Tires; article from Highways Magazine

JoeW4300

Member
October 2006
This article appeared in Highways Magazine, October 2006. I hope it is helpful as it relates to a problem many of us have.
JoeW

Tech Topics
Bob Livingston

1151335_Bob.jpg
Tire Expert
I’m responding as an expert to the many letters you get dealing with tires and tire-related issues. My credentials for writing this letter include that I’m an engineer with a PhD in mechanical engineering and I owned a tire store for more than 30 years. During that time, I attended many training courses taught by many of the major tire manufacturers. As evidenced by recent letters, there is a general lack of understanding of tire issues. I will address several of those issues.

Inflation: This is the source of most tire questions. You never inflate a tire except to that pressure recommended by the vehicle manufacturer. Period. There are occasionally reasons to ignore this rule. An example of this is a severely overloaded pickup truck carrying a huge load of rocks and only going a relatively short distance. Never should this apply to an RV.

The tire pressure on the sidewall of the tire is a “never-exceed pressure.” This is a pressure that has been established by testing and/or design by the tire manufacturer and it’s on the tire because of federal mandates. Most folks don’t know that every tire (sold in the USA) of the same size and ply rating has exactly the same load rating and maximum allowable tire pressure regardless of where or by whom the tire was manufactured. What the sidewall really shows is that the tire can carry a certain amount of load if inflated to the corresponding pressure. It doesn’t indicate that the tire should be inflated to that pressure. The tire manufacturer never knows beforehand on what vehicle a tire will be installed; so, how could they recommend a tire pressure? The vehicle manufacturer knows all about the vehicle and specifies the tire fitment.

The vehicle manufacturer puts every vehicle through a series of handling tests before the vehicle is ready for sale. Of utmost importance is the actual handling of the vehicle, especially in adverse conditions such as swerving or severe braking. Improper tire inflation can and does materially affect the way a vehicle handles in such cases. Further, if the vehicle manufacturer’s inflation specifications are found to be too low, that means the user is overloading that vehicle. Rather than increasing tire pressure, the load should be decreased.

Overinflation subjects the tire to increased danger of damage caused by bruising due to impact with objects on the roadway or with potholes.

Most tire problems occur on the farthest to the rear on the right-hand side of a vehicle, because foreign objects (nails, etc.) are swept to the right-hand side of the road by passing vehicles. A front tire runs over the object and starts it spinning and the rear tire catches it just right so that the object can penetrate the tire.

Tread separations, sudden tire failures and blowouts: These, of course, are very traumatic and often cause damage to the vehicle. These incidents are seldom understood by the vehicle owner. They always blame the tire and ultimately, the manufacturer. These incidents are almost never the fault of either the tire manufacturer or the tire installer. There has never been an owner who thought his or her tire might be severely underinflated due to a leak. I’ve never spoken to anyone who didn’t “just” check his or her air pressure before the tire blew out.

When a tire fails, it’s usually caused by an impact that occurred quite a while earlier, perhaps months. The owner doesn’t even recall the hole he hit so hard it jarred the fillings in his teeth. When nothing happened right then, he breathes a sigh of relief and goes on. But the tire was most likely damaged at that time and it takes many more miles before that damage becomes a tire failure.

There definitely have been many cases of entire tire lines suffering from some defect in the manufacturing process that ultimately leads to tread separations. No tire manufacturer is immune from these problems. They’ve all had them. All tire manufacturers know of these problems and take care of them as they occur. A tire-tread separation should never become a severe problem to an RV owner who is paying attention. A driver can always feel increased vibration, pulling or other handling changes to the vehicle in sufficient time to have it checked by a tire professional before the tire comes apart and damages the vehicle. Obviously, this is more difficult on a trailer but with vigilance, you can usually prevent it from happening on a trailer as well.

As I said earlier, tread separations often result from an impact when the tire is overinflated and might not occur with proper inflation.

Tire life: Tires have a life. It is generally accepted that tires more than six years old should be replaced. This is easy to say but hard to do. But realize that the amount of tread remaining has nothing to do with the strength of the tire. The tread is only there to give the tire traction and, of course, to allow the tire to wear for many miles. More tread adds little to penetration resistance. Over time I have frequently had customers say that they couldn’t see why they had a flat since the tire was new. It adds essentially nothing to the strength of the tire. Tires deteriorate with time regardless of whether they are in constant use or mostly parked. In fact, being seldom used can be detrimental to a tire. Covering a tire can be somewhat beneficial but really does not extend the six-year time limit.

If your tires are more than six years old, replace them. I had a customer who had a spare tire mounted on the back of his motorhome. This tire had never been on the ground and was eight years old. One day it just blew out, causing severe damage to the rear of the motorhome.

I recently replaced the full set of tires on my travel trailer even though they looked great: lots of tread, etc. And please don’t say, “Well, he owns a tire store.” The tires are certainly not free to me.

Anecdotal evidence indicates that tires age about 12-to-1 as compared to humans. You know, elephants age so much compared to humans and so do horses, dogs and other animals. Whether this is true or not, it should give all RVers food for thought as we are mostly a population of, shall we say, “seasoned citizens.” So we should be able to identify with the increased aches and pains of our old tires.
Floyde Adams
Mimbres, N.M.

 

phranc

Well-known member
Not a bad artical,although I feel it was written from the viewpoint of a tire dealer and not from the viewpoint of a RV user.
 

Uncle Rog

Well-known member
I agree with most of the article, although, I usually change out my tires after three years. I used the same tire dealer for 25 years before he sold the business and he pretty much convinced me that trailer tires did not hold up much longer than that. When you consider the damage that can be done by a catostrophic failure a new set is pretty reasonable. I run Bridgestone / Firestone's on my GMC, but I have no problem with the Trail America's that came stock on the rig. I even found a local wholesale supplier that will sell to the public. I am adding a second spare also, as it is hard to find 14 ply tires on the road.
 

cdbMidland

Past Michigan Chapter Leader
A good article, but not in agreement with the folks from Weigh-It who put on our seminar last year. Bob states that the sidewall psi is only a "not to be exceeded" guide, while Weigh-It stated that tires not inflated to that number were underinflated.

Who is right? There's quite a bit of difference between the psi recommended by Heartland and that by Weigh-It.
 

busted2341

Well-known member
I remember seeing a story on RV Today where goodyear officials explained that the tire rating on the tire is a do not exceed. As a matter of fact it is explained how to weigh and figure what the proper tire pressure is per axle based on the load. Pretty neat show. I will research and try to post the show number or title.
 
K

Ken Washington

Guest
Frank,
I will be interested in seeing this also! I have been saying all along that max pressure is not the proper way to go. In fact max pressure may have caused some of the blow outs that we have seen here on this fourm. Please don't hit me over the head over this, just my two cents worth!
Ken
 

WeighIt

Member
All of our information comes directly from the tire manufacturers, specifically Goodyear & Michelin. This is what they want RV owners to do when using their products. The tire air pressure question always comes up, and is different for motorhomes or trailers. Motorhome tire pressures should be based on the actual load which a tire is carrying to insure proper air pressure. This is because some people find max inflation to give them a "hard" or uncomfortable ride.

Trailers/5th wheels are different. Inflate a trailer tire to the max side wall inflation limit, as long as the wheel will support that air pressure. Nowhere & at no time have I ever stated to overinflate a trailer tire. Trailer tires are subjected to much more twisting and abuse, and the sidewalls flex too much when lower air pressures are used. Trailers that carry heavy loads or have high vertical side loads cause extreme side wall flexing when not inflated to the max side wall pressure. The flexing causes heat, and heat is a killer of tires. Many of the tires we have found are running so close to the limit as far as weights are concerned. Driving over a CAT scale will not show you individual tire weights. You will get a weight for the total axle but that does not tell you the differences from side-to-side. I believe Jim already posted the rally weight sheet. You will see how much more weight is being carried on the street side. You need to know this information to properly load your RV & inflate your tires. It is true that several rally attendees had their tire pressures set by the dealer & those pressures were lower than the tire manufacturer's recommended pressure. I can't answer for the dealers as to why they would put a lower pressure in, other than not knowing about trailer tire issues; not having a compressor that can inflate high enough or even inaccurate tire gauges.

Here is a link to an article that explains all this:

http://www.rv-news.com/mar2000/feature2.htm

I would be cautious when taking the advice of the typical "tire store" employee or RV service tech. Selling car tires does not necessarily make one an expert on RV applications. This is not to imply the referenced author is not an expert.
As always, we can only pass along information from the tire manufacturers as presented to us. Everyone needs to make an informed decision as to what they believe is the safest way to go down the road. I hope this makes sense & please ask questions if it's not clear.:)

Stacey Frank
Weigh-It, Portable RV Scales
586-246-3048
weighit@gmail.com
http://weighit.tripod.com
 
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cdbMidland

Past Michigan Chapter Leader
So, we have conflicting comments. The Heartland sticker on my unit shows 80 psi and the sidewall shows 110 psi. That's a major difference. Who to believe?????
 

phranc

Well-known member
IMHO.. I would take to heart the suggestions of Stacy Frank, who has real world experience in RV's .. The artical has some good points , but was not written from the viewpoint of an actual RV (towable unit) user..
 

ct0218

Well-known member
Remember, at 80 PSI your load capacity is reduced to 3042 per tire max, which is the same as a LR E tire. If your Bighorn came with LR E tires, then you should be OK. You could be overloaded on one side and not know it unless each wheel was weighed. Overall, your axles could carry 12,168, less any overloaded wheel. My Landmark has LR G tires, and I'm over 12,168 on the axles, so I carry more air. Personally, I would always believe what the tire manufacturer had molded on the tire in lieu of a label placed by some employee. He/she may not have a clue as to what is right-they were just told to place a sticker on there, and hopefully the right one. I have seen a tire break the bead seal on a tight turn. May have been overloaded, and/or underinflated, just not sure since it was someone backing in next to me. I would think either one, or the combination of both, could do it. Once one is flat, and you are at or near max capacity with the four, then you are automatically overloaded by a large amount. That large overload, even if for a short time, can damage the three remaining tires.
 

cdbMidland

Past Michigan Chapter Leader
That's a convincing statement. I went back to my Weigh-It ticket and see that my lowest tire weight was 2925 on the curbside rear and 3125 on my off curbside front (which makes sense since I have three slides on the off curbside and one on the curbside).

So, as I normally travel with empty black and gray tanks and 1/3 full of fresh water, I have two tires over the 3042 weight.

Sure nice to have the individual weights to go by.
 

nscaler2

Well-known member
Chuck,
Based on what you just said, either you are overloading the coach with other stuff (which I doubt that you are doing) or these coaches don't come with enough carrying capabilty in the tires to match ther grvw. Thanks for the info, it is an interesting cunumdrum. (Spelling?)
 

cdbMidland

Past Michigan Chapter Leader
No, I'm legal. My unit has two 7000# axles and my tire carrying capacity is 3415# each. This gives me a cushion of 10-15% per tire.

My total trailer weight, including pin weight is 14,875#. Pin weight is 2700# leaving 12,175# on the four tires. This is based on Weigh-It scales done at the 2006 rally in Goshen.
 
J

Jim_1899

Guest
Weight

I have read some of the post on weight and load and this is an area that I am wanting to learn more about. While filling up with gas I had my truck and BH weighed while hooked up. The scale broke down the weight into three sections. The weight on the front wheels of my truck 4800 lb, rear wheel of truck 5860 lb and trailer axles 10,880 lb. The total gross weight 21540 lb.

I have not been able to weigh just the truck or weigh each tire seperate, I hope to learn more information at the 2007 Heartland Rally and from the forum.
 

ct0218

Well-known member
What are your truck axle limits (truck door frame, drivers side). My limits are 4800 front, 8550 rear. I believe your front axle capacity is a little higher because of the solid front axle. Looks like you are under your limits on the axles, esp the rear truck axle. The only possible problem is if you are heavy on 1 side of the Bighorn. The GMC front suspension is maxed out on mine--4805. I have to pump my tires on the front up a little to 70 psi minimum, but not the 80 psi max, because of the load. The front tires on mine are 2430 lbs @ 70 psi, 2580 lbs @ 80 psi. I'm not sure what size tire your Ford has, but it would be my size or larger.
 
J

Jim_1899

Guest
Gross Axle Weight Rating

The gross GAWR is 5200lb front and 7000lb for the rear. My tires are 275/70/R18 and have max psi of 80. I set the front tires at 65 and the rear at 75. The trailer tires I set at 80 which is the psi shown on the tire. I have been checking my tire pressure each day and the pressure has not changed on any of the tires.

The weight was done with my wife in the truck and without myself. The trailer seems like it would be heavier on the kitchen side, especially when packed with food. I assume the tanks are in a spot where they are balanced. I will try to weigh the rear trailer axle on the right and left seperatly to see if the weight is evenly distributed.

Thanks for letting me know where the GAWR was on my truck. If you see anything that does not look right with the information above let me know.
 
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