Actually, Schulz is within the SPD more on the right wing. Within the general spectrum of politi in the center.
@fcbforever as a member of the party will know better but as a non-party member, I perceive the left wing of the SPD to be recognizable, with a little influence here and there on the party manifesto but that's about it. On a federal level that is.
As you might know, Germany is a federal state with every state having its own elected
Ministerpräsident. (They lead their states but also convene in a second federal chamber, the
Bundesrat. They have to approve certain bills before they can be implemented in the law, and they can start initiatives for bills, too.)
In some states, the left wing of the SPD has more influence than in others (e.g. Hesse, the state in which Frankfurt and Wiesbaden are located). In the majority of states though, either the center of the SPD or the right wing is. more influential.
In my memory, the left wing had much more influence before then Chancellor Schröder implemented his
Agenda 2010, which weakened workers protection and welfare. Many left wing party members made an exit and joined the party
Die Linken (The Left).