Frequently Asked Questions
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What gear ratio do I need
Do I need posi or a locker
What gear ratio do I have
Do I have a posi or locker
What is this noise...
What gear ratio do I need?
Differential Gear Ratio
determines the number of times the drive shaft (or pinion) will
rotate for each turn of the wheels (or ring gear). So if you have a
3.73:1 gear ratio the drive shaft turns 3.73 times for every turn of
the wheel. 
Gear ratio is calculated by dividing the number
of teeth on the ring gear by the number of teeth on the pinion gear.
The higher the number, the lower the ratio: a 5.29 gear has a lower
ratio than a 4.10 gear. With a lower gear ratio the drive shaft (and
thus the engine) turns more for each revolution of the wheel,
delivering more power and torque to the wheel for any given speed.
Lower ratios are generally desirable when going off-road. Higher
ratios are better for freeway driving since they run at lower RPM’s
and offer better fuel economy.
Changing tire size affects the
final drive ratio. Switching from a 30" tire to a 35" tire changes
the final drive ratio by about 17%. This may drop the engine out of
its' "power band" and result in poor performance and fuel economy.
To restore performance you must change the gear ratio to compensate
for the change in tire size. If you originally had 3.07 gears you
need a ratio that is approximately 17% lower, such as 3.55. If you
want to increase off road performance you might want a 4.10 or lower
ratio.
Recommended Engine RPM @ Highway Speed
4 cylinder: 2200 – 3200
V6 cylinder: 2000 – 3200
Small block: 1800 – 2800
Big block: 1800 - 2600
Diesel: 1600-2800
Check out our handy Calculators!
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Do I need a positraction or a locker?
A limited slip or positraction differential typically uses some form
of clutches that bind up the differential, providing traction to the
both tires. The clutches will slip to some extent to allow tires to
turn at different speeds on corners. Some limited slip differentials
are more aggressive than others, and some can be set up or
"pre-loaded" more or less aggressively. Limited slip units require a
special gear oil additive and may chatter when turning. Clutch packs
may also wear with time and require replacement.
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What gear ratio do I have?
Jack up one tire if you have an
open diff, or both tires if you have a working posi or
locking differential. Rotate the tire one full revolution
for posis and lockers and 2 full revolutions for open
diffs. Carefully count the number of full revolutions the
driveshaft makes. This is your gear ratio. In other
words, if the drive shaft turns 3 ¾ turns, you probably
have a 3.73 gear ratio. Turning the tire for twice the
number of full revolutions and dividing the drive shaft
revolutions by two will give you a more accurate reading.
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Do I have a posi or a locker?
Put the transmission in neutral and jack up both tires. Turn one tire. If the other tire spins the opposite direction you have an open differential,
and if it spins the same direction you have a posi or a locker.
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