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Old 09-19-2007, 05:03 AM   #1
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Durametric Speed Precision

Hi, I was driving around yesterday with my Durametric plugged-in, I realised that the speed displayed by the durametric was always 8-9 km/h under the value displayed by the car Instruments. Witch one is supposed to be accurate if it's the Car computer value ? Did anyone else saw that ?

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Old 09-19-2007, 06:39 AM   #2
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It is very likely that your speedometer reads high. In the old days, before computers ( ) I used run a measured mile at an indicated 60mph and see how long it took (it should take 1 minute) and the two rarely matched over the years and cars I did the test on. I beleive manufacturers would rather have you think you are going faster than you really are for "safety" reasons. I also think most manufacturers account for a small +/- percentage to take into account the use of different sized tires (like taller snow tires) for instance.
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Old 09-19-2007, 08:10 AM   #3
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A PST2 can also display the speed. It is said this is accurate while the speedometer reads high.
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Old 09-19-2007, 10:23 AM   #4
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When I do a speed check using my GPS the indicated speed on the speedometer is always about 4MPH faster than what the GPS claims. I have also run the car with my wife pacing and her speedo is also about 4-5 MPH slower. I have heard this is common with Porsche vehicles. Maybe the Autobahn set is trying to keep our speeding tickets down! ??
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Old 09-19-2007, 01:46 PM   #5
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Yeah, I've found that when my speedo reads 70 mph, I'm really only going about 67. Interestingly enough, my odometer is very accurate.
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Old 09-19-2007, 03:13 PM   #6
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We just drove our "new" '97 Boxster 3.4 from California to Michigan across I-80 and to while away the hours I timed mile markers when I wasn't driving. Anyhoo, we tuned the cruise to give 45 second miles (+/-0.2 s timing 10 mile sections at a shot; hey, it's a long drive!) with the speedo indicating 83 most of the time and flashed 84 occasionally. The odometer showed a similar error, reading about 4% high.

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Old 09-19-2007, 03:23 PM   #7
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My GPS shows the Boxster is off (faster than actual) by about 2 MPH. My Ford Explorer is off by about 3 MPH.

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