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.

Actual Speed	ZR	FTO
30	32	30
40	42	40
50	52	48
60	61	58
70	70	68
80	79	79
90	90	88
100	100	98
110	110	108
120	120	117
130	129	127
140	138	137
150	148	147
160	158	157
170	170	166
180	180	176

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