RE: RE: Ring Gear changes: 3.55 vs. 3.90

From: Bernd D. Ratsch (bernd@texas.net)
Date: Wed Aug 11 1999 - 22:33:29 EDT


Here we go...

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I'm a little confused about your last 2 statements here. If you are
running 4.10 gears, your axle should rotate once for every 4.1 revolutions
of the driveshaft, regardless of tire diameter. That's the problem with
determining your 'effective' gear ratio when altering your tire size - I ran
into this problem when I went to 2" smaller diameter tires (I guess I'm
running close to 3.90, but my actual ratio is still 3.55).
--------------------------

You are correct. My ratio should be 4 - 1 with the STOCK tires. Since i'm
not running the stock tire size anymore, that changes the ratio again. Your
actual DIFFERENTIAL GEAR RATIO may be 3.55:1, but with the smaller tires,
you've changed the effective ratio where the tires meet the pavement.

--------------------------
Other than a little complicated math, I think the easiest way to determine
your overall "effective" ratio is to record rpm's at a corrected MPH before
and after the gear swaps and tire swaps - then you can determine roughly
where you are at based on those figures.
--------------------------

The easiest way (or old-fashioned) is to jack up the rear end, have a buddy
turn the tire ONE revolution and you count how many times the driveshaft
turns. This will give you the ratio.

--------------------------
I neglected to do this when I switched to the smaller tire;
--------------------------

See, you changed the ratio by putting on smaller diameter tires. You get
the same results when you install shorter gears (4.10 in this case) in stock
tires.



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