With the GPS and all of the onboard computer power, it seems that Tesla could put a routine into our cars to periodically calibrate the speedometer. In every range video I watch, the tester has to set the cruise control a little bit high. For my Model 3, when I go through a radar "trap", I am typically going 2 to 3 mph below indicated. I can do the math, and set things appropriately, But it seems like an easy fix for Tesla.
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Calibrating Speedometer
- Thread starter Smitty79
- Start date
Here is an article from 2002 about speedometers reading high (obviously not tesla):
I am not going to copy and paste the entire thing but here is one interesting quote from the body of the articule:
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There's your explanation of high-reading European speedometers, with the highest readings on Porsches and BMWs that are most likely to lure owners inclined to fool with tire sizes. Of course, only the speedometer must conform. Trip computers are free to report average speed honestly. Try setting your BMW or Porsche cruise control and then resetting the average-speed function. Unless you've screwed up the tires, the trip computer should show a nearly accurate reading. Even General Motors, whose domestic speedometers are the best, must skew its readings slightly high on vehicles exported to Europe.
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TL ; DR = not new, not a tesla issue, and the current regulations allow / encourage this because of differences in tire size etc.
ButchAZ
Member
I've never been through one yet that accurately showed my set speed. Every one here in Tucson shows 1-3 mph slower than you're actually going, regardless of what vehicle I'm driving.
At least part of the "error" is caused by the car display intentionally rounding up. Using the scanmytesla app and a blutooth canbus reader you can see what speed the car thinks it is going with 0.1 mph precision.
If the car thinks it is going 59.0 MPH it will show 59 on the dashboard, but if the car thinks it is going 59.1 MPH it will show 60 on the dashboard.
When setting cruise control to 60, the speed drifts around a bit, but it seems like the car is aiming for something closer to 59.1 than 60.0.
If the car thinks it is going 59.0 MPH it will show 59 on the dashboard, but if the car thinks it is going 59.1 MPH it will show 60 on the dashboard.
When setting cruise control to 60, the speed drifts around a bit, but it seems like the car is aiming for something closer to 59.1 than 60.0.
Candleflame
Active Member
I think you mean under read. they certainly are allowed to overread, and they all do.
Candleflame
Active Member
PianoAl
Active Member
They can, and do, read the discussion earlier in the thread. TL;DR they intentionally over report the speed to avoid issues with regulators.
Unless I'm mistaken, regulators only require speedos note to under-read. They don't require an overread. Instead the manufacturer to embeds a margin of error to avoid the issue. They could just as well provide something that is completely accurate and comply with the regulators.
Yes, that's my understanding as well. There is however not enough of an apparent benefit to the manufacturer to report the true speed versus over reading. Over reading on the other hand provides them a buffer from regulators. The technology exists, they report accurate distance data. The point is they can do it but choose not to.
Well, the technology certainly isn't that expensive. My bike computer measures the speed from a wheel sensor and periodically self-calibrates to within 1/10 mph using GPS. If car manufacturers can produce a vehicle that is stable at 150 mph, they can certainly develop an accurate speedo at minimal cost.
I'm pretty certain that modern cars have *precise* speedometers already. The inaccuracy is clearly *intentional*. The problem isn't the ability to do it. While i don't know this first hand I'm pretty sure this is the case of the lawyers/regulators "winning". There is effectively zero incentive for an auto manufacturer to remove the bias that they coded/built-in. This point was made by several posters before me. I'm just here to beat the dead horse.
While there is some propension to over-report as many have indicated, tire wear also affects the reading and makes it hard to be very precise. Does tire size and/or tread wear significantly affect speed and speedometer accuracy?
Granted we're talking a couple percent but at highway speeds that's more than 1mph difference.
Granted we're talking a couple percent but at highway speeds that's more than 1mph difference.
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