After a discussion re speeding at the weekend I wondered how accurate the speed reading is, since it’s linked to cruise how much slower is the actual speed than the reading, looked at the sat nav options for a speed display but can’t find one, an old sat nav I had always displayed speed and it was always lower than the cars display-as expected- just wondering as I travel a road frequented by speed vans and often have the cruise set above the limit as I know they overread. Ta.
Speedo accuracy?
- Thread starter martin j.
- Start date
VAG cars are generally 2-3 mph slower than indicated (GPS vs indicated), despite the ability to calibrate more accurately in this modern digital era.
The car’s ECU logs odometer in addition to the dashboard binnacle, and there is frequently a discrepancy of a few miles. If there is a wild variation this may indicate that the car has been clocked or speedo replaced.
The car’s ECU logs odometer in addition to the dashboard binnacle, and there is frequently a discrepancy of a few miles. If there is a wild variation this may indicate that the car has been clocked or speedo replaced.
At an indicated 70mph my phone GPS says i'm doing 74mph. It's normally off by a % so the faster you go the greater the error - so If I was doing 140! my speedo would be saying 148!
Legally they can over-read by a certain % - something like 10% but speedos aren't allowed at all to under-read so displaying 69 when you're doing 70 for example is illegal.
Legally they can over-read by a certain % - something like 10% but speedos aren't allowed at all to under-read so displaying 69 when you're doing 70 for example is illegal.
I was flat out on a certain private 5 lane road and the speedo said 167 but its limited to 155 i read, iv also had it on my gps i use for rc speed runs which has a refresh rate of 10hz and it was bang on 30 mph on the screen and the gps
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Yes 10% was in my head but I remember Fords being wildly optimistic in the speed displayed, I’ll stick to 74 on the cruise and hope to pass camera vans without worry, people always say they won’t tag you up to 80mph on a dual c but I’d rather not take a chance since Police force advice varies.
Mine is about 4 to 5 km/h less that what the speedo shows, I had installed an AEM obd II gauge that showed the true speed (verified by gps). It was very useful but swapped it with an analog boost gauge for the moment.
If you don’t have access to a stand alone satnav, just use your phone. Waze will do the job, as I expect will Google Maps.
Speedo’s tend to be pretty accurate up to 30mph, but over read a little beyond that. Everyone’s will be slightly different, so your own GPS readings will be your most accurate answer.
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Yes my VAG (Audi) car is up to 2 mph optimistic on the Speedo compared to dash cam GPS speed. Eg. if I set cruise to 72mph shown on the car, the real GPS speed would be 70mph. Also did this 'test' at 50mph, GPS shows 48-49. So I guess if you are to keep to to the speed limits, going 1-2 mph over should be fine.
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