Speed camera query about the different types

Brie

I'm curious about the information I can see when driving....

I can see what my speedometer tells me.  And I can see what those roadside "are you speeding?" thingmes show.  Often there's a big gap.  My speedometer might say I'm doing 33mph in a 30 zone but the "thingmes" say I'm doing 29mph.  Others will say I'm doing 34 when my speedometer claims I'm doing 30.  I'm assuming my VW up speedometer is more consistent than the "thingmes"

The reason I ask is that on my regular route to work (where a lot of people ignore the limits) there is occasionally a van with an official speed camera.  I was zizzing along the other day, my car says I'm doing 33, the "thingme" says 29 so I'm wondering what the official camera might have logged.

I'm not worried about a ticket as I think even if I was correctly doing 33 I am within the variation limit.  If not, ok, I'll pay the fine.  

Just didn't know if anyone had official knowledge on these devices.

Barkin

I'd wager that your car speedo is reading faster than you're actually going. 

TadleyBaggie

Speedometers by law cannot under read, so are often set to over read by 10% or so. So 33 on your speedo is most likely actually 30. Since the threshold for action doesn't even start until 35, I'm confident you will hear nothing further.

Brie

Barkin said:

I'd wager that your car speedo is reading faster than you're actually going. 

Willing to bet the price of a speeding ticket should I get one???  

@TadleyBaggie
I'm liking your confidence.

baser999

Have you fitted different size wheels at any point, that could affect speedo reading.
Just out of interest, if you know there’s the possibility of there being a speed trap along your route, why not just slow down along that stretch, rather than live dangerously and risk a fine. And at the same time, not put other road users at risk through your ‘zizzing along’ 

user1977

Try out Google Maps or one of the other satnavs which give your GPS-derived speed - that's (on the whole) going to be more accurate than your speedo. My last car displayed 33 when actual speed was 30, 74 when 70, etc.

ontheroad1970

user1977 said:

Try out Google Maps or one of the other satnavs which give your GPS-derived speed - that's (on the whole) going to be more accurate than your speedo. My last car displayed 33 when actual speed was 30, 74 when 70, etc.

At least the speedometer will be consistently slightly inaccurate.  I would never rely on a GPS based speed.  

Barkin

Brie said:

Barkin said:

I'd wager that your car speedo is reading faster than you're actually going. 

Willing to bet the price of a speeding ticket should I get one???  

Yup.          

Barkin

ontheroad1970 said:

user1977 said:

Try out Google Maps or one of the other satnavs which give your GPS-derived speed - that's (on the whole) going to be more accurate than your speedo. My last car displayed 33 when actual speed was 30, 74 when 70, etc.

At least the speedometer will be consistently slightly inaccurate.  I would never rely on a GPS based speed.  

While GPS may not be 100% accurate, it'll be more accurate than the car speedo, which will never display a speed slower than you're actually travelling. 

TooManyPoints

I'm not worried about a ticket as I think even if I was correctly doing 33 I am within the variation limit. 

There is no such thing as "the variation limit." What you are probably referring to is the National Police Chiefs' Council's guidance on speeding enforcement. This suggests that speeding should not normally see action under (Limit + 10% + 2mph) - so 35mph in a 30mph limit. The guidance document is here:

Microsoft Word - Speed Enforcement Guidance ACPO_2011 2015_May 2013_Internet (college.police.uk)

you will note that it is guidance, not the law and that it does not replace an individual officer's discretion.

user1977

ontheroad1970 said:

user1977 said:

Try out Google Maps or one of the other satnavs which give your GPS-derived speed - that's (on the whole) going to be more accurate than your speedo. My last car displayed 33 when actual speed was 30, 74 when 70, etc.

At least the speedometer will be consistently slightly inaccurate.  I would never rely on a GPS based speed.  

It's always been consistent whenever I've tried it.