IS300h Speedo Accuracy.

[malcolmw]

I have posted a similar question in another thread but...

Does this calibration error on the speedo affect the computed mpg as it seems that most on-board readouts are also 5 to 10% optimistic on fuel consumption?

[Hadrian]

That may well be the case. It depends on how clever the computer is.

[Herbie]

32 minutes ago, malcolmw said:

I have posted a similar question in another thread but...

Does this calibration error on the speedo affect the computed mpg as it seems that most on-board readouts are also 5 to 10% optimistic on fuel consumption?

First of all it's not an error, it's designed that way.

But to answer your question, although I don't know for sure and this is purely a guess, I'd say that.... I don't know  

What I can say is that my previous cars have run on LPG and the fuel gauge drops from full to empty and the computer shows mpg just as if the car was still using petrol, when of course, it isn't, so I've no idea what black magic is working in the background. I would think that mpg is calculated from various parameters and sensors such as throttle position, air temp, road speed and who knows what else but I don't think it would be affected by the calibration margins of the speedo. I think that he speedo is just a visual aid to the driver to give an indication of what's going on and doesn't actually do any measuring itself, but merely displays what it's told to display by the ECU. I think this would be especially true of the cars whose instruments are LCD displays rather than a physical needle displaying the speed.

But hey, I may be talking complete rubbish, I don't know.

[reeac]

Update. My IS300h had its 3 year service today at the local Lexus dealers. They said that they couldn't recalibrate the speedo. which reads 30 mph at an actual 27 mph. This surprises me, it being a digital instrument, as way back in 2006 we were able to calibrate our new set of boat instruments using the satnav and following instructions which came with the instruments. Seems that I'll have to live with this error and the fact that my 13 year old Jazz speedo is dead accurate and my cheapish quartz watch has an error of less than 30 seconds a month.

[NemesisUK]

Probably because, by law, the speedo must never under-read. So to protect themselves Lexus build-in a good safety margin.

Why is it so important the speedo is absolutely accurate? 

[Herbie]

2 hours ago, reeac said:

Update. My IS300h had its 3 year service today at the local Lexus dealers. They said that they couldn't recalibrate the speedo. which reads 30 mph at an actual 27 mph. This surprises me, it being a digital instrument, as way back in 2006 we were able to calibrate our new set of boat instruments using the satnav and following instructions which came with the instruments. Seems that I'll have to live with this error

Again - it's not an error, it's designed that way!

The technology does exist to calibrate the speedo to perfection but they cannot do that, there has to be a calibration margin because it is illegal for a speedo to under-read.

The fact that you could calibrate boat instruments is neither here nor there as I've never seen a fixed or average speed camera in the water and boats aren't subject to the road traffic acts, rules and regulations that road vehicles are.

[matt8]

Maybe you want one of these if speed is so important to you: https://ebay.us/2AW3zD

[reeac]

At least we agree that calibration of digital instruments is possible. I suppose that as a retired scientist I'm used to precision in measurement as a basis for drawing sound conclusions. Also I assume that we all like perfection in paint finish so why not in other areas?

Re boating, it's a big subject but we're talking sailing boats and speed through the water as measured with a mini paddle wheel and speed over the ground as measured with GPS (satnav in motoring terms) and wind speed and direction   which enable you to judge efficiency of the sail trim, speed of tidal currents ,expected time of arrival and so on. Whilst there are sometimes speed limits through mooring areas speeding is very seldom an issue with a sailing boat.

[Hadrian]

I use one of these.........http://www.indic8tor.com/

Then again, a Sat Nav will do the job.

[matt8]

1 hour ago, Hadrian said:

I use one of these.........http://www.indic8tor.com/

Then again, a Sat Nav will do the job.

You use this for speed cameras I assume. Not just as a speed indicator.

Seems expensive for what it is. And £29.95 a year to subscribe to updates. Ouch.

My dashcam from Thinkware has built in speed camera alerts and provides the updates for free. Not sure what costs are associated with obtaining or collating such data.

[Herbie]

I think the best speed cam database out there is the one done by these guys https://www.pocketgpsworld.com/subscription.php (that links to the description page so you can see how good it is)

It's just £19.99 per year, available for almost all stand-alone satnavs and both Android and apple phones. The database is generated by reports of cameras by the public and if you happen to be the first person to report a new camera, you get a years subscription free. It also covers all the different camera types - fixed, average, red light, mobile etc.

Well worth the money in my opinion.

[ColinBarber]

5 hours ago, reeac said:

At least we agree that calibration of digital instruments is possible. I suppose that as a retired scientist I'm used to precision in measurement as a basis for drawing sound conclusions. Also I assume that we all like perfection in paint finish so why not in other areas?

Not really possible on a road vehicle where the tread of a tyre ranges from 8mm to 1.6mm over its lifetime which affects speedo accuracy.

[Guest]

15 hours ago, Herbie said:

 

The fact that you could calibrate boat instruments is neither here nor there as I've never seen a fixed or average speed camera in the water and boats aren't subject to the road traffic acts, rules and regulations that road vehicles are.

Don't give them ideas 

[reeac]

1 hour ago, ColinBarber said:

Not really possible on a road vehicle where the tread of a tyre ranges from 8mm to 1.6mm over its lifetime which affects speedo accuracy.

We've covered this earlier.  I showed in a post of Aug. 29th that the variation from new to worn out tyre will be about 2 percent on diameter and hence on speedo reading i.e. 0.6 mph at 30 and 1.4 mph at 70 and I was claiming to be able to read the speedo to 1mph at best. I got the feeling though that I was being boring.

[ColinBarber]

27 minutes ago, reeac said:

We've covered this earlier.  I showed in a post of Aug. 29th that the variation from new to worn out tyre will be about 2 percent on diameter and hence on speedo reading i.e. 0.6 mph at 30 and 1.4 mph at 70 and I was claiming to be able to read the speedo to 1mph at best. I got the feeling though that I was being boring.

Speedos have to be within a certain accuracy for European law. Lexus could certainly make it more accurate, but why have that expense added to a vehicle if it isn't needed. On the IS for example there are three tyre/wheel sizes across the different grades - all have a different circumference but have the same speedo calibration, each one could be calibrated differently to improve accuracy but would add to manufacturing costs.

There are two threads on this topic at the moment. I posted the actual allowable speed tolerances that Lexus deem acceptable on the other one, if your speedo reads 70 mph when you are going 70 mph then it is faulty and should be replaced:

https://www.lexusownersclub.co.uk/forum/topic/117015-lc500-speedo-accuracy/

 

[Guest]

26 minutes ago, ColinBarber said:

Speedos have to be within a certain accuracy for European law.

Not from what I've seen on European beaches.

[Hadrian]

22 hours ago, matt8 said:

You use this for speed cameras I assume. Not just as a speed indicator.

Seems expensive for what it is. And £29.95 a year to subscribe to updates. Ouch.

My dashcam from Thinkware has built in speed camera alerts and provides the updates for free. Not sure what costs are associated with obtaining or collating such data.

I've never actually updated it.  It will indicate cameras which are in it's database, and you can add more by pressing a button while driving.

I have this in my BMax, and rely on the speed indicated on my Garmin when driving the Lexus. Although to be honest, I usually keep within

the speed limits anyway.