Cruise control set to 40, typically will be 43/44 on the speedo

Just had a camera detector fitted, and the speed reading on this matches the speedo reading

When im in a 40 specs zone, i now have to put the cruise to about 37 to be on 40 on the camera detector and therefore for me not to want throw the beeping thing out the window

My question though is I thought the detector would be on GPS and therefore 'true' speed, and so would tie in with the cruise control setting, yet the cruise is either too fast, or the detector is under reading?

So which is right?!

The car's speedo is right....it is much more accurate than a speed camera detector.

i have had this on my portable satnav too

I have heard a cars speedo is calibrated to within a certain percentage, so might not be totally true. the satnav been GPS should give you a true speed, but i presume would depend on how precise the GPS is in satnavs, as i have also heard that civillian satnav have a certain amount of wobble in them.

You could always do a measured mile, and time it at a set 40mph speed and work out how long it should have taken you to do it a 40 mph as see which is closest.

Jonny Fresh wrote:

The car's speedo is right....it is much more accurate than a speed camera detector.

Your GPS is likely to be your true speed. Both the cruise control and speedo will have a safety factor to a) eliminate litigation in speeding court cases and b) to allow for variables such as tyre wear. Basically they are both driven from the circumference of the tyres. The GPS computes the time a distance is travelled in and therefore has no variables. Gone - 2008 TDV8, Stornoway Grey, ebony, zabrano trim, TV, Tasmods, mudflaps.

My one tell's me i'm doing 70 and the speedo will say 75/76 = 10%? RRS TDV6 Gone but still around
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Jonny Fresh wrote:

The car's speedo is right....it is much more accurate than a speed camera detector.

Well they give 10% for speed cam's so the speeto must be set plus 10% RRS TDV6 Gone but still around
SL55 AMG
760Li Alpina
BMW 535D M Sport
BMW X6 XDrive35D
BMW 320D Coupe M Sport
And A Van For Rex!

WINNER - 2008's Idler Of The Year
WINNER - 2008's Comedian Of The Year
WINNER - 2008's Funniest Incident

I love boobies i love boobies i love boobies cuz i'm a big kid now! (Come on everybody sing with me you know the words!)

I mentioned this to my dealer after getting the car, speedo = 80km/h ACC =82km/h GPS = 78km/h
Now change the wheels to 255/55 19" MT/R and speedo = 80km/h, ACC = 82km/h GPS = 80km/h  Sons of dogs come hither and get flesh
Clan Cameron

Are you get a speed reading off LR GPS? I.E. The Nav screen? 2022 P440e AB

nope, from either a Garmin 45XL GPS or a TomTom Go910, tried both with same result. Sons of dogs come hither and get flesh
Clan Cameron

PauloAmore wrote:

Are you get a speed reading off LR GPS? I.E. The Nav screen?

I don't think you can get the speed off the LR screen. That is why I asked.  2022 P440e AB

PauloAmore wrote:

Jonny Fresh wrote:

The car's speedo is right....it is much more accurate than a speed camera detector.

It's not. GPS is very accurate, to within 0.2 miles per hour. Speedo is likely incorrect.

Legally, the speedo in the UK must not underestimate, but believe it or not, may overestimate speed (I think by as much as 10%).

My ACC when set to 80, runs at around 78 on the speed. Most annoying.

JayMann wrote:

My one tell's me i'm doing 70 and the speedo will say 75/76 = 10%?

Jay - No wonder your 0-62 times are the same as a TDV8  Gone - 2008 TDV8, Stornoway Grey, ebony, zabrano trim, TV, Tasmods, mudflaps.