Balancing Steering Cable and Front Kingpin Tension
Ėby Ian Carsten
racers advocate significant kingpin tension for maximum speed. But that
makes the car steer poorly if the cable tension isnít high enough. We
experienced this when we first started racing at a faster, smoother track
than we were used to. Both our drivers complained that they had a hard time
keeping their cars straight.
watched their path from the top and bottom of the track. It looked like they
kept swerving from left to right once their cars had built up speed.
Naturally, they didnít do too well. Both drivers were pretty experienced and
usually drove well so we didnít think they were at fault.
only real differences were: the speed and smoothness of the track and the
significantly greater kingpin tension used. We increased kingpin tension
because many of our fellow racers recommended it at this fast track. At the
end of the day, we concluded modest steering cable tension combined with
high kingpin tension was the problem. We donít think the speed of the track
caused this. It just made it much more obvious.
Hereís what we found. With higher front kingpin tension, the axle wonít move
until it gets pulled fairly hard. If the cable isnít tight enough, when the
axle does move, it can pivot too far. Thatís because any slack in the
non-pulling branch of the cable allows the axle to pivot too far.
Suddenly, the driver has to correct by steering in the opposite direction.
But the same over travel of the axle happens each time. The driver has to
fight the steering all the way down the track. This makes the car travel a
snake-like path. Itís unsafe and looses lots of time.
compensate, you have to increase cable tension. When the cables are
sufficiently tight, the steering will be responsive and not over steer. But
the increased cable tension will spring the axle rearward. Now the front
wheels are toed out and that will slow your car. You have to bend the
spindles forward to compensate. For that you have to use a spindle gage,
spindle stands, and bending tools.
the cable is sufficiently tight and the front spindles are parallel, your
car will handle responsively and be easy to keep straight. This helps
maximize speed. Youíll have to keep track of the cable tension. A tight
cable can stretch for a while until it stabilizes. If it stretches, the
cable will loosen making the steering sloppy again.
Youíll have to check the front axle with a spindle gage before each race
day. If the cable loses tension, the axle will relax and return to its
unstressed shape. That allows the front spindles go out of parallel. Usually
all you have to do is tighten the cables until the spindles are parallel
again as determined by the spindle gage.
a good idea to apply some grease between the washers that slide over each
other as the front axle pivots. For example, thereís about 3,274 pounds of
clamping force between the washers on an unlubricated kingpin tightened to
Greasing between the moving washers helps reduce
the steering effort and keeps the washers from galling where they slide over
each other under kingpin tension.
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