Fitted an Origin B2 last night and I'm a little perplexed about how accurate the speedo on it is compared to the cars speedo and the "real" speed.

Car is an MY00 but has 17"alloys with 215x45 tyres - although I understand that it should be 40mm tyre depth to maintain the correct rolling radius - as a result, I was under the impression that the car is actually going slightly faster than the speedo indicates.

Now with the B2 installed - it always displays lower than the speedo - approx 10% less I calculate. I don't expect any system to be foolproof or 100% accurate but is likely to be the more reliable indication?

 

The difference between 205/50/16 and 215/45/17 is the 17's are approximately 43mm larger, because of this you should have been seeing the speed reading 71.6mph when you are actually going 70mph.
You will not normally get a speedo to be that accurate, they normally read over by a few percent on the standard wheel size, consider the GPS speed on the B2 to be accurate.

Thanks
Tebo

 

The police had set up one of those "Your speed is" radar boards up the road from work the other week, I was suprised as I went past with speedo reading about 43MPH the radr board only put my speed at 38MPH. Did not expect a 5MPH difference at such a low speed?

 

This is normal. Vehicle construction and use regulations require a vehicle speedometer accuracy to be in the range of -0->+10%. The implications are that it must never under-read - for obvious reasons - but may over-read. As the cost of manufacturing a speedometer with -0% error would be very costly they all over-read by a few percent without exception. Even if speed is measured correctly the display may not be accurate, so a speedometer error is allowed

 

The Subaru seems to be very poor for accuracy.......On the 2 cars I have it has invariably overstated the actual speed by 10%......... now a few % would be fine but 10%!! - oh well when I eventually get caught speeding it might be a more pleasant surprise than it used to be - I can also sit at 90mph on the Motorway knowing that I'm doing nearer 80mph

I even had Protech check my km to mph converter as I was annoyed it overstated - I really noticed as I was clocking more mileage than was normal for certain routes......thats how I knew it was overstating.............

 

My car has 215/35/19 wheel/tyres on, its a jap import MY95 WRX with the speedo converted to mph, i was surprise/pleased to find out that with my new road angel gps my speedo was reading 90mph and the road angel was reading 89mph. On a private road of course..!!

Dan

 

Does anybody know how accurate the ECU speed reading is?(newage with SECS monitor)

 

My origin B2 reading is approx 5mph less than the actual speedo reading on my WRX MY03 with standard alloys/tyres.

And a 3mph difference on my BMW.

Funny how I tend to look at my Origin for speed reading nowadays.

 

SAme here on my MY03 WRX, i have a Road Angel and that is showing my speed as actually 4 mpg less than my speedo shows. But most cars are set up like that.
Speedo will always show faster

 

about 7mph @ 90mph ish difference here on my MY00 - the difference gets greater as the speed rises
seen some interesting speedo numbers compared to GPS @ SSo and Pod too