Digital Speedo v Actual Speeds

[Ralfi]

Not sure if other states have many of those speed detection gantry's that display speeds of cars travelling in each lane on major highways.

I enquired about them in Victoria, hoping to find some closer to home, but unfortunately they're either a fair distance away, or are being decommissioned.

Reason I ask is I want to find out the MK7 GTI (MY16 manual, just to match my car, if possible) actual speeds are, when the digital speedo is set to 100, 80, 60 & 40km/h.

Haven't been able to work this out as yet, which is frustrating because in my local area, when doing 60km/h, many cars speed past (many of whom are hoons though), so i'm left thinking VW may've been extra cautious with reducing the actual speed as compared to the speedo reading.

Can someone with as similar car to mine, & with the digital speedo confirm what the actual speeds are at 100, 80, 60 & 40km/h? I'd really appreciate it.

[DV52]

^^Ralfi: why not "calibrate" the digital speed reading on your car against a third party SATNAV, or mobile phone SATNAV App?

Don

I've done this on my mk7 (different model to yours) and it's about 6kms/hr lower than actual @ 100 kms/hr

[agentthumb]

I think VW's computer is fairly smart in calculating your speed. It does have an error programmed in, and you can see this with VCDS.

I know it's not what you are asking for, but my 103TSI is negligible difference at 60 (we are talking 60 Displayed speed vs 59 gps) and its bout 3km off at 100 (ie. displayed 100, 97 actual gps)

Here's some reading on how it works: Speedometer fast error adjustment and correction - mk5, mk6 | VW TDI forum, Audi, Porsche, and Chevy Cruze diesel forum


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[Ralfi]

^^Ralfi: why not "calibrate" the digital speed reading on your car against a third party SATNAV, or mobile phone SATNAV App?

Don

I've done this on my mk7 (different model to yours) and it's about 6kms/hr lower than actual @ 100 kms/hr

Thanks Don.

I'm just not sure of the accuracy of mobile phone Navigation App speed detection functions. Have they matured to be reliable enough for what i'm after here? Which one did you use to get your readings?

6km/h sounds like a lot eh. I figured 5km/h at most at that speed, but that does back up my thoughts when travelling at 60km/h (I realise it won't be 6km/h difference at 60km/h).

I think VW's computer is fairly smart in calculating your speed. It does have an error programmed in, and you can see this with VCDS.

I know it's not what you are asking for, but my 103TSI is negligible difference at 60 (we are talking 59 GPS speed vs displayed) and its bout 3km off at 100 (ie. displayed 100, 97 actual)

Here's some reading on how it works: Speedometer fast error adjustment and correction - mk5, mk6 | VW TDI forum, Audi, Porsche, and Chevy Cruze diesel forum

Thanks, agentthumb. Yeah I was thinking 2-3km/h difference at 60km/h would be about it.

Do you have a recommended mobile App to use for speed readings?

Interesting to compare results from two or three Apps.

[agentthumb]

I used Waze and Tomtom. Just make sure you are on a flat straight piece of road


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[DV52]

Ralfi: I did say "about 6kms/hr"!

I'm not sure what level of accuracy you are looking-for, but speed calibration against a fixed measurement device, or against a third party SATNAV for a car traveling on a public road (at any speed) will not be possible at a high standard. For example, an accuracy of 1 km/hr at a base speed of 100 kms/hr (i.e. 1% error) might be difficult to achieve when the test is repeated a number of times IMO.

Don

PS: I used a cheap TomTom SATNAV to get my number

[Hillbilly]

The law states that speedos may read faster than actual speed and may be up to 10% + - 4 fast They may not read slower than actual speed. My two are 6 k fast at 100kph and I check it against the Canbus speed in the secret menu on my RNS510 Have tried several times to correct both cars but despite all my efforts the cars accept the coding but the speedos dont alter.
I now have a HUD that is set to read 101 at a true 100.

[Ralfi]

Ok, Downloaded Waze (which looks like a fantastic App. Google Maps has been my fave App for years, but Waze is right up there).

If only one of them was supported by CarPlay!! (Apple Maps, you suck!).

The speed limit & speedometer features in Waze are great & I just put them to good use around my area, in various speed limit zones.

Here are the Vehicle digital speedo readouts v Waze speed.....

40km/h (Vehicle Speedo): 39km/h (Waze).
50km/h: 48km/h.
60km/h: 58km/h.
80km/h: 77km/h.
100km/h: 97km/h.

To be safe, I won't be worrying about adjusting the speed at below 60km/h, but for 60 & above, I think I can be safe going 2km/h above the vehicle speedo.

[agentthumb]

Ok, Downloaded Waze (which looks like a fantastic App. Google Maps has been my fave App for years, but Waze is right up there).

If only one of them was supported by CarPlay!! (Apple Maps, you suck!).

The speed limit & speedometer features in Waze are great & I just put them to good use around my area, in various speed limit zones.

Here are the Vehicle digital speedo readouts v Waze speed.....

40km/h (Vehicle Speedo): 39km/h (Waze).
50km/h: 48km/h.
60km/h: 58km/h.
80km/h: 77km/h.
100km/h: 97km/h.

To be safe, I won't be worrying about adjusting the speed at below 60km/h, but for 60 & above, I think I can be safe going 2km/h above the vehicle speedo.

Glad you got this sorted. Sounds like you have pretty similar speedo calibration to mine.

I use a general rule of thumb to set my adaptive cruise to 3km/h over the limit at any speed over 80km/h. In 60km/h zones, i'll set it dead on 60 to allow for speed creep on those downhill sections

[Bassik]

There's a speed test screen on my way to work and everyday I drive past it I see my speedo at around 40km (school zone) and the speedo screen thing is always around 36-37kms... it goes up as I drive faster but at around 30kms it's nearly spot on, give or take 1km/p.