:( Yesterday I went on a trip across the country and took my Handheld GPS with me, I loaded up locations and set off. I checked the GPS travelling up the motorway and was shocked to see that I was travelling at 73mph, Shocked because the speedo on the Vrs was telling me I was going along at 80+. Upon investigation the increase got worse at speed here are my findings

Vrs, GPS

80mph, 73mph.

90mph, 82mph.

100mph, 91mph.

And to get a true 100 mph on the GPS the Vrs was telling me I was flying along at nearly 115mph. I know there is always a % of error, but if I get nicked for doing 100mph I want the car to tell me I was doing 100mph.

So the question is. Is this an acceptable false reading or does it need checking?

Cheers

George

George

Those numbers look about right to me, once you get to 100+ the error seems to get much bigger. You can also use the climatronic display to show your speed in kmh this seems more accurate.

IIRC speedos are not allowed to read low - they can only read high (as yours does) and the maximum error is 10% + 1mph i.e 80 could be 80 - 8 -1 = 71mph

Vince

Looks rather similar to the difference on mine. I'd agree with Vince on the permitted error, so nothing to worry about...

Rob.

Manny

How do you get the Climatronic display to do that?

George

Manny

How do you get the Climatronic display to do that?

George

Press Fan Down, Cold and Econ all at the same time. The display should change and the text diagnostic will appear. Then use the Hot button to select channel 16.

To exit just press auto again.

If you follow the octy owners handbook you can switch the display to imperial, this will give temp in Deg F, but also channel 16 will display MPH.

Best solution is increase the rolling radius by nearly 10%.

225/45 R18s?

Press Fan Down' date=' Cold and Econ all at the same time. The display should change and the text diagnostic will appear. Then use the Hot button to select channel 16.

To exit just press auto again.

If you follow the octy owners handbook you can switch the display to imperial, this will give temp in Deg F, but also channel 16 will display MPH.[/quote']

That's Handy, Any idea what the other channels do?

Channel 5 but it's a bit 'fuzzy'.

That's Handy, Any idea what the other channels do?

George

There is a list from a google translation in the FAQ section on my website, check the link in my sig. They are all there just some are not translated.

Best solution is increase the rolling radius by nearly 10%.

225/45 R18s?

That would solve the error on the speedo, BUT you will introduce an error into the milometer which records accurately to start with. You will be putting more mileage on the car quicker.

Manny, I think it will put less mileage since they are less wheel revolutions per given distance.

Robert

Yeah - larger wheels meen speed will show slower than it did and milometer will show less than it did.

My mileometer is accurate to better than 1% when checked against GPS mileage whereas the speedo overreads by up to 10%. This would indicate to me that mileometer and speedo accuracy are not related.

They may not be related directly... but they are certainly both related to the circumference of your wheels. Changing the wheel circumference will effect both.

My mileometer is accurate to better than 1% when checked against GPS mileage whereas the speedo overreads by up to 10%. This would indicate to me that mileometer and speedo accuracy are not related.

So is the average speed trip computer accurate then?

So is the average speed trip computer accurate then?

I think it might be (seems to be on my Fabia TDI at least). My guess is that it works out average speed by measuring the mileage (which seems to be accurate) and dividing by the time taken to do it (which I guess is accurate too). For instance if I travel for an hour, and the trip computer says I've travelled 45 miles, then it will show an average speed of 45 mph.

This is a different way to measure speed to the instantaneous measure of speed which the speedometer is doing.

BTW I've also notice that average consumption seems to drop by a few mpg whenever I get new tyres - I guess because the tyre radious goes up by a few mm.

So is the average speed trip computer accurate then?

I have found that there is usually less than 1mph difference between GPS and computer average speed readings on the 135 mile trips I have been making to and from Yorkshire.

I have found that there is usually less than 1mph difference between GPS and computer average speed readings on the 135 mile trips I have been making to and from Yorkshire.

Yep thought it might have been accurate. It also is accurate in the timing stakes. I once did 50 miles in 50 minutes . Just as well nobody followed me that day!