What is a car trip computer?

Almost all modern cars have trip computers, but what are these systems, and how do they work?

Trip computers are fitted as standard to almost every car currently offered for sale. These electronic components display important information in the driver’s instrument binnacle about the journeys you take. The information a trip computer typically displays, include average and instant fuel consumption, the distance travelled since the computer was last reset, and the estimated range the amount of fuel in the tank of a petrol and diesel car, or power in the battery of an EV, provides.

The first electronic trip computer came along in 1978 and was fitted to the Cadillac Seville. Mechanical systems had existed prior to that, but the Seville’s ability to calculate its own fuel economy and allow the driver to input the number of miles to their destination was a novel idea.

Car trip computers have evolved and become more sophisticated since then (especially where electric cars are concerned), but the principle behind them has remained unchanged. Here, we detail what a trip computer is, how it works, and what sort of information you can reasonably expect to be fed by one.

What do trip computers do?

As the old adage goes, a trip computer does what it says on the tin: it computes data linked to a trip.

There are a five key areas that a trip computer provides information on:

• Time: trip computers will tell you how long you have been travelling since you started your journey. If linked to the sat-nav, they can also tell you how long you have to go until you reach your destination.
• Distance: as you can imagine, this will tell you how far the car has travelled since the trip computer was last reset.
• Speed: this will tell you the average speed the car has travelled since you last reset the computer.
• Fuel consumption: this will generally display the car’s average fuel consumption, and instant fuel consumption – IE how much fuel the car is using in the moment.
• Range: this will estimate you how far you can go before your fuel tank is empty, or an EV’s battery is depleted.

An electric car’s trip computer will typically show you all the information covered above, as well as the electric equivalent of fuel economy: instead miles per gallon, you will be show miles per kiloWatt hour (EG if you have a 100kWh battery and the car does 3 miles per kWh, you will get 300 miles from a charge. Some EVs show how many kWh a car is using to cover 100 miles, instead of miles mer kWh – see here for more information.

In addition to this, many EVs will synchronise their battery ranges with the sat-nav, calculating how far you can go on a charge, and where you will need to stop to recharge if you are undertaking a long journey.

Can car trip computers measure different journeys?

Many trip computers provide information for three ‘trips’: Trip A, Trip B, and since reset.

This allows all the information detailed above to be measured in separately and in parallel across three time periods. You can reset each trip individually, or reset all at once.

As an example, you may want to use Trip A to determine how far, how fast and how efficiently the car goes on each tank of fuel, resetting Trip A each time you fill up the tank.

You may also, however, want to see if a new route to work takes less time, provides better fuel economy or is faster than your usual route. You could therefore reset Trip B to determine this, while leaving trip A to keep ticking along in the background until you next need to fill up with fuel.

As for the ‘since reset’ information, many people never touch this, meaning it may show how far, fast and efficiently the car has travelled since it left the factory (or possibly since its battery was last removed).

Do also note that if you make a series of short journeys (EG pick the kids up from school, pop into the supermarket, head over to football practice) those journeys will often be treated as a single trip by the car, which will typically reset itself to a new ‘trip’ after the car has been switched off for four hours or so.

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