Speedometer accuracy

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J-R
Posts: 55
Joined: Wed Jan 09, 2019 4:02 pm
Location: Israel

Speedometer accuracy

Post by J-R » Mon Mar 11, 2019 7:00 am

Hi all,

At highway speeds, my MY19 Kodiaq's speedometer consistently shows that I am driving 5-6 km/h faster than what Waze is showing me. Since Waze is constantly calculating the speed based on actual distance traveled divided by time, and I have no way of knowing how the car is calculating it, I would tend to trust Waze more.

I realize that this doesn't matter much, and I can simply add a few km/h to what I see, and it will reduce my chances of getting a speeding ticket ... but it's still annoying. :?

Has anyone else noticed this? Is there any way to calibrate the speedometer to be more accurate?

Thanks,
JR
2019 Kodiaq 2.0 TDI 150bhp, 7-speed DSG, 2WD, 18" wheels, 7 seats, metallic silver, Kessy, Bolero, 3-zone climate, wireless cellphone charging, 9 airbags, Adaptive Cruise Control, blind spot warning, front & rear parking sensors, reverse camera.


Professor1999
Posts: 100
Joined: Sat Apr 21, 2018 9:46 pm
Location: London

Re: Speedometer accuracy

Post by Professor1999 » Mon Mar 11, 2019 7:48 am

Hi
My speedo is consistently 2-3 mph above my tomtom satnav speed. I had exactly the same experience with my previous car, a Santa fe. Think it is car manufacturers being prudent. As a result i often drive 2-3 mph above speed limit through speed cameras and average speed camera stretches and have not had any issues.
Kodiaq Sportline 1.4 TSI 7st 4WD Velvet Red
Pan roof; Rear view camera; Adaptive cruise control; Spare wheel


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Colin Lambert
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Location: Poole Dorset

Re: Speedometer accuracy

Post by Colin Lambert » Mon Mar 11, 2019 8:00 am

All car speedos have to be 2-3 mph over actual speed as they are not going to run the risk of being sued for reading low and user being prosecuted.
All modern speedos are electronic and as far as I know they cannot be 'tampered with'.
Accurate speed will be given by at nav, but not unfortunately in Skodas (and most other built in systems) as, for some reason they will not give a speed reading.
ModeratorSE L.1.5DSG. Emerald green. S/s spare, Paddles, f&r sensors, rear camera. KAROQ. :shock: EX Kodiaq SE L1.4 DSG.
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Retirement is wonderful, it's doing nothing without being caught out! :lol:
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J-R
Posts: 55
Joined: Wed Jan 09, 2019 4:02 pm
Location: Israel

Re: Speedometer accuracy

Post by J-R » Mon Mar 11, 2019 8:57 am

Very interesting, Colin, I was not aware that this was done deliberately. I looked online a bit and found the following references on the topic, if anyone besides me is interested!

JR

"Most speedometers have tolerances of some ±10%, mainly due to variations in tire diameter. Sources of error due to tire diameter variations are wear, temperature, pressure, vehicle load, and nominal tire size. Vehicle manufacturers usually calibrate speedometers to read high by an amount equal to the average error, to ensure that their speedometers never indicate a lower speed than the actual speed of the vehicle, to ensure they are not liable for drivers violating speed limits." (Wikipedia)

"The difference between actual speed and the speed dial tends to get noticed more with German cars because their speedometers are designed to never report a speed lower than actual speed. European law (ECE-R39) says speedometers cannot show speeds less than the actual speed, and they must never show more than the 110 per cent of actual speed plus 4 km/h. So, under those rules, a car could be moving at 100 km/h, but the speedometer could legally display as high as 114 km/h." (The Globe and Mail (Canada))

"When traveling at a true 70 mph, as indicated by our highly precise Datron optical fifth-wheel equipment, the average speedometer (based on more than 200 road-tested vehicles) reads 71.37 mph. ... Sorted by price, luxury cars are the least accurate, and cars costing less than $20,000 are the most accurate. By category, sports cars indicate higher speeds than sedans or trucks. Cars built in Europe exaggerate more than Japanese cars, which in turn fib more than North American ones. And by manufacturer, GM's domestic products are the most accurate, and BMW's are the least accurate by far. One other trend: Only 13 of our 200 test speedos registered below true 70 mph, and only three of those were below 69 mph, while 90 vehicles indicated higher than 71 mph." (Car & Driver)

"If we combine [the US & UK] regulations, you end up with a car manufacturer standard of calibrating speedometers to show you are going faster than you really are, by about 3-4 mph. It's my guess they do it this way so they meet both US and UK regulations with one standard." (OEC)
2019 Kodiaq 2.0 TDI 150bhp, 7-speed DSG, 2WD, 18" wheels, 7 seats, metallic silver, Kessy, Bolero, 3-zone climate, wireless cellphone charging, 9 airbags, Adaptive Cruise Control, blind spot warning, front & rear parking sensors, reverse camera.


Daddy2Bears
Posts: 94
Joined: Fri Sep 29, 2017 11:08 am
Location: Cardiff, Wales

Re: Speedometer accuracy

Post by Daddy2Bears » Mon Mar 11, 2019 11:56 am

What annoys me most is if I set the cruise control to 70 the digital speedo will show 70 but the dial shows just above the 70 mark. Why the 2 aren't in synch annoys me only 'cos I believe it's sloppy implementation. would be happy if it was actually 68 but both digital & dial showed 70.
190 TDI 7 Seat Edition
Petrol Blue, Black Leather, Front Isofix, Tow bar Prep, Canton, Spare Wheel, ACC, Park Assist, Heated W/S-Wipers, Alu Pedals, Area View, Ambient Lighting, Personal Drive Mode Select
Various VAG-COM tweaks
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Kenny R
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Location: East Lothian

Re: Speedometer accuracy

Post by Kenny R » Mon Mar 11, 2019 12:58 pm

Daddy2Bears wrote:
Mon Mar 11, 2019 11:56 am
What annoys me most is if I set the cruise control to 70 the digital speedo will show 70 but the dial shows just above the 70 mark. Why the 2 aren't in synch annoys me only 'cos I believe it's sloppy implementation. would be happy if it was actually 68 but both digital & dial showed 70.
They both read the same, the only difference is parallax error on the analog dial.
Candy White 2.0 TSi SE L 7 seat. Heated windscreen/ nozzles, kids pack, front rear parking sensors, reversing camera and spare wheel, Milotec rear bumper inserts.
And for the winter months: 17” Black alloys with 215x65x17 Nokian WR SUV3 winter tyres.


Old and Grumpy
Posts: 113
Joined: Sat Oct 13, 2018 1:59 pm
Location: Melton Mowbray

Re: Speedometer accuracy

Post by Old and Grumpy » Mon Mar 11, 2019 2:26 pm

Why is everybody so obsessed with driving as fast as possible without getting fined? Unless you are driving a very long way and are able to maintain a constant speed, (how often can you do that with today's traffic conditions?), the difference in arrival time between 68mph and 70mph will be negligible. Relax, enjoy the journey and arrive less stressed and a nicer person.

While we are considering this, how about all those people who tell me that the mpg displayed by my "Bear" isn't accurate because the fuel measurement isn't accurate. They claim that they get a better figure by using the miles travelled and the amount of fuel taken to top up the tank. But they are still using the mileage recorded by the car, which is electronically linked to the mph displayed. If the mpg is inaccurate then so are the miles covered. Or do they have some other way of calculating their mileage? If they use a map do they allow for the effects of the map projection, the fact that distances are reduced to nominal sea level, map distances are on the horizontal plane and are not corrected for hills, etc. etc. The best possible measurement of distance is probably from GPS/Satnav devices so do they use these and top ups in their calculations?

Right, rant over. Back to the gardening.
Kodiaq SE 1.4 TSI, 2WD, Manual gearbox, 5 seater, Petrol blue, absolutely standard, no extra toys.
My best car in 55 years of driving, including my previous Superb. :)


DaveM
Posts: 180
Joined: Tue Oct 03, 2017 7:24 pm
Location: West Midlands

Re: Speedometer accuracy

Post by DaveM » Mon Mar 11, 2019 3:46 pm

I agree with most of what's said above, and when adjusting the mechanically-driven speedos of a couple of old cars have used satnav to calibrate them.

As long as you’re getting decent satellite signal, and speed is fairly constant, a satnav unit will give quite a good reading ... on the flat. I understand that they calculate in “flat” mode - that is, the speed which the vehicle seems to be doing when viewed from above. A car charging down a steep hill will be doing a bit more, relative to the road surface, than the top view suggests!
Kodiaq 1.4 DSG SEL 5-seat, capuccino, beige leather, rear camera, front sensors, triglavs, tow hook.


Daddy2Bears
Posts: 94
Joined: Fri Sep 29, 2017 11:08 am
Location: Cardiff, Wales

Re: Speedometer accuracy

Post by Daddy2Bears » Mon Mar 11, 2019 4:47 pm

Kenny R wrote:
Mon Mar 11, 2019 12:58 pm
Daddy2Bears wrote:
Mon Mar 11, 2019 11:56 am
What annoys me most is if I set the cruise control to 70 the digital speedo will show 70 but the dial shows just above the 70 mark. Why the 2 aren't in synch annoys me only 'cos I believe it's sloppy implementation. would be happy if it was actually 68 but both digital & dial showed 70.
They both read the same, the only difference is parallax error on the analog dial.
Kenny,

You are right, although having just tried it out on the way home, I'd need to have my head touching the roof for it to read right, and my arms wouldn't reach the armrests from up there!

Wouldn't have said I'm the shortest of drivers either (5'10 without heels 🤣)
190 TDI 7 Seat Edition
Petrol Blue, Black Leather, Front Isofix, Tow bar Prep, Canton, Spare Wheel, ACC, Park Assist, Heated W/S-Wipers, Alu Pedals, Area View, Ambient Lighting, Personal Drive Mode Select
Various VAG-COM tweaks
Image


Old and Grumpy
Posts: 113
Joined: Sat Oct 13, 2018 1:59 pm
Location: Melton Mowbray

Re: Speedometer accuracy

Post by Old and Grumpy » Mon Mar 11, 2019 4:53 pm

DaveM wrote:
Mon Mar 11, 2019 3:46 pm

As long as you’re getting decent satellite signal, and speed is fairly constant, a satnav unit will give quite a good reading ... on the flat. I understand that they calculate in “flat” mode -
Probably true for Satnav, but GPS receives and records in three dimensions, (Latitude, Longitude, Height), so could be computed to allow for hills. However you would still have the adjustment to convert from WGS84 satellite datum coordinates to "real life" Lat and Long and Height.

It's all too much effort to be worth it. I'll stick to using the "Bear's" brains to calculate my mpg. Even if it isn't absolutely accurate it will be the variations over time that will be useful in monitoring the beast's performance.
Kodiaq SE 1.4 TSI, 2WD, Manual gearbox, 5 seater, Petrol blue, absolutely standard, no extra toys.
My best car in 55 years of driving, including my previous Superb. :)


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