"Bruce" wrote in message

On Sat, 31 Jul 2010 12:36:57 +0100, "Recliner"
wrote:
"Bruce" wrote in message


Oddly enough, however, when I set the digital cruise control, it
doesn't quite agree with the more accurate analogue speedo. In other
words, if I want to do exactly 50mph through motorway road works, a
speedo reading slightly above 50mph is OK, but I need to set the
digital cruise control to something like 55mph to achieve this
precisely (if the traffic is heavy, I don't bother, and just let the
adaptive cruise control keep my speed the same as the cars I'm
following).

When I reach the end of the road works, (if necessary) I change the
target speed on the cruise control to, say, 77 mph to ensure that I
do exactly 70 mph. Again, the ACC slows me down if needed.


That sounds more like 10% over rather than 5%. Please explain?

Yes, the adaptive cruise control needs to be set approximately 10% over
the targeted true speed for some reason. The analogue speedo then shows
a speed about 5% over the true speed. It was a bit disconcerting at
first, but I soon got used to it, and haven't bothered to raise it with
the garage as I doubt that they'd know what I was talking about.