Speedometers up to 10% off

I don't think I've ever driven or ridden a vehicle whose speedometer was bang on. They have always over-read a certain percentage. And it hasn't been a case where the more expensive models are more accurate either. Just remember, tyre wear will cause a small increase in speedometer reading as the wheel rotates faster for the same speed.
I have one of those check your speed signs close to where I often drive and it always corresponds to my speed app on my phone but never to the speedometer.
For every vehicle I own, I know what the overread error is and I drive to that value knowing that I won't get pinged. In Victoria, where I live, you have a 3 km/h grace. Over that and they fine you.
 
It was so long ago I don't remember exactly, but I think there's an obvious listing for speedometer, set at 0, I think I went -7%, if I recall. Don't know much about new model, but I think so.
 
It was so long ago I don't remember exactly, but I think there's an obvious listing for speedometer, set at 0, I think I went -7%, if I recall. Don't know much about new model, but I think so.
Cool, I don't recall seeing that when I tuned it w/ Penner's map, but I'll go look again. I'd MUCH prefer to have an accurate speedo.
 
This is more for a broader information for those that are interested.
I am a process instrumentation technician by trade. So calibration, accuracy and repeatability are all very important terms in my field.

Speedometers, are often not very accurate or deliberately set to over read by a certain amount. However, they are very repeatable. In other words, they will always show the same error every time. In our trade, this is often more important than absolute accuracy, particularly as accuracy can be corrected, repeatability often can not as it is usually the indication of a worn part or poor manufacture.
Speedometers will gradually over read as the tyre diameter slowly decreases with wear, but most would not even notice this.

It's much like the grouping on your target at the shooting range. A wide grouping shows issues with technique, rather than a sighting problem, where a small group off the bull is much preferred as a small adjustment on the sighting will remedy this. Usually a single point correction (with the Rocket this is a field in TuneECU that can be set) and your speedo will be close. Having a rotating needle type speedometer (opposed to a digital readout) an additional user read error (error of parallax) is also introduced. In high end calibration gauges, they had a mirror strip behind to overcome this. Me, at 6'6", would read the speedometer slightly differently than say someone who was 5'.
 
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