WS 2009 Speedo Error

[StormyKnight]

MY wife is complaining that people are passing her even though she is sitting on an indicated 100km/h. Has anyone measured the speedo error against a GPS yet? I have a GPS but its difficult to get the GPS & car together & take it for a run.

Perhaps the rim sizes effect the error too so please provide that information too.

Cheers

[greenfoam]

Yep, my wifes is 5km/h out roughly at 100, about the normal for most cars, people will pass you no matter what speed you are doing, especailly on overtaking lanes almost as if there's a law that you have to pass

[StormyKnight]

Originally Posted by greenfoam

Yep, my wifes is 5km/h out roughly at 100, about the normal for most cars, people will pass you no matter what speed you are doing, especailly on overtaking lanes almost as if there's a law that you have to pass

Yep they will, I think she is used to the 4WD, it has oversized tyres which means when your doing 100km/h the speedo reads 99.

5km/h is a lot & is quite a noticeable difference in speed between cars...

I've always wondered if they do it help with the fuel economy :

Leagally the speedo can be 10% fast but not any % slow so I guess they err on fast side a bit. Pity since with electronics these days it could be 100% accurate. The odd thing is that the odometer is usually not 5% out...:

Thanks

[anonamouse]

also have one that is 5km/h out at 100KM/h. And went back to the dealer as I thought 5% was a bit excessive in the modern era (my FG XR6 speedois exactly the same as the GPS display). the permited error is actually higher than 10%. the latest ADR std looks something like this...

0 <= Speedo Display - Actual Speed <= (Actual*0.1 + 6kmh).

if the speedo displays 100 and a gps is at 95 then

0 <= 100-95 <= (95*.1 +6)
0 <= 5 <= 15.5 (as 5 is greater than 0 and less than 15.5 its in spec)

some what suprisingly; if the speedo was showing 100 and a GPS showing 86 then that is also in spec!

[StormyKnight]

Originally Posted by anonamouse

...some what suprisingly; if the speedo was showing 100 and a GPS showing 86 then that is also in spec!

Yes if you have ever driven a Mazda Diesel 6 this is about the accuracy of the speedo....even sitting an an indicated 110km/h on the freeway, trucks doing 100km/h would pass you. It wasn't until we used a GPS we could see how much it was out....

Mind you it gave great economy siting on 86km/h when you thought you were doing 100!

[GoesLikeAZetec]

How they are allowed to have speedo's so wrong, still blows my mind...

Honestly all the old cars ive tested with my gps are spot on at 99 and 100 at 100kmh...

Its the most used dial on the dash yet new cars are worse than 10-15 year old cars.... I think its p#ss poor and its not just Fiestas.

Our work Mitsubishi's,Mazdas,Toyotas are all way out... The Mazda's are the worst at 11kmh at 100.... Hopeless I tell you, and not up to standards...

[south21]

Checked mine with the gps and it's 5ks out as well.

[vegabass]

My wifes fiesta is the same. My 97 XR6 is like 2 kms slower than GPS. That gives me faith that 1 of them is right. However I guess you need to line up a few GPS's to see how accurate they are.

I wonder how this argument will hold up in court if you were done speeding if your speedo was showing 15km slower than your "clocked" speed.

[StormyKnight]

Originally Posted by vegabass

I wonder how this argument will hold up in court if you were done speeding if your speedo was showing 15km slower than your "clocked" speed.

I found this yesterday whist researching the allowed errors, it makes an interesting read & makes several points about "what the driver should know" about their speedo & what the court will use as evidence.

http://www.trafficlaw.com.au/speedos.html

Basically if you mod you car in any way that may effect the speedo your going to have a hard time! Really you only avenue is if you can prove your speedo is underreading...also if you speedo was still reading over the speed limit then you've virtually lost your case :togo:

Surely with technology these days they could be within 1% & then add 2km/h so anyone driving know what their real speed is...with a needles width safety margin.

How many Mazda drivers are complaining about speeding trucks, when thier doing 90km/h thinking they are doing 100! The mind boggles some times. Like, how safe is that? :

[ratter]

We have speedo tested lots of cars on our dyno and find most stock cars are between 3-7% out and all are actually traveling slower than the speedo indicates.

You also have to remember as your tyres wear the error percentage is going to change as the tyres get smaller

[doctamick]

The speedo on my WS Fiesta (with factory 17s) is about 3km/h fast at 100km/h (i.e. reads 103km/h when doing 100km/h). The strange thing is that the average speed shown on the trip computer does not match the speedo, and actually seems to be more accurate.

For example, when cruising at a constant speed of 103km/h, as shown by the needle on the speedo, if I reset the average speed on the trip computer it will show a speed of around 99km/h. This is quite a notable discrepancy. I'm not sure why it occurs because the trip computer and speedo should both be controlled electronically. Maybe the speedo is deliberately designed to read a little bit fast, to ensure that it complies with the ADRs, allowing for some margin of error.

[StormyKnight]

Originally Posted by ratter

You also have to remember as your tyres wear the error percentage is going to change as the tyres get smaller

But not significantly...works out to be about 1% (loosing 5mm of tread)

Originally Posted by doctamick

The speedo on my WS Fiesta (with factory 17s) is about 3km/h fast at 100km/h (i.e. reads 103km/h when doing 100km/h). The strange thing is that the average speed shown on the trip computer does not match the speedo, and actually seems to be more accurate.

Yes, I suspected as much.....they can measure it electronically quite accurately, however they choose to display the speed faster than real.

This may also be because the speedo is still a mechanical device...perhaps its to cover mechanical tolerences in the guage.

The other issue is that the Fiesta can have 3 factory rims sizes, & a 14inch, 16inch & 17 inch tyre are going to be different circumferences. In addition did you know that even the same size tyre but different manufacturer can have a different circumferances?

I think this all adds up to them knocking 5km/h of the true speed so that it never can fail the ADR's....(people would then be sueing Ford for every speeding ticket - perhaps there has already a precendent in Europe/Japan - maybe involving a Mazda )

[greenfoam]

5km/h out is sensible, if I were building car's I'd build them 5ks out also. So I have no problem with it, just drive at 105 indicated if you want to go 100

[StormyKnight]

Originally Posted by greenfoam

5km/h out is sensible, if I were building car's I'd build them 5ks out also. So I have no problem with it, just drive at 105 indicated if you want to go 100

All you have to do now is guess everytime you get in a car, unless you carry your own speedometer (gps)...

I still don't think its safer to have trucks sitting exactly on 100km/h but car drivers doing 90-95 thinking they are doing 100km/h....

All those people who are happy to sit on 100, are now sitting on 95....& people being people....a certain percentage will not be happy about being slowed unnecessarily. I think it would be better that the speedos where reasonably accurate & trustworthy...

I mean its a bit like the 100km/h limit....is it 100km/h or 102...4,6? I know in Victoria you can get booked for being 2km/h over, which is good I think. The news of this has spread across the Eastern states & most drivers know that....unfortunately the same can't be said for NSW...

I don't know you could probably write a whole book on driving psychology & then another on the laws to make it work for most of us!

[vegabass]

Im thinking about getting a speedo correcter. Its a cheap kit from jaycar.

[StormyKnight]

Yes I have heard of these, very popular with the 4WDrivers going to bigger tyres....perhaps cheaper/easier to get a GPS these days?

[GoesLikeAZetec]

Honestly if they could get them spot on years ago, they got no excuses now. The old Hyundai, 121 and 10 year old cruiser are all spot on no matter what brand tyre etc we put on them.

Im sorry but its the most important gauge you look at in the car (especially in oz with ridiculous speed enforcement we have) yet they cant get it right? Cop out!!!!

If you do the speedo kit and it works let us know vegabass!!

[StormyKnight]

Yep I agree, I had a VY commodore & it was dead on....
Interestingly I have since found out that the diagnostic mode of these cars can show the speed they are traveling at in digital form. Also it seems that none of the guages are driven anymore by the device they are measuring but by the computer, since part of the diagnostics is a guage sweep where the computer tests the guage by moving it around to full sweep.

It will be interesting to see if the digial reading matches the guage reading....

[doctamick]

Originally Posted by StormyKnight

Also it seems that none of the guages are driven anymore by the device they are measuring but by the computer, since part of the diagnostics is a guage sweep where the computer tests the guage by moving it around to full sweep.

Haha... yes. I think that speedos manually driven by cables running from the gearbox is a thing of the distant past. The 'analogue' speedo in my old 1992 Honda Civic was controlled electronically (i.e. no speedo cable).