Re: [SystemSafety] Wheel detachment from a moving car

From: Derek M Jones < >
Date: Tue, 26 May 2015 23:45:26 +0100


The UK Government are getting very good at releasing all sorts of data. Individual road accident data here: wheels coming off looks like it is sufficiently rare that it does not have its own code.

On 26/05/2015 22:13, Mike Ellims wrote:
> There are two questions here,
> First, if fitted correctly will a car wheel wheel come off? The answer seems
> to be if it's fitted correctly no, it won't come off, the designers thought
> of that one.
> Second, how often are wheels fitted incorrectly?
> I should be able to at least partly answer the second question as all
> accidents attended by the police in the UK and in particular all fatal
> accidents have to have a STATS19 sheet filled out, part of which attributes
> causes and code 999 can be used for a write-in e.g. "wheel came off".
> However that's the part of the data set that isn't publically available and
> at the moment I can't get access to the data as;
> a) for the data sets I have the surge protector has gone phut (tech term) on
> the set of computers that hold the data so I can't turn them on.
> b) the UK data archive seems to have decided my login details are no longer
> valid so it won't let me download anything so I have to brace myself to try
> and get readmitted :-(
> I may of course have the wrong user ID/password so I could look it up in my
> email - except that's on an old email system that's mounted on the set of
> computers detailed in point a) above...
> I should have the old data on a backup... somewhere though I'm not sure I
> have the will to go searching just yet. A new surge protector is possibly
> simpler.
> Cheers.
> -----Original Message-----
> From: Steve Tockey [mailto:Steve.Tockey_at_xxxxxx > Sent: 26 May 2015 20:19
> To: Mike Ellims
> Cc: David Crocker; The System Safety List
> Subject: Re: [SystemSafety] Wheel detachment from a moving car
> Mike,
> I don't think you'll ever get a definitive answer. There's no requirement
> for data collection or reporting. Even when it does happen, nobody has to
> ever tell anyone about it. So no way to capture any objective data about it.
> All you will ever get will be anecdotes--unless some law change ends up
> requiring a reporting mechanism.
> -- steve
> ҵ iPad
> wrote:
>> I've been looking for an answer to this since the original email came
>> out but getting a good; but perhaps not definitive answer has been a
>> bit of a slog.
>> First we need to consider that older wheel lugs (e.g. 1940's) are
>> different to the ones currently in use in. Current wheel lugs are a
>> tapered design and so there is no precession, thus having left and
>> right handed nuts on either side of the vehicle body is of no use as there
> is no self tightening action.
>> Talking to various people established the view that on light vehicles
>> at least (Class M1, N1 for instance) if all the lugs are correctly
>> torqued down a wheel won't come off. Indeed the only example I know of
>> where this happened is from 1974 on an Original VW Beetle where a back
>> wheel came off; my guess is that had un-tapered lugs.
>> As to why this is the case is more difficult to answer and I resorted
>> to reading the SAE wheel test standards in the end (not recommended).
>> It all depends on some details of the design involving the interaction
>> between the lug and the wheel which is generally a beveled surface at
>> about 60 degrees which is much easier (i.e. less costly) to machine
>> accurately than say a flat surface.
>> More importantly it seems that the fact that the hole in the wheel
>> into which the lug fits (the nut seat) isn't flat but is rather raised
>> in a truncated cone forming a type of spring washer called a
>> Belleville washer or a coned-disc spring. Applying the correct torque
>> to the lug compresses the spring and locks the lug in position.
>> Conversely if you apply too much torque you can warp the dish and end
>> up with "sub-optimal" brake performance.
>> There are other considerations for wheels on large vehicles and the
>> design differs somewhat and I haven't even tried to dig down into that
>> one in any detail. One important difference however is that on light
>> duty vehicles the lugs are also used to centre the wheel which is why
>> it's important to tighten the bolts across the wheel to prevent the
>> nuts seats from being distorted.
>> Probably not the complete story but I hope this helps.
>> Cheers.
>> ---
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Derek M. Jones           Software analysis
tel: +44 (0)1252 520667
The System Safety Mailing List
Received on Wed May 27 2015 - 00:45:55 CEST

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