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Jam911
Albert Park


Joined: 31 Oct 2010
Posts: 1507



PostPosted: Wed Apr 24, 2019 7:23 pm    Post subject: Speedo Accuracy and Speed Cameras Reply with quote

So how accurate are our Porsche speedos and how fast can we go without prosecution...

https://www.autoexpress.co.uk/car-news/106674/uk-speed-camera-tolerances-revealed-is-your-cars-speedo-accurate

Discuss...
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Current '07 997 C4S
Ex '99 2.5 Boxster
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16540
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Wed Apr 24, 2019 7:31 pm    Post subject: Reply with quote

It's not just down to your speedo. Depends on rolling radius of your tyres. If you want a more accurate measure, use satellites.

You can go as fast as you want without prosecution.......the trick is not to get caught Wink
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2000 Manual 996 C4 Arctic Silver Convertible


 
  
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systech1
Silverstone


Joined: 10 Jul 2016
Posts: 132
Location: Adelaide, South Australia


PostPosted: Thu Apr 25, 2019 1:39 am    Post subject: Reply with quote

If want to know your actual speed, suggest you use Waze or a similar app which shows GPS speed. Typically the speedo is a few % optimistic on speed to account for the full range of tyre wear etc. without showing speed which is less than your actual speed.
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Long time Porsche fan. Previous cars include 911T 2.2, 911E 2.2, Carrera 3.0, 986 Boxster S. Current car is 997.2S Manual (with PSE, H&S Backbox bypass, Sports Chrono, SSK, DSC PASM controller, Carrera Sports wheels, Ducktail/Diffuser and splitter, Sport Design steering wheel etc.)
 
  
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MaxA
Albert Park


Joined: 11 Oct 2015
Posts: 1566
Location: Helsinki


PostPosted: Thu Apr 25, 2019 8:00 am    Post subject: Reply with quote

We have a lot of active speed measurement signs over here to help people understand their speed: my Porsche over-reads quite significantly (even on part worn tyres with 5mm of tread). You really need to use a GPS to see true speed (on the flat).
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997.2 Carrera4S: white over blue, driven and tracked, seldom clean.
 
  
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bakerboy4s
Spa-Francorchamps


Joined: 06 Jun 2015
Posts: 258
Location: Staffordshire


PostPosted: Thu Apr 25, 2019 8:17 am    Post subject: Reply with quote

Not sure about the Porsche speedo , my company supplied work bus reads about 2-3 mph above a gps reading, difference increases as speed does.
 
  
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rabbitstew
Hockenheim


Joined: 21 Aug 2015
Posts: 707



PostPosted: Thu Apr 25, 2019 8:27 am    Post subject: Reply with quote

I was quite impressed with my porsche speedo. I use Waze for every journey and that has the GPS speedo on, and my porsche speedo is pretty much spot on. Once you get over 50mph its about 1 or 2 mph over actual speed.

Comparing that to the wifes Mini, that says you are doing 85mph when you are really doing 78mph!
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2008 997.1 Turbo Manual - 585whp thanks to do88 & 9e
 
  
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FZP
Estoril


Joined: 18 Jan 2015
Posts: 3554
Location: Cheshire


PostPosted: Thu Apr 25, 2019 9:51 am    Post subject: Reply with quote

You must also factor in grandient with GPS as it doesn't compensate. I've had GPS read even slower than normal on a steep hill when set with cruise control. It caught back up on the flat.
Much in the same way when you go through a tunnel, the GPS will assume you last speed as constant and then readjust when you pop out the other side.
Nothing is going to be perfect
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997.2 Carrera 2S GT Silver/Cocoa.
 
  
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Norfolk & Idea
Albert Park


Joined: 15 Jan 2016
Posts: 1541
Location: South Yorkshire


PostPosted: Thu Apr 25, 2019 10:21 am    Post subject: Reply with quote

Porsche are German. Their speedometers are pretty close.

I was beam timed at 196mph on a runway (still climbing). My speedo was reading exactly 200mph. So that’s 2% over actual. I think my Ducati is ~8%
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2012 997.2 Turbo Basalt Black. Bit of a 9E ing.
2008 Ducati 1098R (Track)
2016 Macan GTS
2019 Vito119 CDI Sport- Household Star!
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MaxA
Albert Park


Joined: 11 Oct 2015
Posts: 1566
Location: Helsinki


PostPosted: Thu Apr 25, 2019 10:53 am    Post subject: Reply with quote

The most accurate speedo I've ever experienced is the Land Rover Discovery3. The 9972 speedo over reads, and the speedo reads more than the kph display on a Scanguage plugged into the ECU.
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997.2 Carrera4S: white over blue, driven and tracked, seldom clean.
 
  
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Ian Perry
Spa-Francorchamps


Joined: 04 Sep 2010
Posts: 273


2004 Porsche 997 Carrera 2S

PostPosted: Thu Apr 25, 2019 11:55 am    Post subject: Reply with quote

The only car I've ever owned with an accurate speedo was my 997 it was spot on .Wife's BMW X5 is 10% over not checked my M2 .
My Noble M12 is also slightly optimistic but not by much.
 
  
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resigner
Suzuka


Joined: 19 Dec 2013
Posts: 1225



PostPosted: Thu Apr 25, 2019 3:39 pm    Post subject: Reply with quote

was always told there was a 1% plus 3 rule, but a quick google says it's actually 10% plus 2mph, and it's not law, its a rule, so might not be used.

So, 70mph limit, 79mph should be ok. But isn't law. Think there have just been new laws passed which mean you can get done for being 1mph over the limit, but that is ridiculous......
 
  
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icekay
Newbie


Joined: 03 Mar 2018
Posts: 38
Location: East London


PostPosted: Thu Apr 25, 2019 6:09 pm    Post subject: Reply with quote

In my 997 (and the mk2 Megane RS I had before), plugging in an OBD reader to an app such as Torque will give a reading directly from the ECU which is lower than the digital speedo by about 3mph, pretty much bang on with my GPS readings.

It seems the ECU is calibrated accurately, but you're given a bit of slack on the car reading. Many people theorise that it's better to err on the side of caution hence why speedos tend to read less than your real speed.
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Porkaholic
Spa-Francorchamps


Joined: 11 Jan 2009
Posts: 288
Location: Cornwall

2009 Porsche 997 Carrera 4S

PostPosted: Sat Apr 27, 2019 5:39 pm    Post subject: Reply with quote

My Border Terrier is calibrated to 70 m.p.h. I discovered today. Top down
as soon as you hit 70 she started complaining, ears flapping about too much I think, worked everytime no need to look at speedo.
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2009 997.2 4S manual cab, light mods
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The return of Marty Wild
Kyalami


Joined: 04 Nov 2016
Posts: 1776



PostPosted: Sat Apr 27, 2019 5:54 pm    Post subject: Reply with quote

My Cayman is the closest I’ve seen out of all of my cars I have owned. 70 is only 1 or 2mph out.
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