Re: [SystemSafety] Wheel detachment from a moving car / problem was solved many years ago, not widely adopted

From: Stachour, Paul D BIS < >
Date: Tue, 26 May 2015 13:10:58 +0000

Responding to what David Crocker wrote (see below for his text):

My opinion is that this is another example of a problem that has been solved by a segment of the industry, not adopted by the industry, and later "unsolved" due to lack of adoption.

Back in the ~1950's, all the vehicles made by the Chrysler Corporation had different-direction threads/nuts for each side of the car. The lugnuts each had a "R" or and "L" marked on them to indicate which side of the vehicle they belonged on. The threads/directions were chosen so that as the car drove down the road, the "natural action" would be to tighten the lugnuts. In other words, the car vibration/movement could only tighten the lugnuts, never loosen them. Thus, all that one needed to do to be "safe" was to put on the lugnuts, and tighten them by-hand. In reality, one used a spinning spanner wrench to finish off the tightening (by-hand, there was no such thing then as an air-wrench) once the vehicle was on the ground. But if one did not tighten them (the lugnuts) then, there was not a safety hazard. My dad indicated that most auto-shops did not like this technique, because they had to keep two kinds of lugnuts on hand, and made sure to put the correct ones on each side of the car. [One could not put on the wrong lugnut, it would not turn on, so that {using the wrong one} was not an issue.] None of the other automobile manufacturers adopted the policy, so Chrysler (who was not the titan in the industry) was see as doing an "odd thing" that made more work to do. Eventually Chrysler gave in to "public opinion" and made the job "easier" (but also less safe), and used only one style of lugnuts for their vehicles also..

I know this because as a teen-ager, I worked in my father's garage, and dismounted / fixed / remounted many a tire/wheel on many different makes of cars and trucks.

P.S. One could also start Chrysler-built automatic-transmission cars of that era by pushing them, because of how the transmissions were built. Another example of extra-function/extra-cost feature that was not accepted (and generally not know) that was abandoned.

Paul D. Stachour
Software Quality Assurance
Det-tronics|6901 West 110th Street, Bloomington, MN 55438 USA 952-941-5665, x8409

Learning from accidents is de rigueur but learning through accidents is an unacceptable development method for critical systems. Les Chambers. We may throw the dice, but the Lord determines how they fall. Proverbs 16:33 NLT.

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She had driven 500 miles since having the tyre on that wheel replaced.

This got me thinking:

  1. How often do wheels detach from cars while travelling? Are there any figures recorded? Have any fatalities occurred as a result?
  2. Why is there no requirement on manufacturers and fitters to use locking wire, a cotter pin, or some other mechanism to ensure that the wheel nuts cannot come off? I notice that some HGVs do use locking wire on the wheel nuts.
David Crocker, Escher Technologies Ltd.
The System Safety Mailing List
Received on Tue May 26 2015 - 15:13:20 CEST

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