Speedometer - Is Your Speedo Out By At Least 5mph?

[Mark_P]

Hi all,

This has probably been asked before and its had me thinking about the speedometer on Einstein which seems to be out by 5mph.

If I want to drive 30mph, I have to have the speedometer showing 35mph. Is this normal for the IQ?

Cheers,

Mark

[FROSTYBALLS]

In the UK we have slightly different speedometer regulations to the rest of Europe.

As with the UNECE regulations and EC Directives, in the UK a speedometer must never show an indicated speed less than the actual speed. However the UK differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower than this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph.

For example, if the vehicle is actually travelling at 50 mph, the speedometer must not show more than 61.25 mph or less than 50 mph.

So when your car is travelling at a true 30mph, the speedometer can quite legally show an indicated speed of up to 39.25mph.

[Mark_P]

Hi Frostyballs,

Thanks for the information, very useful. I'm still learning all of this as I only passed my driving test in April :)

[Cyker]

Ahh, that would be why I can be doing 70mph on the motorway and still have people fly past me like I'm standing still and not trigger the cameras!

[fastbob72]

When I passed my test it was all old Fords I bought and ran for a long time,late 70s and 80s models.My first car was a '78 T reg Fiesta 1.1L which at flat out the needle pointed directly straight down,180° lol.

It went up to 100mph on the gauge so if you extrapolated it to where the needle sat it was doing 115mph.

I've noticed,using phone apps inc Torque Pro and Ullyses Speedometer Pro which both use GPS to measure velocity,that my Avensis over reads by upto 10 mph over 85 mph but you have to wonder how accurate the GPS is because the speedo app,for instance,tells me I'm 300m above sea level when I'm parked up at the waterside plus it says how accurate it is i.e within 12m or 24m and it's constantly changing so I'm more inclined to trust my cars speedo than any gps app lol

[FROSTYBALLS]

As far as I'm aware GPS speed caculations are based on an average using a number of position readings

[iQofaMouse]

Interesting thread & very useful information, thank you.

I still miss the digital speedo on my old Yaris, couldn't say exactly how accurate it was but I always took it as read and never had a problem.

Nicola

[Cyker]

I love that digital dash :D

I'm glad the Mk1's are so reliable as it's going to be very painful changing from it to a normal car with their boringly old-fashioned and horribly positioned analogue dials

(Maybe if I can find one with a HUD...?)

I find the digital reading on mine is pretty consistently ~2mph over GPS reported speeds.

[iQofaMouse]

It was painful - I loved it too! In fact if I could change anything about my iQ that would be it, and I have said it to a few people already.

I quite agree with boring and horrible position - it's taken a little while to stop looking over at the airbags on/seatbelt pod in the middle for speed/fuel gauge information!?!

I'm glad it was reasonably accurate too!

Nicola

[iQ-Chris]

Sorry for going slightly off-topic, but I too miss the digital readout I've had in previous cars.

Before the iQ I drove a BMW MINI hatch which had the big analogue 'clock face' in the centre, plus a small digital readout in front of the driver.

Before the MINI, I drove three original (left-hand drive) Renault Twingos and I think the first generation Yaris owed some of its design flair to the little French monobox. Not least the digital readout, mounted in the centre of the dashboard, which came as standard from the start of Twingo production in 1993.

Chris

iQ² in black ☆ red and white leather ☆ sunroof ☆ upgraded interior lighting ☆ white backlit dashboard/switches ☆ auto-folding mirrors ☆ smart entry ☆ auto-locking doors ☆ chrome handles and exhaust

[Cyker]

See Toyota! People DID love the digital dash! Put it back!!! :D

(If only they read this forum... )

[FROSTYBALLS]

Of course BMW took the central speedometer design cue from the original Mini of 1959, and the car with the first digital dashboard was the 1976 Aston Martin Lagonda.

[iQ-Chris]

Sure, though I was only intending to compare small/city cars. I mean, even the Austin Maestro came with a digital dashboard a whole 10 years before the Twingo I mentioned above, but I wouldn't draw many connections.

However, Renault's success may have inspired other makers of small or quirky cars to fit digital readouts and (in some cases) locating them in a central position. I think the first generation Yaris is one of those, and Toyota did an excellent job - The Yaris is still an attractive car 17 years later.

Chris

iQ² in black ☆ red and white leather ☆ sunroof ☆ upgraded interior lighting ☆ white backlit dashboard/switches ☆ auto-folding mirrors ☆ smart entry ☆ auto-locking doors ☆ chrome handles and exhaust

[tarquin]

I am using a custom made HUD ( own design) that gets the data via the OBD2 diagnostics socket. This is far more accurate than the display hence the offsets under legestation due to mechanical and aspect errors

This still has a margin of error due the reliability of the speed sensor and wheel diameter infation etc. By far the speed derived from GPS is better as its linked to an Atomic clock not a random Quarts Crystal clock

David

[iQofaMouse]

The first digital dash I ever saw was in a 2nd generation Astra GTE of the 80's; my best friend at school had an older brother who drove one and I remember thinking it was the most amazing thing I'd ever seen and probably the nearest I was ever getting to the Back To The Future DeLorean!?

It was centrally located though:

My first car was a 1984 Mini with a beautiful centrally located Smiths analogue dial - this was all it had! Oh and a reasonable heater!

Nicola

[iQ-Chris]

Those Astra dashboards made a similar impact on me. My friend's aunt had a white GTE in the '90s and I thought it was the coolest car I'd seen!

Chris

iQ² in black ☆ red and white leather ☆ sunroof ☆ upgraded interior lighting ☆ white backlit dashboard/switches ☆ auto-folding mirrors ☆ smart entry ☆ auto-locking doors ☆ chrome handles and exhaust

[iQofaMouse]

Excellent, I'm glad I'm in good company!

I've always been slightly car obsessed - I have my Dad to thank for taking me along to London motor shows when I was impressionable!

[Mark_P]

I am also using the Torque app on a spare android phone (I do wish there was a decent one for Windows Phone). I need to tweak it to my liking but it's handy for a better speed display but I won't trust it 100% :)

[fastbob72]

The first digital dash I ever saw was in a 2nd generation Astra GTE of the 80's; my best friend at school had an older brother who drove one and I remember thinking it was the most amazing thing I'd ever seen and probably the nearest I was ever getting to the Back To The Future DeLorean!? [emoji38]

It was centrally located though: L-Astra-GTE-Dash.jpg

My first car was a 1984 Mini with a beautiful centrally located Smiths analogue dial - this was all it had! Oh and a reasonable heater!

Nicola

Ah yeah, I had a mk2 Astra GTE, well 2 in fact. An early 1.8 and a later 2.0 16v but those digital dashes were fantastic, not only that but there was a bank of warning lights in a central display in the middle of the fascia too.

Having said that my all time favourite dash has always been the mk3 Escort, escort ghia, XR3 and XR3i, S1 RS Turbo and particularly the RS1600i with it's fuel cut off light aswell. It was the way the rev counter was the mirror image of the typical gauge.A standard speedo or rev counter has the needle at rest pointing down to the left, well the rev counter at rest pointed down to the right so when the engine wasn't running the needles pointed towards each other. I'll go and find an image to add as I don't think I've explaibed well enough to do it justice but I always thought it was the smartest looking set up ever. lol.

In fact, I took the dash from as escort ghia and by bodging and hackimg made it fit my mk2 XR2......wiring was easy but physically making it fit was a herculean task. It worked though, kind of...... till it hit 60 then the needle swept back n forward from 0 to 120 continously and the trip meter rolled backwards till it hit 666 then stopped..... no kidding lol

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[fastbob72]

I am also using the Torque app on a spare android phone (I do wish there was a decent one for Windows Phone). I need to tweak it to my liking but it's handy for a better speed display but I won't trust it 100% :)

Must admit I'm dubious.If you go back and look through the datalog of your journey it has two speeds.... one from GPS and another 'device speed' which I assume is basically the VSS readout, presumably that's how it can calculate the speed diffferential between indicated speed and GPS speed.

I do tend to trust the indicated speed more than the GPS as I've seen the speed fluctuate quite a bit at times on the GPS speed. I remember driving the truck once and a speedo app was reading 55-58mph whixh was around about correct as I was sitting on the limiter but it would spike up to 65 or 70 momentarily and at one point shot up. to 250+mph, obviously i'd dropped down to 2 or even 1 satellite or something but the fluctuating accuracy of GPS puts me off.

I know it uses the atomic clock but that's not for measuring speed but to correct the signal to account for the slightly different rate of time due to the satellite being in orbit and not subject to the same gravitational effects as things on the earths surface... remember old Albert and his Law of Special Relativity and that gravity has an effect on time.... as does speed etc, the differences are in the order off milliseconds but over the distances from my car to an earth orbiting satellite it has a noticeable effect if not compensated for, that's why they use the atomic clock.

Besides the cars speed sensor is directly measuring the speed all be it through the gears and rotation of the wheels but if the parameters are accurate so should be the speed. Unfortunately though,the actual wheel revolutions per mile will differ between one set of tyres and a new set. Also tyre pressuee and temperature will effect it too and I've no idea how well the VSS can accomadate for these variations, if at all.

Buy an ex Police Road Traffic car, they've, in general, probably got the most accurate speedos on the road [emoji12] [emoji12]

[fastbob72]

Have to add that a digital tachograph makes an incredibly accurate speedo......at a constant 79 kph (they always seem to read in kph,eurofriendly of course) the needle on my truck varied between 50 and 55 mph and my GPS speedo app similarly varied too.Was driving a 30 mile stretch with average speed cameras all along it so I set the cruise control to 50mph and like I said,the tacho read 79 kph with no variation but my dash speedo and my android GPS app Ulysses Speedometer Pro were varying by 5-8 mpg