument with the opinions I've seen, just wish to clarify and provide some general information.
Failure Mechanisms: There are basically two ways a rubber part fails; through aging and fatigue. These are separate mechanisms, but interrelated.
Aging: With time and temperature, elastomers age from the time the curative is added to the mix. The rate of aging, for a given compound is a function of temperature; generally doubling for each 16 deg. F increase in temperature. The consequence of aging for most elastomers (natural is an exception) is that the elastomer gets harder (technically - it has a marching modulus). Eventually, you'd get bakelite. Well before that you get cracking
Fatigue: When an elastomer (or laminate) is bent, it incurs some damage due to the strain imposed. A high degree of bending (run low or flat) fatigues at an exponentionally higher rate (basic rate * strain is accelerated by a power between 3 and 5). Engineers will recognize a variant of Minor's law.
Other Factors: Elastomers in general don't like ozone or UV and both of these tend to accelerate hardening and cracking. Modern compounds are very much mproved in these areas.
Implications: Keep your tires cool - tires in Maine. should last longer than in Florida.; all else being equal. Properly inflated tires (not under-inflated will last longer). Slight over-inflation may extend life; but my butt is to delicate to consider this option.
??Park with UV shields (covers) and ideally, unload the tires (jacks?) - less important!
???Use nitrogen or dry air - this has no benefit I can see until interior cracks appear - then it might be more benign than oxygen or water within in the laminate. Eventually, any of these will result in delamination (blowout).

The biggest benefits will come from proper inflation and avoiding extreme temperatures.

Note: We typically rate critical parts fior 5-7 years service; but these are usually significantly overdesigned. The FAA has picked six years for elastomer aircraft parts and my tires will get replaced on that schedule.

I hope some find this helpful.

Ernie
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Old 04-30-2009, 09:27 PM   #2
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Thanks for providing the view of a knowledgeable professional, Ernie. It takes some of the mystery out of this subject.

And by the way, welcome to IRV2.
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Old 05-01-2009, 04:07 AM   #3
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ERNIE,
thanks for this info.
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Old 05-01-2009, 05:48 AM   #4
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Ernie: Thanks for your outstanding information!! YOURS has been the most succinct, clear and understandable tire care info I've yet seen. Too bad "natural rubber" won't work for tires...huh? Thanks again! Steve
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Old 05-01-2009, 06:15 AM   #5
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Thank you Ernie!! And welcome.
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Old 05-01-2009, 06:25 AM   #6
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Thanks Ernie and welcome to iRV2.com -- informative and 'factual' tire information that every Rv'er should read/heed!
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Old 05-01-2009, 07:29 AM   #7
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Thanks for the post, Ernie, and welcome.

As a former plastics engineer, I spent a lot of time in the lab and on the shop floor with the rubber guys in our company. Although I couldn't have stated it as succinctly as you did, your information is spot on.
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Old 05-01-2009, 11:08 AM   #8
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Good info thanks for posting!!!
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Old 05-02-2009, 08:25 AM   #9
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Quote:
??Park with UV shields (covers) and ideally, unload the tires (jacks?) - less important!
Ernie,
This comment is a bit cryptic. I read it as saying that tires covers or taking the weight off the tires with jacks is NOT an important thing to do? Is that what you meant?
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Old 05-03-2009, 11:35 AM   #10
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Gary,
What I mean is that UV shields (Tire Covers) are of lessor importance and removing the weight still less as compared to temperature and fatigue. They are both very good ideas, particularly if you will be parked for a long time. I should also note that there are aftermarket materials that provide effective ozone protection for some elastomers. Since I don't know what the cover rubber is on tires, I'm somewhat hesitant to recommend a brand name. One I use for neoprene's (not likely to be a tire material) is Agemaster #1. This is not a coating, but effectively an after the fact anti-ozonant that combines with the rubber.
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Old 05-03-2009, 04:45 PM   #11
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Thanks for clarifying, Ernie. Good thing I asked, since I was not interpreting it quite right.
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Old 05-03-2009, 09:05 PM   #12
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Ernie

Good post with lots of information for us "non-techs."
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Old 05-03-2009, 09:28 PM   #13
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My ques in this is: why do old tires hold air sooo long (with and w/o tubes) vice todays that wont go a week w/o losing air? You see the 20-30's autos sitting on the side of the road for sale or found in the back of a barn and the tires are still inflated and sometimes the rubber is still in great shape. Ozone, being the major culprit to tires just setting, does not affect them as bad as todays tires. Any explanations avail (that might make sense)? Realizing that todays tires are compounded for speed vice "getting it down the road" with additional leaning towards road conditions, could this be the reasons for air losses or sdid it make a difference when we started adding the cords to them.

Another looking for answers.........
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Old 05-04-2009, 06:48 AM   #14
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Quote:
why do old tires hold air sooo long (with and w/o tubes) vice todays that wont go a week w/o losing air?
My experience is the opposite of yours, Ben. My 2007 car and 2004 RV tires never need air.

Tires don't leak air through the tire itself unless there is a puncture somewhere. Air leaks around the valve, sometimes through the valve, and around the bead where the tire seals to the rim. Constant slow leaks are usually the result of poor quality valves or damaged/corroded rims.
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