Ask a stupid question

[ol' dirty]

Being a bit dense, I would like to know why you can get prosecuted for speeding if there is no calibration requirement for the speedometer on the MOT.
I have wondered this for ages so thought I would ask some guys in the know!

[smeggy]

You're not being dense. I highlighted exactly this not too long ago, I got no satisfactory response!

[jasandjules]

ol' dirty said:

Being a bit dense, I would like to know why you can get prosecuted for speeding if there is no calibration requirement for the speedometer on the MOT.
I have wondered this for ages so thought I would ask some guys in the know!

I guess because it is a strict liability crime.

[glassman]

IMO, an interesting subject.

I asked the question a couple of months ago after noticing that the actual speed I was travelling showed up discernably less on the satnav sys.

[Dwight VanDriver]

Out of my remit but does not type approval of a vehicle have to conform to EEC Regs on speedometer and its performance in that it cannot read more that the actual speed travelled?

Et voila: www.unece.org/trans/main/wp29/wp29regs/39rv1e.doc

dvd

[flemke]

Dwight VanDriver said:

Out of my remit but does not type approval of a vehicle have to conform to EEC Regs on speedometer and its performance in that it cannot read more that the actual speed travelled?

Et voila: www.unece.org/trans/main/wp29/wp29regs/39rv1e.doc

dvd

Yes, although different tyres could effect a meaningful change in accuracy.

[Flat in Fifth]

flemke said:

Dwight VanDriver said:

Out of my remit but does not type approval of a vehicle have to conform to EEC Regs on speedometer and its performance in that it cannot read more that the actual speed travelled?

Et voila: www.unece.org/trans/main/wp29/wp29regs/39rv1e.doc

dvd

Yes, although different tyres could effect a meaningful change in accuracy.

:Removes wooden spoon from kitchen drawer, inserts into pot, stirs furiously:
And on another thread last year I showed results of an investigation which showed that if I fitted the winter tyres recommended by my vehicle manufacturer the speedo would be changed from reading about 1% fast to ~2% slow.

Yet if a vehicle defect is found which causes an incident, say, it is a viable defence if one has maintained the vehicle exactly in accordance with manufacturer's recommendations:

:Puts first wooden spoon away and opens drawer to discover even bigger wooden spoon:
Now speedometers are analogue instruments. Scientific teaching in determining experimental errors tells that the most accurate one can read an analogue instrument to is +/- 0.5*the smallest division on the scale. So if the minor graduations are in increments of 5mph, which is very common and 10mph not unheard of, this means that the most accurate such an instrument can be read is +/-2.5 mph. That is for laboratory conditions taking a careful reading having eliminated parallax errors and so on. What about a quick glance in a vehicle dashboard?

Thus the old rule of thumb which VH questioned, but it was valid and appropriate in my book, that lower limit of enforcement as in prosecution as opposed to word in shell like consisted Limit + 10% + 10 mph.

10% to take care of instrument and reading errors.
10 mph so "they must have known they were OPL"

: puts both wooden spoons in washing up bowl:


edited typos and to consider posting wooden spoons complete with red ribbon to HQ North Wales plod complete with instructions upon where to insert.

Edited by Flat in Fifth on Monday 15th January 09:45

[glassman]

Flat in Fifth said:

:Removes wooden spoon from kitchen drawer, inserts into pot, stirs furiously:
And on another thread last year I showed results of an investigation which showed that if I fitted the winter tyres recommended by my vehicle manufacturer the speedo would be changed from reading about 1% fast to ~2% slow.

Yet if a vehicle defect is found which causes an incident, say, it is a viable defence if one has maintained the vehicle exactly in accordance with manufacturer's recommendations:

:Puts first wooden spoon away and opens drawer to discover even bigger wooden spoon:
Now speedometers are analogue instruments. Scientific teaching in determining experimental errors tells that the most accurate one can read an analogue instrument to is +/- 0.5*the smallest division on the scale. So if the minor graduations are in increments of 5mph, which is very common and 10mph not unheard of, this means that the most accurate such an instrument can be read is +/-2.5 mph. That is for laboratory conditions taking a careful reading having eliminated parallax errors and so on. What about a quick glance in a vehicle dashboard?

Thus the old rule of thumb which VH questioned, but it was valid and appropriate in my book, that lower limit of enforcement as in prosecution as opposed to word in shell like consisted Limit + 10% + 10 mph.

10% to take care of instrument and reading errors.
10 mph so "they must have known they were OPL"

: puts both wooden spoons in washing up bowl:


edited typos and to consider posting wooden spoons complete with red ribbon to HQ North Wales plod complete with instructions upon where to insert.

Edited by Flat in Fifth on Monday 15th January 09:45

Gulp

But a sure and for that.

[fangio]

Dwight VanDriver said:

Out of my remit but does not type approval of a vehicle have to conform to EEC Regs on speedometer and its performance in that it cannot read more that the actual speed travelled?

Et voila: www.unece.org/trans/main/wp29/wp29regs/39rv1e.doc

dvd

I think you'll find somewhere that it can't read LESS than actual speed. If my old memory serves me right, the tolerance is not more than 10% over @ 30mph.

[fragile_al]

I have not had a working speedo for over 2 years, and i've flown through both MOT's- it's not illegal, it's just not an excuse if you get caught!

[blindswelledrat]

ol' dirty said:

Being a bit dense, I would like to know why you can get prosecuted for speeding if there is no calibration requirement for the speedometer on the MOT.
I have wondered this for ages so thought I would ask some guys in the know!

The reason that you can be prosecuted is simply that if you couldn't then people could simply fit dodgy speedo and have a complete defence for any kind of speed. This is why, as JasandJul mentioned, it is a strict liability crime.

As long as Police use common sense (which I know they don't always) combined with court taking into consideration any dodgy speedos (which I assume they would if you could prove it) then it is a workable system really!

[glassman]

Doesn't this suggest that there actually may be reason to dispute some speeding allegations, therefore, for there to be a call for speedos to be callibrated at [x] intervals?

[Timberwolf]

My thoughts -

The crime is travelling at greater than the speed limit.
The speedometer is a driving aid that helps you to avoid that.

(And going under a speed camera in a car without a speedometer is an interesting experience, particularly all the occupants suddenly going very quiet...)

Or am I just over-simplifying?

Now, question, what happens when a cyclist breaks a 20 or 30 urban limit? Or is that covered under furious cycling and nothing to do with laws that govern us as car/motorcyle users?

[andmole]

Flat in Fifth said:

edited typos and to consider posting wooden spoons complete with red ribbon to HQ North Wales plod complete with instructions upon where to insert.

Edited by Flat in Fifth on Monday 15th January 09:45

Insertion sideways I presume?