AXLE TILT - Derby Tech - June, 1985

By Ollie Brower


In the May 1985 issue of Derby Tech, in "Tips From The Tops In A Nutshell" a 2 1/2 degree axle tilt was mentioned for a Junior Car. I received many questions as to how this could make the car faster, and how can it be done.

The theory behind this tilted axle is to keep the axle on a horizontal plane while it is coasting down the hill, as opposed to having the axle on the plane of the hill slope and slightly as a diamond to the horizon.

The. axle will flex more, and not be as restricted when it is horizontal, which will make the axle run slightly faster. This has been tested on an axle tester with consistent results. This does not take into consideration any change in aerodynamics due to a larger frontal area, or a slight leading edge. But a 3/4" axle will run faster on the tester if it is in the horizontal position.

This tilting theory has been tested by myself and others a few years ago in actual hill tests. After a couple of weekend tests we concluded that we could not prove this theory to be true. The margin of error during hill tests could not be overcome, which means that if it is faster, it is less than a foot faster. (These tests were conducted on a constant 5 degree slope with a 5 degree rearward tilt, and with no axle trees).

The All-American rules state that the kingpin can have a maximum tilt of 2 1/2 degrees. In theory you would like to have the axle tilted back the same amount as is the hill slope, which would position your axle exactly in the horizontal plane. Since almost all hills change slopes, and end up near level at the finish line, you must select an average tilt. You are limited by rules, and I can't tell you how the officials will interpret the rules, but I can tell you what the rules technically state. They state that the kingpin can tilt 2 1/2 degrees. They also state that ALL measurements, unless stated otherwise are plus/minus 1/8". If you drilled the hole in the axle on an angle that did not violate the 1/8" rule you could, if desired, have more than the 2 1/2 degree axle tilt.

If this axle tilt works on the rear axle, it will also work on the front axle for the same reasons.

This tilt was mentioned for a Junior Division racer. If it increases the speed of a Junior racer, it will also increase the speed of a Senior racer for the same reasons.


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