(Public Domain)
This game is known in Chinese as tuo la ji (拖拉机) (meaning 'tractor') or bashi fen (八十分) (meaning '80 points'). It is an expanded version of sishi fen ('40 points') using two or more decks, and is related to zhao pengyou ('looking for friends'). All these games are collectively known as Sheng1 Ji2 (升级), which means "raise level" or "promote". Tractor is widely popular in China, especially in Shanghai and south of the Yellow River where it has practically displaced the older single deck game.
The scores of the teams are expressed as card ranks. At the start of the game, each partnership has the lowest possible score, which is two. By winning games, a partnership can increase its score to a higher rank: three, four, five and so on. Above ten come jack, queen, king and ace. The objective is to achieve a score higher than ace - the partnership that achieves this wins the game.
In each hand, one team forms the declarers, sometimes known in Chinese as dang1 zhuang1 (当庄), and the other team forms the opponents. In the first hand, either team can be the declarers, depending on who makes trumps. In subsequent hands, the team that won the previous hand is the declarers, and the other team is the opponents.
One member of the declarers' team is the starter, who has the advantage of taking the last cards in the deal, discarding some cards, and leading the first trick. While the declarers try to increase their score, the opponents' objective is to take at least 80 card points, in which case they become the declarers for the next deal.
Source: edited from Pagat, http://www.pagat.com/kt5/tractor.html
