Speedo accuracy

[NowGottaIbizaMk5]

Happy Christmas!

According to our SatNav our lil 1.2s Ibiza is doing 67 mph when cruising at a steady indicated 70mph

Could this be due to tyre wear - having done 15k miles and so change in wheel diameter or is it just a feature of the Ibiza???

 

[DEAN0]

Happy Christmas!

According to our SatNav our lil 1.2s Ibiza is doing 67 mph when cruising at a steady indicated 70mph

Could this be due to tyre wear - having done 15k miles and so change in wheel diameter or is it just a feature of the Ibiza???

Part of it will be tyre wear - the main part is the construction rules that say the speedo must show equal or slightly higher than the car is actually doing.

Speedos can be up to 5% over reading but NEVER under reading.

 

[byerss]

Normal in most cars they are never 100% compared to satnavs. My mentor told me a few year ago it's deliberate at factory's but I don't know how much truth is in that but every car I've been in has been out so far so.


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[CraigFrTsi]

That's why police and speed cameras have a 5% leeway as stated the speedo always read less than what your actually doing! digital speedos are meant to be more accurate(somehow) I use torque app on my phone and with gps speedo I could be doing 30 but it reads 27.

 

[DEAN0]

That's why police and speed cameras have a 5% leeway as stated the speedo always read less than what your actually doing! digital speedos are meant to be more accurate(somehow) I use torque app on my phone and with gps speedo I could be doing 30 but it reads 27.

The speedo should always read MORE than you are actually doing.

The leeway that the police have is to do with the accuracy of the equipment they use.

Unless different wheels/tyres/gearing has been fitted to the car - I have never known a speedo to read LESS than a GPS says you are going

 

[CraigFrTsi]

Sorry meant to say reads more, had one to many to drink and got it wrong way round lol

 

[byerss]

Aye it can't read low it's set high so you can't sue manufactures for speeding


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[DEAN0]

had one to many to drink and got it wrong way round lol

I should be doing the same but i'm going to bag me a reindeer if one lands on the front lawn tonight - haha

 

[NowGottaIbizaMk5]

Thanks for replies.
Does seem useful that it reads 70 but we are doing less.
Hypothetically 75 readout could well be 72 according to the SatNav ...

Our earlier - Jan 2000 - Ibiza poss read wrong too BUT we didn't have SatNav in those days and trusted the readout ;-)

 

[Dougster]

My GPS reads 60mph when speedo says 70!!

 

[Nath.]

As above, I have never seen a car speedo read the same as a satnav, always read over.

I have found that tyre wear makes a small difference.

 

[ALAN H]

Satnav reading will be accurate and car reading will be higher.

 

[Nath.]

Satnav reading will be accurate

Only if you're on the flat and straight.