Speedo accuracy

[AWo]

At least for Germany I think that is fully legal and quite normal. A 10% difference is fine, as long as the measured speed is higher than the real speed. The other way around is not allowed.

You need to check the speed and maybe adjust it, when you mount wheels with a larger diameter, as that speeds up the car while measuring the same speed at a given RPM.

With 5% lower I wouldn't worry about.

AWo

 

[Jeremy996]

The rules for the UK, (and still for EU), are never over the true speed and up to 10% under. If you change wheels and tyres, it is your responsibility to ensure that you still comply.

How you would recalibrate the Grenadier's speedo is anyone's guess at this time!

 

[LeeroyJ]

Sorry to rez an old thread, but I have my Grenadier in the shop getting the door button recall done and updating to the newest OS. The dealer gave me a loaner and I noticed on the loaner vehicle that the GPS speed through Apple Car Play does not match the speedo. On my Grenadier with 315 tires, the two are basically always matched. So, on stock tires the Grenadier is reading that it is going faster than it actually is (by ~5% according to earlier posts in this thread). I was considering on the drive home, what does that translate into in terms of impact to owners? Three main things came to mind, each negative:

1) Your fuel economy is 5% worse than you are calculating

2) Your service intervals are 5% more frequent than needed

3) Your warranty is 5% shorter than it should be

These may not be big deals, but they are worth considering, especially if there are any warranty claims that get denied within that 5% margin (i.e. in the US before five years or 63,000 miles on stock tires).

Ironically this is another positive attribute in favor of getting larger tires

 

[landmannnn]

Sorry to rez an old thread, but I have my Grenadier in the shop getting the door button recall done and updating to the newest OS. The dealer gave me a loaner and I noticed on the loaner vehicle that the GPS speed through Apple Car Play does not match the speedo. On my Grenadier with 315 tires, the two are basically always matched. So, on stock tires the Grenadier is reading that it is going faster than it actually is (by ~5% according to earlier posts in this thread). I was considering on the drive home, what does that translate into in terms of impact to owners? Three main things came to mind, each negative:

1) Your fuel economy is 5% worse than you are calculating

2) Your service intervals are 5% more frequent than needed

3) Your warranty is 5% shorter than it should be

These may not be big deals, but they are worth considering, especially if there are any warranty claims that get denied within that 5% margin (i.e. in the US before five years or 63,000 miles on stock tires).

Ironically this is another positive attribute in favor of getting larger tires

The speedometer over reads by about 5%, however the odometer is correct.
Standard for vehicles outside of North America as the rules on speedo accuracy differ.

 

[LeeroyJ]

The speedometer over reads by about 5%, however the odometer is correct.
Standard for vehicles outside of North America as the rules on speedo accuracy differ.

How do you know the odometer is correct? How would that even work?

 

[Jeremy996]

How do you know the odometer is correct? How would that even work?

In the UK you can check it against the 100m posts on motorways.

 

[landmannnn]

How do you know the odometer is correct? How would that even work?

I've tested the odometer against GPS over a set distance and they both agree. (Unlike the speedometer of course)

 

[pmatusov]

Changing from 32” standard tyres to 33” corrects that to almost spot on.

Especially changing from 31.6" factory tires (265/70R17) to a slightly tall 33". My speedometer is now frighteningly accurate, and previously-accurate odometer is not.

 

[pmatusov]

1) Your fuel economy is 5% worse than you are calculating

2) Your service intervals are 5% more frequent than needed

3) Your warranty is 5% shorter than it should be

With new tires 5% taller than factory, your odometer reads 5% short of actual.
So, your fuel economy is 5% better than you are calculating.
Your service intervals need to be 5% more frequent than what odometer shows.
Your odometer mileage-derived warranty is 5% longer than actual.

 

[LeeroyJ]

With new tires 5% taller than factory, your odometer reads 5% short of actual.
So, your fuel economy is 5% better than you are calculating.
Your service intervals need to be 5% more frequent than what odometer shows.
Your odometer mileage-derived warranty is 5% longer than actual.

That is only true if the odometer is accurate, which I still scratch my head at. What is the Grenadier using to drive the odometer if it is not the speedometer? Is there a second speed reader that is not 5% off like the speedometer? That seems strange to me.

Edit - Unless the speedo is accurate and Ineos has programed the display unit to add 5% more speed to what it shows us? That also would be strange. The laws that permit variance in speed rating within a permissible range were written back in the analog days when speedos were a challenge to manufacture beyond a certain tolerance, those days are effectively gone.

 

[pmatusov]

That is only true if the odometer is accurate, which I still scratch my head at. What is the Grenadier using to drive the odometer if it is not the speedometer? Is there a second speed reader that is not 5% off like the speedometer? That seems strange to me.

Both odometer and speedometer are likely driven off the same tone wheel in the drivetrain or ABS sensors. What the gauges display is up to the engineers.

In a stock vehicle, the speedometer must read higher than actual speed by law in many countries. There's no such requirement for an odometer; Tesla apparently has been caught red-handed racking up odometer miles faster than actual. I found my Grenadier's odometer error less than 0.5% with factory tires, but the speedo used to read about 5% high (exactly the same in every Land Rover I owned). The 33.1" tires are taller than factory by about 4.6%, which made up for speedo error but now I have to account for it in anything related to the odometer (gas mileage).

 

[Blackwolf]

Speedometers are designed to over-read. The reason is that (in the UK at least) historically the regs say the accuracy must be in the +10% to -0% range ,i.e., it can show a speed 10% higher than the actual speed but must not display a speed lower than the actual speed. Since it has generally been impossible to manufacture a traditional mechanical speedo to these tolerances, makers have fitted instruments designed to over-read by 5% +/- 5% thus assuring compliance.

There is no correlation on modern electronic instruments between speedometer and odometer functions, they both count pulses (usually from the ABS reluctor rings, sometimes from the transmission) but are calibrated independently so there is absolutely no reason why an over-reading speedo can't be paired with a perfectly accurate odo. Change the rolling circumference of the tyres, however, and accuracy of both will change.

In the UK the Association of Chief Police Officers (ACPO) used to issue guidelines recommending that motorists exceeding the speed limit but under the limit plus 10% plus 3 mph were not prosecuted but these was just a recommendation, it was still an absolute offence. These guidelines seem to be rather ignored now that motorists seem universally to be considered evil.

 

[OkGo]

Driving through a couple of villages with the 'check your speed' thingy bobs and they seem to agree with the speed displayed inside the G, but this in the 25 to 40mph range.

Pretty sure 66mph is reported as 70mph on the motorway.

 

[Blackwolf]

In the UK, SIDs (Speed Indicating Devices) also tend to exaggerate your speed to encourage you to slow down. Do not count on them to be spot on, some are, most are not.