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Monday, November 24, 2014

RV tire reference links. Load / Inflation tables etc

Based on posts I see on various RV forums it appears that some RV owners are having difficulty finding the appropriate technical information on their tires. As a result sometimes they post questions such as "I have a XYZ RV with ABC brand tires what is the correct inflation for my tires". If you are a frequent reader of this blog I trust you can see that much critical information is missing and any answer that says "Use QQ psi because that is what I use on my RV" is not much better than a wild guess.

I have decided to assemble links to tire Load & Inflation tables for the "major" brands of tires likely to be found on RVs. Now I know that there are many tires out there that are not made by or for the major tire manufacturers that have been selected by the company that assembled some RVs so this is not a list of each and every tire out there. If you have a tire not identified from one of the manufacturers I have listed, please send an email (address posted in the About Roger info on right side of this blog) and I will endeavor to update this list. Unlike most blog posts I plan on updating this post when new or additional information becomes available so you might want to Bookmark this page to your list of Favorites.

Note: I will use the term "TBR" for Truck Bus Radial and this in general means tires with 17.5, 19.5 and 22.5 rim diameter. "LT" of course means Light Truck and "ST" stands for Special Trailer. "P" or Passenger type tires would only be on passenger vehicles or very small trailer.

Sometimes it is difficult to know who actually made your tires. I have seen tires with the brand name "GT" which is obviously not the name of a tire company but simply a name used for marketing a line of tires. If you do not know who or where your tires were made HERE is a web site that will allow you to use the first two characters of the DOT serial molded on the tire sidewall to learn the facts. For example if the DOT serial on your tire was   4DHLABC4513  you would look uo the "4D" and discover the tire company to be BRIDGESTONE/FIRESTONE NORTH AMERICAN TIRE, LLC.  and the plant location to be Morrison Tennessee, USA, with a manufacturing date of 45th week 2013 or the week of Nov 3 2013.
If the first two characters were  4V you would discover the tire company was actually CHONCHE AUTO DOUBLE HAPPINESS TYRE CORP., LTD, TAIYUAN CITY, SHANXI, China.


Bridgestone RV application info.
While this company does not appear to actively market to RV owners they do have tires that will fit and work on many types of RVs that use LT or TBR type tires. This web page has general information on RV applications and a "how to guide" to help RV, travel trailer, mini-bus, van, light truck and ambulance owners learn how to properly weigh their vehicles and maintain their tires". The page also has a worksheet to help owners to properly weigh and calculate the correct minimum inflation needed for their unit. Much of the information on the web site is general in nature so is of value to many RV owners. Here is the Load Inflation chart in download PDF format for RV size tires made by Bridgestone. This brand is sold and serviced through both company stores and independent dealers.

Continental USA
This company has a line of smaller "commercial" tires based on European designs aimed at the Utility/Van market in addition to both LT and larger TBR size tires,  Some of these tires might fit trailers including larger 5th wheel trailers and come in 14", 15" & 16" rim diameter. NOTE these tires have sizes like 225/70R15C LR-D. The "C" after the rim diameter stands for "Commercial" and is a European background. Do not confuse these commercial tires with LT type. The sizes may be similar but the loads,  inflation and even some of the dimensions are different.
TBR size Load Inflation tables starting with 17.5" diameter can be found here
LT & European Commercial type tire Load Inflation 

Dunlop is a subsidiary of Goodyear Tire & Rubber Co.
They have a selection of LT type tires. This brand is sold and services through both Goodyear company stores and independent dealers. I could not find Load/Inflation tables specific to Dunlop but would expect that the Goodyear charts should line up 100%.  

Firestone is a subsidiary of Bridgestone Tire Co.
Like their parent company, Firestone does not actively market to RV owners. They do have their own line of LT and TBR type tires. You can download their Data Book HERE. This contains technical on both current and many discontinued tire lines along with numerous pages of tire, wheel and vehicle technical and safety related information. Load / Inflation tables for Firestone brand tires can be found in both the Data Book and downloaded separately HERE. They also have a page of general tire information and links HEREThis brand is sold and services through both company stores and independent dealers.

This company actively markets tires to the RV community is ST, LT and TBR type tires. They have a web site specially designed for RV owners with numerous links to pages with supporting technical information on "Tire Selection" and "Care & Maintenance". They have four videos featuring a now retires tire engineering friend of mine, Tim Miller as he explains various concepts of proper tire use and care in the RV market. I definitely recommend that everyone in the RV community watch these videos. If you want you can go directly to their Load & Inflation tables and learn about your tire capacity if you have this brand.  This brand is sold and services through both company stores and independent dealers.

This smaller tire company has a line of tires for RV application covering  LT and TBR application. I find they have a number of heavy duty LR-G and LR-H tires in 16" and 17.5 diameter that may solve some heavy load issues that some RV owners seem to struggle with. These tires are sold through independent dealers and I could not find any company owned store information of on-line Load/Inflation information. Info from them indicated "Hercules Tire follows the guidelines published by The Tire and Rim Association. " so you can look at the tables used by Goodyear, Bridgestone, Firestone or Michelin.

This company was founded in 1967 and has a variety of different type tires. For the RV market they focus on ST and LT including small commercial type tires. You can review their web info on ST type tires including their Load Inflation tables HERE.  The information on their Commercial and LT products can be found HERE. I do note that they have a 5 year warranty on their trailer tires unlike many of their competitors that have only 12 month or less. These tires are sold through independent dealers and I could not find any company owned store information

This is one of the two major tire companies that focus on the RV Motorhome market. Their Load/Inflation numbers are sometimes confusing as they sometimes show the load for a axle rather than individual tires so it is very important that you read the numbers and table headings closely. Remember when selecting the inflation needed for your tires based on the actual load you need to select the loads on the heavier end of the axle. All tires on an axle should have the same inflation (i.e. based on heavier end) and you still need to add at least 10% to the minimum inflation specified for the load for your Motorhome. While most of the inflation ratings are the same as seen for Goodyear or Bridgestone there are a few exceptions so this is another example of you needing to confirm the ratings of the tires IN WRITING before you make your purchase. 
You can find general information on Michelin RV tires HERE. There are links to Load & Inflation tables HERE.

Private Brands
Many of the smaller tire companies are in reality just "Private Brand" marketing companies. They do not design, engineer or manufacture tires themselves but simply place large volume orders from other manufacturers. Many times these companies can offer lower prices since they do not have the overhead of design or testing staff and facilities but this means that if you are trying to get technical information form the company you may end up talking to a "customer service" person with no actual tire experience. They also do not have company stores so if you have a warranty claim you may have to return the tire to the location where you made your purchase or sometimes it will be your responsibility to ship a failed tire to some service location many states away.

Private branding is just a marketing plan and is sometimes used by Major companies. Goodyear makes and sells Kelly brand tires. Firestone made Dayton brand. This is why it is important for you to read the DOT serial to learn who really made your tires. In some cases a marketing firm may have one size made by tire company ABC but a different size made by company XYZ. Other times the marketing firm might have 10,000 tires of a given brand and size made at one location but the next batch could be made at a completely different location or tire company. This "flexibility in manufacturing could man that the performance or reputation of a "brand" of tires may depend on which size or even what date of manufacturer we are talking about.


Trailer Owners need to remember that they need to run the inflation on the tire sidewall to minimize the damage done whenever turning. You can refresh your understanding by reading THESE posts.

WARNING to Trailer Owners.
For the most part you will find that brands not listed here will follow the US TRA published Load Inflation tables as used by Bridgestone, Firestone & Goodyear.  BUT I have run into a few instances where the RV trailer assembler and the tire distributor "played games" and have adjusted the load capacity upward just enough to meet the legal requirements for the GAWR to be equal or less than the total capacity of the tires. These loads are not in the Industry Standards and means you are stuck with the size, LR and brand tires as supplied by the assembler or you will not be able to carry the load specified in the owners manual or on the placard affixed to your trailer. This is one major reason why you should ask to see the tables for your individual tires and compare them to the industry standards otherwise your tire replacement options will be limited to a single tire.

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Sunday, November 9, 2014

Is monitoring tires "Rocket Science?"

I get asked this question quite a bit. I think that after reading various posts on tire inflation and load, some people want to complain a bit and are hoping to use the excuse that it is too much work to monitor tire pressure every travel day.

Here is an example from a trailer owner:

"I've noticed that 50 psi cold at sea level at ambient 65F is 54-55F at 6,000 to 7,000 feet.
  While touring should I deflate to 50 psi cold at 7,000 feet if I'm hanging around there for a day or two

I am hoping that if I share my personal experience, it will provide a down to earth view on the topic that some want to turn into "Rocket Science"

I just finished a two-month cross-country trip.  Ohio > Oregon > Seattle  > Calgary, Canada > Yellowstone > Ohio in my Class-C MH with LT type tires that are 7 years old but have always been covered whenever parked for more than a couple of days, Always running inflation about 15 psi above what is needed for actual max load based on 4 position scale weights that are confirmed to have not changed significantly each year with a trip across CAT scales.
 Fastest I ever run is 70 mph but most of the 7,400 mile trip was with cruise set at 62mph. In other words, the tires have had a good life with good care.

Elevation ranged from about 25' at Olympic Nat Park to 8,000'+ in Rockies. Morning temperature ranged from 33 F to 94 F. I have TPMS (both internal and external) so I am able to constantly monitor both pressure and temperature.

I adjusted the tires once during the trip. I think I needed to add from 1 to 4 psi in the 6 tires. Since I run a nice inflation cushion of +25% I don't get all bent out of shape when the cold inflation is off by 3 to 5 psi from my goal.

You don't have to make the task of monitoring inflation a big deal. While I may set my pressure to +/- 0.5 psi, you certainly don't need to be that fanatical, and I would consider it completely acceptable to be +/- 2% for  the average user as long as the "goal" cold inflation has an appropriate safety margin.

With TPMS I simply hit the button a couple times a day and get a real time reading of tire temperature and pressure. Yes, the temperatures vary and so do the pressures, but unless I see a sudden drop in pressure and there have been no external changes such as a sudden rainfall or one side constantly hotter than the other after spending hours with one side in full sun, I just do not worry about it.

Relax.  Let your TPMS monitor your tires and enjoy the scenery.

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Tuesday, November 4, 2014

Goodyear RV tire Load / Inflation calculation

Had a request for assistance of how to calculate the proper inflation to run on a set of Goodyear  G670 RV 255/70R 22.5 tires
 on the Motorhome. The owner was a little confsed by the charts.

Here is what I did based on the AXLE weights provided by the owner. Maybe if you have been a little unsure on how to do the calculations this post will help.
While it is always better to know the actual loading on each corner of your motorhome, I know that not everyone can find a local facility that can weigh individual positions or they hav not attended a large RV event where RV Safety & Education Foundation provides the service so hopefully this will help until the time you learn your actual loading.

He said he had the coach weighted at a CAT SCALE facility in California. The axle weight is the only weight he has so far.

The front axle weight is    7,580 lb
The drive axle weight is  15,760 lb
1. Calculated individual tire loading
   7,580/2= 3,790
15,760/2= 7,880 per side

2. Applied 5% factor for not having actual axle end weights
  3,790 x 1.05 = 3,980
   7,880 x 1.05 = 8,510    Divide by 2 to get individual tire loading 8,510/2 = 4,255#

3. Go to Goodyear RV tire page

4. Downloaded the Load Inflation Table.

5. Find the 255/70R22.5  (pg 3)

6. Look up the Single load that is equal or above 3,980 and find 4,190 at 80 psi

7 Add 10% to that inflation  80 x 1.10 = 88 psi. 

8 Looked up the Dual load equal or above 4,255 and found 4,275 @ 90 psi
9 added 10% to that inflation  90 x 1.10 = 99 psi
10 You now know the absolute minimum inflation to ever see on your TPMS  80/90 F/R

11. You know your "Goal" or "Set" pressure for each day of travel is 88/99 F/R

If you ever drop below 84 Front or 95 Rear you should add air. I would not let air out unless the COLD pressure exceeded 93F or 104R

The extra 10% inflation is so you do not have to chase your tire inflation around with day to day temperature & pressure changes.

Remember you need to be sure you do not exceed the cold inflation molded on the sidewall of your tires or the max inflation rating for your wheels. If you find yourself calculating pressures that exceed these ratings it means you need to put your RV on a weight loss program.

You can use this step by step post as a guide for learning the correct Cold Inflation for your tires.
You can learn more by reading the posts on my blog with Temperature, Pressure or Inflation as "Labels" I do not expect you to remember all the information but if you review the posts you will probably remember that I wrote something on the topic of interest in the future so you can then go back and review to answer to whatever your questions is.

 This is NOT the method for you to use. The above is ONLY for MOTORIZED RVs.

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Picture from Goodyear website. I figured they would not mind since I am helping their customers.