Accuracy of JDM Speedometers
The subject on the accuracy or inaccuracy of stock speedometers in Honda cars
have been often the subject of many discussions. The main concern is the amount
that the stock speedometer will be off the actual value at various car speeds.
Common misconception is that the stock speedometers are way-way off at higher
speeds. People have even tried to imply that they can be off as much as 20kph or
more at speeds exceeding 160kph (100mph).
I have some Japanese magazines that conducted complete car tests. So called
JARI (Japan Automobile Research Institute) tests, one of the many components
included a stock speedometer accuracy check using an optical wheel mounted on
the car. Maximum speeds tested will by necessity be 180kph or so because of the
mandatory 180kph artificial speed limit imposed on all stock JDM cars.
The list below matches the speedometer indicated speed versus the actual
measured speed for a Mitsubishi FTO GPX (manual) and a Mitsubishi Mirage Cyborg
R (automatic). Unfortunately I do not have any JARI tests for Honda models so I
will have illustrate this point with Mitsubishi cars. They often use
speedometers from the same OEM anyway.
As can be clearly seen from the two tables, even at speeds of as high as
180kph (110mph), the stock JDM speedometers are inaccurate to at most around 2%,
sometimes optimistic, other times pessimistic. No values in either tables
exceeds a 3% inaccuracy for the entire 180kph speed range capacity of both cars.
The same is quite definitely true for Honda's JDM speedometers too.
Hopefully, this installment of topics have finally resolved the question.
Copyright Temple of VTEC - World. July 23 1998