We are not talking about directions, we looked at the speed readings compared the the cars speedometer

To most drivers, the satnav must rank among the top 5 of useful driver aids. Indeed many new cars, whether your get them through vehicle leasing or purchase are fitted with a satnav system as standard. This reflects both the absolute usefulness of the device and the fact that map reading has probably gone the way of 8-tracks and sunroofs.
The choice is usually between an in-car system or separate removable satnav and every driver has their own preference about which type is best. Some car manufacturers fit systems which are specially made for them. If you buy a satnav separately, the biggest names are Garmin and TomTom ( However, other satnavs are available).
There are multiple software and user options in satnav technology depending on what you need to use it for so careful research is needed before you commit. Of course, if you’re looking at vehicle leasing as an option the best thing is to discuss your satnav requirements with a vehicle leasing expert who can guide you to the best vehicle and the right equipment for you.


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How do satnavs work?

If you’ve ever used a satnav you will have noticed a difference between how fast your speedometer says you’re going and the speed shown on the satnav screen. This is down to how speed is measured. The speedometer reading in your vehicle is measured on the basis of wheel or driveshaft rotation and in relation to the rolling circumference of the wheels. The faster your wheels or driveshaft rotate the higher your speed. A satnav reading is measured by satellite signals which work out your GPS position. Your location is constantly updated by GPS and speed is calculated by measuring the time it takes to travel between co-ordinates.

So, which is correct?

Your car’s speedometer, because of how your speed is measured which can be affected by the car’s age or by something as simple as tyre wear or having bigger wheels and tyres fitted, has to allow for a certain margin of error; speedometers can be completely accurate or can read out by a couple of miles per hour. This is why, it is said, that some police speed cameras assume a margin of error of around 3 mph, but this is not always the case with the latest high-tech camera systems. A car’s speedometer can legally overstate a vehicle’s speed by up to 10% but must not understate it. This means your speedo may always read at a higher speed than you’re actually doing, which probably helps you avoid speeding – and the resulting tickets.

A satnav system can sometimes show inaccurate readings in certain terrains where satellite signals are patchy, such as tunnels, rural areas and even valleys or inclines. A satnav is always going to be the most accurate when you drive on a level, straight road such as a motorway or major route. The very latest satnavs and particularly those that are factory fitted also use technical data from the vehicle to constantly update and work with GPS signals.

In conclusion, a satnav will usually be more accurate than a car’s speedometer – as long as there’s a signal. If you’d like to know more about what type of satnav systems the latest car lease deals come with, simply get in touch.

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