Speedo Accurate?

I defended a couple speeding matters in court recently, 245/40R19 is 3% slower than reading, 255/40R19 is about 1% over speed.

 

Yep run my Satnav all the time and will show a 5klm variation. Speedo will read 100klm and GPS says 95 or 96 (variation). I've been told that the speedo in VE can not be calibrated to correct it, something about an ADR compliant thing or similar - I'm happy to be corrected and if there is a fix please post how it is done and who can do it. I was told by one of the holden techs that they could play with the tyre sizing setup in the ECM but not sure how that works..... Our VY commodore speedo is spot on with the GPS.

 

Hexem not a fix per sé, but the wider tyres on the wheels above give a circumference near enough to perfect. OFC not a good a reason to change tyre spec by itself but I find the lil bit wider makes vertical side walls, is OK still, no flab.

 

It is legislation, speedos are to be a few KM/h slower than actual.

Cut and paste

Australia has standards for speedometers similar to those of the European Union; and most car manufacturers aim to adhere to these standards. The rules say that no speedometer should read lower than the speed you’re travelling – so you should never be going faster than what the speedo reads.
But in terms of your speedo reading higher than your actual speed, a huge margin of error is allowed. For a car, the international standards allow a speedometer to be higher by as much as 14km/h at 100km/h – which means your car is doing 86km/h when your speedo is showing 100km/h. For a motorcycle, 84km/h actual speed is allowed to read as 100km/h on the speedo.

Source

http://www.consumer.org.nz/news/view/speedometer-accuracy

 

^^ true dat, found in court that ignorance of circumference was not an ideal defence in itself regarding choice of replacement tyres, but useful rebuttal tactic by way of contribution to the unavoidable cumulative error of the VSS reading, its interpretation by the cruise control program, going downhill immediately after an apex, hit by LIDAR, in a two tonne automatic.

 

Hi,

With the speedo's now run by computers and not a cable, there seems to be a fixed underead of 2 to 3 KPH on each of my SV6,s - MY09, MT11 and MY13 Z.

Back in the days of my VS with a three window cluster, it was possible to enter a correction for distance and fuel flow to get the trip computer spot on. That did not change the analogue speedo reading or odometer though.

It's a bit of a pain, but I set cruise control at +2 with my current SV6 and know that the speed is spot on.

 

My VE reads 5K over.
On 110K roads I set cruise at 117 and have never had a problem, touch wood. I don't like dawdling along holding up other road users as I don't like being held up by people "thinking" they are driving close to the limit.

 

Discussion of speeding on public roads is not allowed, so allowing for slightly greater yet unquantifiable speedo error... because technically you believed that was not speeding, right...
In my all-too-familiar experience if you travel at 117/110kph as indicated on your speedo you will either be pursued and issued with a warning or ticket in every State, else you will receive a camera notice in the mail.
A defence in court is entirely possible with a human police officer, and is your right, but clearly a waste of everyone's time and money on the day. Even when armed with an intricate knowledge of the law, not worth it.
115kph is arguable, not with camera detected, and not easily with video footage accompanying LIDAR.

 

Have you tried a measured kilometre, my VE is close enough when I use the digital display.

 

Did you win though, I would think a magistrate would blame you if your speedo was out and blame the cops if the radar gun was out, after all it's up to you to be sure that your speedo is correct and up to the cops to make us the radar is reading correctly and operated/service per manufactures specifications.

 

Negative, found guilty as alleged, despite a couple of valiant efforts to blame it mainly on the speedo, Arrr!

 

You should have tried the never fail excuse "I heard the area was a speed trap so I was trying to get out of there quickly"

 

yep, what I tried to explain that in the other thread before all the ADR speedo % experts chimed in. It is the drivers responsibility to stay at or under the speed limit. Blame Holden or ADR% or coasting down a hill or whatever all you like but you will lose in court if you exceed the speed limit - even in a 1922 Model T Ford that does NOT have a speedometer. It is the drivers responsibility. The law does not care how you keep under the limit - but keep under it you must.

There are only two reasons people speed...............

(count up by 1 bird bloke)

 

My 2 SSV's each were doing 96 km/h when the speedo indicated 100. My E3 does 97 km/h & 100 on the speedo. The most accurate way to check is use a GPS based speedo on your smart phone or satnav. There are plenty of free android based speedo apps and I presume there are iPhone ones too.

 

You should be aware that in most states the fitment of replacement tyres (or tyres/wheels) is conditional on your vehicle retaining speedo accuracy. If you fit a larger tyre or a new wheel/tyre package that also results in a larger diameter tyre which is sufficiently oversize to cause the speedometer to under read the true vehicle speed, then that is your problem and it is a violation. You are either required to recalibrate the speedo to correct the under reading of the true speed or if that is not possible to fit the correct size tyre that will not result in the true vehicle speed being under read by the instrument.

If you are caught speeding and have an inaccurate (under reading) speedo because you fitted tyres that are too over size then you have 2 FAILS :

1. Non compliance with the tyre/wheel replacement regulations

2. Exceeding the legal speed limits.

Ignorance is no excuse and nor should it be.

Given that some people will fit a slightly oversize (in diameter) tyres on their car it is not a bad idea if manufacturers are in fact calibrating speedos that under read the true vehicle speed by a small percentage (say 3-5%). Hence if I can fit a 255 35 20 tyre (686 mm diameter) instead of a 245 35 20 tyre (680 diameter) on the VE it will read approx 1% below the indicated speed compared with running on a 245 tyre because of the larger diameter. Thus, with such a tyre change, I don't have to be concerned about the true vehicle speed being above the indicated speedo figure with the bigger tyre. If GM has in fact set the speedo at about 5% under true speed on a VE (100 kph indicating when actual running speed is approx 95 kph) I would be well within the margin in this example. (Similarly some guys like to run a 285 30 20 tyre on their big (9.5 or 10 x 20 inch) rear wheels on the VEs rather than a 275 30 20. It is useful if you can do this without worrying about your speedo under reading true speed due to a slightly larger diameter tyre (285) being fitted).

 

Thanks for taking the time to explain that Sean.

 

I have argued many times with Holden Dealers (Workshops) in regard to inaccurate speedometers. According to ADR (Australian Design Rules) manufacturers are allowed up to about 5% fast. This means at about 100 km/ph you will actually be doing about 95 km/ph One good thing is that if you stick to the indicated (speedo) speed you should never get any speeding fines. Not bad eh !! Before you all jump in (boots and all) YES Police speedometers can be adjusted for greater accuracy.

 

About all we can do so good, but

what is the accuracy of the gps? (the civilian data system)

Also, you must realise that the US govt controls gps data (and has been known to 'adjust' the data when it suits them. What else, as the satellites fail the US govt is not launching replacements for civilian system and fewer sats mean less accuracy.