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Friday, January 11, 2019

Did you really read your Owner's manual?

Ya, I know that if you are like me you were given a stack of Owner's manuals with your new RV.

 I doubt that many have ever read every page of the 6" to 8" stack of papers.

However, I would suggest that you at least check the section of the basic manual that covers "Tire Safety".

I was recently involved in some litigation on tires and quickly learned that the folks who were complaining about their tires may have claimed to have read the manual, but for some reason didn't understand the information or felt the information didn't apply to them or just didn't care as it was obvious that they had failed to follow the tire maintenance and safety instructions when it came to RV weight or tire inflation.

A review of the table of contents will find section titles such as "Tire Safety" or "Weighing your RV".

I have to wonder why so many seem to feel that instructions such as "Before using your RV, you should inspect all the tires for proper inflation, uneven wear on the tread, cracks, foreign
objects, or other signs of wear or damage. Don’t .forget to inspect your spare tire!"
  do not apply to them.

I read questions on tires on the many RV forums I follow, and almost every week someone is saying  things such as " I have looked everywhere for tire inflation information but can't find out about my tires" 
 or "What size tire can I run" or similar questions. In reality, they have the information in their personal files.

I have found that copies of many Owner's Manuals are available for free on-line so even if you lost your manuals or didn't get them when you purchased a pre-owned RV, you should be able to find them online.

While I might be able to nit-pick at some of the details in the information, in general, I believe that if people read and followed the instructions, the percentage of people who have tire problems could be reduced significantly.

It really doesn't take a lot of time or effort to read and review the information on tires, proper inflation and correct loading of your RV. It also doesn't take much time to actually follow the instructions. If there is some part you don't understand I along with others would be more than happy to help out our fellow RV owners.

Certainly making a little effort to educate yourself will take less time than it would take to change out a tire after it had failed and also MUCH less expensive too.

Friday, December 28, 2018

"Safety Factor" or "Reserve Load"

"Safety Factor"   The dictionary offers this "the ratio of the maximum stress that a structural part or a piece of material can withstand to the maximum stress estimated for it in the use for which it is designed."
While that sounds reasonable it really only works when talking about pieced that fail from simply increasing the load placed of the component.

Items like tires do not really have a "Safety Factor" as tires generally do not fail from simply increasing the load too much. In a non-rolling situation, I would not be surprised if we could load tires to 200% or maybe even more than 300%  of the load marked on the tire sidewall. However as soon as you introduce rolling or time or operating temperature the maximum load before failure is much closer to the max load molded on the tire sidewall. The exception to Max speed is affected by temperature time and load. With zero load many tires can probably handle 200+ mph but again for how long and at what temperature?

Since tires are basically a structure made of "organic" components tire and temperature can have a significant impact on the maximum load capabilities of the tire.

If we think of non-organic items like a steel girder or maybe even a stone block as used in the pyramid we can see that time and normal atmospheric temperatures have essentially no impact on the long-term maximum strength. The exception would be if we were to allow steel to rust or stone to be exposed to water and freeze/thaw cycles.

Tire Engineers prefer to use the term "Reserve Load" when talking about the load capacity of a tire. Here we would find Tire Engineer definition as the difference between the tire's maximum capacity when inflated to the stated level for the specific application (the inflation on the tire Placard) and the actual load to be placed on the tire.

Here are a few comparisons: First some normal car and truck applications.


Next a larger 5th Wheel RV


When you compare the reserve load percentage of the different groups you can easily see the different level of reserve load.

What should the reserve load be for your RV?  Currently, RVIA considered 10% to be the minimum Reserve Load. However, the few actual Tire Engineers that are posting on RV forums are suggesting a MINIMUM Reserve Load of 15%  with more being desirable.
I know that on my Class-C I am running closer to 20% Reserve load based on actual "4 corner" weights i.e. individual tire position scale readings.

What is your actual Reserve Load?