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Tuesday, April 23, 2013

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.


  1. good article. should be in printable form(eliminating the side bar and ads) so it can be carried in the rv.

  2. If you look at your browser it should say "Reader" in the URL window and if you hit that it should open up in a printable form.

  3. You can print the post as you can print just about any web page. Under Windows hit the ctrl and S keys. When the window pops up simply save the file as TXT. You might need to change the file name suffix from HTLM to TXT to do so. Mac should be able to do similar but I don't know the key strokes
    It would be nice if you checked out some of the ads as purchases from advertisers are what pay the electric and internet blog bills.


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