I recieved an excellent explanation from a Sunbeam racer who seems to have a
good handle on the mysterious locking action, his name is Carl McLelland...
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Hi David,
Geez, I had forgotten all about that letter I put out on the vintage race and
Alpine nets...... As it turns out, another physicist wrote a thread that
explained what's happening. It was so simple I was ashamed that I didn't see
it right away. What causes the knockoff to tighten instead of loosen is the
same principle that allows a train to go around a curve.
Picture in your mind a cross section of railroad track, and the wheel on a
train car. (Remember, the wheels on a train are part of the axle.... the
'inside' wheel turns at the same rate as the 'outside' wheel). Thus, when a
train car goes around a curve the inside wheel is turning the same rate as the
outside wheel. Which means(!!), one of the wheels must be sliding/skidding on
the track because you have a different radius for the inside track and the
outside track. SO, how does the train go around a curve?
The top of the track is curved and the wheel surface is slightly slanted
(larger diameter on the inside of the wheel and smaller diameter on the
outside of the wheel). As the train goes into a (for example) left curve,
centrifugal force pushes the train axle(and wheels) to the outside of the
curve. The outside of the "left wheel" is in contact with the "lower" edge of
the track and the inside of the "right wheel" is in contact with the "center"
edge of the track. This results in a slight increase in the mathematical
radius of the inside wheel and decrease in the mathematical radius of the
outside wheel, which makes the radius for inner and outer wheels nearly the
same, which allows BOTH wheels to "roll" on the track rather than slide.
If your still with me, if you haven't fallen asleep and your eyes glazed over
(!!!!!), the same basic thing is happening between the knockoff and the
"knockoff mating surface" of the wheel. They are both slightly curved, thus as
the axle rotates with the knockoff on the axle and tight against the mating
surface on the wheel, there is just enough difference in radius' to
effectively be constantly tightening the knockoff.
DON'T EVER REVERSE THEM!! (Left on right and right on left)! You would not be
able to tighten them enough to prevent the knockoff from coming off the
axle!!!!! The knockoff WILL COME OFF and you will lose the wheel..... just
before becoming the first person to the scene of the accident!
I was safety wiring the knockoffs because I had this fear of losing a wheel.
I've since lost that fear. If the knockoff is tighened properly to begin with
it cannot come off. As an experiment, I beat on my knockoffs with a lead
hammer until they wouldn't tighten any more. I safety wired them with the
safety wire TIGHT! After a 20 minute practice session at Thunder Hill I
checked and sure enough, they had tightened! I retied the safety wire (again
TIGHT), and after a 20 minute race they had tightened more!! The same occurred
on the next days practice and race. A couple months later, at Sears Point (I
had not removed the wheels between races), I went throught the same drill, and
after each session the knockoffs had tightened. Two weeks later, again at
Thunder Hill (I had intentionally NOT removed the wheels between races) I went
through the same drill, and SAME SCENE, TAKE THREE! After each session they
had tightened!
Lastly, Thunder Hill is a counter clockwise course and the fastest corners
(which means the greatest wheel loading) occurs in left hand corners. I've
noticed that the right side knockoffs tighten more than the left side
knockoffs, which would be consistent with greater loading on the right side of
the car.
I hope this answers your questions.
Carl
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