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Old 06-08-2022, 11:09 PM   #9 (permalink)
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Join Date: Dec 2011
Location: New Zealand
Posts: 5,001

ND Miata - '15 Mazda MX-5 Special Package
90 day: 42.54 mpg (US)
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To me, a 48mpg highway fuel economy rating is outstanding. One of the pieces of that is Mazda's transmission. Here are a few fun bits about it:

Mazda managed to shave a full 46lbs out of the transmission, compared with the previous generation.

Gear ratios:
1st: 5.087
2nd: 2.991
3rd: 2.035
4th: 1.594
5th: 1.286
6th: 1.0
Final/rear: 2.866

With a tire diameter of 23.7 inches, that works out to 2400rpm @ 60mph. Compared with the previous (3rd) generation, that's 20% taller gearing with 33% lower engine displacement. Compared with the first generation of MX-5 (and we have a member on here who has had 50+ mpg out of one), the gearing is a full 30% taller, with 6% lower displacement. Pretty economical for a sporty car!

6th gear is also a 1:1 ratio, straight through without the countershaft. To keep highway RPM down, it has a very tall 2.866 rear differential. The previous generation had 4th gear as the 1:1.

The earliest versions of the transmission are known to be fragile, unfortunately. Cars with the larger 2.0L engine, stickier tires and limited slip differential have had failures in the first 30,000 miles. That said, I don't expect it to be a problem here.
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