Speedo vs satnav.

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Misery
Posts: 6
Joined: Sun Jun 10, 2018 9:36 am
Location: Bedfordshire

Speedo vs satnav.

Post by Misery » Sun Jun 10, 2018 9:44 am

Morning all,

Driving 1.4 corsa excite so hopefully somebody else with the same can confirm for me.

Speedo out by about 3-4 mph? I’ll set cruise control to 70 and sat nav reads about 66-67

Or going through a 30 where it shows your speed on those signs. Sign will read about 27 when cruise is set at 30.

Thanks
Previous Corsa 1.2 54 plate

Now Corsa Eco flex excite 1.4 15 plate


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DarrenKC53
Posts: 88
Joined: Wed Oct 05, 2016 6:27 pm

Re: Speedo vs satnav.

Post by DarrenKC53 » Sun Jun 10, 2018 10:33 am

Yes, mine is out by the same when compared with video footage on my dash cam (GPS set).
The law for car speedometers in the UK
The UK law is based on the EU standard, with some minor changes. A speedo must never show less than the actual speed, and must never show more than 110% of actual speed + 6.25mph. So if your true speed is 40mph, your speedo could legally be reading up to 50.25mph but never less than 40mph. Or to put it another way, if your speedo is reading 50mph, you won’t be doing more than 50mph but it’s possible you might actually only be travelling at 40mph.

To ensure that they comply with the law and make sure that their speedometers are never showing less than true speed under any foreseeable circumstances, car manufacturers will normally deliberately calibrate their speedos to read ‘high’ by a certain amount. As your satnav is not the designated device by which a car’s speed is measured, it does not need to incorporate any fudge factoring.
https://www.thecarexpert.co.uk/how-accu ... eedometer/


TheGeorge
Posts: 33
Joined: Tue Apr 25, 2017 6:26 am

Re: Speedo vs satnav.

Post by TheGeorge » Sun Jun 10, 2018 10:43 am

Satnav is lower than speedo by about 2.5 mph (4 km/h) as well on mine.
Corsa E - 1.4T
MY 2016


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srihaggis
Posts: 376
Joined: Tue Feb 16, 2016 11:52 pm

Re: Speedo vs satnav.

Post by srihaggis » Sun Jun 10, 2018 5:29 pm

Mine is the same. I do find if i'm on the motorway doing 73-74 according to car speedo (where satnav says it is 70mph), it really does hammer the fuel comsumption, so I generally stick to the car speedo and use the higher values to claw time back if I need to!
MY16 1.4T Energy 5 door Royal Blue, Panoramic Glass Roof & Park Assist, Intellink 4.0.
MY16 1.4 Auto Energy 5 door Persial Blue, OnStar & Intellilink 4.0.


Misery
Posts: 6
Joined: Sun Jun 10, 2018 9:36 am
Location: Bedfordshire

Re: Speedo vs satnav.

Post by Misery » Sun Jun 10, 2018 7:03 pm

I really only ask because I don’t want to be done for speeding,

I understand the whole 10% + 2 but sometimes for example on a bypass will set cruise st around 73 which then reads on satnav at 70
Previous Corsa 1.2 54 plate

Now Corsa Eco flex excite 1.4 15 plate


Rickardo
Posts: 83
Joined: Thu Jan 26, 2017 1:23 pm

Re: Speedo vs satnav.

Post by Rickardo » Mon Jun 11, 2018 12:44 pm

Sat Nav is accurate as using technology to pin point your location and speed

Your speedo is not


mattb_srivx
Posts: 384
Joined: Sun Nov 27, 2016 6:24 pm

Re: Speedo vs satnav.

Post by mattb_srivx » Wed Jun 13, 2018 7:59 pm

Every car I've ever owned has always under read on the speedo, even the digital style ones! Not sure if this is by design but it's not uncommon really.
Corsa SRi-VXLine 1.4T


baloki
Posts: 13
Joined: Sun Mar 12, 2017 7:18 pm

Re: Speedo vs satnav.

Post by baloki » Thu Jun 14, 2018 12:42 pm

Misery wrote:
Sun Jun 10, 2018 7:03 pm
I really only ask because I don’t want to be done for speeding,

I understand the whole 10% + 2 but sometimes for example on a bypass will set cruise st around 73 which then reads on satnav at 70
I’d say if you’re having to do the math to figure out if you’re speeding, you’re probably speeding.


Susan44
Posts: 280
Joined: Tue Jan 05, 2016 12:33 pm

Re: Speedo vs satnav.

Post by Susan44 » Fri Jun 15, 2018 8:29 am

If you rely on the speedo you are safe by 10%.
If you rely on the satnav then part of your safety buffer is gone.
The remaining 10%+2 is an ACPO recommendation and not law. The new uk police commissioners can now overrule it if they get short of cash.
1.4 Auto SE. Intellilink R3.0 software version 109.0-39112275 :geek:


Rickardo
Posts: 83
Joined: Thu Jan 26, 2017 1:23 pm

Re: Speedo vs satnav.

Post by Rickardo » Fri Jun 15, 2018 10:17 am

Susan44 wrote:
Fri Jun 15, 2018 8:29 am

If you rely on the satnav then part of your safety buffer is gone.
This is where cruise control comes in

If you set it to Sat Nav speed as i do particularly in road works with variable speed limit camera's you can't go wrong


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