speedo accuracy
Discussion
if they are doing a zero tolerance on speeding, is there anywhere in the south where you can get your speedo checked and calibrated ???? even if it just dots on the cover to show 30 40 50 60 70.
also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
metelmickey said:
if they are doing a zero tolerance on speeding, is there anywhere in the south where you can get your speedo checked and calibrated ???? even if it just dots on the cover to show 30 40 50 60 70.
also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
Speedos will always over-read, so you'll need to be going ~54mph on the speedo to be actually going 50mph real speed.also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
Presume the op has a BMW given the post in the BMW section. Cars made for the EU must have speedos that are either correct or over read. BMW speedos normally over read slightly. If you want you can reprogram the cluster to give the actual speed with software such as Carly.
Or real speed as a digital display and the normal (over reading) speed on the dial.
Or real speed as a digital display and the normal (over reading) speed on the dial.
thebraketester said:
metelmickey said:
if they are doing a zero tolerance on speeding, is there anywhere in the south where you can get your speedo checked and calibrated ???? even if it just dots on the cover to show 30 40 50 60 70.
also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
Speedos will always over-read, so you'll need to be going ~54mph on the speedo to be actually going 50mph real speed.also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
Where issues can occur, is when people put different size tyres on a vehicle and don't ensure that rolling radius remains within the manufacturer's specification, or a replacement speedometer is fitted that is not from the same version of the car (think along the lines of fitting a replacement speedometer from a 320 into a 335)
Always wondered about this. Both cars I've owned in the past 10 years (1999 e46 and a 2012 f10) have matched my GPS speed from my phone upto 70 "or so" mph. Maybe 1mph off but I really didn't see anything more than that. Whys that then? Is there some sort of variance between models and I've been lucky? My f10 shows the speed on the HUD so I compared with that not the speedo.
thebraketester said:
metelmickey said:
if they are doing a zero tolerance on speeding, is there anywhere in the south where you can get your speedo checked and calibrated ???? even if it just dots on the cover to show 30 40 50 60 70.
also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
Speedos will always over-read, so you'll need to be going ~54mph on the speedo to be actually going 50mph real speed.also if they did how can they prove it, if your car says 50 mph who is to blame if you are doing 52 or 53 mph.
By law, speedos have to over-read in the UK, but by how much, there’s no official standard.
If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
obviously therefore, the automakers can calibrate quite accurately if they want to. I also think that modern cars (anything with a signal controlling the needle, rather than a cable) tend to be much more accurate - which is logical. My first car was a 4-speed mk2 1600 cavalier. It was geared for 19.9mph/1000 in top. 5krpm was about 115 on the speedo...
From my last 4 BMW, I’ve done numerous comparisons. Typically your speed will be fast by 2-3mph until 60mph (ish) at which point, there’s nothing in it. A cruise requested 160kph (100mph) is 100mph in the 7, is flickering between 99 & 100 in the M6. Same in the z4 or 335d previously owned.
If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
obviously therefore, the automakers can calibrate quite accurately if they want to. I also think that modern cars (anything with a signal controlling the needle, rather than a cable) tend to be much more accurate - which is logical. My first car was a 4-speed mk2 1600 cavalier. It was geared for 19.9mph/1000 in top. 5krpm was about 115 on the speedo...
From my last 4 BMW, I’ve done numerous comparisons. Typically your speed will be fast by 2-3mph until 60mph (ish) at which point, there’s nothing in it. A cruise requested 160kph (100mph) is 100mph in the 7, is flickering between 99 & 100 in the M6. Same in the z4 or 335d previously owned.
Prinny said:
By law, speedos have to over-read in the UK, but by how much, there’s no official standard.
If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
obviously therefore, the automakers can calibrate quite accurately if they want to. I also think that modern cars (anything with a signal controlling the needle, rather than a cable) tend to be much more accurate - which is logical. My first car was a 4-speed mk2 1600 cavalier. It was geared for 19.9mph/1000 in top. 5krpm was about 115 on the speedo...
From my last 4 BMW, I’ve done numerous comparisons. Typically your speed will be fast by 2-3mph until 60mph (ish) at which point, there’s nothing in it. A cruise requested 160kph (100mph) is 100mph in the 7, is flickering between 99 & 100 in the M6. Same in the z4 or 335d previously owned.
There IS an official legal requirement, basically speedo reading to actual has to be between plus zero and plus 10% plus 4kph.If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
obviously therefore, the automakers can calibrate quite accurately if they want to. I also think that modern cars (anything with a signal controlling the needle, rather than a cable) tend to be much more accurate - which is logical. My first car was a 4-speed mk2 1600 cavalier. It was geared for 19.9mph/1000 in top. 5krpm was about 115 on the speedo...
From my last 4 BMW, I’ve done numerous comparisons. Typically your speed will be fast by 2-3mph until 60mph (ish) at which point, there’s nothing in it. A cruise requested 160kph (100mph) is 100mph in the 7, is flickering between 99 & 100 in the M6. Same in the z4 or 335d previously owned.
UNECE regulation 39
You will notice that there is no test requirement for conformity below 40kph (just over 24 mph)
https://www.unece.org/fileadmin/DAM/trans/main/wp2...
Pica-Pica said:
There IS an official legal requirement, basically speedo reading to actual has to be between plus zero and plus 10% plus 4kph.
UNECE regulation 39
You will notice that there is no test requirement for conformity below 40kph (just over 24 mph)
https://www.unece.org/fileadmin/DAM/trans/main/wp2...
Dind’t know that! Interesting, & thankyou.UNECE regulation 39
You will notice that there is no test requirement for conformity below 40kph (just over 24 mph)
https://www.unece.org/fileadmin/DAM/trans/main/wp2...
The problem with using cheap satnavs and the GPS systems on phones for determining speed is that their scanning frequency is only about 1Hz, this isn't fast enough for accuracy. Couple this with systems which calculate based on positions, distance between recorded position vs time taken, and whilst these give an indication they are nowhere near enough accurate for the level of accuracy you are after. Two options, sorry three options, one go to a firm who can calibrate the equipment, thus is expensive.
Second option, is to use proper data logging kit with higher scanning frequency, 20Hz is minimum, 100Hz is good, and uses doppler shift on the GPS signals to calculate speed. This is my method, simply as I have that sort of kit available.
Third option is the old fashioned way. Find out the location of publicly available measured miles and the identifying marks. The county surveyor will know, alternatively traffic coppers if you explain nicely are usually helpful. Once you have identified that, get yourself an accurate stopwatch, go out to the location with a reliable passenger operating the watch, and time how long it takes you to cover the set distance at a number of steady speeds. It's hard as a driver to hold it for a mile from start to finish at an exact 60, and you will have a number of runs where you either cock it up or have to abort due to other traffic. If you pick a quiet time you'll get enough decent runs at various speeds so tgat you know for example it take 61/ 61.2 / 60.9 seconds to do a mile at indicated 60 mph, average those out and you will get an idea of how much the speedo is out. My method then would be to bang the data into Excel, graph it out in an XY chart, draw a best fit line through the data, from that you can interpret the estimated speedo indication for a true 30, 40, 50 etc and mark up the dial how you wish.
No doubt the usual multiple identity trolls from the speed enforcement industry will be along to spout their twaddle. They can FRO.
Second option, is to use proper data logging kit with higher scanning frequency, 20Hz is minimum, 100Hz is good, and uses doppler shift on the GPS signals to calculate speed. This is my method, simply as I have that sort of kit available.
Third option is the old fashioned way. Find out the location of publicly available measured miles and the identifying marks. The county surveyor will know, alternatively traffic coppers if you explain nicely are usually helpful. Once you have identified that, get yourself an accurate stopwatch, go out to the location with a reliable passenger operating the watch, and time how long it takes you to cover the set distance at a number of steady speeds. It's hard as a driver to hold it for a mile from start to finish at an exact 60, and you will have a number of runs where you either cock it up or have to abort due to other traffic. If you pick a quiet time you'll get enough decent runs at various speeds so tgat you know for example it take 61/ 61.2 / 60.9 seconds to do a mile at indicated 60 mph, average those out and you will get an idea of how much the speedo is out. My method then would be to bang the data into Excel, graph it out in an XY chart, draw a best fit line through the data, from that you can interpret the estimated speedo indication for a true 30, 40, 50 etc and mark up the dial how you wish.
No doubt the usual multiple identity trolls from the speed enforcement industry will be along to spout their twaddle. They can FRO.
Pica-Pica said:
I find that hard to believe, can you quote a regulation?
No, afraid not. Many years ago I looked into it as I had a Japanese import MR2 with a Kmph speedo which I converted to mph. I found the info about Japanese speedo law online-the source seemed reliable but I can’t find anything currently to back up the info. E-bmw said:
^^^^ Wot 'e said.
But just bear in mind that if your wheels/tyres are a different size to standard they could read differently.
Use a satnav/phone to calibrate it if you need to as on a straight road at a steady speed it is MUCH more accurate.
If you od the traditional kind of wheel swap and go up 1" on the wheel and down a profile size, the new wheel will have a rolling radius about 3% bigger. In my experience this means the tacho is often corrected to close-to-precision as most speedometers over-read by 3%-10%But just bear in mind that if your wheels/tyres are a different size to standard they could read differently.
Use a satnav/phone to calibrate it if you need to as on a straight road at a steady speed it is MUCH more accurate.
Prinny said:
By law, speedos have to over-read in the UK, but by how much, there’s no official standard.
If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
That's strange, because one of my BMWs that apparently reads 30 when doing 27 is a Z4, so it was built in Spartanburg! If you get a US car (any manufacturer), you’ll typically find the speedo accurate to within 1mph. Relating that to BMW, a Z3 speedo (as built in SC) will typically be more accurate than the equivalent in the e30/e36 3-series.
Do they maybe calibrate them differently according to where they are being sold?
My other one is an E91, so it was built in Munich.
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