Speedo calibration

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Water Hound
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Speedo calibration

Post by Water Hound » Fri Aug 03, 2018 7:44 pm

Anybody know how to recalibrate a speedo? The 2004 C4S is off by 9km/h (5.5mph) and is driving me crazy. Starts immediately by jumping straight to 10km/h and is consistently wrong at any speed, same amount. The odometer reading is correct and trip meter is also correct for distance.

Short drive to drive me crazy I suppose.
2004 C2 Cabriolet, Midnight Blue/Savannah Beige
2004 C4S Coupe, Atlas Grey/Black

wyovino
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Re: Speedo calibration

Post by wyovino » Fri Aug 03, 2018 8:49 pm

The speedometer should be off by about 3 mph by design. 5.5 mph sounds high. There is a built-in offset to adhere to EU regulations to over-report the speed. You can check the actual speed via a WiFi or Bluetooth ODBII reader and a mobile app.

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gnat
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Re: Speedo calibration

Post by gnat » Fri Aug 03, 2018 9:21 pm

Actually 5.5 is "within spec". Has to be more than 10mph off before dealers will do anything about it.

The core of the issue as I understand it is that the MFG can get some pretty hefty fines if their speedo under reports so they over report just to be safe regardless of any reasonable wheel/tire combinations the owner might put on the car.

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Water Hound
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Re: Speedo calibration

Post by Water Hound » Fri Aug 03, 2018 9:34 pm

Same issue with the cabriolet at 4km off and no issues with this small discrepancy. With the 4S at 9km/h it's a pain in the ass though especially at parks and school zones. Have checked speed with gps, radar guns and confirmed correct odometer reading on a fixed course with mileage markers.
2004 C2 Cabriolet, Midnight Blue/Savannah Beige
2004 C4S Coupe, Atlas Grey/Black

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Machu009
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Re: Speedo calibration

Post by Machu009 » Mon Aug 06, 2018 6:05 am

My car is over as well 02 C4S. What is interesting is that the trip computer on the dash shows one mileage and the computer on the PCM2 unit shows another. Just did a long drive and those were a couple percent off from one another. I’m wondering if the sumitumos are slightly smaller circumference then the “approved” tires (guess I can just look it up on tirerack).

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b3freak
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Re: Speedo calibration

Post by b3freak » Mon Aug 06, 2018 7:13 am

wyovino wrote:
Fri Aug 03, 2018 8:49 pm
The speedometer should be off by about 3 mph by design. 5.5 mph sounds high. There is a built-in offset to adhere to EU regulations to over-report the speed. You can check the actual speed via a WiFi or Bluetooth ODBII reader and a mobile app.
Yep... both of my Carreras were about 4-5 mph over on the speedo.

quote AIRPLANE!

I guess it's better OVER than UNDER, Roger Under? Over! Huh?!


:lol:
2002 Porsche 996 Carrera - bare bones basic, but still a blast to drive! Heck, I don't even have PSM on it. Ha!

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32wildbilly
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Re: Speedo calibration

Post by 32wildbilly » Mon Aug 06, 2018 7:17 am

b3freak wrote:
Mon Aug 06, 2018 7:13 am
wyovino wrote:
Fri Aug 03, 2018 8:49 pm
The speedometer should be off by about 3 mph by design. 5.5 mph sounds high. There is a built-in offset to adhere to EU regulations to over-report the speed. You can check the actual speed via a WiFi or Bluetooth ODBII reader and a mobile app.
Yep... both of my Carreras were about 4-5 mph over on the speedo.

quote AIRPLANE!

I guess it's better OVER than UNDER, Roger Under? Over! Huh?!


:lol:
...and stop calling me Shirley!

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gnat
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Re: Speedo calibration

Post by gnat » Mon Aug 06, 2018 10:34 am


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32wildbilly
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Re: Speedo calibration

Post by 32wildbilly » Mon Aug 06, 2018 12:22 pm

gnat wrote:
Mon Aug 06, 2018 10:34 am
As long as you aren't this guy...

https://www.bbc.co.uk/news/world-middle-east-45085991
"...but...but...officers it is well known that the speedo in these crappy Lambos are off at least 100 km/h!"

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