《周礼·冬官考工记·轮人&輈人》
因此大车行走在平地上，车辕平衡适于任载，到上坡的时候，不向下伏压车辕，就一定会悬勒牛脖子。
是故大车，平地既节轩挚之任，及其登阝也，不伏其辕，必缢其牛。
Therefore, when a large wagon is traveling over flat ground, the crossbar is balanced and suited to carrying loads, but when it reaches a slope, if you don't press down on the crossbar then it will definitely hang and strangle the ox's neck.