over-reading estimates

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   If it helps, I use GPS in my car - Autoroute 2005 has a handy little GPS correct speed indicator - in MPH or KMH.
On the cruise control, at an indicated 75mph, my proper GPS speed is 69mph.  I think this gives an error margin of 8%.  The rear (driven) tyres are almost new, so the rolling radius is about as big as it's going to get (and hence this will be as accurate as the speedo will be!).
Can you get the extra info on the dash computer?  Test no.8 shows a non corrected speed in KMH - on mine this test is only out by 0.5kmh at 100Kmh, so you might find how much your own speedo over-reads from that (I assume they will all be overreading by differnt amounts!
The maximum a speedo can be out is 10% (although this will probably increase with age/wear etc.) It is only allowed to over-read though, not under!
I believe the Police have now scrapped the 10% plus 2 rule anyway - that way the camera can collect more cash!
The bad news is I have it on good authority that the limitation on a speeding fine being issued is 6 weeks!

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bmw325tds Members Profile Send Private Message Find Members Posts Add to Buddy List Really Senior Member I Joined: 05-February-2005 Status: Offline Points: 361	Posted: 22-April-2005 at 15:56
	If it helps, I use GPS in my car - Autoroute 2005 has a handy little GPS correct speed indicator - in MPH or KMH. On the cruise control, at an indicated 75mph, my proper GPS speed is 69mph. I think this gives an error margin of 8%. The rear (driven) tyres are almost new, so the rolling radius is about as big as it's going to get (and hence this will be as accurate as the speedo will be!). Can you get the extra info on the dash computer? Test no.8 shows a non corrected speed in KMH - on mine this test is only out by 0.5kmh at 100Kmh, so you might find how much your own speedo over-reads from that (I assume they will all be overreading by differnt amounts! The maximum a speedo can be out is 10% (although this will probably increase with age/wear etc.) It is only allowed to over-read though, not under! I believe the Police have now scrapped the 10% plus 2 rule anyway - that way the camera can collect more cash! The bad news is I have it on good authority that the limitation on a speeding fine being issued is 6 weeks!
	Carl Ford Focus 1.8TDdi Estate Ford Focus 1.8TDdi Porsche 944 Turbo BM's gone, but maybe only temporary!

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