Using a gps app ,  it looks like the speedo (  on  standard specced tyres / wheels  )   over reads  by about 5 %   

 

 

120  kmh gps =  126 kmh speedo 

 

100 kmh gps =  105  kmh speedo 

 

80 kmh gps =  84 on speedo 

 

60 =  63 

 

50 = 53  

 

just in case anyone wishes to know .

 

 i measured this on straight road/ motorway over a few trips 

 

 

 

 

Sounds about right. Most vehicles are usually about that

& if you fit slightly different tyres (size) as manufactures do, and if tyres wear as they do, that will change possibly, 

as it might if you check again sometime.

http://kouki.co.uk/utilities/visual-tyre-size-calculator

I did some tests also on our pevious Roomster. I found out that even though the speedo overreads, the distance travelled is still correct (with the original tire size). At some point there was also some information about training mode in the radio with the possibility to show the correct speed so the car has the correct speed it just does not show it to the driver.

A setting for 'Driving Instructors' & very useful.

(or something you might not want to share with passengers.)

About 4 years ago I was stopped for speeding 33 in 30 limit and did a speed awareness course instead of a fine and points. At one point the instructor stated that speedometers were deliberately calibrated slightly under the speed shown his example was true speed 28. mph while showing 30 mph. His view was it kept you on the right side of the law which works for mph or kph no matter what the speed limit is. Joe

Exactly.

So when you were stopped for doing 33 mph, was your Speedo showing 35/36 mph?  'Fair cop!'

Exactly.

So when you were stopped for doing 33 mph, was your Speedo showing 35/36 mph?  'Fair cop!'

It was a mobile unit that caught me I had just moved from a little Daewoo to a 1.9 Fabia estate so was still getting used to it. I think it was showing about 35 mph. I thought I had got away with it till the little brown envelope dropped through the door. I soon got used to the skodas cruise control and kept myself on the safe side of any speed limits more or less

Joe

On my SEL I miss not been able to press the clutch to switch off the cruise control

You have to remember as well that GPS is not accurate either, it only samples periodically and the low positional accuracy of potentially 7 meters out or more can lead to false speed readings. For example you could stand perfectly still outside and possibly see a speed reading displayed.

The GPS is perfect for checking out for Cruise Control as you move from one vehicle to another if you are moving it with you, 

or just check out a vehicle for the cruise control and any difference as yo change tyres (size).

ie Average Speed Cameras of which there are lots covering many longer distances in Scotland.

 

I drove 2 different cars yesterday through the same 30 mile section of the A9 with a 70 MPH NSL.

One car can be set on the CC @ 74 & the other @72 mph and the GPS is showing 70mph.

Edited 23 December, 201510 yr by GoneOffskiroottoot

About 4 years ago I was stopped for speeding 33 in 30 limit and did a speed awareness course instead of a fine and points. At one point the instructor stated that speedometers were deliberately calibrated slightly under the speed shown his example was true speed 28. mph while showing 30 mph. His view was it kept you on the right side of the law which works for mph or kph no matter what the speed limit is. Joe

Yeah thats it.

Apart from Police ones. Im sure they have theirs calibrated to the proper speed?

In Suffolk, the Police a short time ago allowed your normal max of 10% speedo error, plus 2mph as the baseline before they give you a ticket. So my lil sis was caught for going at 36mph (actual) in a 30mph limit and received a ticket. Had she been doing 35mph (that would include the 3mph 10% error, plus 2mph) she would have been ok. It varies from force to force so be careful. 

I do think road safety is long over-due a rethink. Slightly off-topic, but only slightly.

All the hardware installed road-side, and in police cars etc, all of it only measures speed. Tickets and fines are issued based only on speed. But speed is not the cause of accidents on our roads. Lack of awareness is the main cause. None of the equipment measures how aware people are behind the wheel.

So, 33 miles an hour in a 30 mile an hour area means nothing if the driver is aware of everything around and paying attention. Perfectly safe. Whereas 20 miles an hour in a 30 miles an hour area can kill, if the driver is looking at a phone, or shouting at children being naughty in the back, or too senile to concentrate...

Edited 6 January, 201610 yr by EdinKent

I do think road safety is long over-due a rethink. Slightly off-topic, but only slightly.

All the hardware installed road-side, and in police cars etc, all of it only measures speed. Tickets and fines are issued based only on speed. But speed is not the cause of accidents on our roads. Lack of awareness is the main cause. None of the equipment measures how aware people are behind the wheel.

So, 33 miles an hour in a 30 mile an hour area means nothing if the driver is aware of everything around and paying attention. Perfectly safe. Whereas 20 miles an hour in a 30 miles an hour area can kill, if the driver is looking at a phone, or shouting at children being naughty in the back, or too senile to concentrate...

Younare totally correct but speed measuring equipment that can generate fines is financially more attractive that BiB in patrol cars. Roadside kit cannot measure awareness. Ergo, awareness is not a major cause of accidents/road fatalities. Yes, I know, very cynical.

Younare totally correct but speed measuring equipment that can generate fines is financially more attractive that BiB in patrol cars. Roadside kit cannot measure awareness. Ergo, awareness is not a major cause of accidents/road fatalities. Yes, I know, very cynical.

Yes,correct about money, correct about statistics based only on one measurement. And yes, very cynical. Hence the requirement to rethink road safety.. It's us road users that can push such a rethink, and when I pass weekly fatalities due to poor awareness, I'd be happy to get off my butt and do something... just needs inspiration about where to start... Mirrorlink, Smartlink, or centre-consol displays generally... perhaps? Make them illegal?? *laughs cynically*

Edited 8 January, 201610 yr by EdinKent

Yes,correct about money, correct about statistics based only on one measurement. And yes, very cynical. Hence the requirement to rethink road safety.. It's us road users that can push such a rethink, and when I pass weekly fatalities due to poor awareness, I'd be happy to get off my butt and do something... just needs inspiration about where to start... Mirrorlink, Smartlink, or centre-consol displays generally... perhaps? Make them illegal?? *laughs cynically*

I think you are right about awareness and the centre console!. I find the Sygic road map requires you to take your eyes off the road to view the map on the centre console. I have gone back to using my old tomtom satnav which is at eye level. It is easier to see the screen at that level and gives a loud audible warning if you go over the speed limit. Joe