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 ?

Thanks

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.

A PST2 can also display the speed. It is said this is accurate while the speedometer reads high.

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! ??

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.

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.

Eric

My GPS shows the Boxster is off (faster than actual) by about 2 MPH. My Ford Explorer is off by about 3 MPH.