Is your speedo the biggest bullshitter on your entire instrument panel? Find out next.
This question, is from Andrew P.
"Why have I notice lately they Speedo’s in cars a lieing. In my mums brand new xtrail her car seems to be doing 6 Kms less ph then what the gps says in my Audi it’s less then 3 kmph and my other aunties xtrail it’s 6kmsph again and my partners RCZ 5kmph ah is this so? Are manufacturers doing this on purpose?"
Yes, Andrew, they are.
About 11 years ago the essentially globally homogenised regulations for speedos in new cars changed. Essentially they’re not allowed to under-report your speed. So a speedo cannot display - say - 100 when your actual speed is 105.
On the 1st of July 2006, here in ‘Straya, they updated the speedo compliance regulation called ADR 18.
New ADR 18 says speedos cannot indicate less that the true speed, and over-indication accuracy is limited to a maximum 10 per cent plus 4km/h. This means that at a true speed of 100 kilometres per hour the speedo can’t be displaying 99, or under, but it could be displaying up to 114.
Before 1 July 2006 the speedo accuracy was simply plus or minus 10 per cent - so the true speed could be 100 and the indicated speed could be anything between 90 and 110 - something to bear in mind if you own an older car.
It’s not really a conspiracy to slow us all down - it’s a compliance issue. What galls me is this this: I want to drive on the freeway at the limit. For example, it’s 300 kays door to door from my joint to Canberra - mostly freeway.
If ‘Strayan Prime Minister Malcolm Turnbullshit calls me for an urgent consultation on running the nation, some thorny issue (which tie makes me look like less of a Churchillean git) I have no tolerance for dilly-dallying on these pressing matters of national security.
If I drive at the 110 kilometre per hour limit the drive to save the nation will take me two hours and 44 minutes. And, just like my hero Jack Bauer, I don’t want to keep Bullshit Mountain waiting. The PM needs my help, to prevent Tiegate.
However, should I happen to be in a car with the least-accurate (but still compliant) speedo, I’ll be staring down at 110 but my actual speed over the ground will be just 96 kays an hour. Transit time: Blown out to three hours and eight minutes. Nobody wants that.
This means I’ll be keeping Bullshit 6 Actual waiting for 24 minutes longer than absolutely necessary. I hate that - also, back in the real world, that’s not driving: it’s just wasting your life bored shitless on the freeway, and I have no wish to do that for a nanosecond longer than needs must.
So, you could use GPS - but not integrated GPS, from the carmaker, because it generally does not display speed. Presumably because manufacturers don’t want to open the floodgate of complaints about speedo inaccuracy from indignant customers, when they see two mutually irreconcilable readings on the same instrument panel.
If you want to drive legally, but at the maximum permitted speed, you can suck a GPS unit to your windscreen (but remember not to burn your lips approaching the summer solstice here in ‘Straya). Once sucked on enthusiastically, you might compare suck-on receiver’s speed to that of the speedo and derive a correction factor. Or, if you want to use the correct technical jargon, a ‘fudge factor’.
Couple of caveats on this - I’d be doing it on a flat, level section of road, because GPS accuracy is potentially compromised uphill or downhill. The system itself is reasonably robust for the Z-coordinate, but the receiver you use might not be paying that much attention to elevation in practise.
I’d also use a wide-open road without overhanging trees - because canyons and trees that occlude the sky can block the line of sight to multiple satellites and degrade the suck-on unit’s accuracy.
If you’ve ever been on the freeway in a 110 zone and blasted over a crest or around a curve and come face-to-arse with a highway patrol interceptor lying in wait, and then - visceral reaction - you look [LOOK DOWN] down there and you’re aghast that the speedo is nudging 120 kays an hour.
...and then you wonder why the blues and twos never actually go on, in this situation, like a deleted scene from Mad Max (you know, the first one, before Mel Gibson emerged like a butterfly from the anti-semitic nutbag cocoon) it’s probably because your actual speed could have been as low as 105 on a perfectly legal speedo.
Негізгі бет The Truth About Speedo Accuracy | Auto Expert John Cadogan
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