This
misunderstood tuning option explained—finally!
By Greg Vogel
One-way
bearings are still considered the "mystery" option in
racing. We see them listed on the "Options" pages in kit
instruction manuals, but how do they work? What do they do? And how
will they affect your car's performance? There are several types of
one-ways, and they can be installed in a variety of locations on the
car. In this article, I explore the types of one-ways available and
explain how they affect a car when it's racing.
INSIDE A ONE-WAY
As the name implies, a
one-way bearing functions in only one way: it rides on various types
of shaft that pass through its center, and the shaft, or bearing,
rotates freely in one direction but locks in the other direction. A
one-way bearing comprises numerous roller, or needle, bearings inside
a metal case. The shape of the race allows the bearings to rotate in
one direction but not the other (hence the term "one-way").
These bearings are installed so that they "lock up" to drive
the shaft they're on when powered. When no drive force is being
applied, the bearings are released from their locked position and will
spin freely. The bearings can be in several places in the drive train,
and they may be found in both nitro and electric cars.
- Front-differential
one-way. This unit
replaces the front differential. The replacement unit usually
incorporates two one-way bearings—one for each outdrive. This
setup allows the wheels to spin independently of one another, but
it doesn't allow "true" differential action in a corner;
the outside wheel will simply freewheel.
- Center
layshaft one-way.
These units are used on both nitro and electric vehicles. On an
electric car, you'll find the one-way bearing on the layshaft (the
shaft to which the spur gear is attached). The one-way bearing
transfers power to the front diff under acceleration but allows it
and the front belt to "freewheel" while decelerating or
braking. Unlike a one-way "diff," a center one-way
allows front differential action. Since most nitro-powered cars
have three belts, they also have two layshafts; the one-way
bearing is usually installed on the layshaft that drives the front
end.
- Clicker
one-way. A clicker, or
ratcheting, one-way system doesn't use bearings; instead, it has a
spring that pushes on toothed plates. The teeth on these plates
are directional, meaning they can skip rather easily in one
direction (as long as the spring tension that holds them together
isn't too great), but they lock firmly in the other direction.
Adjusting the tension of the spring that holds the toothed plates
together allows the amount of "freewheeling" to be
adjusted and even locked out completely. Set the spring loosely,
and the teeth will slip easily to allow a one-way action; tighten
it, and it's increasingly difficult for the teeth to slip against
one another, thus limiting the one-way action.
- Adjustable
one-way. Like the
"clicker" one-way, this setup allows freewheeling action
to be adjusted or locked out. It works like a miniature slipper
clutch. A center one-way unit is usually fitted with a
spring-loaded friction plate or plates that can be adjusted to
limit one-way action when decelerating or braking. Set it loosely,
and the front drive system spins freely; tightening it decreases
the freedom with which it spins, and that increases front braking.
Left: A one-way
bearing is installed in the silver pulley of this center-layshaft
one-way setup. The one-way bearing in the pulley locks on to the shaft
when power is applied, but it's released and spins independently of
the black pulley and shaft when the car is braking or decelerating.
Right: This is a
typical front one-way differential for a belt-drive system. The pulley
is bolted directly to a center hub that's fitted with one-way
bearings. The one-way bearings lock on to the drive cups when power is
applied, but they allow the drive cups to spin freely when they start
to spin faster than the pulley.
UPS AND DOWNS OF
INSTALLING
A ONE-WAY BEARING
By installing a one-way
bearing, you change a car's driving characteristics. There are
conditions for which one-way systems are very beneficial. These
conditions are narrowly defined and oddly contrary to what most of us
would assume to be the "ideal" conditions, so I'll explain
how each type of unit affects a car.
- Front
differential one-way.
This has the most dramatic effect on handling. These are generally
best for high-bite surfaces with sweeping, high-speed turns. When
entering a corner off throttle, the front drive spins freely and
isn't affected by deceleration or braking. Under these conditions,
the front tires have exceptional bite, and this results in maximum
off-power steering. Conversely, only the rear tires are used for
braking, thus reducing rear bite. These conditions, without the
proper chassis setup and tire combination, could result in
excessive off-power oversteer. The rear-wheel-only braking is what
makes this type of one-way best suited to high-bite tracks. The
car would simply take too long to slow down, or it would be too
difficult to control on a low- to medium-bite track. It's
something like yanking the parking brake on a full-size car; it
doesn't slow the car really quickly, and its rear end wiggles all
over the place. This is also why front one-ways are better suited
to tracks that allow cars to carry higher speeds through the
corners where rear-wheel-only braking is sufficient to scrub off
enough speed to make the corner. The car can be driven with more
of a rolling motion—coasting through the corners and smoothly
accelerating on to the straights more like a pan car. Conversely,
tracks with 2x4 barriers outlining a series of tight, low-speed
corners require very hard braking to haul the car down to a safe
cornering speed—not a strong point of a one-way system.
Under acceleration, a
front one-way eliminates differential action. In a perfect world
in which all the tires are perfectly stuck to the racing surface,
this wouldn't have much of an effect on handling. What's more
common, however, especially in high-speed turns, is that the diffs
will unload in the direction of the inside tires and this bleeds
off power that could be used for better drive out of the corners.
A front one-way locks under power and delivers 100 percent of the
power to the ground.
- Center
layshaft one-way. A
center one-way is similar in function to a front one-way, but
there's a very distinct difference between them: there's still a
traditional front diff in the car. The center one-way allows the
front wheels to freewheel when they want to spin faster than the
rears, so it still eliminates front braking, and it's also better
for high-bite tracks. The presence of a front diff, however, makes
the center one-way somewhat of a compromise between having no
one-ways at all and the aforementioned front one-way
configuration. In some ways, the center one-way is better for
tighter turning and low-bite surfaces than a front one-way. The
front diff scrubs a little more off-power speed during corner
entry, so it makes the car more manageable in slower corners. It
also allows "true" differential action when exiting the
corners—exactly like a car without any one-ways.
- Clicker and
pressure-plate units.
Clickers and pressure plates are designed to limit the action in a
center one-way configuration. Tightening these units limits or
eliminates one-way action for better braking, and that's best for
tracks with sharp, low-speed corners that require radical
acceleration and braking. Loosening the clicker or pressure-plate
units allows the one-way mechanism and, subsequently, the front
drive system, to freewheel under deceleration and braking, and
that's better for more open tracks on which faster cornering is
possible. These are the most versatile systems because they can be
adjusted to suit varying track conditions.
An important note about
one-ways and foam tires on touring cars: a one-way system should
always be installed on a car that runs foam tires. They wear unevenly,
and that makes the wheels rotate at slightly different speeds, even
when the car is going straight. Unless there is a mechanism such as a
one-way system to compensate for this, the drive train will bind, and
this will worsen as the tires wear. The binding won't cause any
immediate damage or significantly reduce performance. If you're
reading this article, however, you probably race and want to get the
most from your car. The subtle binding caused by running uneven foam
tires without a one-way system could be enough to cost you the victory
in a Main.
Left: This optional
layshaft one-way was designed for the Kyosho Spyder chassis. Gas cars
tend to have more belts and pulleys, so it's easier to find a
convenient place for installation.
Right: A clicker
one-way functions similarly to a layshaft one-way. This clicker may be
adjusted to limit or even eliminate one-way action, so this is one of
the most versatile configurations.
WRAP-UP
Now that you understand
what a one-way bearing is and how it works, you'll be able to
determine whether you need one. If you do decide to try one, keep in
mind that you will have to change your driving style. Driving a car
with a one-way requires a smoother, more flowing line rather than the
choppy throttle/brake extremes used on tighter tracks. Given the right
track conditions and the proper adjustments to driving style, however,
a car that has been properly set up with a one-way drive system will
be very tough to beat!
Above: The
self-locking nut and spring on the end of this layshaft are part of an
adjustable one-way system from HPI. The friction disc and plate to the
right of the silver pulley determine how much one-way action there is,
depending on the amount of spring pressure. A loose setting allows
more one-way action for large, sweeping turns; a tight setting limits
one-way action for slower tracks with tighter turns. |
