Speedo accuracy

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tdiman

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I have a problem, my speedo is constantly reading 3-4mph high, I know this because I have a GPS scamera warning device in my car. I asked my Audi dealer to check this ou & was informed 'its within specification' what the hell is that supposed to mean 'we know its wrong but are not going to fix it' I think most other cars speedos are out also judging by the number of drivers passing scam cams at 27mph, how do you manage to get a ticket when they are supposed to be set at the 110% of the speed limit plus 3mph, this equals 35mph before the scamera flashes which means drivers must be doing at least 38mph indicated.[3]

A2 TDI Sport Leather, climate control, Bose cruise control
 
Most speedos read 3-4 mph more than your are actually travelling (I tested both my A2 and smart and both give 3mph over the actual at all speeds)- they can by up to 10% out, but must always read over - if they read under you have a real problem! As for your speed camera comment you are correct. The reality is if you get a ticket for speeding at the time the photo was taken your speedo was probably reading 10mph over the posted limit - no excuse to be that much over.
 
My other half's Allroad is about 5mph out, reading higher than his Origin B2 gatso spotter (marvellous thing!), and Daveyjp is spot on. There are tolerences set and must always read higher. I have also heard that as you increase speed, the less accurate the speedo becomes? Wonder how accurate the mileage is!

Fi

2002 TDi Sport
 
The higher the speed the less accuracy may not be the case now with electronic systems replacing the good old speedo cable. My A2 was consistent at 3mph over at all speeds up to well in excess of 70mph!
 
We have a gps as well and I took the thing in my wife s A2 to proof to her that the Audi was slower than the clock showed.
128 km an hour was exact 120 km on the GPS.
She did not believe it when I was driving my car and she was in hers. till our portable gps was in her car[25]

Jeff Huisman
car is gonna be changed during this year *(2005) so almost ex a2 owner
GroetenvanJeff.jpg
 
Well in a way I'm glad I am not on my own here, funny how my Honda Accords speedo was spot on all the way to 100mph (not in uk obviously!!!) why can't the make a speedo accurate these days with all the electrotechniwizzythings they put into our cars, wait until the gov decides to compell the fitting of black box 'accident' recorders, you think scamcams are bad, you ain't seen nothing yet.

A2 TDI Sport Leather, climate control, Bose cruise control
 
Legally, in the UK, a speedo can read high but not low so the manufacturers deliberately make them a litle high so those at the bottom of the tolerance band still read slightly high.

Oddly my Accord reads about 5% high - not been over 90 yet! Was recently in a pool Laguna which read 2mph high at 90!

1.4 Petrol Special Edition, Ebony Black, grey leather, heated seats, climate, opensky, five spoke alloys for SWMBO (Replaced a 2002 1.4 Petrol SE) Honda Accord Tourer 2.2 iCDTi for me.
 
Strange how cars differ, even within the same make/model.
Fact: my speedo difference (to TomTom GPS) is not a constant 3-4mph, but more like 8-10%. So it is much closer at low speeds, especially speeds below the 80km/h mark (where the scale goes from 5km/h intervals to 10km/h intervals).

'Pedal to the metal' reads about 185 on the speedo and 172 on GPS. And it won't go over, as if my car has read its own top speed specs ;)


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(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
 
My speedo is 3~4mph optimistic at lower speeds, but is spot on at 80~85. I'd better say I'm not sure of error(s) above that speed! This is by comparison with my Road Angel at a steady speed. This is the only car I've ever owned that's had a speedo which gets more accurate at higher speeds.

My understanding is that GATSOs were set at Limit+10%+2mph, ie. 35, 46 etc. with patrol cars also using these figures as a baseline. They would then look at driver behaviour and road conditions before deciding whether or not to turn on the blue lights.

2002 FSi SE, Ebony Black with Red Nappa Leather, 17" Sport Wheels, 2004 grill, Tinted Security Glass (+Road Angel)
 
mlarner - you are correct ACPO guidelines stipulate posted limit+10%+2mph as a baseline. In reality GATSO are set higher dependent on policing areas and priorities. I would imagine that North Wales used the minimum figure whilst some of the metropolitan forces set them higher.

This picture says it all though:
no_burglars_caught.jpg




Regards - The Foghorn

2001 TDI SE Atantic Blue, Open Sky, 16" 6 spoke alloys, Satellite cloth & space box system. The "Dogs Twitchers"
 
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