Speed Awareness Course

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al_yrpal
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Re: Speed Awareness Course

Postby al_yrpal » 15 Nov 2018, 10:39pm

My old Mitsubishi ASX's speedo read about 10% fast. My SEAT Ateca seems much quicker at indicated 30 and its accurate. Both cross referenced with GPSs. As a consequence I always feel I am speeding in the Ateca! I have no explanation regarding the odometer Mick perhaps its just a deficient speedo needle? The speedo in my 1980 VW Camper is spot on, probably as a consequence of rarely getting above 60 :lol:

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meic
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Re: Speed Awareness Course

Postby meic » 15 Nov 2018, 11:05pm

mjr wrote:
meic wrote:I was no more dangerous than when I went down there the time before at 40mph legally, which isnt a judgement on what the speed limit should be, it just illustrates that the accidental speeding was not a leap from safe to dangerous, merely crossing a line drawn through a statistical scatter. I was just as dangerous perfectly legally the time before but thats fine.

It wasn't fine because driving faster than is safe was still illegal no matter what the signed limit - it's a limit not a target or recommendation. It's just much easier to punish people for exceeding a signed limit, plus too many people still driving faster than is safe is a valid reason to set a lower signed limit.

But the only place where it wasnt "safe" to do 40mph on that bit of road was in your mind.
If somebody was sitting their driving test or their advanced driving test on that bit of road and they failed to be near the present 30mph limit, or if sitting it earlier failed to be near that 40mph limit, they would fail their test for not making progress.
You would not be able to find an expert witness who would fault a driver just for driving at the posted limit for that road whether it was the older 40mph or the newer 30mph.

Of course conflating the offence of speeding with the offence of dangerous driving is Safespeed/ABD's trick.
Speeding is its own separate offence and that is the crime that you have committed and been convicted for if you are caught speeding. That it is safe is no defence, equally being unsafe because you are driving too fast for conditions doesnt mean that you are guilty of speeding.
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meic
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Re: Speed Awareness Course

Postby meic » 15 Nov 2018, 11:59pm

al_yrpal wrote:My last speeding fine was 1972, I often speed on motorways but not on urban or country roads. Since 72 I have never been caught for anything.

The speedo inaccuracy doesnt surprise me. They fit lots of modern cars with different size tyres and I think thats why many models have overoptimistic or underoptimistic speedos.

Al


Underoptimistic speedos are not allowed, the 10% tolerances are strictly towards overoptimistic.
My present car, which is my first to not have a speedometer cable, records its mileage with an accuracy which perfectly matches Googles distances and the GPS but its speedometer reading is almost 10% over.
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Mick F
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Re: Speed Awareness Course

Postby Mick F » 16 Nov 2018, 9:44am

Speedos are usually a meter, and as such suffer from mechanics of the spring.
The odometers are fed these days via the computer and detectors on the drive shafts, and not a bowden cable up from the gearbox.

The speedo is likewise fed from the computer, but because they are a meter rather than a readout, they are rubbish. There's no reason at all for speedos not to be accurate these days.
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Re: Speed Awareness Course

Postby kwackers » 16 Nov 2018, 10:07am

Mick F wrote:Speedos are usually a meter, and as such suffer from mechanics of the spring.
The odometers are fed these days via the computer and detectors on the drive shafts, and not a bowden cable up from the gearbox.

The speedo is likewise fed from the computer, but because they are a meter rather than a readout, they are rubbish. There's no reason at all for speedos not to be accurate these days.

Even analogue looking speedos are digital, usually using stepper motors so they can be as accurate as they need to be.

There's a 2% ish variation in speed based on tyre wear so at the very least on fresh tyres the speedo would have to under read by that amount. (Probably more for cars with 'rugged' tyres).

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Re: Speed Awareness Course

Postby mjr » 16 Nov 2018, 12:07pm

I don't think it's possible to discuss this usefully while meic is going to misinterpret impersonal comments as personal accusations, beg far more questions than anyone has time to deconstruct fully (for example, "Any body who claims they are not equally fallible as such a person who got caught [...] is talking rubbish" - maybe good drivers deal with fallibility by deliberately erring on the side of caution and doing 30mph on lit roads until they see confirmation of a higher limit instead of assuming it's unchanged?) and keep red inking comments.
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Mick F
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Re: Speed Awareness Course

Postby Mick F » 16 Nov 2018, 3:54pm

kwackers wrote:Even analogue looking speedos are digital, usually using stepper motors so they can be as accurate as they need to be.
I'm well aware of that, but they are analogue in principle.
Stepper motors to move them yes, but they are often spring-loaded to zero as well. They can have them accurate or less accurate, but choosing less accurate and reading high because it looks better.
If they can have the odometer spot on, they can have the speedo spot on too ........... but they don't, because they sell speed. They design these things to look good - not to be functional and useful.

Car makers sell speed. The cars have speedos that read up to 120mph or even 140mph when the car in incapable of going any more than 90mph despite what the speedo says. The all-important 30mph is way down the scale maybe only an inch up from zero so a variable scale would be better with the slower speeds taking up more scale than the faster speeds.

The car we have at the moment is the worst one we've ever owned for an over-reading speedo.
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Re: Speed Awareness Course

Postby kwackers » 16 Nov 2018, 4:02pm

Mick F wrote:I'm well aware of that, but they are analogue in principle.

In what way are they "analogue in principle"? Their principle of operation is very much digital.
The position of the needle is set digitally and moves in discrete digital steps (same as a CNC machine and nobody claims they're analogue.)
(They're also not spring loaded, if you cut power to them they simply stop at whatever the current reading is. Ditto fuel gauges, tacho's etc)

Of course that doesn't mean they all are. I'm sure there are a few that use spring loaded, zero stops with some form of PWM driven coil, just that I haven't seen one for years.

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Re: Speed Awareness Course

Postby Cunobelin » 16 Nov 2018, 5:27pm

kwackers wrote:
Mick F wrote:I'm well aware of that, but they are analogue in principle.

In what way are they "analogue in principle"? Their principle of operation is very much digital.
The position of the needle is set digitally and moves in discrete digital steps (same as a CNC machine and nobody claims they're analogue.)
(They're also not spring loaded, if you cut power to them they simply stop at whatever the current reading is. Ditto fuel gauges, tacho's etc)

Of course that doesn't mean they all are. I'm sure there are a few that use spring loaded, zero stops with some form of PWM driven coil, just that I haven't seen one for years.


For years the understanding of the terms referred to the display.....


If it was numbers then it had digits and was a digital display

If it had hands, then it was not showing digits and was analogue

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Re: Speed Awareness Course

Postby kwackers » 16 Nov 2018, 6:25pm

Cunobelin wrote:For years the understanding of the terms referred to the display.....


If it was numbers then it had digits and was a digital display

If it had hands, then it was not showing digits and was analogue

But for years that's because they actually were analogue.

Just because you rely on an analogue display to read it doesn't mean it's analogue. Suppose I programmed a robot to hold its hands out as the time - would you call that analogue?

The needle on a modern gauge has discrete digital positions, it's positioned digitally and with 100% accuracy and repeatability.

It's nit picking I know, but calling them analogue for historical reasons doesn't mean they're analogue.

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Cunobelin
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Re: Speed Awareness Course

Postby Cunobelin » 16 Nov 2018, 6:29pm

kwackers wrote:
Cunobelin wrote:For years the understanding of the terms referred to the display.....


If it was numbers then it had digits and was a digital display

If it had hands, then it was not showing digits and was analogue

But for years that's because they actually were analogue.

Just because you rely on an analogue display to read it doesn't mean it's analogue. Suppose I programmed a robot to hold its hands out as the time - would you call that analogue?

The needle on a modern gauge has discrete digital positions, it's positioned digitally and with 100% accuracy and repeatability.

It's nit picking I know, but calling them analogue for historical reasons doesn't mean they're analogue.

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Re: Speed Awareness Course

Postby Vorpal » 16 Nov 2018, 7:49pm

Mick F wrote:Car makers sell speed. The cars have speedos that read up to 120mph or even 140mph when the car in incapable of going any more than 90mph despite what the speedo says. The all-important 30mph is way down the scale maybe only an inch up from zero so a variable scale would be better with the slower speeds taking up more scale than the faster speeds.

The car we have at the moment is the worst one we've ever owned for an over-reading speedo.

First, the manufacturers want people to think they are going faster than they are.
Second, the standard as has been discussed on here before, allows tolerance, based on international agreement (UN / ECE and adopted as EU directive)

The speed indicated shall not be less than the true speed of the vehicle. At the test speeds
specified in Paragraph 5.2.5. above, there shall be the following relationship between the
speed displayed (V ) and the true speed (V ).
0 ≤ (V − V ) ≤ 0.1 V + 4 km/h


This is an old standard, based upon the capability of systems from the 70s.

Finally, as noted above, all sorts of other things, such as tyres fitted, temperature, wear, etc. can affect the output. Because of this, it is necessary for the manufacturers & dealers to be somewhat conservative.
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Mick F
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Re: Speed Awareness Course

Postby Mick F » 16 Nov 2018, 7:56pm

kwackers wrote:
Mick F wrote:I'm well aware of that, but they are analogue in principle.

In what way are they "analogue in principle"? Their principle of operation is very much digital.
The position of the needle is set digitally and moves in discrete digital steps (same as a CNC machine and nobody claims they're analogue.)
(They're also not spring loaded, if you cut power to them they simply stop at whatever the current reading is. Ditto fuel gauges, tacho's etc)
No they don't.
Not in my experience, they don't.

The facts are, that speedos are wrong and over-read by design, but the odometers are correct by design.

If the tyres and pressures are variable, the odometer is still correct. It could be a tiny bit out, but the speedo is always wrong and always over-reading by loads.
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Re: Speed Awareness Course

Postby NATURAL ANKLING » 16 Nov 2018, 8:34pm

Hi,
Seem to remember that you did swap tyres a little while after buying a car?
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Mick F
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Re: Speed Awareness Course

Postby Mick F » 17 Nov 2018, 9:21am

New tyres, yes. Same size and profile.

Odometer is spot on by GPS and by the 200metre markers on the A30.
Long-ish thread on the Yaris forum.
https://www.toyotaownersclub.com/forums ... 014-yaris/
Mick F. Cornwall