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.