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 ?
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.
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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"97 Boxster" Guards Red, Coppell, TX 36,500 miles
2010 Mazda CX-7 AWD, Turbo, Grand Touring
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.
) 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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