A large range of electronic devices for km/h to MPH speedometer conversion of all imported Japanese cars is available. This well-established range of devices has been available since 1997 and has been proven to be 100% reliable, with many hundreds of satisfied customers. The design and manufacture of these devices was commissioned by Dartford Tuning and Automotive Services, one of Kent's leading Bosch tuning and diagnostic centres. (Dartford, Kent, England.)
These circuits are supplied and fitted exclusively by Dartford Tuning who have a calibrated rolling road which is used to check the speedometer of each car after fitment. Because staff work closely with the designer of these devices, it is often possible to configure special circuits for individual applications, particularly for very new models which use other technologies. Special circuits have been made for repatriated European models which have returned from Japan with km/h speedometers as it is sometimes cost-effective to do this.
These boxes have been designed individually for each type of vehicle as there are several different systems in use, even on different models from the same manufacturer. There are versions for both digital displays and analogue movements and versions which additionally provide top-speed delimiting of high-performance models. These fixed ratio boxes provide the quickest and most cost-effective solution.
Although the conversion ratio accuracy and linearity of these boxes is high, an accurate speedometer reading is only achievable when the car is fitted with the correct wheels and tyres. Even incorrectly inflated tyres and tread wear can make a difference to a speedometer's accuracy at high speeds. It has also been noted that a few cars seem to have rogue speedometers which are inherently inaccurate, giving a much higher than normal error. To overcome all these problems, we have looked into designing an individually calibratable speedometer conversion device. We now have available a range of devices which can convert km/h to MPH at a slightly variable ratio, currently plus and minus 15%. With the car on the rolling road, and with the wheels rotating at a known fixed speed, the conversion ratio of our box can be electronically adjusted to give an absolutely correct indication on the speedometer throughout the range. Once set, this calibration value is used each time the engine is started. If larger tyres are later fitted, for example, then a recalibration can be done by retesting the car on the rolling road. Currently, versions exist for most of the mainstream Japanese cars.
It is recognised that some customers use their cars mainly in the United Kingdom but regularly take their cars to territories where km/h speedometers are the norm. For this purpose we have created a switchable converter, able to display in either km/h or MPH at the push of a button. For cars with digital speedometers, this can be achieved with little extra complexity. The circuit also is able to extinguish the km/h legend so the driver is able to instantly see which mode the speedometer is in. This device is available now and a switchable and calibratable device for digital speedometers is in prototype form.
For cars with analogue speedometers, there is more to consider as it would be possible for the driver to change modes and overrange the speedometer. Various solutions to this problem have been thought about and are being prototyped currently. It is also necessary to provide an external indication of the operating mode of the speedometer. Watch this space for details. If customers for this future device are forthcoming, then the development progress can easily be accelerated.
As with the calibratable ratio speedometer conversion box, above, this device provides an output that is the same as the input but with the plus and minus 15% calibration facility. It works in exactly the same way but does not firstly convert the km/h signal to MPH. If a km/h signal is applied, then the output will be in km/h, similarly with MPH. If a home-market car is proven to have an incorrect speedometer due to incorrectly sized tyres having been fitted then this box will provide the solution. This device can also be used for race & rally cars to maintain speedometer accuracy after the final-drive ratio has been altered. As with the conversion box, the calibration factor can be altered at any time by retesting the car on the rolling road.
For price and availability of all these devices, please contact Dartford Tuning and Automotive Services.
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