Speeding

[crofter]

Have been reading the comment attributed to Chief Constable Anthony Bangham re his remarks about the penalty should be introduced for going over the limit by as much as 1 or 2 MPH. To my mind it raises the question as to the accuracy of the mass produced speedos fitted to our cars. Could this leave us with the extra cost of something like Tachometers, being forced on us along with the annual testing demanded on these recorders to ensure they are accurate and not adversely affected by wheel and/or tyre sizes that some like to do to give their motor a bit of modding.

[Heidfirst]

Bear in mind that it is illegal in the UK for speedos to under read which is why in a Toyota they are typically set to read over by ~6 or 7 % ...

[Cyker]

<angry rant>

The man is an idiot if were to try to push that through. For one thing it would be unenforceable 99% of the time, and for another it would make the roads *more* dangerous if everyone was staring at their speedos instead of keeping their eyes on the road.

Most drivers only know they're vaguely going at 30mph because how can anyone be expected to drive exactly at 30 with crappy dial-based speedos?

Heck, even with my Yaris' digital speedo it's hard to keep it at exactly 30mph when e.g. cresting a hill! Even cruise controls can't keep a car going at exactly a single speed!

The speed limit is supposed to be there to increase safety, not reduce it!

If he wants to increase road safety, he should help improve driving standards - Reward calm careful drivers and penalize aggressive intimidating ones instead of just blaming everything on speed and encouraging dangerous driving!

These 'smart' motorways without hard shoulders are becoming a huge hate of mine. It's bad enough half the time they don't close the lane when a car is broken down and trying desperately to hide in the verge until hours after it's already been recovered, but even more annoying are these arbitrary SURPRISE! speed limits they keep switching on!

Recently, on my return route, a single gantry just out of the blue lit up a 40mph limit despite clearly visible free flowing traffic far intoi the distance - At first everyone ignored it, as the one right after was blank, but then there was a camera flash on the opposite side of the road and *immediately* a sea of brake lights from everyone to the right of me as people slam on their brakes just before the 40 gantry!! At no further point were there any other limits displayed. And this is not an isolated incident!!

How is that helping to improve road safety?!

 

[deano20010]

Most spedos are over so when you do 30mph you are actually doing around 23-25pmh :)

[Mike J.]

On ‎31‎/‎01‎/‎2018 at 6:21 PM, Cyker said:

Even cruise controls can't keep a car going at exactly a single speed.

With the regeneration facility, the Toyota hybrids can keep to exact speeds using cruise control - very steep hills can cause problems though and there is no regen if Battery full and there is also a maximum regen current.

[Mike J.]

54 minutes ago, deano20010 said:

Most speedos are over so when you do 30mph you are actually doing around 23-25mph :)

Our Yaris hybrids seem to show a speed that is 3-4 mph above reality over speeds between 30 and 70 - it is by design as the ECU knows the real speed!

[FROSTYBALLS]

2 minutes ago, Mike J. said:

Our Yaris hybrids seem to show a speed that is 3-4 mph above reality over speeds between 30 and 70 - it is by design as the ECU knows the real speed!

In fact it is down to legislation. 

[Mike J.]

3 minutes ago, FROSTYBALLS said:

In fact it is down to legislation. 

But not the actual speed. It would be possible for Toyota to choose just 0.5 mph over read with new tyres - it is just maths and software.

[FROSTYBALLS]

Speedometers being optimistic is due to legislation.

[Heidfirst]

2 hours ago, deano20010 said:

Most spedos are over so when you do 30mph you are actually doing around 23-25pmh :)

That would be illegal - the max. variation allowed in the UK for a car is 10% so for a car with a legal speedo indicating 30mph the minimum actual speed allowed is 27mph.

56 minutes ago, Mike J. said:

But not the actual speed. It would be possible for Toyota to choose just 0.5 mph over read with new tyres - it is just maths and software.

They won't operate to that tolerance because changes in tyres (pressure, wear, different manufacturers or owner fitting a slightly different size) alone could negate that. That could potentially leave the manufacturer open to law suits/prosecution.

They aren't allowed to underread & they are only allowed to overread by 10% so it isn't surprising that most overread by ~5% i.e. the middle of the range.

[FROSTYBALLS]

The UK regulations are slightly different to those of the EU in that for all actual speeds between 25 mph and 70 mph, the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph. So in the UK for an actual speed of 23mph, the speedometer could legally show up to 31mph.

[Heidfirst]

2 minutes ago, FROSTYBALLS said:

The UK regulations are slightly different to those of the EU in that for all actual speeds between 25 mph and 70 mph, the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph. So in the UK for an actual speed of 23mph, the speedometer could legally show up to 31mph.

Fair point, however, whilst it is possible that Toyota could change the speedo calibration setup just for the UK to take advantage imo it's unlikely to but will install the same ECE compliant to all European vehicles.

[PeteB]

I find the radar cruise control in my Prius very helpful in staying legal (and it doesn't get intimidated by morons trying to enter the exhaust pipe!).  Like the ordinary cruise control in my previous Gen 3 Prius, it will put the brakes on if necessary going down a steep hill (Gen 1 & 2 Prius cruise control wouldn't use braking).

I don't understand why, though, (at least on the Hybrids which have no conventional gears) you can't set the cruise control below 28 mph (on the speedo).

At least the Gen 4 also has a speed limiter, which is brilliant in a 20 mph limit (I set it to 22 which is a true 20).  But again, strangely, it won't allow you to set it for a speed below 20 mph.  WHY????

Some private estates I used to visit have a limit o 15 or even 10 mph, and the security people used to get really shirty if it was exceeded by just one mile per hour (maybe they are related to that policeman!).

[Mike J.]

1 hour ago, Heidfirst said:

They won't operate to that tolerance because changes in tyres (pressure, wear, different manufacturers or owner fitting a slightly different size) alone could negate that.

Fitting different tyre sizes is not applicable in this case. Wear is not applicable as it would lead to more over-reading. Pressure might have an affect and same with manufacturers - anyone with a tape measure and a friendly tyre supplier 

[FROSTYBALLS]

3 hours ago, Mike J. said:

But not the actual speed. It would be possible for Toyota to choose just 0.5 mph over read with new tyres - it is just maths and software.

There is no reason for Toyota or any other manufacturer to do this. The speedometers meet current legislation requirements, and that is all the manufacturer would be interested in.

[Mike J.]

32 minutes ago, FROSTYBALLS said:

There is no reason for Toyota or any other manufacturer to do this. The speedometers meet current legislation requirements, and that is all the manufacturer would be interested in.

Which therefore ignores the customer - well some of them.

[FROSTYBALLS]

1 minute ago, Mike J. said:

Which therefore ignores the customer - well some of them.

No - the speedometers meet legal requirements. End of.

[Heidfirst]

2 hours ago, Mike J. said:

Fitting different tyre sizes is not applicable in this case.

It might be - some people do fit non-oem sizes sometimes if they have them to hand or can get them cheaper etc. etc..

[Mike J.]

2 hours ago, FROSTYBALLS said:

No - the speedometers meet legal requirements. End of.

Those requirements were probably set before ECUs worked out the speed. We know that the ECU is very accurate and so it is not beyond the wit of Toyota to get the speedo closer to reality. I wonder how accurate the new flat screen displays are as seen on Teslas and new VWs?

[Mike J.]

2 hours ago, Heidfirst said:

It might be - some people do fit non-oem sizes sometimes if they have them to hand or can get them cheaper etc. etc..

You would be foolish to fit different tyre sizes on the original wheels and hope to have a legal speedo readout, but different wheel tyre combinations 16 to 15 inch and 195/50 to 175/65 I can agree with - this gives +1.3% change which would be within the minus 3-4 mph error at 70 mph that the (Yaris Hybrid) speedo gives.

[FROSTYBALLS]

Whenever the requirements were set is irrelevant. There is no impetus for manufacturers, whether they are Toyota, VAG, Tesla or whoever, to improve the accuracy of speedometers beyond the present levels of accuracy. Speedometers meet the current, legal requirements.

As regards fitting different wheels/tyres, some people would use a speedometer error calculator to determine whether the intended combination is legally suitable, plenty of which are easily accessible on the web. Some do fit slightly wider tyres on existing wheels.

[PeteB]

From discussions with other Prius owners around the world over the years, it seems they over-read in many (if not all) countries in Europe and as has been said, the internal speeds are very accurate.

However, it seems that in the US and maybe some other countries (can't recall which now, but I have a vague recollection that Japan and Australia were amongst them), the speedos  displayed the same very accurate speed as was found via the OBDII port.

In fact, some old fashioned dial speedos of the 1970s and 80s were also very accurate (and some were horrendous).  These speedos used a rotating cable from the gearbox to turn a magnet in the speedo, which in turn deflected a needle attached to a coil of copper wire, held against a spring.

Where I lived in those times, there was a link road to the M25 where the local traffic Police had placed a pair of wooden posts exactly a quarter of a mile apart.  It's purpose was for the Police to check their calibrated speedos.  (They disappeared years ago before anyone asks where they were).

Whenever I got a new car, or had a loaned or hired car, I would take it to this road and drive past them at a steady 30, 60 and 70 mph.  I would do each speed 3 times, or until I got 3 identical timings.  Using a stopwatch and a chart I'd typed, I converted the number of seconds into speed.

A few that stick in my memory:

• Austin Allegro - spot on at all three speeds
• Morris Ital - spot on at 30, 1 mph over-reading at 60 and 70
• Fiat 132 - at indicated 70 mph, really doing 56!   [1]
• Fiat Strada - 3 mph over at all speeds   [2]

[1] - I think it stemmed from a face-lift of the model where they changed the gear ratios, final drive ratio, wheel and tyre size, and no one at Fiat thought to rework the speedo drive gearing!

[2] - as far as I know, this was the first car to have a conventional dial speedo operated by an electrical signal rather than a rotating cable.

[FROSTYBALLS]

Most countries in Europe abide by the UNECE or EU standard for speedometers, where speedometers should show no more than 110% of the actual speed. Australia adopted the UNECE standard in 2007. The UK has a slightly different standard for speeds between 25 and 70mph, where the speedometer should show no more than 110% of the actual speed plus 6.25mph.