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Old 11-28-2007, 03:11 PM   #9 (permalink)
MetroMPG
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Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
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Some more thinking out loud... (have a highway trip coming up in the next couple of weeks, which gets me thinking about aerodynamics and gear ratios)

If I had a hypothetical 1st gear ratio of 3.0 and a final drive of 4.0, that means my engine turns 12 times (3.0 x 4.0) for each turn of the axle, correct?

If that's the case, then the taller diff on the 4-cyl tranny isn't horribly different than the 3-cyl car. From a few comments I've read, it sounded like starting out in first gear would be made much harder - like the equivalent of starting in second gear all the time with the stock tranny.

But if I compare the 1st and 2nd gears of the stock tranny to the 1st gear of the taller one, I get:

3-cyl tranny: gear 1 (3.416) x final drive (4.39) = 15.0 wheel revolutions per engine revolution

3-cyl tranny: gear 2 (1.894) x final drive (4.39) = 8.3 wheel revolutions per engine revolution

4-cyl tranny: gear 1 (3.416) x final drive (3.52) = 12.0 wheel revolutions per engine revolution

By that math, it's not quite like starting in my current 2nd gear. It's roughly in the middle of my existing gears 1 & 2 (slightly closer to 1).
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