Car Care: Stick to the speedo to avoid tickets

An onboard GPS gives a truer indication of actual speed.

Manufacturers set your speedo to read faster as a safety net

When speeding tickets are issued, drivers often go into instant denial and are adamant they were not travelling over the legal limit when they were nabbed.

The reality is that 99.9 per cent of the time the speed on their vehicle's speedometer would have been faster than the actual speed they had been ticketed for. Assuming a vehicle has not been modified inappropriately in terms of wheel/tyre size and pressures are set correctly, manufacturers' built-in speedos will always read faster than the actual road speed.

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If your speedo is indicating 100km/h your true speed is more likely to be somewhere closer to 96km/h.

Speedometers are always calibrated to over-estimate a vehicle's true speed to help stop drivers from unintentionally speeding.

It acts as a safety net working in favour of drivers who may drive over the legal speed limit without realising it - something most drivers do on occasions.

It also helps stop manufacturers being held responsible for, or being accused of, their vehicles consistently travelling above the legal speed limit through no fault of owners.

So if the driver's eyes are checking a vehicle's speedo regularly, in theory they should not fall over the no-go line - especially when the authorities build in a tolerance level.

One distraction can be an onboard GPS, which have become a fairly common and handy accessory and driver aid in recent years.

The risk of getting caught speeding increases if drivers travel to the speed indicated on the GPS system, and ignore the vehicle's indicated speed.

GPS systems that indicate a vehicle's speed have no built-in safety margin. What you see on the screen is pretty much a vehicle's true and actual road speed. Even for the most fanatical and focused driver, trying to consistently drive to the maximum speed limit even for the shortest distance is pretty much impossible.

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Navigation systems are a helpful driver aid but they should not replace or override a vehicle's speedo reading. Each has a specific job and drivers should make good use of both to ensure they arrive on time without breaking speed limits.

At the opposite end of the scale, those who drive conservatively and religiously use their vehicle's indicated speed to travel well under the speed limit can create serious traffic flow issues on busy highways.

By driving too slowly they can cause following drivers to take unnecessary risks when overtaking and cause following distances to reduce to potentially dangerous levels. While the speedometer is an indication of speed only, it's safe to say by travelling close to, or even a fraction over, the speed indicated on your speedo, you are comfortably within the legal limits for that piece of road.

Be warned: as drivers should be well accustomed to by now, over a long weekend or extended holiday the police and speed camera presence continues to increase and the tolerance levels around the legal speed limit are reduced.

And as a follow-up to our previous article on this subject, always seek professional advice whether any increase in wheel and tyre size will have a dramatic effect on your vehicle's speedometer accuracy.

Checking those tyre pressures regularly will also provide the peace of mind that the speedo is as accurate as it can be, as well as saving fuel. If you have a navigation system fitted, ask a passenger to help make comparisons to gauge just how much discrepancy there is between actual and indicated road speed.

Finally, if you do have a portable GPS onboard, ensure it is positioned in a way to ensure the driver is always concentrating on the road ahead.