For some reason i find this move wrong.
Either you put a 180 rear to allow a full option for every street purpose, or they should put a 150/70-R17 , as the older GS, Capponord and others.
Surely a 180 tire would fit on a 170 rim, but from my experience this does not bring the best results.
If i'm not mistaken dunlop has the road smart with a 170 which is a decent tire. As i said , my main concern a multi porpose tire of the given factory size.