Hi, folks.

I was curious why the Japanese market 6-speed gets a different 3rd gear ratio from everywhere else in the world (1.539:1 instead of 1.645:1). I asked the folks at Mazda, and was told that "Japanese national emission regulations mandate the differences in the gear ratio."

Can someone from that part of the world, help me understand that rule? Do Japanese cars have to meet certain emissions limits in each gear, perhaps?

Thanks.

 

I read an article on the 3rd gear setting in Japan before, but I could not remember where I found the article.....


In Japan, the tax changes depeding on the emission of the car.
This emisssion test is done according to a test drive pattern which is defined based on Japan traffic enviroment.

The test pattern is like....
idling 20sec
acceleration 0->20km/h 7sec
constant velocity 20km/h 15sec
.......
.....

I think Mazda changes the 3rd gear ratio in Japan to optimize for this test pattern.

 

Thank you, Yuhki-san.

But I'm still puzzled - if that gear ratio allows the car to produce less emissions and/or consume less fuel on a standard test, I wonder why they don't use that ratio everywhere.

 

It sounds like they set the Japanese third gear ratio so that it offers the best fuel economy at a particular speed for the test. And while it might offer the best fuel economy at that speed, it might not be the best combination with the second and fourth gears overall.

In other words, it sounds like they "tweak" the JDM 3rd gear to be optimum for the test, not to be optimum for performance. And it sounds like you'd rather have the USDM version after all.

---jps

 

I agree with you.