I've been told by many a person that GPS speed is more accurate than a speedometer's speed.

Well last night I noticed that doing *cough* 70 on my speedo resulted in my GPS showing that I was doing 62mph.

Could there be a fault?

GPS is not as accurate as people would have you believe, its a historic figure based on speed distance time, speedo's give an actual figure.

So unless you can hold a speed over a measured distance then GPS like the speedo is just a guide no more than.

All cars over read by a small amount, but never more than about 5mph at any speed.

Well that's what I thought, but with my GT and company car, it is about 5mph out, just with the Cinq it's more which concerned me.

cinq speedos are not the most accurate,hence why we often get 'enthusiastic' performance reports

As long as it's nothing out of the ordinary I'm happy.

I've been through several radar speed signs and GPS speed matched the displayed radar speed. Speedo displayed a few mph more.

Hellcat said:

I've been through several radar speed signs and GPS speed matched the displayed radar speed. Speedo displayed a few mph more.

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As I have said before GPS signals come from US military satellites they control the accuracy and therefore they are not accurate to within 50mm therefore when using speed time distance they are can't be accurate, this is why they are not certified for aviation use for exact position reports like over the North Atlantic where it would be very useful as there is no radar coverage there so have to use time reports which means that there are less planes flying than there could be.

Also at times of conflict the US can move the satellites to give them better coverage of where they want to look at, so signal becomes less strong elsewhere.

Yeah you have said that before. I did take notice honest.

Just saying last time I checked my GPS gave a speed that was verified by a roadside radar speed trap.

Hellcat said:

Yeah you have said that before. I did take notice honest.

Just saying last time I checked my GPS gave a speed that was verified by a roadside radar speed trap.

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LOL

yeah they are a good indication when travelling at a steady speed which is more than likely when you see one of those signs, but when the speed varies it can be a bit slow to update.

I believe speedo's have to over read to ensure that they remain legal, if they under read they are illegal as the drivers could then unwittingly break the law, though this is why there should be a buffer of approx 10% on speeding fines to take into account they could under read but really they do not, this is why some law enforcement areas were wanting to introduce zero tolerance so 31mph in a 30 is a fine/points as they know that the car was probably reading 33+ on the speedo so driver is at fault, seems harsh but there you go.

Cleveland police have been known to prosecute for 31mph in a 30mph zone.

Quite evil since my speedo only just has 5mph markings.

J333EVO said:

I believe speedo's have to over read to ensure that they remain legal, if they under read they are illegal as the drivers could then unwittingly break the law

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That don't make no sense though as you don't have to have a working speedo...

Mine is 10mph over what the gps unitS read. The cinq is made even worse by fitting low profile tyres.