Why are there more Su Beiren in Jintan?

There are more Su Beiren in Jintan. Some people think that one-third of Shanghainese are from northern Jiangsu, and two-thirds of Jintan people are from northern Jiangsu. The only difference is that Su Beiren in Shanghai speaks Wu dialect, while Su Beiren in Jintan speaks Jianghuai Mandarin. Jintan is the only northern Jiangsu area in Suzhou, Wuxi and Changzhou.