The little-known UK dashboard rule that may help drivers avoid fines

A little-known dashboard rule may help drivers stay within the speeding limits - and avoid fines as a result. In the UK, car speedometers are allowed to over-calculate how fast individuals are travelling but can never under-read speeds.

It means speedometers can indicate a road user is travelling slightly faster than they really are but can never say they are going slower. Most vehicles will likely under-report speeds by a couple of miles per hour. As a consequence, road users abiding by the law may be even less likely to go over the speed limit, and avoid speeding fines with penalties set as high as £100.

Carwow explained: “Car speedometers are allowed to be inaccurate by 10% plus 6.25mph (IE at 60mph they could say you are travelling at 72.25mph) – but they can only over-read, not under-read, meaning they can tell you you are travelling faster than you really are, but not slower.

“In reality, most car speedometers are far more accurate than 10% + 6.25mph, typically over-reading by no more than 3mph or so at 70mph.”

Drivers caught breaking the speeding limit will be hit with a minimum £100 penalty and three points on their driving licence. According to the RAC, some speeding road users could face higher fines of up to 175% of their weekly income.

The fine is usually capped at £1,000 but this can rise to £2,500 for those caught speeding on a motorway.

For minor speeding offences, drivers may be offered the chance to sit a paid speed awareness course but does mean road users can avoid having points on their licence.

Haynes said: “We can see from the above calculation that the car’s speedometer is reading a little slow – by just over 2 mph – which is to be expected. It’s when a speedometer is off by 5 mph or more that you may want to consider having it checked.

“If the car is modern, with an electronically controlled speedometer, your dealer may be able to adjust one of the car's brains. But older models may need a different speedometer drive gear installed in the transmission.”