I've found that compared to my Road angel 2, the speedo on my MY03 wagon (standard wheels tyres etc) is reading 10% over, ie when it shows 70mph the road angel shows 63mph . I guess that the road angel is accurate as it uses gps ,and I understand that most speedo's show over by a small amount but does this sound a bit over the top , or is this normal on the new age cars ?

Thanks in advance

Dave

 

I get a difference of approx 5pm at 100 mph (speedo at 100, GPS at 95), so yours is worse than I've found. However I noticed a 5mph difference between by old Origin Blue i (almost 10% lower than my speedo) and my newer Origin B2 which the manufacturer couldn't explain. So I wouldn't always rely on GPS.

 

I've found my GPS device shows around 75 and the speedo 80 ish.

Speedo's always read over, GPS is more accurate.

 

10% iswhat manufacturers aim for so your's is within limits. Having comared the speeds on my Tomtom with my Origin b2, they are both pretty much identical. But when I compared my 1994 Rover 214 with my 1997 Porsche 993, the Rover had a far more accurate speedo (at GPS 80mph, the Rover read 78, the Porsche 74). Just goes to show that technology isn't always perfect in expensive cars...

 

My MY02 WRX is 4mph over according to my Snooper S6-R.

Mac.

 

Thanks for the replies, so it looks like mine is at the top end of the range , if so does that mean that the ,odometer will be showing the car has done 10% more miles than it really has ??

 

The funny thing about speedo accuracy is when you plug in the diagnostics computer into the engine ECU, and go for a drive reading the live data. You can on most cars access the speed of the car (usually in kph though ). Which is almost always at least 5kph below what the speedo says. So teh car knows the true speed it is travelling at, but tells you your going faster "just to be safe"

Bit like the petrol guage - most cars will go for miles and miles with the guage reading empty.
Also engine temp, some cars will read normal, and when the engine temp climbs only slighty by a few degrees, the guage will zoom up into the red, making you think the engine is in meltdown, when its only 5 degrees above the norm.

 

Legal tolerance is -0% -0MPH, +10% +2MPH, so at 30, anything between 30 and 35 is ok, and at 100, anything between 100 and 112 is ok.

Fundamentally, the speedo is not allowed to under read. So with worn tyres at their lower pressure limits, the speedo must be in spec. As a result, a car with new tyres at their upper pressure limit will be at the top end of the accuracy range. Most car manufacturers calibrate their speedos to be around 5-7% over with new tyres at nominal pressures.

The legal accuracy range used to have to take into account the accuracy of the mechanical, cable driven guage as well, but most modern cars use an electronic speed sensor (usually in the gearbox), and a stepper motor for the gauge, so this part of the system is usually pretty accurate these days.

 

Thanks chaps


Dave

 

Bike rather than car, but still relevant I guess. I was two-up on my mate's Pan-European the other week. Looking over his shoulder (a bit difficult with the wind blast) his speedo was reading 100mph and the GPS (Garmin) 92. At an indicated 74 it said 67.5mph.

 

I also thought that this is down to the "consumer" GPS, compared to the real deal that the Military get... something about the amount of feedback per second to the system.....

Dan

 

So it sounds like I shouldn't rely on the GPS too much either then I guess it's a case of take an average between the two

 

GPS is very accurate at constant speed, it doesnt matter which application its under, be it consumer or military.

 

Testing my 05 wrx using a RA2 I got 56mph at an indicated 60 and 94mph at 100 ~ 6% over read.