Are you smarter than a tire dealer? Part 1

With apologies to the TV show "Are you smarter than a 5th grader"...

I sometimes wonder if RV owners are or at least need to be smarter than the average tire salesperson.

I bring this up based on a few recent observations and experiences. Let me give you some examples and then some suggestions to help you get the tires and service you want and need for your RV.

I have read a number of examples where RV owners had their tires inflated by a tire dealer only to later discover a variety of issues such as too much air, too little air, loose or missing valve caps or even loose valve cores. While I am sure that many dealerships want to provide good service, I think it important to remember that many times it is the "new kid" that gets the job of doing a pressure check and the on the job training may be done at your expense.
I would suggest that if you are going to have a dealer do tire inflation, it is in your best interest to provide the tire tech with clear instructions on the pressures you want. If you have more than a single inflation (fronts different than rears for example) maybe just an index card with a simple graphic along with the inflations you want will avoid confusion. You might even consider specifying a few psi higher than your real Cold Inflation Pressure or CIP so the next morning when you do your check with your Master Gauge you can let the pressure down which is always easier than needing to add a couple psi.
Also I suggest a quick walk around after the inflation check to be sure you have metal caps on all your valves. A light tightening twist may not be out of line to ensure you don't loose a cap on the way home.




Now the biggie Tire Buying.

 Next to going to the dentist, buying tires may be one of our least favorite activities in life. I do not expect to change your mind on this and turn the act of visiting a tire store something you look forward to, but I would like to offer some advice to make the task less stressful and possibly extend the time between visits so you have to go tire shopping less often.


Here is where some fact based knowledge can pay off in making the activity less stressful and might even end up saving you some money in the long term for I believe that a better purchasing decision will lead to lower probability of problems.

Lets start off by deciding if we are simply "replacing" out tires with more of the same or if we are "shopping" for tires that might deliver better performance, fewer problems or longer life.

Tire Replacement
If the tires you currently run have delivered satisfactory service, why would you think you need to make a change to a different size, type or brand? To me this would fall under the "It ain't broke, but I'm gonna try and fix it" approach. If your plan is to simply replace the tires you have with a newer set then you have it easy, simply shop for tires identical to what you already have.
When shopping I suggest you first go out and read the sidewall of your current tires. Note the Brand i.e. Goodyear, Michelin, Maxxis, Duro, Cooper etc. Next the type or design. This might be a name like "Marathon" or a number like "S637". Finally and maybe most important the COMPLETE tire size this includes the letters and numbers in front of and after the dimensional numbers and would also include the Service Description part, if any, that comes after the rim diameter. Service Description has two parts: Numbers for Load Index and a letter for the Speed Symbol or Speed Rating

For size something like "235-15" isn't correct and if that is what you tell the tire dealer, what you are really doing is sending the message that you really don't understand tires so an unscrupulous dealer may try and take advantage of you.
Technically an "LT235/75R15 107/110Q Load Range D"
is a different tire than an "LT235/75R15 Load Range D".


If you are not completely clear on this you might want to review THIS post that covers the differences for Passenger and Light Truck type tires.


Trailer or "ST" tires will have markings similar to LT type tires


Class-A Truck Bus Radials or TBR type and European commercial tires will also have size information similar to LT but with no letters in front and of course bigger numbers like "275/80R22.5 Load Range G". For TBR type tires the Service Description part is optional. If your current tires have a Service Description I would include that information when identifying the tires you want to the dealer.

You may find that shopping on the Interweb an exercise in confusion as I find many tires listed with incomplete or even incorrect tire information. Poorly designed web site may not be an indication of the competence of the dealership but it is not a good sign. This might be the first sign that you actually are smarter than the tire dealer.




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Have you read a tire lately? Tire Marking

Have you read the information provided to you by the tire manufacturer? If you have, did you bother to record the important numbers in your log book so you only need to do this job once in the life of a tire?

There is a lot of information molded into the sidewall of your tires. Most of this is required by law. Most of this is important for you to know so you can look up the correct inflation for your tires or if buying new tires be sure to get replacements that can carry at least the same as the original tires.
Here is some information from one tire.

First the SIZE

This tire is a "Passenger" type as it starts with the letter "P" other types might be "LT" for Light Truck, or "ST" for Special Trailer. Small tires intended for passenger cars migth not have the "P" if made to European specs. Large tires like 19.5 or 22.5 rim dia have no letter and are "TBR" of Truck Bus radials and are found on Class-A RV. The "114S" is the Service Description which is a Load Index (from a published table but using the actual Max Load is better). The "S" is the Speed Rating or max operating speed. Like the Red Line on your engine. Not all tires have this description.

The DOT Serial

This has important information used in determining the tire age. Other information such as the location of the tire plant that made the tire is part of this code ( first two characters  8X in this example). If there is a recall, this code is used to identify which tires are covered by the recall. NOTE that the last portion, the 4 digit date code, 3908 in this example is only molded on one side of most tires. Every tire sold for use on the highway in the USA must have a full DOT serial including the date code molded on at least one side. This tire was made the 39th week of 2008.

The Load & Inflation information

This is the maximum load capacity for the tire when the cold inflation is set to this pressure. In this example (2601 lbs) when the inflation is set to( 44 psi max press) when the tire is at ambient temperature. NOTE for LT and TBR type tires there is a second lower load limit for dual application (tires side by side on the same axle as on the rears). If you have two axles and ST type tires I personally suggest you not exceed the "dual" tire load as you need a safety factor in your tire loading due to extreme side loading unique to tandem axle trailers.

Tire Materials

This is really just FYI and is more like truth in advertising to let you know the materials used in the sidewall and center of the tread of your tires. In this case there are two ply of Polyester in the sidewall and in the tread there are two ply of polyester + 2 ply of Steel + 1 ply of Nylon. Most TBR tires will only have 1 ply of steel in the sidewall.

Safety Warning

This is for the person mounting and inflating the tires for the first time. Do not confuse the inflation number here ( 40 psi) with the inflation number associated with the load (44 psi). This is the max inflation to seat the bead. If you have ever watched a tire being inflated it is the "Pop" or "Bang" first heard. If the tire doesn't seat by this inflation then it should be deflated, re-lubed, re-centered and re-inflated. People can die if they ignore this warning.

Bottom line
If you get new tires and they match the Size and Load & Inflation information you are good to go. If ANY of these numbers are different you need to be sure you completely understand why and that you are not getting a tire with lower load capacity.

How fast is safe to drive on your tires?

I found and responded to a forum thread on tire speed ratings and thought I would share what I learned with you here.

I think it best to think of a tire's "maximum speed" a bit like the engine red line. Can you exceed the red line on your engine? Yes, occasionally, but is it good for the long term durability of your engine? I think you will agree that it's not a good policy unless you like blowing up engines (or tires).

A tire has a finite life. Heat and cycles consume that life. Heat comes internally from under inflation, overloading and fast speed and externally from spending all your time in the South where temperatures are higher than in snow country. Cycles are simply miles.

Heat generation occurs inside the tire structure at the molecular level. It is not linear so one mile at 75 mph “uses up” more of that limited life than two miles at 40 mph. It’s even possible that a mile at 80 mph is worse than two miles at 60mph.

The maximum speed rating is also based on the assumption that the tire has NEVER been operated while 'flat." Note that a loss of 20 percent of the minimum inflation needed to carry the load is considered flat.

Also if the tire has ever been repaired, the manufacturer may no longer support the speed rating marked on the tire. You need to consult the manufacturer's publications to confirm its policy. This would apply to tires with a speed symbol letter as found on most Class-B and Class-C motorhomes.

An example might be LT235/85R16 LR-E 120/116Q. The 120/116Q is the service description with the 120 and 116 being the load index for single and dual position. The “Q” is the speed symbol for 99 mph max. A Class A motorhome might display 255/70R22.5 LR-G 138/134L. The “L” is the speed symbol for 75 mph.

As I cover the topic of speed rating in my tire seminars, there are different requirements for tires in Europe than the USA and Canada. In Europe vehicles are capable of higher speeds (100+ mph). Roadways exist to run them, and it’s legal. The tire description system was created to assure replacement tires were also capable of those higher speeds.

However in North America we have speed limits that do not allow driving at excessive speeds. So the emphasis is placed on handling, not "all out" speed.

The same construction features required to achieve higher speed ratings also improve handling. So, in the Americas a speed rating also tends to be a performance or handling rating.

I know of no highway tire that can run its entire life of 40,000 to 90,000 miles at its maximum speed. The tests to establish the speed rating only require an hour or so to complete and most of the test time is well below the maximum. This test is used to measure the rate of heat energy generated with tires failing due to too high an operating temperature.

Finally.
If you tow a trailer that has ST type tires you need to remember that they are rated at 65 mph maximum. A few trailers come with commercial tires that are only rated to 62 mph. So your maximum speed is based on the lowest rating of all your tires.

Class-A TBR type tires

Previously we talked about the full tire size nomenclature for Passenger and Light Truck applications.

Large RVs usually run what are known as Truck or Bus type tires. With most new applications being of Radial construction we use the acronym TBR. Here are some examples:
255/70R22.5 LR-G 138/134 M
In this example, the various numbers and letters are similar to those for Light Truck except the Load Index numbers and Speed Symbol are optional so may not be marked on the tire sidewall as part of the complete size nomenclature. The Load Index 138/134 and the Speed Symbol "M" make up the Service Description. If this is on your tire please include it when asking a question.

11R22.5 LR-H
This is an old “Inch” size description with the tire being about 11” wide. This would be a tubeless type tire.

10.00R20 LR-H 146/142 L
This is an old “Inch” size description with the tire being about 10” wide. This would be a tube type tire. Again the Load Index and Speed Symbol are optional

8R19.5 LR-F 124/122 L
This is another old “Inch” size description with the tire being about 8” wide. This would be a tubeless type tire with the example showing the optional Load Index numbers and Speed Symbol.
The two Load index numbers signify that the tire is rated for a higher load in single application and a lower rating when in a dual fitment.

The Speed Symbol for TBR tires are associated with the following MAXIMUM operation speeds.
F = 50 MPH G = 55 MPH J = 62 MPG K = 68 MPH and L = 75 MPH
If no Speed Symbol is marked on your tire you need to consider the tire is rated for a MAXIMUM of 65 unless you can find printed documentation from your tire manufacturer stating some higher speed limit is acceptable.
If you are writing to ask a question about your tires please include the complete nomenclature including Load Index, and Speed Symbol if marked on the tire.

SPECIAL SAFETY NOTE: Maximum Inflation
In July, MOTORHOME magazine published an article on TBR tires. The author offered his personal opinion that it was acceptable to set inflation higher than the Max marked on the sidewall of a truck tire. Exceeding the max cold inflation on the sidewall has serious potential safety consequences. Large TBR tires have been known to explode and personal injuries and even deaths have occurred when proper inflation procedures are not followed. I can find no industry guidelines that allow this procedure of exceeding the maximum inflation when setting the pressure for normal highway application of any tire.

Rims also have a Maximum rating for both Load & Inflation.
Many wheels have these ratings marked on the rim. If you can’t find that information I strongly suggest you contact the manufacturer and obtain the ratings for your rims. Again Serious injury or even death can occur if a rim fails due to damage and overinflating or improper assembly.
Accuride Safety information and Product Literature you can consult.

Alcoa also has product literature online.



Inflation Safety
Whenever we are talking about setting the inflation in a tire, we are talking about “cold” inflation. This means the tire is at ambient temperature and not warmed from operation or sitting in the sun.
I would suggest the tire not be driven more than two miles in the last hour and not in direct sunlight for at least two hours. When I did my tire cover study – See my post from June 16 on Tire Covers, I saw almost 40° increase in tire temperature in about one hour for a tire in full sunlight.

I would strongly suggest you never attempt to inflate a TBR tire if the tire beads are no longer fully seated against the rim without using an approved Safety Cage. If there is a problem, the tire and wheel can separate and components can easily go through concrete block wall never mind the side of an RV.

Any tire that has lost more than 20% of its rated inflation is considered flat and if it was driven on in a “flat” condition it needs to be dismounted and inspected by trained tire company store technitians. Not a Mom & Pop garage but a store run by a tire manufacturer.

What do all those letters mean in the tire size?

A fairly consistent problem I try to provide answers about specific tire applications, is the fact that we are usually only given part of the tire information we need to provide an informed answer. I have been asked “What load can my 16” tires carry” or “I have 8 ply tires, how much load can they carry?” or “Can I replace my 235/70R16 tires and carry more load with a 245 tire?”
While I really want to help you get the information and answer you seek, I do not want to guess what tire you have as I may guess wrong and give you incorrect information.

The reality is that the numbers alone are not all the information we need. To help us do a better job of answering your questions, you can help us by giving us the needed details.

Here are some examples of how you can help us all if you provide complete size information when you ask a question.

A P235/75R15 105S is rated at 2,028 Lbs at 35 psi maximum. This would be a “Standard Load” tire, while a P235/75R15 108S XL or Extra Load is rated at 2,183 Lbs at 41 psi max.

We can break down the different parts of the complete size designation as follows. The P stands for Passenger. The 235 is the width of the tire in millimeters and the 75 is the Aspect Ratio of how tall a tire is relative to how wide. In practical terms it is how close the wheel is to the road. The “R” of course stands for Radial and if the tire were Bias as tires were before the introduction of Radials it would have a D for Diagonal. Don’t ask me why they didn’t choose the letter B. I have no idea.

We all know the 15 is the rim diameter. The 105 or 108 is the Load Index. You can consider any passenger tire to be Standard Load unless marked “XL” or “Extra Load”. The “S” in the size above is the speed or handling rating. Passenger tires are not rated for dual application. The combination of Load Index and the Speed rating make up the Service Description.

When you ask a question about a tire don't worry about what all the letters and numbers mean just look at your tire and copy all of the information and leave it up to me and other tire engineers to decipher the mumbo-jumbo. If you tell us your tire size is a P285/35ZR19 87Y we will know this ultra wide, very low aspect ratio large rim tire with a high speed rating indicates you are driving a Corvette and that those tires are not meant to be used on your RV.

Next time we can move on to other type tires that many will find on their Pick-Up, Trailer or RV.

Load Range - Ply Rating - Standard Load and related markings

Had a good question from George. He said "The tires on my Chevy Silverado say "Standard Load" rather than Load Range. What does Standard Load actually mean?"

The simple answer is that your tires are rated equivalent to Load Range B. But I am sure that raises more questions.

This is a good time to clarify some of these terms. To do that we need a bit of a history lesson so we understand why the term "Ply Rating" is out of date.

80 years ago when tires had cotton for the body fabric four Bias plies were needed for use on passenger cars. Trucks needed more air to carry their heavy load which meant more layers or plies were needed to hold the increased air pressure, so truck tires had 6, 8, 10, or more actual layers of cotton body fabric. They needed the even number because they were Bias not Radial construction.

With the invention of synthetic materials such as Nylon, Rayon, Polyester fewer layers or "Plies" of fabric were needed to hold the same air pressure. The term "Ply Rating" came into use when the actual number of plies of these synthetic materials was less than the number of cotton plies.

I remember when I started working in truck tire design in 1969 using terms like "6 for 8" meaning we were using 6 plies of Nylon to deliver the strength of 8 plies.

With the introduction of Radial construction from Europe a new size standard based on actual tire dimensions was used but something was needed to address load so about this time the use of "Ply rating" was replaced with "Load Range" and a letter was used instead of a number as the number was misleading the consumer. We ended up with Load Range, or "LR" B replacing the number 4 and C replacing 6, D replace 8 etc. Since essentially all passenger cars came with Load range B tires it was decided this was the "Standard" load and this did not need to be marked on the tire. There are a few "Extra Load" passenger type tires which you could consider like a LR-C and they are marked as such.

All Light Truck and Heavy Truck tires are marked "Load Range x" with the x being the Load Range for that tire. They may also simply have the Load Range letter right after the size.

To further confuse things there is now a "Service Description" which includes the speed rating. So you may have a passenger tire marked:
P205/75R15 84H The 84 is the "Load Index" and the H is the Speed Symbol.

A Light Truck tire might be LT205/75R15 98/95Q LRC with 98 being the single Load Index and 98 the Dual Load Index and Q the Speed Symbol and LRC indicating the tire is rated a Load Range C tire.

A heavy truck or bus tire might say 255/70R22.5 LR-G 138/134M At this point I trust you can figure out what the letters and numbers mean. If not and want more info check out
this link or simply ask the question.