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just a general question chaps.
has anyone calibrated their speedo, towards the top end reading with GPS?
mine's a standard car and is factory-limited to 174mph (plus spec).
if i were to find an empty 3-lane private road, and if the speedo was to read 185, what would the real speed likely to be ?
and is the factory-limiter set at true speed, or is it a "soft" limit, under the "gentleman's agreement"

Hi, against my road angel my beast is 10% out all of the time

mine is spot on till about 100mph, then it starts to lose accuracy.

Anything above fifty mine is about 3mph lower

Mine reads about 5% higher than my Road Angel - so it only really becomes noticeable above about 50MPH.

It will vary with what tyres you have on, level of inflation etc - that's why they put a safety margin on so you won't get caught if you follow the needle.

Dave

I've always wondered about this. In the past speedos with cables were notoriously inaccurate, so they'd over-read by quite a lot to make sure you weren't going faster than they said you were. Today's car can be very accurate. I take note of your point on wheel diams, Dave, and it makes sense.

However, I rent a lot of cars in the USA and they are always spot on, in terms of what the speedo displays compared to the GPS.

It must not be an accident that in Europe the accuracy is less.

Mine over-reads by about 10% until 40mph when the clock shows about 3mph more than GPS. I've nearly been caught out a few times because my other Audis have consistently shown 80mph at a true speed of 72/73mph.

Road angelplus
100mph speedo=97gps
150mph=146mph
180mph=172mph
201gps is waaaaay off the clock.......

Tomtom
150speedo=148
170speedo=170.....= who knows???

My Roadangel and Pioneer Satnav both show exactly the same readings. Could be due to them both using the same GPS antenna on a splitter? If im at 70 on the clock then the GPS states 68. 100 on the clock is 97 on the GPS. If i remember correctly (when i was on Pirrelli's) 189 on the GPS was 195 on the clock.

Im on Vreds now so im not sure of the difference at 189mph GPS but I know its exactly the same at 70 on the 30mm Vreds as it was on the 35mm Pirrellis. Weird bearing in mind there's a 5mm difference.

The tomtoms aren't accurate unless they're locked on to lots of satellites. Not easy in the rs6 - unless you hold it out the window. Anyone want to try that at 200?