speedo accuracy??

[johnakay]

it is generally believed that car speedos inc bikes have to read over by 10% but no more.
my car inc my bike reads 30 but according to those electronic road sign's tells me I'm doing 30 mph.
doing 40,50,60 and 70 at these speeds will these be 10 % higher on the clock.
with the new speed limits coming to force one has to make sure we dont get caught doing 1 mile over at any given speed limit.

 

[ukracer]

What new speed limits?

 

[knighty]

wait... what new speed limits ?


rules for speedos say they can;t read under, but they can read up to 10% over... means you can;t blame it on your speedo if you get caught speeding... guess manufacturers always make them read a little over as it's safer (for them) that way

 

[johnakay]

just found this.....
http://www.thecarexpert.co.uk/how-accurate-is-a-car-speedometer/

 

[octo0072000]

What new speed limits?

new fines not limits see BBC link

http://www.bbc.co.uk/news/uk-39686894

 

[johnakay]

What new speed limits?

we were allowed 10% plus 2 but that no longer applies from today.

 

[Wozzaaah]

we were allowed 10% plus 2 but that no longer applies from today.

To my knowledge that hasn't applied for some time, people have been penalised for being 1 or 2 mph over before now.

 

[lshigham]

The 10% plus 2 has only ever been advisory from the association of chief police officers, they always could prosecute for 1 mile over.

 

[CompoSimmonite]

I check my vehicles speedo's against SATNAV and they all over read by around 5 mph no matter what speed I'm doing. I would therefore say they are very accurate and needle is set slightly high.

 

[Robotstar5]

The 10% plus 2 has only ever been advisory from the association of chief police officers, they always could prosecute for 1 mile over.

North Wales police were quite strict on speed limits.

 

[skotl]

My 2006 pickup always over-read by 10%, according to the satnav. Now I have bigger tyres on it, that add 10% to the circumference and whaddyaknow - the speedo pretty much exactly matches the satnav!

My Audi has a digital speedometer and that seems to be exactly spot-on from the get-go.

In related news, as octo says it's not new limits but the fines that have changed - non-motorway speeding fines can now go up to £1,000 and motorway fines max at £2,500!

 

[steve_s]

Just another way to extract more money from legal motorists. The ones who flout the law and drive with no tax/insurance etc wont get caught!!!!!!!!!

 

[colnerov]

Hi, Satnav isn't any more accurate than a speedo because it doesn't take into account going up or down hill for example. It's not accepted as a speedo for the purposes of the MOT for instance (and yes I know it's not tested but has to be present). Digital speedo's will be more accurate because they count the revolutions of the drive shaft, provided it's fitted with the tyres it was calibrated for.

Colin

 

[Justme]

No new law just new punishments.

 

[ukracer]

No new law just new punishments.

And new implimentation.

 

[Rannsachair]

Many years ago I recall reading up on the legislation surrounding speedo's for Triumph Motorcycles. The reason for the 10% (I seem to recall a friends Guzzi Lemans that it was way more optimistic than 10%) is to allow for the maximum tyre diameter to minimum tyre diameter (allowing for range of tyres that can be fitted, tolerance on tyre diameter and wear) without exceeding the speed indicated. Like @skoti I run oversize tyres on my Landy and it is almost spot on according to my satnav.

 

[rtbcomp]

Hi, Satnav isn't any more accurate than a speedo because it doesn't take into account going up or down hill for example...

It could do because you can determine altitude from GPS data.

 

[Richard.]

All my speedos have always read slightly under on every vehicle I've owned.
The fines have increased and like the phone thing no doubt the points for speeding will increase one day too.
What ever the money is spent on and whether we like it or not what can we do.
Simple answer really don't exceed the limit.
I'm no goody two shoes mind and I've had a couple of fines/points over the years.

 

[colnerov]

It could do because you can determine altitude from GPS data.

Hi, Yes, the military stuff would do but I think the 'cooking' version generally available doesn't.

Colin

 

[Johnseat]

Old Tachos running the round card could read up to 10% under or over the set check speeds of 40kph and 60kph, that's where the old 10% allowance came from but these old style Tachos are rare and the rules have changed.
New digital Tachos are accurate to with 0.1kph at the given tyre circumference on the calibration day.
Even with a brand new tyre and a fully worn tyre, you are talking less than 0.5kph difference.
Due to the accuracy of new dash boards which are preprogrammed with the tyre size from factory, breaking the limit by 1mph is now easily punishable but it's always been a punishable offence, reason they didn't was proving the speedo accuracy.