UK Speedo accuracy of the Tesla MS

Rluner said:

I've been reading some posts on another forum, and it seems that speedo accuracy on some EVs is like most ICE cars I've ever had ie about ten percent faster than it should be. These weren't Tesla owners btw.

Ive checked a number of times my Tesla speedo against at least two other GPS devices and every time the MS has been bang on accurate to real speed shown on the independent GPS devices.

So now I'm wondering are all UK MS speedos accurate but other EVs aren't , or an I just lucky?

Click to expand...

Tesla speedo (worldwide) is generally regarded as extremely accurate, unlike those of pretty much all other cars which deliberately overstate speed.

I think it's bang on real speed. Maybe it is itself tied into the car's GPS, if not augmented/calibrated by it.

Certainly at 70 mph cruise control you are over taking many people on the motorways who probably also have their cruise set at "70".

It's been my experience to get a circa 10% over read in most cars (VW Group, Nissan, BMW all seem to do it) but it's not guaranteed. In my "toy" car I have a GPS tracker dashcam, and the speedo is accurate within 1 mph up to 150. (Yes this really was on an Autobahn).

Finally a car sold in the UK with an accurate speedo!

It has always been a personal bugbear that instantaneous speed is reported to the nearest mph on digital speedos but is only accurate to the nearest 5 mph or so at typical cruising speeds (my experience in many different car makes & models): the mismatch between accuracy and precision really grates. One more item to add to the list of Reasons I Love the Model S!

I thought that manufacturers deliberately give a faster reading so the Speedo accuracy/inaccuracy couldn't be used as a defence for speeding, and therefore, they couldn't be sued.

TC56 said:

I thought that manufacturers deliberately give a faster reading so the Speedo accuracy/inaccuracy couldn't be used as a defence for speeding, and therefore, they couldn't be sued.

Click to expand...

I think it's more to do with getting type approval. The regulations have a tolerance range of 0% to 10% (not +/-5%) so the mainstream manufacturers just aim for the middle. Whether type approval rules were done to prevent using inaccurate speedos as a speeding defense is possible, but it's more likely they don't have to worry about different wheel options within the same model line causing the speedo to go outside the accepted tolerance.

TBH this might be why the Lotus is accurate, because it has very specific tyres (the correct ones have LTS stamped on them) and there are no wheel options. Either way both it and the Tesla flash up on those roadside speed signs as accurate to the speedo reading.

My p85+ consistently reads 1mph faster than actual. I've tested this with multiple GPS units as well as a stopwatch along measured miles.

This is between 60 and 80 mph.

HankLloydRight said:

My p85+ consistently reads 1mph faster than actual. I've tested this with multiple GPS units as well as a stopwatch along measured miles.

This is between 60 and 80 mph.

Click to expand...

Interesting.. but it still falls into the car reads more than actual, which is good

I think the issue here in the UK is most cars (esp. VW) at 60mph indicated speed would show be nearer 55mph in GPS terms, so for us UK owners even 1mph out is something of a novelty

interesting, I always test my new car's speedo against gps.
My previous Audis (A5/RS5) have been pretty much spot on -0/+1mph; the MB i have now is +2mph (all at 60mph), Mini is +3mph

The +/-10% is a really old regulation back from the days when speedos were spring balanced, these days they are almost invariably stepper motor driven so there is no reason for such a wide tolerance.

The practical effect is you can no longer assume your speedo is 10% fast when interpreting it vs the speed limit!

Displayed Fuel readouts funnily enough seem to be less accurate whic his odd given the picolitre accuracy of injection! Audi typiclly are invariably -10% so the disaply reading 37mpg actually would be more like 33mpg. This always inceansed me as you would hear people claiming they got over 40mpg and effectively selling this performance to all who would listen, when the reality was that is was in the mid 30's. A disgraceful practice on the part of Audi.

thegruf said:

Displayed Fuel readouts funnily enough seem to be less accurate whic his odd given the picolitre accuracy of injection! Audi typiclly are invariably -10% so the disaply reading 37mpg actually would be more like 33mpg. This always inceansed me as you would hear people claiming they got over 40mpg and effectively selling this performance to all who would listen, when the reality was that is was in the mid 30's. A disgraceful practice on the part of Audi.

Click to expand...

Tesla aren't immune from playing silly games with numbers. Of course in Audi's case they use it to gain over competitors, in Tesla's case (as they don't really have any direct competitors) they use it to up sell in the line-up.

My car, an S60 uses a different Wh calculation than an S85, and the only logical explanation is like Audi they are going for "sales optics" over accuracy

I can almost guarantee to exceed range even driving at 70mph, where as the 85 will show a much harder figure to achieve. However Joe Punter takes a quick test drive in both, and going off the dashboard thinks the gap is even greater than it is in reality.....

It will certainly be interesting to see how they position the 70D's calculation

Regarding fuel/energy consumption, for ICE cars I've found a site like fuelly.com is a good way of judging real life fuel consumption. The figures there are based on fuel supplied to the tank so doesn't rely on the car's dashboard estimates. Averaged over several years my Prius has over-estimated its mpg figures (i.e. presented better fuel efficiency than it is really achieving) by about 7% or 3-4 mpg (but still reports them to 1 decimal place :cursing

I don't know if there is something similar for BEV cars? I can see there is a thread on here where drivers report their lifetime Wh/mile but it would be more helpful to have a bit more granularity, e.g. monthly averages to see seasonal effects. Also the figures are relying on Tesla's calculation which, as smac comments, can be tinkered with for different models. A more helpful real-world figure would be the amount of electricity drawn from the supply but maybe that isn't typically metered, either at home or at public / supercharger points?

cezdoc said:

but it would be more helpful to have a bit more granularity, e.g. monthly averages to see seasonal effects

Click to expand...

Completely! My Wh/mi swings wildly. There is a definite "setting off" tax below 15c. The first few miles the regen is limited, and it destroys WH/mi, I think because the car is also actively heating the pack.

Bear in mind my car does 99% of it's miles going between my home and office in start stop city traffic. I'm getting c.250 Wh/mi some days on my commute, which is frankly amazing.

However during winter, the car leaves with a cold battery, tiny amount of regen, and I struggle to get below 500Wh/mi for the same journey, the regen is just starting to become uncapped at this point but by then it's too late. The car sits outside cooling off, all day, then I get back in and repeat this process.

My last 1500 miles (all "summer" usage) I'm at 311Wh/mi average.
However this pattern of constant usage with a cold pack for short journeys has meant my overall average has been as high as 375Wh/mi.