Speedo inaccurate.

[Acko1991]

After conducting a rather long trip....

and constantly going the same speed and using my GPS....I have noticed that my speedo is out by about 8 km/h

I think that is rather poor for a brand new car.


I wondered if this is standard or should i go get it checked out.

when i was travelling 113km/h it said i was going 121 km/h

wonder what people think.

[Diesel_vert]

After conducting a rather long trip....

and constantly going the same speed and using my GPS....I have noticed that my speedo is out by about 8 km/h

I think that is rather poor for a brand new car.


I wondered if this is standard or should i go get it checked out.

when i was travelling 113km/h it said i was going 121 km/h

wonder what people think.

EU regulations state that the speedometer shall never underestimate a vehicle's true speed.

There is nothing wrong with your car.

[danntsi77]

think the australian design rules from what ive herd allow upto 10% margin of error. alot of manufacturers will mostly show a slower speed on your speedo than what you might actually be doing. helps in not getting speeding tickets etc...........

cause of this when im on the motorway doing an indicated 110kph on my speedo i know im actually doing 103kph.......i have tested this with my gps before.....

If you also increase or decrease wheel sizes this can have an effect as well. larger wheels in turn will decrease this error in the reading.

[team_v]

This has been covered numerous times before in every other section of the forum.

ADR's state a 10% margin of error to account for tyre wear and air pressures etc.
This can be overcome by increaing the rolling diameter of your wheel/tyre combo or by ignoring it and doing the speed limit on your speedo and therefore not getting any speeding fines as you are under the limit

[Ryan_R]

Or work out how much the car is out by and compensate. Test the difference at various speeds as it will probably be out by 8%, not 8kph.

i.e. for me:
60kph true = 64kph indicated (MDI)
70 = 75
80 = 86
90 = 97
100 = 108
110 = 119

Each car is different though to be sure to test (also test against advisory speed radars if there are any nearby).


Of course you could argue that when travelling at 140kph the speedo is out by more than 10%, but I don't think anyone will listen to your complaint.

[ATYPIC]

Test the difference at various speeds as it will probably be out by 8%, not 8kph.

i.e. for me:
60kph true = 64kph indicated (MDI)
70 = 75
80 = 86
90 = 97
100 = 108
110 = 119

I had a chuckle...yes its 8%...but still had to chuckle.

[bigfoot]

have you changed wheels or tyres? doing so will affect the speedo's accuracy. Even a change tyre pressure or wear will have a small effect. for this reason no speedo will ever be 100% accurate

as mentioned, speedos will overestimate from the factory.

with the 18s mine is out 3km/h at 110

[Ryan_R]

I had a chuckle...yes its 8%...but still had to chuckle.

Hehe, it's fun doing mental arithmetic while driving

I have 16" wheels.

[brad]

After conducting a rather long trip....
and constantly going the same speed and using my GPS....I have noticed that my speedo is out by about 8 km/h
I think that is rather poor for a brand new car.
I wondered if this is standard or should i go get it checked out.
when i was travelling 113km/h it said i was going 121 km/h
wonder what people think.

There's quite a few threads on this subject if you do a search.

It's standard VW group calibration & within ADR tolerances. Our 2009 Calais & our 2010 Outback are about 4kmh under.

I think it sux but there are plenty of folk on VWwc that defend it to the death. Personally, I'm sick of being stuck behind VW group cars on the motorway that *think* they are doing 110kph & they are really doing 100kph & holding up traffic.

My fix was to fit bigger diameter tyres - 110kph on the speedo is 108kph actual & 107kph on the digital readout (which I don't use).

The discrepancy from true also affects the odometer. I've tested it against a known distance & IIRC it meant that the 15,000km service intervals were more like 14250km.

In short, the speedo is way out but within the limits of the law.

---------- Post added at 11:07 AM ---------- Previous post was at 11:01 AM ----------

ADR's state a 10% margin of error to account for tyre wear and air pressures etc.
This can be overcome by increaing the rolling diameter of your wheel/tyre combo or by ignoring it and doing the speed limit on your speedo and therefore not getting any speeding fines as you are under the limit

They state "up to" 10%. VW seems to take it to the extreme. My wife has been through a truckload of comapny cars lately & they seem to be more like 4kph at 110kmh (Australian Commodore, Belgian Mondeo, Japanese Subaru).

You don't get speeding fines if you are *on* the limit either.

Drives me insane when I'm driving to work doing a legal 110kph & theres a HWP car or fixed radar & all the numpties jam their brakes on & slow down to 95kph.

---------- Post added at 11:08 AM ---------- Previous post was at 11:07 AM ----------

with the 18s mine is out 3km/h at 110

You are so lucky.

[Ryan_R]

95kph... which is actually 88kph in a 100 zone.

Which is more than 10kph under the limit which you can be pulled over for.

Drives me nuts as well.