One related thing is that my speedo is very accurate in my vrs at 70mph its 2 mph different from gps, my Superb was at least 5mph often more, after all if your speedometer is 10% out so is your mpg readings

 

That doesn't necessarily follow - they can be right or wrong independently of each other.

That doesn't necessarily follow - they can be right or wrong independently of each other.

So where does the odometer get its reading from ?

Why have a vRS and then drive like an eco warrior?

I guess I don't feel the need to drive like a p****, the car isn't about willy waving for me   .  in seriousness, i dont drive it hard but do push on in places, the a roads.  I used to find it really frustrating to catch someone doing 55 ish on nice a roads in good conditions and not be able to pass safely for a while.  That doesnt happen now.

 

Btw, ive found the maxidot very accurate for tank long mpg figures.

Just went and checked mine , car reckons 34.2mpg , actual is 33mpg , pretty close on average

I really dont know why you'd need diesel when the petrol is so economical.

On a steady motorway trip i find it difficult to get below 42mpg and will even hit 52mpg on occasion.

Its a shame traffic exists as that ruins the whole tank to tank reading    

I guess I don't feel the need to drive like a p****, the car isn't about willy waving for me   .  in seriousness, i dont drive it hard but do push on in places, the a roads.  I used to find it really frustrating to catch someone doing 55 ish on nice a roads in good conditions and not be able to pass safely for a while.  That doesnt happen now.

 

+1.

I bought a a vRS with a view to the styling & having an engine with a bit of grunt when its needed.

But I wouldn't have bought it if I didn't expect to get >50mpg fuel ecomony out of it either.

99% of the time I am crusing in a way that the 1.6TDI would be more suited but its nice to have it for the weekends.

So where does the odometer get its reading from ?

 

The vehicle speed reading comes from wheel speed sensors fitted in each wheel & usually takes the average of the driven wheels.

GPS isn't used for vehicle speeds because coverage/accuracy is not the same everywhere & doesn't work e.g. underground.

 

Depending on the country of sale for your vehicle the vehicle speed reading can be intentionally up to 5-10% high.

In the UK & Europe for example it will be about 5% over.

In the US it would read the "real" speed wihout an offset.

etc

SatNavs sometimes have an option to display "real" or "offset" speed for your location/country.

The vehicle speed reading comes from wheel speed sensors fitted in each wheel & usually takes the average of the driven wheels.

GPS isn't used for vehicle speeds because coverage/accuracy is not the same everywhere & doesn't work e.g. underground.

 

Depending on the country of sale for your vehicle the vehicle speed reading can be intentionally up to 5-10% high.

In the UK & Europe for example it will be about 5% over.

In the US it would read the "real" speed wihout an offset.

etc

SatNavs sometimes have an option to display "real" or "offset" speed for your location/country.

 

 

Largely inaccurate post there, GPS has nothing to do with apart from as my own personal method of determining speedometer accuracy

 

There is one speed signal (Not to be confused with ABS wheel speed sensors) usually in the gearbox, it supplies both the speedometer and odometer (and ECU in many cases) , any inaccuracy in the speed signal  will be shown on both, of course there is the unlikely scenario that the speedometer itself is faulty or by the same rational the odometer is faulty and the speedo not , usually one or both will fail totally if this is the case due to the way they are constructed.

 

If the speedometer is out by 5% so is the recorded mileage. If you do a fill to fill mpg check and the speedo accuracy between the two vehicles is different by 5 or 10% so is your mpg data. 

 

Speedometer accuracy is set in EU regulation (EEC Reg 75/443/EEC & ECE Regulation 39 ) this governs the requirements for type approval , in the UK we have Construction and Use regulations which also refers to this legislation, there is no requirement in the UK to ever have a system checked or calibrated beyond TA

 

 

 

ECE Reg 39

 

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:120:0040:0048:EN:PDF

Largely inaccurate post there, GPS has nothing to do with apart from as my own personal method of determining speedometer accuracy

......

 

Dr Zoidbergs comment was that both the speedo & GPS can be inaccurate. I was just agreeing with him.

 

Agreed that you can also measure speed with an gearbox speed sensor but most passenger cars I have worked with don't have this sensor & use speed derived from the wheel speed signals calculated by the ABS module or engine ECU.

 

The speedo & odo for most cars these days are just a digital display, so what you see does not have to be linked.

The speedo can show an "offset" value & the odo can display the real vehicle distance provided both are stored accurately internally.

It doesn't mean that the distance or fuel economy calculation has to also be wrong.

 

As stated in the standard you reference, the calculated speed cannot be lower than the real speed.

But it can be 0.1xSpeed + 4kph higher (which is around 12% tolerance @ 160kph).

 

As stated in the standard you reference, the calculated speed cannot be lower than the real speed.

But it can be 0.1xSpeed + 4kph higher (which is around 12% tolerance @ 160kph).

 

 

GPS is pretty accurate at a stable speed on a flat road with a clear view, certainly accurate enough for checking a speedometer

 

The speedometer could read absolutely anything at 160kph , there is no requirement for them to be tested beyond 120kph

 

http://www.briskoda.net/forums/topic/335265-gearbox-speed-sensor-location-19tdi-90/

Edited 17 April, 201511 yr by Richf