Illustrated Explanation of Chariot Construction: Volume I

Page Twelve

When the joined spokes are not tapered original: 殺 (sha), meaning to reduce or pare down, they appear exactly flush with the rim and do not protrude outward at all. Furthermore, the reason one must taper the spoke to create a geng a ridge or "neck" where the spoke meets the rim is simply to prevent the wheel from being hindered by mud.

The Record states: "If the spoke is divided into three parts [forming a ridge], then even in deep mud, the wheel will not be hindered."

There is no other complex or clever reason for this design. However, Master Dai Dongyuan Dai Zhen (1724–1777), a preeminent scholar of the Qing dynasty known for his work in mathematics and philology also interpreted Master Zheng’s explanation regarding how a "wheel calculation" prevents wobbling. He proposed that if a wheel lacks a geng, it will inevitably rock and shake from side to side; but with a geng, the weight and force are directed inward, eliminating the risk of tilting or wobbling.

This is even further from the original intent of the author of The Record the Kao Gong Ji. Generally, if the hub the central block of the wheel is long and the axle-hole fits the axle snugly, the wheel will be stable. If the hub is short and the axle-hole is too wide, the wheel will wobble. Making the rim protrude beyond the plane of the wheel has absolutely no bearing on whether the wheel wobbles or not.

Furthermore, in investigating both "large carts" ox-drawn freight carts and "small carts" horse-drawn passenger or war chariots, the width of the spoke is equal to the thickness of the rim, and the geng measurement is exactly one-third of that rim thickness.

How do we prove this? The Section on Cart-makers states: "The spoke is three inches wide." From this, we know the rim of a large cart is three inches thick. It also states: "The geng is one inch." Thus, we can see that the geng is one-third of the rim's thickness. Now, regarding the Section on Wheel-makers...