Cruise control
 

My cruise control has been u/s for some time so today I became a Houdini and managed to fix the displaced hall effects switch on the clutch pedal - it's almost invisible but once you've worked out where it is it's a doddle of a quick job. For the past 6 or so months I've also had an upgraded IP screen (fitted by Rick) with the digital speed function activated so now I find when the digital speed is showing the set speed (in this example 50mph) my analogue dial is showing 52-53mph. Just out of curiosity, is the digital readout the definitive speed the old girl is travelling at, is it the analogue figure or is it something else?
I've a 2004 manual KV6 Contemporary SE Hi-line factory supplied with 17" Meteors fitted with 225x45 91V Goodyear Eagle F1 - does this size tyre make any difference to either readout?

If my car is anything to go by then no, the digital speedo is more accurate but it is still wrong.
Sat nav possibly or in my case a Dash cam, seems spot on, never been done for speeding if I go by he speed on my dash cam.

macafee2

Sat nav and dash cam are both using the same base data

On our regular trips to the North East we sit on the M42/M1/M18/A1 for 2-3 hours. The cruise is set to 70 from our Garmin sat nav. The sat nav speed never moves over that time so I'm working on the theory that it's "correct" with plenty of voodoo magic to work out the speed accurately.

Speedo reads about 75 and digital one 72.

I've got the OEM sat. nav. fitted (actually the BMW Mk4 DVD reader/16:9 bord monitor neither of which don't actually affect the GPS function) so how does that (like Garmin) interface with the speed function?

I go by Google Maps to check actual speed against car display. Invariably you can traverse an average speed section, say 50mph at a vehicle displayed 55 without any fear of receiving a speeding ticket.