Speedo Inaccuracies 2014 Yaris

[Goffy]

Interesting thread chaps!

In the good old days before GPS I used to drive a lot for my work (40000 - 60000 a year) and very early in my tenancy of a new car would do a primitive speedo calibration by finding a quiet stretch of motorway and timing my progress at an indicated 60mph using the 100 metre marker posts and a stop watch.

A mile is 1610 metres, so 16 posts = 1 mile, which should take 1 minute. It almost always took longer, often by more than 10%!  The speedos were reading fast. Never had one which read slow. The most accurate was fitted to the family 1986 Citroen CX, I couldn't measure any inaccuracy using this method. For years I was the smart pants cruising past the bottled up traffic and the "70 mph" police car at the front of of it, they were doing less than 70! Never got stopped as a result.

If  the instrument head unit has an actual needle rotating around an actual dial then it is an old fashioned analogue mechanical device regardless of what it is driven by. Therein lies the problem, simple cost, it is possible to make such instruments much more accurate than they are, but it would be very expensive! A pound saved in every speedo head (and it's MUCH more than that) is saving the maker millions a year.

 

[Mick F]

Just got back yesterday from holiday in Spain.  Couch transfer back to the airport, I was sitting near the front and could see the dials on the dash.

Analogue dial speedo plus a digital readout too.  100Kmh speed limit and the coach was doing spot on 100Kmh on the dial and the digital readout read 99Kmh. The driver may have been using Cruise Control as it was a steady reading.

I had my trusty Garmin Montana with me and switched it on and it hovered around 62.2mph.

If they can do it with a coach, they can do it with a car.

Mick.

[jonquirk]

They can do it. The question is why do they choose not to. I have already referred to the chart in the workshop manual that basically states the speedo is working correctly when it over reads by between 5 and 10%. I have seen figures from the OBD-II port that closely correspond with the GPS readings so I know the underlying figures are correct before they are altered on their way to the display.

[Heidfirst]

23 minutes ago, jonquirk said:

They can do it. The question is why do they choose not to.

Cost. Commercial vehicles (coaches & trucks) have to be fitted with tachometers which, by law, have tighter allowed tolerances & are subject to regular mandated checks. Not surprisingly those cost more than the speedo in your car but that can be accepted in vehicles that cost so much more than your average car - especially as they don't have any choice. 😛

Plus, of course, every mile/minute is costed in the aim for efficiency/minimum cost/max. profitability so 5% could be the difference between profit & loss .

[jonquirk]

Did you read my reply to the end? My car is taking accurate readings, available at the diagnostic port, then sending them to a display that deliberately over reads. Cost doesn’t come in to it. It’s a deliberate choice by Toyota, but why?

[Heidfirst]

19 minutes ago, jonquirk said:

Did you read my reply to the end? My car is taking accurate readings, available at the diagnostic port, then sending them to a display that deliberately over reads. Cost doesn’t come in to it. It’s a deliberate choice by Toyota, but why?

& have you thought why all the other manufacturers, not just Toyota, do it too ...? It's a conspiracy 😝

[Mick F]

I think it's because car manufacturers sell speed and design.  If you have a speedo that reads up to 140mph it looks much better than one that reads (only) up to 90mph.  They like you to want to see that you are going fast, and the car you own is capable of doing 140mph.  So long as they comply with the law, they will make them read fast, rather than accurately despite the info being available.

The technology and the information is there.  It's just the will to do it ................ but upset the drivers that think they are doing the legal motorway speed of 70mph when in actual fact they are doing only 64mph.

Mick.

[FROSTYBALLS]

The speedometers are optimistic within certain parameters to comply with current legislation - period.

[Mick F]

I don't agree.

The car knows its distance as the odometer is spot on.  It has been said up-thread that the OBD port can read the speed correctly.  The speedo is a modern digitally operated one and not the old fashioned rotating magnet and spring unit driven by a Bowden cable.  They do not need to have the speedo 7% high, they could have it spot on just like the odometer.

All they need is the will to do it, but they don't have the will at all.

Why not?  It's because it looks better and the manufacturers sell speed.  Why have a speedo that reads up to 140mph, when the car would struggle to reach 90mph?

Mick.

[FROSTYBALLS]

Whether or not you agree is immaterial. The speedometer meets legal requirements and there is no reason for any manufacturer to go beyond this.

[Mick F]

No reason?

That is an absolute statement.

You and I know that there is a reason (or even more than one reason) why they could or even should fit better speedos.  The fact that they don't make their speedos accurate as well as read up to a ridiculous 140mph, is a conscious decision that they make.  Also, the data from the OBD is there but they deliberately choose not to use it.

Mick.

[FROSTYBALLS]

Obviously the fact that speedometers may be capable of reading a higher speed than one model within a range may be capable of, is part of production standardisation, which allows them to fit the same instrument across the majority of the range.

Of the 21 new cars we've owned from a variety of manufacturers (Nissan, Mazda, Honda, Hyundai and Toyota), all have had a similar arrangement.

Similarly all the speedometers on our cars have been optimistic within certain parameters, allow for a certain margin of error to take account of things such as tyre wear, etc and meets legal requirements - which is all the manufacturer is concerned with, whether that is Toyota, Mercedes, or whoever.

Whereas having a speedometer which is 100% accurate at one point in the vehicle's use, may not meet legal requirements throughout the use of a car due to tyre wear, etc. 

Overall there are more important things to worry about whether the accuracy of your speedometers is 100% or 109%.

[Mike J.]

1 hour ago, FROSTYBALLS said:

Whereas having a speedometer which is 100% accurate at one point in the vehicle's use, may not meet legal requirements throughout the use of a car due to tyre wear, etc.

It is possible that some tyres may actually be a few percent oversize and so, if I was involved, I would set the speedo software to take this into account as legally it must not under-read. Note that as tyres wear, the speedo will increasingly over-read.

[bathtub tom]

8 hours ago, Mick F said:

The car knows its distance as the odometer is spot on.  It has been said up-thread that the OBD port can read the speed correctly.  The speedo is a modern digitally operated one and not the old fashioned rotating magnet and spring unit driven by a Bowden cable.  They do not need to have the speedo 7% high, they could have it spot on just like the odometer.

 

The speedo and odo can never be spot on, unless they use GPS or similar and even then there will be some error. New tyres normally have around 8mm of tread and assuming they're replaced at 2mm, that means there's a 12mm difference in diameter between new and old. When you also take into account manufacturing tolerances and the difference between the total diameter of different manufacturers of the same size of tyre..................................................................

[FROSTYBALLS]

4 hours ago, Mike J. said:

Note that as tyres wear, the speedo will increasingly over-read.

Yes - and the vehicle manufacturers have to take this into account to ensure the speedometer won't exceed the maximum parameter of current legislation.

[Byzii]

This is such a weird thread. The correct answer has been posted numerous times and yet few individuals keep coming back and stew in their own close-mindedness. Really weird.

This reads like that thread where people were discussing why the fuel gauge doesn't move for the first few dozen miles when tank is full. This is what happens when people have no problems, they create them.

[mrpj]

 

13 hours ago, Byzii said:

This is such a weird thread.

Because FB always has to have the last word and hates to be contradicted!

[FROSTYBALLS]

27 minutes ago, mrpj said:

Because FB always has to have the last word and hates to be contradicted!

Got no issue with being contradicted, as I have been numerous times on the forums. So back to the topic subject please.

[Mick F]

I started this thread in an effort illustrate the inaccuracies in speedo.  I feel I've done that fine.

The issue of the reasons for the inaccuracies are in contention.  You all know my opinion on this.  Speedos are no more accurate than they have ever been in my nearly 50years of car ownership despite the massive advances in technology.

Mick.

[FPSUsername]

On 10/8/2018 at 6:07 PM, YarisHybrid2016 said:

As for GPS recorded speed - this is also subject to error and is NOT precise!

At least the GPS recorded speed seems more accurate. Most road limits here are 100/120kmh. I usually drive 103-105 or 123-125 on the GPS, while the tacho shows 110 or 130. I haven't had a single ticket for speeding, so I believe that the speed of the car is way off. It only makes me think that manufacturers do this so that in the end, your car drove more kilometers than it actually has, thus decreasing the value of your car.

[Catlover]

The manufacturer, if they have any snens, will always be on the safe side of the law....in my opinion. Can you imagine the problem if a car was pulled up for speeding and it was proved the speedo (fitted by a manufacturer) was incorrect, thus making you think you were at or under the speed limit, when actually you were over it.

All car manufacturers seem to do the same with the speedos...... tells a story. Tells me the manufacturers are not stupid, if nothing else.

[FROSTYBALLS]

2 hours ago, FPSUsername said:

It only makes me think that manufacturers do this so that in the end, your car drove more kilometers than it actually has, thus decreasing the value of your car.

Nothing to do with the quoted extract.

Most countries have legislation that requires speedometers to not under read, and to over read within certain parameters.

For example in the UK it is illegal for speedometers to read less than the true speed. Speedometers are also required to show no more than 110% of the true speed, and for speeds between 25mph and 70mph, must not read more than 110% of the true speed plus 6.25mph. So for a car travelling at a true speed of 50mph, the speedometer must show no more than 61mph.