Six blowouts! Help! "I'm at my wit's end"

 

Here is a series of posts on tire blowouts from an RV forum. I am inclined to think that the experiences are not that unusual. This is a long post, but I thought that giving the background, and my recommendations, might help others that have tire problems know that they are not alone.

John wrote:

"I'm at my wit's end on tires. 2000 Winnebago Journey, I have blown out 6 tires since I have had this unit, over 10 years, and done over $30,000 of damage to it. Just got back from a 2,000-mile trip to Colorado and back, after blowing two tires in two days. I have tire sensors, the unit is always kept garaged, no sun on tires, always check pressures, have moved up to 255/70R22.5, which is slightly larger than stock but a lot easier to find. I run 110 psi cold, which is less than the listed 120 PSI. Maybe the age of the tires is getting me, but none are older than 6 years. I am going to start buying two tires every 2 years, to keep the age down. Any other suggestions?"

John continues in another post:

"This is really getting annoying to find tires on the road and then repair all the damage. Thank goodness for insurance. The original tires were 235/80. I upgraded to 255/70, and still have over an inch between tire sidewalls. The tires are not rubbing. It would appear that I have overlooked a very important detail in my quest, and that would be the tire pressure chart many have referenced. I have been running pressure at 110 or slightly below, thinking that might give me a softer ride, when in fact, at that pressure I do not have much "free space" between the load capacity of tires, and the weight of the motorhome.

My coach has a GAWR on the rear of 15,500, and with my tires at 110 psi, the load capacity is uncomfortably close to capacity. I never really understood pressure charts, but do now and will abide by them. In addition, I am going to put my coach in a weight reduction program by removing things I do not need to carry all the time. That, and a program to ensure my tires are not over 6 to 8 years old, and spinning my tires instead of sitting on my concrete slab for months at a time should cure my ills. Thanks to each for your suggestions and help."

There were some replies and suggestions from myself and other RV owners concerning the RV weight.

John posted in reply:

Okay, I finally got my rig weighed, and here are the results. My GVWR on the rig is 24,850 lbs. The weight of my rig with just me was 7,760 lbs. front axle and 13,460 lbs. rear axle for a total of 21,220 lbs.

I figure loaded with people and stuff add 3,000 lbs. with 75 % on rear axle, so that would be 15,710 rear and 8,510 front axle, for a total of 24,220 lbs. weight when loaded.

This is pretty close to GVWR, but the front axle rating is 9,350 and the rear axle rating is 15,500, for a total of 24,850.

Tires are rated 4,670 lbs. @ 110 psi X 4 = 18,688 lbs. rear and front 5,205 lbs. @ 110 psi X 2 = 10,410 lbs. front for a total capacity of 29,098 lbs. for the coach.

So I am close to GVWR but slightly under, closer to limits on axle capacity, but axles aren't breaking, tires are. Seems that I am within limits, and would be even safer if I air tires up to 120 psi, which would give me 5,070 X 4 =20,280 on the rear and 11,020 on the front. Tires will carry far more than the coach is rated for, so my problem must be just old tires. Thanks for all the suggestions on this.

Another RV owner, Mike, offered:

John, do yourself a favor and don't guess what your loaded weight is. On your next trip, at your 1st gas up, go to a station with a CAT Scale, and immediately get your MH weighed at it's full travel weight. You're at 6 blown tires, and counting, with oversized tires and super high pressures. You need more than a back-of-the-envelope estimate of your real travel weight. Somewhere in that combination is a problem unique to your setup.

At this point, I added another and hopefully a final post:

John, it's good that you got some info on the weight, but I think Mike's suggestion to get actual weights and not guess, especially since you are close to the limit, is spot on.
Another point is that GVWR is not what you need to be concerned with. Ideally, you should try and learn the load on each tire position aka "4-Corner Weights". The reason for this is that tires on one end of an axle do not share the load on the other axle end. The load is almost never split 50/50. One end of an axle could have 200# to 500# more than the other end of that axle. I have seen an extreme case with one end supporting 1,000# more than the other end.

To learn the load on individual tire positions you can check with building supply or gravel sellers. But until you can get "4-corners" I suggest you confirm your GAWR from your Certification Sticker and go to a truck scale. But be sure to get individual axle weights as there will be a significant difference Front vs. Rear. I have a few posts on "4-Corner Weights" on my blog you can read HERE to help you understand how and why this is the best system of weighing.

Then:

1. For each axle weight, I suggest you assume there is a side-to-side load split of at least 51/49% and use the 51% number for inflation selection until you get actual 4-Corner weights.

2. Look on the Load Inflation Tables to learn the MINIMUM inflation for all the tires on that axle based on the 51% number. Yes, all tires on an axle should be inflated to the same level.

3. For your "cold" inflation, I recommend you run at least 10%, with +15% more than the inflation shown in the tables better, if possible. This will provide a larger "Reserve Load". BUT DO NOT EXCEED the max inflation number for the wheels which might be 120 psi for your coach. So do a bit of research.

4. I also suggest you set your TPMS low pressure to the psi in #2 above.

Hopefully, this confirmation of load and a little bit of math and adjusting your inflation will solve your tire problems.

Why did I have three Blowouts? A question on an RV forum

 So I came across another post on an RV forum. I am sorry to report that many of the posters did not understand the concept of Cold Inflation.  The OP asked:

Why did I have three Blowouts?

I’m pulling my hair out. I’ve had three blowouts in 18 months of ownership of our 2020 Keystone Outback. We have ST225 75 R 15 Load E.

The blowouts have been on 3 of 4 points on our dual axle TT.

First blowout was road hazard / excessive speed (I was routinely doing a few mph over on the interstate), and second and third appeared to be heat related in that both tires were running hotter than others and PSI had climbed to 95 on our max 80 PSI.

I feel like I’m inflating my tires every few days when leaving a camp site. This can’t be normal. When starting this trip from SC to FL, I found them all down 3-6 PSI in GA after I had inflated all to 80 (cold) two nights before in the SC storage yard.

Before this last blowout they were all sitting around 74/75 PSI in the morning and I topped them up to 80 PSI according to TPMS. I had barely left the campground when each had climbed to 82. One went to 95 within an hour and temp was running mid to high 70s and the other three were in mid 60s. I pulled over and let air out of them all. But the eventual blown tire just kept running hotter and then popped within 2-3 hours later. Center tread separated completely from tires.

No I haven’t weighed my trailer but I’m just a guy with a wife and three kids 5 and under, no modifications to my trailer, etc, and I don’t pack every inch of floor space with gear that then spills out at the campsite upon arrival, so I can’t imagine I’m overloading.

I don’t understand why I’m having to top up my tires all the time, and it’s not unclear why the last two blowouts have occurred when I’ve been trying to stay on top of the cold PSI and staying under the speed limits.

We are “on the road” so I’m contemplating buying whatever replacement tire I can get, and then asking my local RV service center to check bearings and alignment upon our return. Could either of these be the underlying issue?

Then if that isn’t the case, I’ll consider investing in a complete set of tires with a better reputation, in case the current tires are truly bad.

I will welcome any thoughts or comments!

My reply:

• There were 3 tire failures. A puncture is not the fault of the tire as any tire can be punctured or cut. An increase of 20 to 25% in pressure is an indication of a combination of excess load and excessive speed. A dragging brake or wheel bearing problem can also generate excess heat which can affect both TPM temperature reading as well as increase tire pressure. We do not know what the Ambient was or the TPM pressure readings were which might provide additional clues as to the reasons for their failures. Others have posted that bleeding air out of a hot tire is definitely the wrong thing to do. There is the potential that this action resulted in two tire failures depending on the actual loads and how much air was actually let out. We do not know the actual truck scale load for each axle so this is important information that is missing. 80 psi on the tire is the minimum inflation needed to support the load number on the tire sidewall. It is NOT the max operating pressure. The ONLY pressure we need to be concerned with is the "cold" inflation which is the inflation measured before the tires are driven on or exposed to direct sunlight for the previous 2 hours. 

   

  Inflation pressure when the tires are stationary and out of direct sunlight will change about 2% for each change in the ambient temperature of 10 F. A 6 psi drop with no other cause would indicate a drop in Ambient of about 37°F for a tire inflated to 80 psi. We do not know the Ambient at the time of tire measurements but that is a considerable drop in temperature so I think there is probably some other reason for the reported pressure loss. We do not have to fill every space with "stuff" to end up overweight. The RV Certification sticker indicates the maximum load for each axle when the RV is fully loaded. This load GAWR should not be exceeded. If a scale indicates the RV has an axle at GAWR then the tires MUST be inflated to the pressure stated on the sticker BUT we can still have one tire overloaded as most RV have a side to side imbalance of their axles. They also have an imbalance between the two axles so that is why we need to confirm the actual load on each axle. This can be learned on truck scales as long as we get readings for each axle which requires careful parking on the platform scales. I have seen air loss due to small tread punctures, leaks around rubber valve stem, Leaks between TPMS and the valve stem. leaks through the aluminum due to casting errors. and leaks between the tire and the wheel due to improper mounting. I have posted example of leak through the valve core. See the link below. I and a couple other actual tire engineers follow some of the RV posts. Plus there are many self-appointed "experts" so you do need to always consider the source of the information you find on the Internet as not everything you read here is the truth believe it or not. https://www.rvtiresafety.net/2012/11/why-do-valves-leak.html

  

##RVT1041