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Friday, July 12, 2019

Why inflate Motorhome tires differently than Trailer tires?

Found the following in a thread on an RV owner's forum. This came after there were comments about the advantages of inflating trailer tires to the tire sidewall inflation number but inflating Motorhome tires based on the measured load on the tires.

 "Such a hard concept for most to understand."

As an actual tire design engineer, not just someone that has used a lot of tires or bought or sold a lot of tires, I feel I might have a slightly better understanding of the science behind why tires fail.
I try and make the information easy to understand but I find that many simply refuse to accept the fact that my 40 years experience that includes thousands of failed tire "autopsies" might qualify me to give sound advice.
If you simply look at the experience of three groups of tire users. Excluding punctures or pothold impact breaks.
1. Regular motor vehicles. People get about 40 to 50,000 miles before the tires "wear out"  less than 1% experience tire failures.
2. Class-A and Class-C motorhome users. Many only drive 5 to 8,000 miles a year. It is recommended that starting at 5 years of age, tires be professionally inspected. This does not mean a simple walk around to look at the tread depth but close inspection with good lighting. Maybe even using a pit to allow the inner sidewalls to be inspected. Annual ispections thereafter are recommended and replacement at 10 year tire age "no matter how good a tire looks" This group also has a low structural failure rate not tracable to air leak or impact.

3. RV Trailer users "Towables". Based on numerous reports of higher structural failures i.e. belt/tread separations, and some strange patterns left in lose gravel where a trailer was turned 180 degrees I had some computer simulations run and the numbers provided an explination for the "why" towables have a mush worse structural failure rate. The forces inside the tire structure are significantly higher (+24%) in trailer application (i.e. towables) than in motor vehicle applications This force is identified as Interply Shear and it shows up as trying to separate the top steel belt from the bottom steel belt in radial tires.

While it would be possible for RV Trailer companies to make design changes to trailer suspension to allow for "passive steering" as seen on large cement trucks with a tag axle, I doubt they would go to the expense simply to extend tire life.

While lowering the actual load on a tire in trailer service can lower the Interply Shear force I doubt that it is possible to lower the load by 40 to 50%. One thing trailer owners can do to lower this force is to increase the cold inflation to the tire sidewall "max" Sorry to say you can not reduce the Interply Shear to zero as this is the nature of radial tires.

Friday, July 5, 2019

Modern radial tire assembly -Worldwide

A very good 10 min video from a number of different companies on how modern radials tires are "built," how some of the material is processed, tires are cured, handled in the warehouse and even how some retreads are made.

There isn't a tire plant worker in the world (China, Europe, or the US) that would not recognize what the equipment is doing.

Yes, the machines are painted different colors and the robotic handling of the tires is done with different equipment but the end result is almost identical.

This uniformity in the process is why, I have so much difficulty in accepting the idea that because a tire is built in one country, it is automatically more likely to fail than when it is made in another country.