Okay - here goes. Smaller tires (short sidewall) is like putting in "deeper"
gears. This would be like changing from 3.90's to 4.10's. Bigger (taller)
tires are like putting in "taller" gears, like going from 3.90's to 3.55's.
Sometimes the description of the gears can get confusing, because
NUMERICALLY lower gears (like 3.23's) are not what we think of when we think
of "lower" gears. Likewise, NUMERICALLY higher gears (like 4.10's) are not
what many people would think of when someone says "higher" gears.
We have to uderstand the relationship between driveshaft rpm and the distance
that the truck travels for each driveshaft revolution in order to discuss the
"effective" ratio, which includes the gear ratio and tire size. With 4.10's,
the driveshaft has to turn 4.1 times for every time the axle turns once. With
a 3.55 set of gears, the driveshaft has to make 3.55 revolutions in order for
the axle to turn 1 revolution. Now, for the same set of 3.55's, if you have a
26" tall tire, the truck will move about 82" forward for each axle revolution.
However, if you have a 30" tall tire, the truck will move forward
approximately 93" for each axle revolution. In this case, going from 26"
tires to 30" tires would be like installing NUMERICALLY lower gears, which are
sometimes called "taller" gears. In this particular case, if the 3.55's and
26" tires were the "stock" size (which I realize they are not), then switching
to the 30" tires would give an "effective" ratio of approximately 3.10,
compared to the "stock" setup.
I hope this helps a little, although I realize it may still be a bit
confusing.
Steve M.
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