retired-tech wrote: I have been wondering about this as i roll down the road on my serioiusly outdated tires and driving 55mph getting passed by a bunch of RVs.
Are your tires rated for only 55mph? Or is that a state law for highways where you are?
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The FLEX that kills trailer tires is more likely to be the flex caused by "dragging" a duel axle trailer through a turn. Since neither axle is a steering axle, the trailer must PIVOT in order to go around a corner. Since it CANNOT easily pivot on two points at once (duel axles) then BOTH axles are essentially dragged around each corner putting tremendous stress on the tire side walls.
Back or drive forward, into a tight turn while towing a double axle trailer then stop half way through the turn and get out, walk to behind the trailer and observe the condition of the tires and you will SEE the pressures being placed on the tires. After enough of this torture, THEN the flex from high speeds can cause the tire to finally fail.
That's why I practically never tow at speeds greater than around 70 MPH. It probably also is the reason that in MANY thousands of miles, I've never had a blow out on a duel axle trailer. I HAVE blown a couple of pop up tires in years past but they were on single axle trailers and at even lower speeds.
If speed (or even tire flex at all) were the sole reason for tire failures it certainly would not explain the LARGE number of Chinese made ST tires that blow up while mounted on the spare tire carrier. I feel there MUST be a large number of this sort of thing as I've personally witnessed it twice.
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retired-tech wrote: Riddle me this, if we all know that trailer tires arent rated for the speed that traffic normaly travels at how many of these ST tire failures are being caused by driving to fast. I have been wondering about this as i roll down the road on my serioiusly outdated tires and driving 55mph getting passed by a bunch of RVs. In the last three outings I have probably seen a dozen vehicles that had passed me sitting beside the road with at least one exploded tire.
We all know that flex creates heat and the faster you go the more flex you create. After long stints at speed the tires can become overheated. This is why cars built for extended long fast runs are adorned with those rediculously low profile tires. However flex is needed for traction and ride quality.
Any thoughts on this.
IMHO in my case, none. I will give you a little of my info to think about.
I have run bias ST's for over 40 years. In all of those years I have blown 1 tire. In the last 15 years I have averaged 4K to 5K a year in the summer heat. My trailer weighs about 7K loaded and it is a tandem axel with 14" tires.
I take all my vacation time at once and we usually see relitives back east so I have to roll and make time when I'm on the road. 70 to 75+ towing is the norm not the exception for me.
In all of those years towing I have had many flats that I have cought in time and 1 that I did not. I'm almost positive that the blowout I had was caused by a low tire pressure and that was the 1 I did not catch in time.
I air my tires up to max and sometimes I add 5+ to that.
Do I claim to understand why so many of my fellow RV'ers have so many blowouts? Nope, nor do I really care. I have some guesses but it's not speed or I would be collecting blowouts like some of my fellow RV'ers.
I know what works for me, so I won't change what I do.
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Flexing is part of how a tire works and very little can be attained, but then
ride quality is gone to made worse
Flexing has to do with the class of tire (ST, P, LT and commercial), the rim it
is mounted on, the weight it is carrying, the PSI vs the rated PSI and weight,
the speed driven and the style of driving plus many more attributes
A narrow rim will have more sidewall bendback, therefore more flexing. A wider
rim will have less sidewall bendback, therefore less flexing. A lower PSI will
also have more sidewall bendback than the same setup with more PSI
Flexing is also referred to as squirm
Flexing happens on both side walls and on the tread. On the tread there is a leading
and trailing wave with the flat spot in between them
There is the same amount of flexing going 1MPH or 100MPH, just the time interval
and the subsequent cooling attributes
If not cooled quickly, the heat can and does build up to the point of actually
over heating. I have even seen pictures of the plastic fabric of the plies melted
The carcass material (not all rubber, but a mixture of compounds) also degrades
with heat. Also ozone, UV, etc
There is centrifugal issues and the tire material is sized for the weight rating
and speed rating.
All of the above and more are for the specified ambient conditions.
The OP's comment of higher ambient temps does play, but if the tire is used within
it's specifications, the ambients have been dialed in with safety margin.
But, it at either end of the spec bell curve, pushing it will have reduced
safety margin
Finally, the production methods are critical to meeting the specifications of
the tire OEM. The way they make it, the quality of materials/labor/tooling/etc
all play
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Aren't ST-rated tires supposed to have "stiffer sidewalls" to deal with the pressures of being dragged around corners as mentioned above?
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mkirsch wrote: Aren't ST-rated tires supposed to have "stiffer sidewalls" to deal with the pressures of being dragged around corners as mentioned above?
Stiffer, no I would not use that term. My ST sidewalls are very soft.
Different, yes. Trailer tires have to put up with "twist" loads so they are different then lets say a LT tire.
mkirsch wrote: Aren't ST-rated tires supposed to have "stiffer sidewalls" to deal with the pressures of being dragged around corners as mentioned above?
Not according to Carlisle who says ST sidewall stiffness is a compromise between the P and LT tire. The ST is designed for a softer ride with the flexy basketball shape sidewall design. More speed = more flex = more heat on a load carrying tire.
Firestone and Goodyear at one time had tire cutaway samples for the customer to feel and look at and compare. The thing I remember was how thin and liteweight the sidewall on the ST sample was compared to same size/load range truck tire sample.
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Think about this. As the OP wrote, ST tires are only rated up to 65MPH. Yet they are routinley run at that speed or very close to it.
If your TV or any auto was only capable of 65MPH....would you drive it at that speed for hours on end?
Of course not. That would be foolish and asking for trouble.
Well the same goes for the tires.
But, just for discussions sake, let say that one tows at say 63 MPH.
On occasion when passing a slower vehicle, or descending a hill, or just from inattention ones speed is likely to exceed the 65 MPH limit.
Which tires would you rather have. Ones rated to a max of 65MPH, or ones rated to say 88MPH?
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Huntindog wrote: Think about this. As the OP wrote, ST tires are only rated up to 65MPH. Yet they are routinley run at that speed or very close to it.
If your TV or any auto was only capable of 65MPH....would you drive it at that speed for hours on end?
Of course not. That would be foolish and asking for trouble.
Well the same goes for the tires.
But, just for discussions sake, let say that one tows at say 63 MPH.
On occasion when passing a slower vehicle, or descending a hill, or just from inattention ones speed is likely to exceed the 65 MPH limit.
Which tires would you rather have. Ones rated to a max of 65MPH, or ones rated to say 88MPH?
Depends. Which would you rather have, a tire that was specifically designed for twist and stresses that trailers put on their tires or tires that were not designed to be put on trailers or endure their stresses? I want the former.
You have to understand that tires just don't blow up if you exceed 65 MPH. 65 is not a magic number and if you go 5 mph over "IT'S NOT GONA BLOW!!!" I have done it many, many, many, many times with only one blown to show for it.
Design parameters are very underrated for tires IMHO. At least that is my experience. When I was crew chief for many race car teams I would punish the tires to unbelievable ways. 7 PSI in very hot days at 80+ mph lap after lap. Just like my trailer tires, never had any problems.
Obviously, saying you're exceeding the rating of tires will cause certain blow out is like saying exceeding the rating of your hitch by 100 lbs will make it fail. There is a margin for error. Just remember engingeering is a guess, too. Educated, yes, but still a guess.
I had a blow out on a chinese tire at 45 mph. The same trailer, loaded the same way, on the same day, had run over 70 mph and cooled down for several hours before the blow out. I can't prove overspeeding the tire cause the failure, but it's the only factor that applies which would have caused the blowout. True, it could have been a road hazzard that I didn't see and rolled over, but not likely.
I keep the speed to about 62 mph nowadays. No need to go any faster and within the mfg rating. Why push it when my family is in the truck? What am I trying to prove?
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