speedometers

Any one know tolerances allowed on speedometers between recorded and actual
speed and would sat nav be more accurate

thanks

Steve

 

http://www.justfuckinggoogleit.com/

 

police are supposed to allow 10% + 2mph. so in a 30mph area you could be ok
until 35mph but don't put a lot of faith in it. we have a sign with a speed
checking display (in a local industrial estate) but it never reads the same
for two vehicles so its very hit and miss.

R

 

In

If sat nav uses GPS, it's not going to care how fast your bike thinks it's
going.

 

The mythical 10% + 2mph refers to your actual speed so if your speedo
overreads by 10% you could be ok up to an indicated 38mph
(but don't put any faith in it.)

Calibrate your speedo with sticky tape and a GPS. YKIMS.

 

AIUI the construction & use regulations stipulate that a speedometer may
never under read. A tolerance of 10% or so is allowed for it to over
read. I could of course be completely wrong.

 

A bit of context in your reply is nice, then it is easy to see what
you are on about.

Bollocks. You can't have both, man.

The Association of Chief Police Officers (ACPO) guideline is that
nobody should be done for exceeding the speed limit by less than 10% +
2mph. I believe that roadside cameras are set to this sort of figure.
However, there have been cases reported of drivers being prosecuted
for speeds only just over the posted limit, so draw your own
conclusions.

You would not get away with adding another 10%, though. A vehicle's
speedometer is allowed to over-read by up to 10% (presumably to allow
for manufacturing inaccuracy and possibly tyre wear) but must not
under-read.

 

Wasn't the bike , it was the van Speedo way way out methinks time to have a
chat with Mr PSA

 

Supposed is the wrong word. "Generally" is better - as Pip mentions it
was/is an ACPO suggestion.

 

A speedo which underreads is what the cops allow for.

i.e. speedo underreading by 10%, reads 32, actual speed is 35.

You're not going to get away with 38.

 

If your speedo overreads by 10% and you are doing 38 the speedo would be
reading ~42 n'est pas?

 

And about 30% when you get up to 150

Considering speedos are genernally digital these days, what do you reckon
the formula used is and why do they make it larger the higher the speed?

 

But wouldn't an indicated 38 be at least 34, i.e. 2mph more than the 2
mph allowed by the ACPO guidelines?

Or is my maths letting me down?

 

No, it won't. As you just pointed out, it will be reading 38.5mph for
a real speed of 35 mph.

See above.

 

That isn't an actual road speed of 30mph though, man.

Indeed.

 

But it's very entertaining. Please continue.

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Ah no, my laziness in not reading more of the thread brfore shooting my
mouth off

 

Beav wrote

At last the accurate reply.

My local camera (one of the few genuine roadside safety accessories)
was set to 10%+3 in the early days and is now, according to local
legend, over 50 somewhere now.

 

Checked two cars recently with my GPS -

1997 Vauxhall Omega was exactly 5% out (up the way, obviously) but this
figure stayed the same over a range of speeds (but nothing excessive).

1987 Toyota MR2 was at 64MPH actual when speedo read 70, so out by 8.5%
(didn't get much chance to check over a range of speeds).

My point being don't take the 10% figure as a guide to what every car or
bike will be out by, or you could be in bother!

 

Um, isn't that out by ~9.4% ?

Very true. I got nicked years ago in my company Rover 214. I was holding
the speedo dead on 99 (the copper praised me for my throttle control), but I
was timed at 96.5mph

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