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Monday, April 28, 2014

Can I use a tube in my "tubeless tire?

 Saw this question  
"Is there any reason why we can't use inner tube?

When I was younger (45 - 50 years ago), we wear the tire to the bare bone, people use inner tube."

Inner tubes are made of a special type of rubber that is better able to retain air than the rubber used in the rest of the tire. Different types of rubber have different performance characteristics. Some wear better, some have better energy (fuel economy) performance, some are real good in ice & snow. All of these and other types also have negatives. Some might be bad wear, easy to cut, create more heat etc.

The challenge for the tire engineer is to balance the performance trade-offs.

The invention of the "Tubeless" tire allowed the elimination of the separate tube. Most of today's tires have rubber that is very similar to the rubber used in tubes on the interior of the tire. This is called the "innerliner". A major advantage is that if you get a puncture in a tubeless tire the innerliner doesn't rip like a tube would, so you have less chance of a true "Blowout".

Using a tube in a tubeless tire creates some problems.

It increases heat & cost are probably the biggest.

It also can temporarily trap air between the tube and the tubeless tire innerliner but this air will leak out around the valve hole over the next few days which means you would need to check the air pressure every day for many days to ensure proper inflation.

I have trouble thinking of any circumstance where using a tube in a tubeless tire would be a good thing.

Monday, April 21, 2014

Tire Blowout - China-Bomb or Pothole?

Hardly a week goes by without someone posting that they had a "Blowout" and since they had checked the tire air that morning, they "knew" the blowout must have been caused by a defective tire. Many times they jump to the conclusion that because the tire was not made in the USA, that fact seems sufficient in their minds to establish certainty.

I have posted replies that just because they had checked their tire a few hours prior to the failure, that is not sufficient proof that the failure was due to a defective tire. In my experience the vast majority of so-called "Blowouts" are actually "Run-Low-Flex" failures. A tire can loose air for any number of reasons such as puncture or valve leak or even an impact.
I am a strong advocate of TPMS as they can warn of air loss but even the best TPMS cannot provide warning of a catastrophic air loss that can occur after impact damage.

Those that have attended one of my seminars may remember my story of the two impact failures my then fiancee had and how both tire failures occurred some 20 miles after the actual impact. I am sad to report that I suffered an impact on my personal car. I do not remember hitting a specifically large or deep pot-hole with the LF tire but luckily for me I noticed a bulge on the outer shoulder of that tire.

When I saw the bulge I knew at once I had a failed tire and it was only a matter of a few miles before there would be a sudden rupture of the sidewall and the air would rush out the 1" plus hole. Too fast for my TPMS to provide a warning. I recognized the signs of an impact because I have inspected hundreds of tires with similar damage. Some were hard to find as the damage was not even visible after dismounting the tire while others had "blown" while the vehicle was parked so there was no damage from running on a tire with zero psi.

The silver lining to this is that it gives me an opportunity to show the results of my step by step examination. Hopefully this will allow you to have a better understanding of how proper failed tire inspection is done and note that simply jumping to conclusion that since the tire was not made in the USA the country of origin played no part in causing the failure.

Here is the dismounted tire.

 Note the signs of damage are essentially invisible BUT since I did a complete examination before dismounting the tire I can show the physical evidence on the rim that shows the marks left by the tire as it was severely deflected and bent down over the rim even though fully inflated.

  The small lines were left from the sidewall decoration on the tire where it contacted the rim.

Here you can see the break in the interior where the body cord failed under the shock load.

Before I dissected the tire I continued my visual inspection and noted marks on the interior opposite the fracture. You can see where the tire was bent and over extended but did not fail.

A close-up showing the failed body cord. This "crack" measures about 0.6" long

Here is a video.

Watch the rubber to the left of the break. See how it stretches in a strange manner. The body cord under this rubber is also broken but not visible as the interior rubber has not failed yet. Sometimes all I find are signs of this stretching that indicates hidden failed body cord.

Hope this helps some understand what can happen. If I hadn't happened to see the bulge I definitely would have suffered a rapid air loss with possible vehicle damage or even loss of control and worse.

Wednesday, April 16, 2014

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.

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.

Friday, April 4, 2014

Another post on "Calculating" inflation to avoid a blowout or tread separation

It seems this will be a never ending task of explaining the "Why and How" of setting tire pressure on RVs.

Quick answer:
A. Trailers should follow the placard which is probably the tire sidewall pressure unless the size or type has been changed. BUT they should also confirm that no individuakl tire is overloaded due to un-balance.
B. Motorhomes should run the tire placard inflation unless they know the actual load on each tire.
C If a Motorhome owner knows the actual corner load he should consult the load inflation charts from the tire manufacturer for his brand in RV use. Select the inflation needed to exceed the actual load of the heaviest side of each axle and then inflate all tires on that axle to the minimum inflation plus 10%
D, If the tires on the trailer have been changes then the individual loads for each tire need to be known. Using load inflation tables select a tire with sufficient Load Range to carry that load and then set the cold inflation to the inflation shown on the tire sidewall.

Following the above should decrease the damage done by running a tire in overload and under-inflated condition. Hopefully this will also prevent Tread separations and Blowouts.

 I try and follow a few RV forums. Some are general and others are focused on a single brand or manufacturer. I would prefer it if I could simply post a few links to this blog so I don't have to spend time saying the same stuff over and over but some sites will not allow a link to this blog. (If you are reading this you should know that you can post a link to this blog but as the Blog writer I am not allowed to.)

Here is a recent post on a thread titled "Calculating the correct tire pressure". This forum is 95% trailer oriented.

 "A while back, we weighed our travel trailer on the CAT scales and got a total weight of 7,300 pounds, rigged for towing. Rigged for towing means with a full water tank, all of the misc. junk that we normally carry and weight distribution bars tensioned, but no clothing or food on board. On average, this translates to 1,825 pounds per tire.
Today, we were able to obtain individual wheel weights using portable scales. The results are (rigged for towing)

Left Front - 2,000 pounds Left Rear - 1,900 pounds

Right Front - 1,900 pounds Right Rear - 1,700 pounds

We can immediately see the unbalance in this trailer with the heavy tire having 27% of the total. We also learn that the TT was not fully loaded with food or cloths which would add more weight. We also see that when the owner simply used the original CAT scale weight he assumed equal weight distribution of 1825# per tire.

In this case the owner was not aware of the special loading seen by trailer tires.

In this same thread we found one owner that switched from ST235/75R15 LR-D to P23575R15/XL ! giving up about 23% of the load capacity. This thread is at 85 posts and counting.

Clearly the need for more knowledge on care and maintenance of tires in RV application is needed. I hope I have provided helpful information here and in my seminars. Please spread the word. If you have a specific question you can send a question to   Tireman9   at  Gmail  dot com