Speedometer vs GPS Speed

Hi Everyone,

just got a 1988 928 S4 and noticed the speed on the odometer differs from the spped indicated on my GPS.

Any thoughts as to why?

Although it has after market rims, the tire sizes front/back are correct.

Thx

RJ

I am a big boater the GPS speed should be right it is speed over ground and if you stay the same speed the delay should not matter. I would think the car mechanical one would be wrong. There should not be a big difference. The is a small delay on the GPS so if you are trying to measure ¼ mile or 0 to 60. The GPS will be incorrect. Steady speeds go with the GPS.

thx Denhamfly,

hmm..driving is at normal driving/ highway speeds. The difference is approx 15kms.

Can this be easily fixed?

I would not know why it is off, tires would be my first guess, but you stated that they are the correct size. I will bet you that some of our club members will be able to help you out. That is the number 1 benefit of this club, someone always has the right answer.

RGJ;10232 wrote: thx Denhamfly,


hmm..driving is at normal driving/ highway speeds. The difference is approx 15kms.

Can this be easily fixed?

You can always time it from mile marker to mile maker to double check.

The 928 speedometer almost always reads inaccurately these days. Just one of the many small 928 nuisances. Cleaning your grounds should restore the accuracy of all your gauges though. Always worked for me.