... I've found my dash overreads speed - when I am sitting dead on 60 km/h, my iPod tells me I'm only doing 57km/h - If I do 65km/h, apparently I'm only doing 63km/h! Has anyone seen similar results?
Federal Law (last I knew, may have been updated) states that the speedo of a new car must read within 10% of true. So if your car speedo reads 100kmh, you may be going anywhere between 90km/h and 110km/h. Older cars (pre 06 to my knowledge) are often set at 6km/h under speed. Car manufacturers erred on the side of caution to ensure that a) they were within tolerances and b) it was not over speed, so they could not be sued if you crashed and proved the actual speed.
I do not know if the law changed, I have asked an automotive engineer who is at the cutting edge who also knows not of any changes to the law, but I have noticed that any car I have driven that was manufactured post 2006 seems to only be 3km/h out. So when my car reads 100 on the clock, I'm actually only going 97.
Pre 2005 police radar and speed cameras were set to start taking photos at the speed limit + 10% + 3km/h. So in a 100 zone, it would not snap you unless you were traveling at 114 or more. After I found this out as a dumb P plater I went about testing the theory, factoring in the factory speedo tolerances and found this recipe to be correct, no snappy snappy in a 100 zone till my speedo read 119 (speed limit + 10% + 3 + 6km/h speedo variance) but the fine was for all that minus 3km/h for variances. I think the extra 10% may have been to compensate for the government letting the car manufacturers have the speedo out by 10%. However post 2005 the money hungry mongrels changed the laws, I believe they are now set at the speed limit + 4Km/h, but they deduct 3km/h from your detected speed to allow for variances, so in a 100km/h limit, you will get a photo taken at 104, but be fined for 101.
So now if you are in a pre 2006 car, in a 100 zone, if you are sitting with your speedo reading 110 and get your photo taken, you will only be fined for traveling at 101 (detected at 104km/h). In a post 2006 car, if you are sitting on 110 and get snapped in a 100 zone, you will be fined for traveling at 104 (detected 107).
I have 3 cars and 2 bikes, I traveled around 60,000kms just commuting to and from work in the past 12 months which has 4 fixed and generally 2 or more mobile speed cameras every day, in addition to the johnny hoppers floating through the traffic or hiding in bushes. I also drive for a living so do a 12 hour shift driving on top of my commute. You could say I have extensively tested my theories, just in case you were wondering
Oh and just for a bit of added fun, in Victoria it is not a requirement of roadworthyness to have a working speedo at all.
