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Learn How To 1-8-Scale Diff Tuner |
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For many of us, differentials in 1/8-scale vehicles are
among the most abused and neglected parts on the
kit. But for many they are the #1 tuning option when
they hit the track. All 1/8-scale buggies and
truggies have three of them: one for the front, one
for the center, and one for the rear of the car. As
a racer, I usually search the hot combination, but
rarely use it as a tuning aid. The effects that the
diffs have in the handling of the car are huge; they
can drastically alter the way a car handles bumps,
exits a corner, and accelerates. We decided to talk
to one of the pro drivers who has been experimenting
with different combinations for years. Chad Bradley
recently switched to Jammin' where he's been tearing
up the track with both the X1 CR and the CRT. Most
of today's differentials are tuned in with silicone
oil, and the most common weights used range from
1,000wt to 50,000wt. Understanding what each
differential has to offer, and how to tune them
properly, can give you an edge over the track
conditions as well as the competition. |
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Front Differential
Buggy and truggy front (Steering): Depending on how your
buggy/truggy is handling, you can alter the amount of
steering by altering the weights in the front diff. If you
want more steering entering the corner try running lighter
oil (3,000wt buggy, 7,000wt truck) This will give the
vehicle more off-power steering, which is better on tight
tracks. Heavier oils (7,000-10,000wt buggy, 10,000-20,000wt
truck) will give your car better on-power steering and will
help on higher speed tracks.
Why Have Differentials
Hopefully it's no surprise why we have differentials, but if
you were just born here's a quick explanation: During a turn
the inside wheel travels a shorter distance, and therefore
can spin at a slower speed than the outside wheel, which has
to go farther. Since both are on the same car, it would be
difficult for that to happen without the invention of the
differential. A diff allows one wheel to spin faster than
the other, which improves handling in corners. In
four-wheel-drive vehicles a third diff is used in the
center, to allow the front and rear wheels to travel at
different speeds as well.
Without any friction with the ground, the system would
transfer power to the wheel with the least resistance, and
result in a loss of speed in a corner and over bumps. We've
all seen Subaru commercials explaining that having power to
the wheels that grip (have the most resistance) improves
handling. The way that is controlled in RC vehicles is with
silicone diff fluid (and in some cars thick grease). This
acts as a "limited slip" differential, and allows the wheels
to spin at different speeds - but maintain power delivery to
the wheels with more traction. The thicker the oil, the
closer to a solid axle the diff acts, and the thinner the
closer to an open differential it is.
It is by controlling the diffs with fluid viscosity that we
alter the handling characteristics of a car for faster
acceleration or more steering. Chad went through the ranges
for his vehicles, but they hold true as starting points for
any brand, and how you drive may alter what you end up with.
Quick Oil Reference: what should be in your diffs:
OIL CHANGE
Fluids wear out. Even though you really cannot judge the
effectiveness of any oil by the color, it is a good
indicator that it's time for a change. Chad usually changes
his diff oil every three to four club races, and rebuilds
his diffs before any major event, and if he's comfortable
with the setup he generally doesn't change it. Regular
rebuilds are a cheap way to make sure the differentials stay
consistent.
Buggy and truggy front (Bumps): You also have to consider
how the diff affects the handling through bumps. Lighter
oils (3,000wt buggy, 7,000wt truggy) are better for bumpy
conditions. If the oil is too heavy it will make the car
want to change direction or oversteer in the rough or rhythm
sections.
Center Differential
Buggy and truggy: Lighter center oils help the buggy or
truck track straight while accelerating (3,000-5,000wt
buggy; 7,000-10,000wt truck). Running lighter oils in the
center has a negative effect on the acceleration. The
lighter oil allows the power to be directed toward the front
of the car and hamper acceleration out of corners. If you're
having trouble clearing jumps that are out of a slow corner,
that could be a sign that the center diff is too light, but
for really bumpy sections having lighter oil in the center
will allow the car to accelerate better and straighter.
Rear Differential
Buggy and truggy: I don't adjust the rear too often, and if
I do it's usually only in 1000wt increments. Lighter oil in
the rear diff gives the vehicle more off-power steering, but
can make the car or truck feel inconsistent around the
track, especially in long main events. The majority of the
time I will use 2,000 and 3,000 in the rear diff in both
buggy and truck.
Differential Tuning With Chad Bradley
We ask these questions all the time when we're racing, and
have heard them asked at least seven times while at the
track... and we're sure that as you're reading this you may
be asking "What do I do when...?"
...the track is rutty:
Buggy: Try changing the center to a lighter setting first
(3,000-5,000wt); if the car is changing directions out of a
bumpy corner, try making the front lighter (3,000-4000wt).
Truck: Same as buggy but the diff setting to try for the
front (7,000wt) and for the center 7,000-15,000wt.
...the track is loose and smooth:
Buggy and truggy: The best way I've found to increase
traction with the diffs is to increase the oil weight in the
rear diff slightly -3,000-5,000wt.
...if the track is loose and rutty:
Buggy: A "square" diff setup here helps -5,000wt front,
5,000wt center and 3,000-5,000wt rear.
Truck: Lighter center and front -7,000wt front, 10,000wt
center.
...the track is blue groove:
Buggy: Most of the time I run between 5,000-7,000wt in the
front, and 7,000-10,000wt center.
Truck: Most of the time on blue groove the cars and trucks
on throttle turn-in good because of the weight transfer to
front tires, but you lose some steering coming out of the
turn. So to sacrifice some turn in for out of the corner
steering and acceleration, a heavier front and center is
better suited majority of the time -20,000wt front,
30,000-50,000wt center.
...the track is blue groove and rutty:
Buggy: I would normally just go lighter in the center, but
not too light (5,000wt)
Truck: Since most trucks handle the bumps I wouldn't change
the diff settings from the smooth blue groove setup.
... I want more steering entering the turn:
Buggy: Lighter front oil (3,000wt) and rear (1,000wt)
Truck: Lighter front oil (5,000-7,000wt) and rear
(1,000-2,000wt)
...I want more steering exiting:
Buggy: Thicker front oil -5,000-10,000wt
Truck: Thicker front oil-10,000-20,000wt
...I want more acceleration out of a turn:
Buggy: Thicker center oil - 7,000-10,000
Truck: Thicker center oil - 20,000-50,000wt
...I want it to go better through a rough section:
Buggy: Use thinner oil for the center (3,000-4000wt) and
thinner oil for the front as well (3,000wt).
Truck: Use thinner oil for the center (7,000-10,000wt) and
thinner oil for the front as well (5,000-7,000wt).
...it pulls around too much through ruts:
Buggy and truck: Usually this happens because the oil in the
front and center differentials is too thick; reduce weights.
Starting Point
All this is worth nothing if you don't have a starting
point. Chad gave us some starting weights for a variety of
conditions that will be good at most tracks. You can apply
what we've gone over in the article to fine tune your
vehicle:
Conclusion
Once you understand the principal of how a diff works and
how different weight oils slow the action you will be a
master tuner in a few short days. This doesn't mean that
dropping 1,000wt in the front will make you a better driver.
Learning how to drive is something that has to be done
before you can fine tune to get the car to behave like you
want. |
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