Slight discrepancy between speedo and C/C

[obcuz]

Maybe this is common.... I now see a slight discrepancy between the indicated 'speedo' speed and the Cruise Control setting, only about 2 MPH -example. set to 30 MPH on cruise control, and car will attain/show 32 MPH on speedo, this seems to have happened over the last year or so, previously this was spot on, any thoughts?
Not a big deal I know, but just wondering if there is a simple fix like a 'reset' procedure.

 

[Louis]

The CC will be more accurate than the Speedo (it is in my case anyway) but I'm not sure if there's a way to reset it. I believe it'll partly come down to tyre Size,wheel Size, tyre pressures etc.

 

[obcuz]

The CC will be more accurate than the Speedo (it is in my case anyway) but I'm not sure if there's a way to reset it. I believe it'll partly come down to tyre Size,wheel Size, tyre pressures etc.

OK Louis' thanks for reply.
If C/C perhaps gets data from ABS rings and speedo from final drive - these two must be mechanically linked anyway, so thinking about it - speedometer mechanism is over-reading, I feel relieved....and can sleep at night knowing I wasn't exceeding the speed limit.:innocent:

But still want to know if it possible to adjust?

 

[McGherkin]

It's intentional. A speedo must overread by law so most manufacturers add a couple of mph offset to the actual speed, which is what the CC shows. Pretty sure you can't change it.

 

[obcuz]

It's intentional. A speedo must overread by law so most manufacturers add a couple of mph offset to the actual speed, which is what the CC shows. Pretty sure you can't change it.

Yeah, thanks, I can see that there could be an in-built margin for error, however, at one time both c/c & speedo were in unison throughout the speed range, so wondered why that changed, mechanically is much the same e.g. wheels/tyres, only springs were changed during the period mentioned and I can't see how that would make any difference

 

[chris blue]

Yes, my speedo out by about 4mph at 100mph, compared to a sat nav (Track confirms)
Never seen a speedo yet that is accurate