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Ludicrous Speed!
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When I have the analog gauge display up running a datalog, the mile per hour displayed is less than the digital display on the dash, at about a 3% variance. Roughly 1mph slower at 33-35, 2 or so at 45, etc.

Just wonder if GM rigged it that way to encourage people to drive slower, thinking they are going faster than they are... and yes, I may be slightly paranoid, but I have seen the same thing on all my new cars, regardless of manufacturer. Cobra, Expedition, Lightning, Evolution VIII, and even the wife's new Titan all have a slight but measurable overspeed reading. Confirmed with roadside radar etc. Weird to see it verified in a datalogger though...

Only car I had read accurate lately was my MINI Cooper S.
 

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Its quite possible that this is true. I know some motorcycle manufacturers have built in errors on the speedos to read faster than actual for the reason you mentioned
 

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Former Goatherder
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Just about every car I've ever driven was about 3mph off at highway speeds. I'm sure it's done on purpose.
 

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No, the GTO is unique -- there's some funny business going on for sure :secret:

I datalogged the drive in this morning for this sole purpose -- to see what was up with the reported MPH on the cluster.

I set the cruise control at 60 MPH indicated on the cluster (using the needle and the large digital readout).
On EFILive, the reported speed was 57 MPH.
On the GPS, the reported speed was 57.6 MPH.

I'm going to repeat the test on the way home, this time logging km/h to see if its an error in the metric to imperial calculation.. One thing that has me VERY concerned, and could very well be the start of a big class-action suit if it gets out of hand, is the fact we're racking up miles faster than the car is actually being driven. Not by a huge margin, but 36,000 indicated miles is actually 34,200 driven miles..
 
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