Wheel failure

I recently read some comments about early (1970's)  wheels flexing enough to eject wheel covers (full hub caps) when radial tires were first used to replace the original bias tires. This is an example of why it is important to know if your steel wheels are rated (designed) for radial tire use if you have an older RV that came originally with bias tires and are considering changing to radials.

I think this is more likely to be an issue on old "classic" trailers but it is possible that there are some older (60's vintage and earlier) motorhomes that might have originally come with bias tires also, so this info applies.

Excess flexing can result in steel fatigue which can result in wheel failure. A quick search of the internet found a number of examples:

Note the crack between the two red dots. This is early sign of fatigue crack of the wheel disk.




 If the wheel is not replaced this type of crack can grow till the wheel comes apart like this:

Here is a trailer wheel with a complete failure of one spoke:

Fatigue can also occur in the flange area of the rim as seen in this example:

As far as I know most cast aluminum wheels made since the 80's are probably OK for use with radial tires but with the extra side loading seen with multi-axle trailers failure of aluminum wheels is possible too.

I found an excellent video that shows the results of these forces at Keystone RV. Watch the section from time 0:46 to 1:07 and note that the tires on one axle bend inboard while the others are forced outward. This puts tremendous strain on both the tire and the wheel and may lead to failure of either or both parts.
This type of failure may occur after the third or fourth set of tires.

A side note on wheel failure. I have experienced wheel failure on my race car after about 3,000 miles usage but these were light weight multi 3 piece wheels with cast center and spun flanges that bolted together. Application on a relatively heavy car (Camaro) resulted in fatigue failure. Luckily we were doing magnaflux dye penetrant inspection and discovered the cracks when doing off-season re-build and not during a race.

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If your RV came with Bias tires you need to read this.

SEMA, or Specialty Equipment Manufacturers Association, put out a nice document explaining why it is important to understand that mounting radial tires on old wheels that were originally designed and built for Bias tire application may not be a good move.

Now this really only impacts people with "Classic" RVs but maybe some have a hobby that involves old classic cars.

If so I STRONGLY suggest you download and review THIS information.

While we are on the topic of Bias tires there is one very important thing to remember if you decide to keep running them on your vehicle. You should NEVER mix Bias and Radial type tires on an axle of your motorhome, and if you have a multi-axle trailer never mix the two different types on the trailer.

The sidewall stiffness difference can result in handling or braking problems and even tire failure in an extreme case.


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Is it OK to Replace Bias tires with radials

My 25' 1985 trailer has a plate on the left front street side that indicates 7.00 X 15 and 45 psi. D range, I think.
Right now, there are Roadkings LT on it. I inherited the Airstreem from my aerospace engineer Dad and know based on 5+ years it's time to replace them So, what manufacture would you recommend and what pressure? GVWR is 6,800#, axles are 3,200lbs. I believe the original tires were bias.

It really isn't difficult to find a new radial tire for your RV but there are a few basic steps needed.

You gave the GVWR and Axle rating but made no mention of the actual load on each tire. There are a number of posts showing that the load is seldom split evenly between axles or evenly side to side.
There are worksheets available to help you calculate the individual loads if you can't find a location with individual scales (this is difficult to do so use the worksheet). Here are 2 sites with forms you can use.
Bridgestone Commercial Truck Tires
RV Trailer Weight Calculators - Towing Capacity - Ratings


OK Lets assume you get or calculate the individual tire loads. For this example I will use the following numbers 
LF 1,550      RF 1,390
LR 1,500      RR 1,440

I would recommend a 15% "Safety Factor" or "Reserve Load" when looking at the tire loading.
1,550 + 15% = 1,782#

I also recommend an additional "Safety Factor" of +10% on the air pressure
You need to find a tire capable of carrying at least 1,782# at its Max pressure -10psi

The +15% is a safety factor for possibly different loading in the future
and -10 psi is to allow you to set a pressure and not need to worry about changes in ambient day to day.

Now since we are talking a multi axle trailer you need to run the max pressure in the tire all the time. This has been covered in other posts in this tire blog but it has to do with the unique side loading for trailers.

Consult the tire Load/Inflation tables and tire specification sheets to find a tire that meets the above load & inflation capability and fits your trailer for width and OD.

One final consideration. Years ago when there were still many bias tires in the market the wheels were not always designed for radial tire loading. You should probably also either confirm your wheels are approved for radial tires or also get some new wheels.


It's not hard to do this but you do need to spend a little time doing the research correctly.

PM me if you need help

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Autopsy of a failed tire

I continue to see posts on various RV forums saying "I had a blowout on my tire. I checked the inflation every day and I didn't hit anything. It must be because it was a (fill in the brand)  or  because it was made in (fill in the location). I'll never buy that brand or tires made in that location again cuz they are junk."

If you are a follower of this blog you have seen this topic discussed previously but clearly there are folks out there who just do not want to be confused with evidence that doesn't support their pre-concieved notion of why tires fail.

Lets follow an "autopsy" of a failed tire and see if we can improve people's understanding of how to "read" a  failed tire so we have a better idea of the real reason it failed. If we don't properly understand the "WHY" then we probably will not take the appropriate action to prevent a re-occurrence.

 Here we note the size as 8-14.5. This is a low platform trailer tire. Many times used on Mobile Homes or construction equipment trailers. It is a bias construction and we can see the body ply at an angle.







We see this tire is a Load Range F (12 Ply rating) tire.
 


rated to carry  2835# at 100psi cold.

Looking at the tread we see the tire "looks" great.
 






As we continue to read the tire sidewall we see it was made in Thailand..
 




Now for some, that is sufficient. They say it wasn't made in the USA so it is a piece of junk. Lets continue and see if they are correct in their analysis.


 
The DOT date is 2812 so since this tire failed mid June 2013 or about 2613 the tire is only 1 year old and clearly since it came from Thailand there were probably 3 or 4 months for shipping and handling in a warehouse. Clearly the tire age is not the problem.

The first two characters of the DOT"2B" can be translated using out decoder web site  and we learn the tire was made by Deestone Ltd in Samutsakom, Thailand.

Continuing on we see the tire is Nylon body which would be consistent with a lower cost, bias, heavy duty construction.

Now we get to the interesting part. Looking at the actual area of the failure.
 In the picture at the top of this post you can see that both sidewalls have significant damage.

 As we look at the area of the tire that actually failed we see frayed cord.  This is what Nylon and Polyester look like when they fail in tension. Looking closer we see that not all cords are frayed.


These three cords have the look we see when we cut Nylon rope and fuse the ends with a lighter.


Warning Technical Information to follow:  Nylon and Polyester both melt in the range of 395°F to 495°F depending on the treatment and exact material involved. These materials also lose about half their strength when heated to over 300°F.


Looking even closer at those cords it is clear the ends are not frayed but fused. So we now have the physical evidence that parts of this tire saw temperatures approaching or exceeding 400°F. The only way to generate that kind of temperature is with rapid, extreme flexing.
 We see rapid flexing at highway speeds. We see extreme flexing when a tire looses say 50% or more of its proper inflation.

The heat in a tire comes from the bending of the cord material and radiates outward to the cooler surface.  It is illogical to think that only a few cords somehow flex enough to see high temperature and if we look closely all around the area of the most damage there are a number of cords showing similar heat damage.

So we now have physical evidence that proves operation at highway speed for a number of miles while the tire is significantly under-inflated.

Knowing this, I think you can understand that there was probably some other cause such as a leaking valve or puncture or cut of the tire that allowed the air to leak out over time. If the tire had in fact been properly inflated we would not see the 360° circumferential flexing and signs of high heat.

How do we avoid this type of failure?  Will changing the brand prevent air loss?  Will buying tires made in a different country prevent them from getting too hot when over flexed? Clearly neither of these "fixes" will prevent a reoccurance of this type of failure.

I would suggest a TPMS could provide warning if there is an air leak. That warning might be early enough to allow the driver to stop before the tire fails and maybe even before the tire is significantly damaged.

BOTTOM LINE
I would say that 95+% of tires I have seen with this type of "blowout" failure were in fact Run Low Flex failures. Having inspected many thousands of tires in my 40 years as a tire engineer, I have accumulated enough experience to be able to observe and find the physical proof of high heat damage similar to what we see here. Many times I can find and identify this proof in less than a 30 seconds. It's easy once you know what to look for.

Hopefully the next time you meet someone that says "I just had a Blowout" you will be able to identify the evidence that points to a run low flex so the person learns they need to know why the tire lost air. If it were say a leaking valve it certainly will do them no good to buy a new tire and mount it only to have it suffer the same fate.