Speedometer Accuracy One thing we often get people asking about is the readings from their vehicles speedometer. With other geographical tracking devices, such as GPS, becoming increasingly popular, we know people now have access to several sources of information on things such as vehicle speed. And when these devices report something different to your speedo, that can definitely be a confusing situation. So heres the facts on speedos and GPS units, and the way they measure vehicle speed. Your speedo: For reasons of safety, technical reliability and compliance, Vehicles’ speedos are designed to slightly overstate the speed. This means they show a marginally higher speed than you are actually travelling. Under recently revised Australian Design Rules, it is no longer allowable for a vehicle to be travelling faster than the speedo reading. The speedo reading must be equal to or greater than the actual vehicle speed, with an accuracy of 10% plus 4kph. The law allows for this buffer of overestimation because speed measurement is an imprecise estimation, affected by many different circumstances; it can differ significantly under different scenarios. GPS units GPS systems will often show a different speed to your speedo. These systems measure speed by time and distance, not taking into account elevations and curves that can impact on speed and distance. The flat distance of a road measured by a satellite is not always an accurate representation of the real roads we drive on. What affects your speed? The speedometer reading is based on your tyres’ rolling radius, which can be affected by: *Side wall construction and stiffness of different model tyres *Tyre pressure, temperature and wear *Vehicle load This means that speedo readings cannot be 100% accurate under all driving conditions. The benefits: Safety is the obvious benefit in having a speedo reading higher than actual speed as it supports responsible driving. Of course, another benefit could be preventing unwelcome speeding fines!
Posted on: Thu, 16 Oct 2014 11:44:13 +0000
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