[SystemSafety] Wheel detachment from a moving car

[Derek M Jones]

Mike,

The UK Government are getting very good at releasing all sorts of data.
Individual road accident data here:
http://data.gov.uk/dataset/road-accidents-safety-data
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 construx.com]
> 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
>
> 发自我的 iPad
>
>
> On May 26, 2015, at 12:00 PM, "Mike Ellims" <michael.ellims at tesco.net>
> 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  blog:shape-of-code.coding-guidelines.com