Calibrated speedo's. why don't we have them??
Discussion
mcflurry said:
With all this emphasis on exact units of speed, why don't the government give us a fighting chance and make the car manufacturers give us accurate speedo's?
Costs too much..
(and would be inaccurate as soon as tyre wear kicked in)
Ok, I know nothing about this sort of stuff but surely it can't be expensive (per car) to make the speedo's accurate when you are building 1,000,000 cars exactly the same?
And regarding the tyres, atleast you would know your speedo was right if your tyres were good.
Dwight VanDriver said:
Seeing its you Hedders...
DIY
http://tinyurl.com/blolh
dvd
Ta for that DVD...But I realise we can go to the trouble of doing speed tests and have our speedo's calibrated at our own expense..my point is that surely it should be compulsory to have a correctly calibarated speedo to begin with.
Seeing as that 34 mph is deadly but 30 mph is perfectly safe and all that gumph...if its so important, why is it not law? Your speedo has to work, but not properly?
hedders said:Agree with mcflurry.
Ok, I know nothing about this sort of stuff but surely it can't be expensive (per car) to make the speedo's accurate when you are building 1,000,000 cars exactly the same?
It was impossible for older cars with mechanical speedo mechanisms to ensure accuracy over all speeds.
Modern speedos can be much more accurate. However, manufacturers won’t make 1,000,000 cars exactly the same; the more they make, the greater the chance that 1 will be wrong. I guess they don’t want to face the possibility of a ‘child being killed’ (among other more realistic consequences) resulting from an under-reading speedo.
IMO, the manufacturers wash their hands of all potential liability simply by deliberately ensuring all speedos over-read by more than the error they could ever expect from them.
hedders said:
Seeing its you Hedders...
DIY
<a href="http://tinyurl.com/blolh">http://tinyurl.com/blolh</a>
dvd
Ta for that DVD...But I realise we can go to the trouble of doing speed tests and have our speedo's calibrated at our own expense..my point is that surely it should be compulsory to have a correctly calibarated speedo to begin with.
Seeing as that 34 mph is deadly but 30 mph is perfectly safe and all that gumph...if its so important, why is it not law? Your speedo has to work, but not properly?
Your speedo can over-read but not under read therefore you can never be over the speed limit if it is showing you at the speed limit.
I have checked all the speedos of my recent cars and found them to be approximately the same percentage out at all speeds (checked at 30, 60, 120 and 150 kmh). The Skoda was exactly 10% fast, the Audi 7.5% fast, and both Pug 206s 8% fast. The Ferrari is the closest at just 2% fast. Interestingly they all are pretty accurate at distance measurement, thus the speed factor must be intentional.
smeggy said:
IMO, the manufacturers wash their hands of all potential liability simply by deliberately ensuring all speedos over-read by more than the error they could ever expect from them.
Not the manufacturers, the government... as Tycho says the regulations state that the speedo error must be within -0+10%.
7db said:
Where can one find a measured mile? Are the VASCAR lines a mile apart?
Assume you will need a passenger to operate the stopwatch as otherwise you would not be in a position to have proper control of the vehicle.
Vascar lines NO varies depending upon site and vantage points etc.
Ask a proper traffic car crew, they don't bite.
Bet there will be some not too far away from the traffic ... smack my wrist... Road Policing Unit base.
Failing that County Surveyor Dept will tell you. In addition to asking for location also remember to ask for details of start and finish marks.
Re passenger assistance not strictly necessary in my book but in case of a first time "calibration" I would suggest you need to do a series of runs at different speeds and draw a correction curve. A passenger certainly helps to operate chrono and write down all the times / speeds.
Not quite calibration as such but near enough. I just whack it all into an Excel sheet.
FiF
kevinday said:
I have checked all the speedos of my recent cars and found them to be approximately the same percentage out at all speeds (checked at 30, 60, 120 and 150 kmh). The Skoda was exactly 10% fast, the Audi 7.5% fast, and both Pug 206s 8% fast. The Ferrari is the closest at just 2% fast. Interestingly they all are pretty accurate at distance measurement, thus the speed factor must be intentional.
Similar findings to mine though Citroens of BX era used to be spot on.
Comment re accuracy of odometers is spot on. Seeing as the allowable error of speedometer is offset a sensible mfr would set it to be +5% I would expect.
Best bet - get a decent GPS/Satnav system it will tell you the speed you are actually doing. Im using tomtom nav 5 with a bluetooth GPS and an Ipaq PDA. Had the TVR speedo checked on a rolling road , turns out the speedo and road both agreed - then re-checked with GPS which also agreed. TVR speedo 100% spot on. Then used the satnav and checked the Omega which is 4% out and VW Golf which is about 5% out.
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