speedometer error

[rocklandroger]

I have discovered that when I set the cruise control to 100 kph, the speedo reads 103 and Waze App reads 97! Which of the 3 is the right number? Is there any way to synchronize the Cruise to the speedo?

 

[Steel188]

My UK spec car (2015 no MMCS) does not have a separate speed value when I set the cruise control but as with all speedos (in Europe, Asia and Australia/NZ), they are required to be inaccurate by law.

Using my Garmin SatNav, the following speeds are found

Speedo Sat Nav
50mph 47/47mph
60mph 57mph
70mph 66/67mph
75mph 71/72mph

Needless to say, I use the SatNav speed when setting my cruise control, especially on the motorway at night when I have 300 miles to cover.

 

[MadTechNutter]

My UK spec car (2015 no MMCS) does not have a separate speed value when I set the cruise control but as with all speedos (in Europe, Asia and Australia/NZ), they are required to be inaccurate by law.

Using my Garmin SatNav, the following speeds are found

Speedo Sat Nav
50mph 47/47mph
60mph 57mph
70mph 66/67mph
75mph 71/72mph

Needless to say, I use the SatNav speed when setting my cruise control, especially on the motorway at night when I have 300 miles to cover.

Interesting that it shows a constant +3 km/h deviation, not a relative one like 3%, so this could be a deliberate 'calibrated' setting that may be adjustable with the right service software.

It would be important that the cruise control have the same deviation.
The car's inertia physically can not immediately respond to a sudden downhill slope for example.
At some point you would be likely over-speeding while it tries to correct and could get a ticket from a cop hiding on the down hill slope, where they preferably hide :twisted:
You can NOT use your cruise control as an excuse for speeding !

A margin of 3% would be reasonable thanks to the regen braking with this car.
The speed with cruise control on my old diesel would vary +/-10km/h even on light slopes.

 

[greendwarf]

The car's inertia physically can not immediately respond to a sudden downhill slope for example.

Really? - In my experience, the CC responds to "sudden" downhills faster than I would be able and only "over-speeds" by 1mph.

 

[Steel188]

MadTechNutter
The sppeds given are mph not kph so the varience is larger than you think and I do vary how close to SatNav accurate I travel depending on the terrain. However, here in the UK with a 70mph limit on the motorways (if they're not dug up or jammed solid!) you will not be bothered by the police (or the average speed cameras) if you are travelling at a constant 71 or 72mph.

greendwarf
I agree, especially as I tend to always put the car in B5. I do not find over speeding a problem and on UK motorways and major dual carriageways there is no such thing as a 'sudden' downhill slope anyway

 

[MadTechNutter]

MadTechNutter
The sppeds given are mph not kph so the varience is larger than you think and I do vary how close to SatNav accurate I travel depending on the terrain. However, here in the UK with a 70mph limit on the motorways (if they're not dug up or jammed solid!) you will not be bothered by the police (or the average speed cameras) if you are travelling at a constant 71 or 72mph.

greendwarf
I agree, especially as I tend to always put the car in B5. I do not find over speeding a problem and on UK motorways and major dual carriageways there is no such thing as a 'sudden' downhill slope anyway

Yeah, I got some tricky coastal drops to negotiate where I live, not much over 60m but sudden and short, bit like a roller coaster.
If I am 'a bit' over the speed limit in the bottom I can sometimes get to a top again in B0 barely using the throttle at all.

3mp/h speedo 'error' is quite high.
I definitely have a consistent 3km/h between a SatNav and my speedo.
...err... the velocity indicator, not the budgie smugglers

 

[ThudnBlundr]

Mine speedo ties in quite closely with my ACC setting, but it under-reads consistently by 3mph from 30-70mph, according to Waze and those signs that flash your speed at you as you approach a built-up area.

 

[BIKERMGA]

I think this "over reading" of the speedo is a Japanese thing, and related to legal requirements in that country to show more than you are actually doing. Cars built in North America do not over read.

Strange that the Cruise Control setting is always 3 - 5 kph less than the speedo indication. (2019 model) This makes no sense.

 

[jaapv]

Not just Japanese, "rest of the world" except USA. USA cars overread outside the country as well, to comply.

 

[greendwarf]

Strange that the Cruise Control setting is always 3 - 5 kph less than the speedo indication. (2019 model) This makes no sense.

Interesting - can you "dial in" specific speeds to the cruise control on 2019 model? On my 2014 car you just switch on the cruise control when you reach the desired speed.

 

[jaapv]

And then there is an up-and down switch to regulate the speed - at least on my Dec. 2013 car.

 

[DibbyDibbyDJ]

Strange that the Cruise Control setting is always 3 - 5 kph less than the speedo indication. (2019 model) This makes no sense.

Interesting - can you "dial in" specific speeds to the cruise control on 2019 model? On my 2014 car you just switch on the cruise control when you reach the desired speed.

ACC or Active cruise control

 

[greendwarf]

I thought that just ensured you kept a safe distance when in traffic by adjusting the speed around the set point. How do you input the desired speed to it?

 

[jaapv]

Flip the switch downwards (flicking it upwards will reset the previously chosen speed) when at the desired speed and adjust to taste by the "speed up - speed down" switch. Flicking it will give 1 k(m)ph increments, holding it 5 k(m)ph increments in series. The ACC sets the maximum speed at which the car will follow the car ahead. The distance can be adjusted by the distance push button, which we ill give you a 1, 1.5 or 2 second braking interval. As soon as the car loses the front vehicle it will give you a double beep to warn of the speeding up to maximum set speed after one second. In stop-go traffic it will disengage when the car comes to a full stop (double beep and make sure you hit the brake against creep!* FCM won't work on a creeping car ) Without vehicle in front it will act the same as the basic CC.

*IMO this is a design fault; the car should revert to N in this situation.

 

[greendwarf]

Ah, as I thought - in which case, what is this nonsense about? - "Strange that the Cruise Control setting is always 3 - 5 kph less than the speedo indication. (2019 model) This makes no sense."

Does he just mean that when you activate the CC there is a drop in speed before it takes over - especially if you lift your foot at the same time? I find I can now activate it spot on where I want it - must be your "muscle memory" helping me :lol:

 

[jaapv]

I second your diagnosis: Twitchy Right Foot. :mrgreen: However, I think that he means that the -set- speed readout of the (A)CC differs slightly from the analog speedometer -which it does-

 

[greendwarf]

And like you (if I remember correctly) I only really pay attention to the GPS speed on my SatNav.

 

[jaapv]

Well, nowadays it is the GPS speed displayed in my Flitsmeister app. :lol:
People don't seem to realize that the speedometer does not measure the speed of the car, but the RPM of the wheels, which is related to the road speed, but also to the diameter of the wheel, which in turn is influenced by the state of wear of the tyres and tyre brand. The manufacturer must keep a safety margin to avoid under-indication which would generate fines.

 

[greendwarf]

Is that an app on your 'phone? I stopped using the phone as a SatNav as it got very hot with prolonged continuous use - probably contributed to partial demise after a year. :lol:

 

[ThudnBlundr]

On previous cars I've used a clip on the airvent to mount my phone when using it as a satnav, which had the beneficial side effect of also keeping it cool. I can't use it on the PHEV, though