European speedos with 6% "Error"

**p.dath** · 30th September 2009, 08:13

In Europe, at least for cars, they have a rule that a car speedo can never read more than the actual speed it is travelling at.
So how do the car manufacturers handle this? They introduce a deliberate 6% error, and report the car is travelling faster than it is. For example, if it says you are travelling at 100km/h, you are actually doing 94km/h. It stands out a lot when you use a GPS.

Most European cars are affected by this, like BMWs.

In NZ we don't have any such rule, and typically we have used "average speed" speedos. So if your car (assuming it wasn't made in for for Europe) says you are doing 100km/h, you are (within a small +/- range).

What I'm trying to find out is what regulations NZ has with regard to speedo accuracy. I've had a good search, and just kind find it.
I'm sure we must have something that governs this.

Does does anyone know the regulation/rule/legislation that covers this, or better still, can give me a URL so I can read it myself?

**ghost** · 30th September 2009, 08:30

I believe NZ is around 9% lower, must never be higher. Mine is 8 ks out, ie 92 wheel speed when 100 GPS speed. Funnily enough, cruise control wont engage unless the car is doing 100 kph or less, and this is GPS speed not off the speedo speed, if you manually increase cruise speed over 100 k's it will slowly shift it back down to 100 k's over time.

Jappa car too.

**vifferman** · 30th September 2009, 08:35

Originally Posted by p.dath

In Europe, at least for cars, they have a rule that a car speedo can never read more than the actual speed it is travelling at.

This is twaddle. I think you meant "never read LESS than the actual speed".
I think you'll find that almost all speedos are designed so that they are optimistic - that is, they read slightly higher than the actual speed you're traveling at. The convention is that odometers are fairly accurate, but speedometers tend to err on the side of over-reporting your speed. This is probably so that no-one can then go back to the manufacturer and say, "I got a ticket - I had the speedo calibrated, and it's your fault because it under-reads by 5%!"

But regardless - we've had this thread already recently.

**Devil** · 30th September 2009, 08:35

Before you run out of braincells to waste, it is very very rare to come across a car with an accurate speedo* regardless of it's country of origin.

They're all over the place, with varying accuracies between brands, even within Japan.
There is no flat percentage rule amongst carmakers.

(* calibrated speedo's obviously excepted).

Note: Many car mag tests now show actual speed at an indicated 100km/h

**Morcs** · 30th September 2009, 08:37

Nothing stops you:

Fitting a speedohealer to your bike

Disconnecting/ignoring your speedo on your car and using GPS.

I have my speedohealer setup to account for 6% overread, and it is still 1kph out at around 50kph.

**nosebleed** · 30th September 2009, 08:48

If you really do want to add to your library, give Robinson Instruments a call.
They're in Sale St. Ak.

They should be able to point you in the right direction

**Stirts** · 30th September 2009, 08:52

Dammit, I got all excited for a minute. From the title I was thinking that 6% of the Surf Lifesavers would be showing their budgies in error!!

My Mazda 121 Bubble speedo is spot on according to the GPS.

**p.dath** · 30th September 2009, 09:06

Originally Posted by vifferman

This is twaddle. I think you meant "never read LESS than the actual speed".
I think you'll find that almost all speedos are designed so that they are optimistic - that is, they read slightly higher than the actual

Originally Posted by Devil

Before you run out of braincells to waste, it is very very rare to come across a car with an accurate speedo* regardless of it's country of origin.

Believe it or not, as I said, in Europe speedos for cars are regulated so that they can not return a reading which is greater than the actual speed you are travelling at.

The last Holden I had that was manufactured out of Australia and used an average speed approach (and was pretty much spot on).
We mostly have Holden's at work, and we have GPS units for all the cars, and I can say all of them are also spot on.

Maybe I've been spoiled by Holden for too long.

**Devil** · 30th September 2009, 09:12

You're contradicting yourself.
You mean: "they can not return a reading which is less than the actual speed you are travelling at."

**steve_t** · 30th September 2009, 09:35

Most car reviews I can remember reading generally say that when the speedo indicates 100km/h, the car is actually doing 94-97 km/h.
Not sure about bikes but I have a feeling the accuracy is even less. There's a speed indicating sign down the road from me. I'll have to ride past and check out the difference. The only problem is once you get over a certain speed, it stop saying your speed and says "SLOW DOWN"

**Morcs** · 30th September 2009, 09:37

I know my import honda cage overreads quite a bit. 60kph on the speedo is about 54kph

**p.dath** · 30th September 2009, 09:39

Originally Posted by Devil

You're contradicting yourself.
You mean: "they can not return a reading which is less than the actual speed you are travelling at."

You are correct.

**NDORFN** · 30th September 2009, 09:44

We've got an Audi that I'm pretty sure is bang on. Haven't tried GPS yet but it's always on the dot with those electronic signs showing your speed. It probably did have the 6% margin built in originally but putting 2 inch bigger rims on it must've evened it out. With all the aftermarket wheels people use these days, having some kind of manditory margin is pointless. I like the way there's a 9km margin for issuing speeding tickets though. Makes sense.