[SystemSafety] Wheel detachment from a moving car

[Heath Raftery]

As far as prevalence goes, I don't have any numbers but I think you'd be 
unlikely to find anyone that doesn't know someone that has experienced 
this. However, the hazard vs mitigation tradeoff obviously hasn't tipped 
over into the realm of it being worthwhile addressing.

The exception of course is in heavy vehicles. Some jurisdictions require 
wheel nut indicators and they're certainly very common here in 
Australia. They solve a slightly different problem though - the wheel 
nut indicators are installed after the nuts are torqued, and then 
passively indicate gradual loosening.

The passenger car scenario is usually thus: car goes in for service, is 
hoisted and wheels removed. After servicing the wheels are replaced and 
the nuts hand tightened - any more torque and the wheel is likely to 
spin making tightening difficult. The car is then lowered on to the 
wheels and the mechanic *should* then torque the nuts. But they get 
distracted, it's knock-off time, or they just forget, and the nuts 
remain hand tight. That works while you drive home, but next time you 
hit highway speeds a vibration picks up and you get overtaken by one of 
your wheels.

A procedural change might help, but humans have a way of working around 
procedural changes. Wheel nut indicators and cotter pins wont work 
because most passenger cars do not have proud wheel nuts (aside - the 
wheel bearing nut on the other hand, has been designed to accommodate a 
cotter pin. Someone must have decided it was worth it there.). Other 
solutions like vibration or torque detection are likely to be too 
fiddly, too expensive or too unreliable.

Maybe there's an opportunity there?

Heath

On 22/05/2015 1:25 AM, Scott Nowell wrote:
> Nearly thirty years ago I was driving our SUV with a snow plow mounted on the front in a small town in New Hampshire.  The vehicle was driving fine.  Travelling at about 35 mph I applied the brakes and the left front wheel came off and continued down the road at speed until it hit a snow bank and bounced twenty feet in the air.  Fortunately the skids of the raised plow hit the road first, preventing damage to the underside of the vehicle.
>
> Similar to your partner, the car had been in for service the previous day.  Their best guess was the lug nuts had only been hand tightened.  The ride had seemed OK, but the ice and snow on the road may have obscured any vibration.
>
> Unfortunately it seems likely that any locking wire or cotter pin would also have not been installed.
>
> -----------------------------------------------------------------------
> Scott Nowell
> Validated Software Corporation
> 6848 Embarcadero Lane
> Carlsbad, CA  92011
> Tel: (760) 230-5299
> snowell at validatedsoftware.com
> www.validatedsoftware.com
>
>
>
>
> -----Original Message-----
> From: systemsafety-bounces at lists.techfak.uni-bielefeld.de [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of David Crocker
> Sent: Thursday, May 21, 2015 7:26 AM
> To: The System Safety List
> Subject: [SystemSafety] Wheel detachment from a moving car
>
> My partner has a nasty near-accident on Tuesday. While travelling on a dual carriageway at 60mph, she became aware of a new noise from the vehicle. Shortly afterwards, the front nearside wheel detached and she saw it roll into an adjacent field. Fortunately the car did not tip over. She is a skilful driver, so she allowed the vehicle to decelerate without using the brake. She was not rear-ended, and when at a slow speed she drove it into the adjacent grass verge. She was shaken but unharmed. The car is beyond economic repair because the steering assembly and other parts are wrecked.
>
> 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.