Speedometer Conversion

Why consider speedometer conversion?

Picture of the dials on an imported Japanese car, showing the need for speedometer conversion to mphYour imported Japanese car will have a speedometer reading in km/h only.  In general they do not have a smaller mph scale in the same way that UK cars often have a smaller km/h scale.

So if you’re buying a car direct from Japan you may want to consider speedometer conversion.  This may well already have been done for you if you’re buying an imported car already in the UK.

The conversion work can be done in Japan before the car is exported, or it can be done in the UK once the car has arrived.

Reasons to avoid speedometer conversion

There are a number of situations where you might want to avoid speedometer conversion:

  • You want to keep the car as close to original condition as possible.
  • You’re an experienced driver or have a particular head for figures and can do the conversion from kph to mph in your head whilst you’re driving.
  • You always drive with a satellite navigation system that displays the speed in mph.
  • You want to save money on the costs of speedometer conversion.

Do you have to convert the speedometer?

Having said all of the above, do you have a choice about speedometer conversion?  In some situations, yes you do!

If the car is over 10 years old when it has its first MOT in the UK, you do not have to convert the speedometer.

Many people will tell you it is a legal requirement for the MOT.  This is incorrect.  The car does have to have a speedometer, but the MOT regulations do not state that it has to read in miles per hour.

However, if the car is under 10 years old when it arrives in the UK, it will need to have an IVA test.  The speedometer will need to be in miles per hour for the car to pass this test.

Speedometer conversion methods

There are a few ways to convert the speedometer on an imported car.  Two of them are electronic and one is more of a physical adjustment to the car.  If you’re going for one of the electronic methods, make sure the person doing the work knows what they’re doing!  If these conversions aren’t done properly they can affect the gear change points of automatic gearboxes, having a substantial knock on effect on fuel consumption and driving enjoyment.

Speedometer conversion chip

These are wired in to the car’s electronics.  Speed is displayed in mph and distance is recorded in miles from the point of fitment onwards.  They do not convert already recorded distance on the odometer from kilometers to miles.  The speedometer dial face is amended to reflect the new units but is otherwise unchanged.  This is done by covering the kmh lettering with a mph sticker, or in a ‘budget’ conversion by blacking out the k of km/h to leave m/h.

ECU reprogramming

In some cars, speedometer conversion can be done by reprogramming the ECU.

Replacement dial face

The original speedometer dial face in km/h is replaced with a new face with mph and km/h scales.  Distance will continue to be recorded in kilometers and it is acceptable in the UK to have speed and distance in different units.

Speedometer conversion costs

This could be anything from £50 to several hundred pounds.  The cost depends several factors, with the key factors being:  the type of car involved (specifically the type of wiring/electronics or complexity of dashboard) and whether you’re doing the conversion yourself or having it done for you.

What about the odometer reading?

Speedometer conversion often goes hand in hand with converting the odometer reading from kilometers to miles.  From the point of conversion onwards, speed is displayed in mph and distance is recorded in miles.  This is not the case when using a replacement dial face because this doesn’t interfere with the signal from the speed sensor.

This changing of the odometer reading is one of the main reasons I like to avoid electronic speedometer conversion wherever possible.  I think it can present an opportunity for the dishonest to ‘remove’ a few thousand kilometers/miles from the car.  However, if the speedometer is converted using an electronic method, I agree that the odometer should be converted as well.  It can get confusing for the speed to be in miles per hour but for the distance to have been recorded partly in kilometers and partly in miles.

There are a number of ways you can check the odometer reading of your imported Japanese car.  These depend on how and where you buy the car.

Have your speed displayed in MPH without the conversion

There are a few more options that will let you see your speed in mph without the full conversion process.  They are less permanent and can be moved from car to car.

Mobile phone speed app

There are numerous mobile phone apps that can display speed in your chosen units.  I’ve had good results with DigiHUD and there are many others.

Satellite navigation

If you always travel with your sat nav on, you could just use the speed display on this.

Standalone speedometer

You can buy a removable speedometer that reads in MPH. Most of these use GPS to work out the vehicle speed, although some can plug in to the OBD port.


There are lots of options for seeing your speed in mph in Japanese import cars, each with advantages and disadvantages.

I prefer to leave the car as it was made and use the mobile phone/sat nav options.  I realise I’m probably in the minority with this.  The replacement dial face method is my other preferred option because it doesn’t involve interfering with the car’s electronics.

If you’re buying a car that has been converted, make sure it has been done properly and satisfy yourself that the car hasn’t ‘lost’ some distance from the odometer in the process.  Feel free to send me a message or post a comment below if you’d like to know more about this.

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