In a message dated 29/4/1999 5:38:00PM, ulix@u.washington.edu writes:
<< Simply not true! The rpm spacing between gears is determined only by the
transmission ratios. I had recently used the analogy of a 10-speed
bicycle, but here the ratio change (front sprockets) is on the INPUT side
of the transmission (rear sprockets) and does in fact change the "close
rationess" of the rear gears. >>
Ulix, you were right the first time so I guess you are not full of the
proverbial after all. The (admittedly incomplete) calculations prove your
original point - a taller diff has the effect of widening ratios, a shorter
diff brings them closer.
3.9 diff x wheel rpm = 3.9 x 911 = 3555.45
3.7 diff x wheel rpm = 3.7 x 911 = 3370.70
3.9 diff 3555.45 divided into 60,000 = 16.875mph per 1000rpm direct gear (4th)
3.7 diff 3370.70 divided into 60,000 = 17.800mph per 1000rpm direct gear (4th)
3.9 diff direct = 16.875 divided by 3rd gear (1.357) = 12.3455 mph
3.7 diff direct = 17.800 divide by 3rd gear (1.357) = 13.1171mph
rpm increase 4th to 3rd on 3.9 diff at 3000rpm = 1,101rpm
rpm increase 4th to 3rd on 3.7 diff at 3000rpm = 1,071rpm
RPM increase is greater on 3.7 (taller diff) and this is why all you guys
with 4.22 diffs don't worry about the wide ratios on the Jap boxes. Fit a
3.9 diff and you might think twice about the Ford box (er hum which I happen
to have in my Sprite, er hum with close ratios anyway).
Daniel1312
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