The Service Dept

THE SERVICE DEPT

JODY NICHOLAS

TIRES AND TUBES

Recently I have learned of a case in which a motorcycle rider reached an unfortunate conclusion to his trip because of a flat tire (rear), As informed persons on motorcycling, I would be most interested in your opinion as to causation and avoidance. The known facts, not all of which may be material, are as follows:

The motorcycle involved was a Moto Guzzi 750; it was being ridden by a 220-lb. rider with a 140-lb. passenger; it was loaded with 50 to 100 lb. of gear; it was being ridden on a concrete-surfaced highway at 60 to 65 miles per hour at a time of day when the temperature was between 90 and 100 degrees; the parties had traveled approximately 35 miles prior to sustaining the flat; the tire pressure at the beginning of the run is unknown, but is presumed to have been within normal limits; one or two months before the incident the owner had a new Avon tire installed on the rear due to wear, but the innertube (Pirelli) was not replaced since there had been no trouble with it; there were approximately 3000 miles on the new tire at the time of the incident and presumably 5 to 7000 miles were on the innertube; the flat tire was occasioned by a failure of the innertube rather than a puncture of the tire; and there is an indication that there may have been a latent manufacturing defect in the tube.

Do the above facts suggest any possi ble or probable cause(s) of the failure to you? If so, what reasonable measures, if any, could have been taken by the rider or the party installing the tire to avoid the incident?

A pertinent question is raised about the wisdom of installing a new tire with out installing a new innertube. I have been advised that a new tube should always be installed when a new tire is installed. One reason given is that the old tube seats differently in a new tire, causing undue wear and stress on the tube. For the same reason, I am in formed, a tube should be reinstalled on a wheel and in a tire the same way it came off and out. Is there any merit to these points, and are there any other reasons for changing tubes at the same time as tires?

Another point of particular interest is the role played, if any, by the weight of the bike and its load, its speed, temperature, etc., involved in this case.

It gives a rider an uneasy feeling to think that a motorcycle tire or tube can fail after several thousand safe miles for no reason, or for no avoidable reason. In this case the rider was killed. How could the incident have been reasonably avoided?

John F. Biehl Mercer Island, Wash.

There are many factors influencing the decision to change a motorcycle tube when changing the tire for a new or different one. Of primary importance are the age of the tube and its condition. If the tube has been patched several times and if it's more than, say, two years old, it should be replaced because air pumped into the tube has a small amount of water in it which will condense inside and tend to rot the tube's rubber. A close visual inspection of the tube will show any signs of weather cracking.

Motorcycle tires and tubes are mass produced items and are not individually inspected. It's therefore the responsibility of the installer to inspect the new tire and tube before fitting them on a motorcycle. The chances of getting a defective tire or tube from any reputable manufacturer are remote indeed.

There is no truth to the old wive's tale about installing a tube the same way inside a tire as it was removed because of the "seating" of the tube inside the tire. It is a good idea to mark a spot on the tire and the rim when fixing a flat or replacing a tube to keep the wheel/tire in balance, however.

In the instance you gave of the Moto Guzzi 750, the all up weight of the vehicle at the time of the accident was in the neighborhood of 960 lb., being shared by two 4.00-18 tires. If the tires were properly inflated, even an ambient air temperature between 90 and 100 degrees, a speed of 60-65 mph, coupled with the heat generated by the tires' flexing, would probably not raise the temperature to an unsafe level.

I'm inclined to believe that the inner tube was at fault, probably because of a manufacturing defect, however small; but it must be remembered that nothing made by man is perfect. The only way to be certain of not having a puncture is to install solid rubber tires, which are not being manufactured! 0

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