LC500 Speedo Accuracy

malcolmw · August 28, 2018

I have checked my LC500 speedo accuracy against my phone with a GPS speed app.

I am seeing 5% fast (i.e. at an indicated 80 I am actually doing 76mph).

Hope this is of interest. Can anyone else confirm this?

Jules640 · August 28, 2018

I have noticed that on a speed check sign near to where I live that it often shows that I am going 1-2 mph slower than the car speedo is showing.

I always assumed that it was the sign that was wrong but maybe it is the car. It would be a similar amount, about 5% difference and so is similar to what you are experiencing.

Herbie · August 28, 2018

Yep, all car speedos read on the high side. It's illegal for a car to be travelling faster than the indicated speed so manufacturers are allowed a margin of error.

Quote

A speedo must never show less than the actual speed, and must never show more than 110% of actual speed + 6.25mph. So if your true speed is 40mph, your speedo could legally be reading up to 50.25mph but never less than 40mph. Or to put it another way, if your speedo is reading 50mph, you won’t be doing more than 50mph but it’s possible you might actually only be travelling at 40mph.

The above is taken from https://www.thecarexpert.co.uk/how-accurate-is-a-car-speedometer/

steve2006 · August 28, 2018

Another thing to consider is if you have changed your wheels/tyres to a different size as this alters the rolling radius which can then affect speedometer accuracy including travelling at more than the indicated speed.

rayaans · August 28, 2018

3 hours ago, malcolmw said:

I have checked my LC500 speedo accuracy against my phone with a GPS speed app.

I am seeing 5% fast (i.e. at an indicated 80 I am actually doing 76mph).

Hope this is of interest. Can anyone else confirm this?

Sounds about right.

Try driving an Audi, its 10% or so! Makes you wonder about all those Audi drivers.....

ColinBarber · August 28, 2018

The following are from a couple of different Lexus repair manuals - the different laws in each country govern to some extent what is or isn't acceptable.

malcolmw · August 29, 2018

Now, if the speedo reading is taken from the wheel rotation sensors, what about the odometer output?

As per my original post above, my speedo is about 5% fast. Coincidentally, my fuel consumption readings are also about 5% too good when measured on the car computer compared to reality. Is this connected?

CallTheBall · August 29, 2018

17 hours ago, malcolmw said:

I have checked my LC500 speedo accuracy against my phone with a GPS speed app.

I am seeing 5% fast (i.e. at an indicated 80 I am actually doing 76mph).

Hope this is of interest. Can anyone else confirm this?

Just ask a policeman to follow you at 76mph as his speedo should be calibrated 😁

MNMJ · August 31, 2018

On 8/29/2018 at 10:46 AM, CallTheBall said:

Just ask a policeman to follow you at 76mph as his speedo should be calibrated 😁

Or drive at a steady 150mph on the clock and wait for the video to appear on one of those 'Police, Camera, Action' type shows?

ColinBarber · August 31, 2018

On 8/29/2018 at 9:33 AM, malcolmw said:

Now, if the speedo reading is taken from the wheel rotation sensors, what about the odometer output?

As per my original post above, my speedo is about 5% fast. Coincidentally, my fuel consumption readings are also about 5% too good when measured on the car computer compared to reality. Is this connected?

Speedo is designed to read over, the odo is designed to be accurate - probably to within 2%, due to tyre wear and different tyre/wheel size options the manufacturer offers which alter the circumference of the tyre.

MNMJ · September 1, 2018

The RC-F has a posted top speed of 270kph, which is limited. The limiter kicked in repeatedly on the autobahn at an indicated 285kph, which is about 5.5% over

September 1, 2018

38 minutes ago, MNMJ said:

The RC-F has a posted top speed of 270kph, which is limited. The limiter kicked in repeatedly on the autobahn at an indicated 285kph, which is about 5.5% over

can you recall the rpm in top when limiter hit?