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Tuesday, August 15, 2017

"Run Flat" vs "Blowout" protection

Saw a thread on run flat fixtures to be used on the front of an RV to provide some protection against losing control if a front tire were to fail. A lot of discussion and conjecture but not many facts. Before I start it's important to be sure we all are on the same page with these terms.

"Run Flat" capability in today's tire market is a reality for passenger car tires. Tires designed and so labeled can provide mobility at reduced speed for various number of miles even after a complete loss of air. Some advertise 50 miles at 50 mph. I know of no true run flat tires for LT, Truck or RV application.

"Blowout" is a generic term used by many to describe a tire failure. This term does not provide information to tire engineers on the condition or possible cause of the failure.

"Rapid Air Loss" or "RAL" is any sudden loss of all the air in a tire.

"Belt or Tread Separation" -- This is when the belt and or tread portion of a tire separates from the rest of the tire. The carcass or body of the tire many times will still hold air.

"Run Flat Device" -- This is some equipment that fits inside a tire. It may prevent the beads from De-seating from the rim or may limit the collapse of the tire after the loss of air.

"Steering Stabilizer" -- This is vehicle equipment that may lessen the "jerk' of the steering in the event of an RAL.

I do understand the concern of some about the loss of control of a large RV in the event of a front tire failure. Yes, I have seen some of the videos and they are spectacular, but a front tire failure does not have to mean you will have a crash.

Back in the early '70s I worked extensively on a new type of tire from Firestone, the LXX, which was intended to replace 10.00-20 and 11-22.5 size tires but used a 26.5 rim. I even spent a week in Texas at the test track intentionally puncturing front tires with a 2" diameter hole to test vehicle control. While the tire worked as designed, the cost of new wheels made the tire design not viable in the truck tire market.

Here is a picture in the Akron newspaper at the time showing the tire with my then boss Ed Henry.



The main challenge for vehicle control is to either limit the "drop" when a tire suffers an RAL or to limit the steering response which can send the vehicle into another traffic lane.

There are a number of systems on the market:

Tyron is designed to keep the tire on the wheel. It does not appear to lessen the collapse of the tire.

Rodguard inserts for 14" to 17" tires appears to partially support a flat tire.

Safe-T-Plus steering stabilizers take a different approach to vehicle control.

Hutchenson seems to focus on extreme situations, such as military applications.


I recall hearing about multi-piece inserts like this one from TAC but was not able to find current info for 22.5 RV size tires.

IMO the best approach to preventing a loss of vehicle control is three steps:

1. Use a TPMS and have it set to tightly monitor your inflation. Test your sensor to confirm it reports pressure loss at the level you expect. It may not be set correctly and a test can confirm.

2. Closely inspect your tires at least annually and if possible even have your tire dealer check for out-of-round or lateral wobble of the tread and bulges in the tire sidewall. These can be early warning of separations or other structural damage to a tire.

3. Study and review the safety videos on how to maintain vehicle control in the event of an RAL.
   Here is one from Michelin, and another, and yet another.


##RVT807







1 comment:

  1. Review the videos, there is truth in them. My wife was attending to a patient in the back of a van type ambulance with a professional truck driver at the wheel of the on-call ambulance when a newer tire had a tread-sidewall failure. The driver did as indicated, as he was trained. Today, all three are alive because he was properly trained and know what to do.

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