Ive never had a UK car with an accurate speedo . You have to do 74 on the clock to actually do 70. rear tyres are new .(You are allowed up to 10% over before you get fined in UK)
And so it is in the Jag. I recovered an old Scangauge from my garage and fitted that to show in the main the water temperature but also MPH and although its fed from the OBD it shows an accurate MPH figure. Also jambs easily between the steering wheel and the dash by adjusting the wheel position .
Would not buy one today as the price has rocketed since 2004.
SGII-UM-601.pdf

 

Well, did you check by what % does the speedo differ from what you get via OBD?

 

Reads about 4-5% low. so does that mean that the distance covered is also low ?

 

In the UK no speedometer is allowed to show a speed lower than the actual speed. So if it shows 50mph then by design it will never show anything less than 50 mph. As you say it can show up to +10% (55 mph) hence the odd rules on speed cameras and when they flash as I am sure you know.

I have wondered about the distance as well. On mechanical speedos the answer was yes and I assume the answer is still yes which won't do real mpg any favours.

 

The speedo on my U.S. '06 is a 'Dead-on' as one can read it with a rotary dial, and needle. I back it up with a Garmin GPS and also check it occasionally with radar signs posted by local police.
Maybe the roads in the U.K. are wrong. After all, you all drive on the wrong side of them......

 

On mine the speedo and the OBD both read low compared to GPS. My OBD gauge has a function to set a percentage adjustment for the speed displayed, so I assume this is common enough.



The gauge is set up to show speed in KMH, temp in °C and battery voltage.

 

I assumed the OBD reading would be what's sent to the speedo while the GPS would be separate to the car. I have a speedo app on my phone that agrees with Google maps (surprise) but is about 7% lower than the car.

 

My car also reads higher. Probably 5% higher I think. Not the end of the world as it means I'm never breaking the speed limit. Unless I want to.

 

Mine is off 2 mph at 100 mph actual speed, ie reads 100 when going 98. Info Based on three different iPhone GPS apps.

That small error can be due to tire wear alone.


Z

 

Your display is showing 13 mph average speed. Now that’s a crying’ shame.




Z

 

Its clear that US speedos are built to show the correct speed while UK ones comply with the UK regs and read faster than you are going.
As for the right side of the road its all to do with being right handed and horses. In times of old when you road towards an oncoming horseman, you kept left so that you could if necessary draw your sword and fight him off without leaning across the horse. Its only politics ie George 3 and Napoleon that changed the side of the road you use. Same applies to US wedding etiquette. V UK . changed by politics

 

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