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Trip computer vs Speedo? What should I believe?

A

ajonesy

New member
Hey All,

So.... I've had my 993 for a week now and there's an 8mph difference between the speed on the trip computer and the speed on the speedo (trip is 8mph faster).

Is this common? Which should I take as the most accurate speed?

Cheers,

Al
 
If you are in a speed limit area then believe the trip.

Porsche speedos do tend to read higher than actual speed, the common figure is 10% over. Try using a Sat Nav with a speed readout on it to give you a better idea of which is the more accurate.
Cheers,
 
Al,
It would seem surprising if the trip computer and the speedo got their speed info from different sources. But I've read somewhere (probably on this forum) that speedo's can be "calibrated" so presumably they can wear too - so get out of adjustment.

Like Fred say, speedo's often read over speed, but maybe your's in under.

Does it vary at different speeds or is it always 8mph out?

Mine's dead on in the 30-40mph range (according to several GPS tests I've done) - and at virtually every speed camera I'm typically trying to travel a little faster than other drivers.[8D]
 
Hmmmm..... Wheels are the turbo 'hollow spokes' and the tyres are Bridgestone SO2's 18". I believe that they were standard on the C2S.

My money is with the trip being the more accurate reading but I'll borrow a TomTom and compare and will let you know.
 
Maurice,
Is there some way to adjust the speedo ("calibate" it) - eg if you change tyre size. (Have to do this for my mountain bike, so I supposed I'd expect it do it for my car!)

But presumably the tyre size is not relevant to the trip/speedo difference?
 
My speedo and computer disagree too. The computer is about 4mph faster at an indicated 30mph and some 6/7 mph faster at an indicated 70mph. I have yet to be flashed at 30mph or 50 mph by relying on the speedo so my guess is that my computer over-reads a bit.

Richard
 
My speedo also over-reads compared with the OBC. I have a Origin B2 GPS jobbie and at 80mph (GPS) the speedo reads 87mph.
 
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