No the track width of the 17 and 18 models is no different than earlier ones. From what I have been able to find, all the 850s from 2014 and up use the same wheels. Offset is a measurement of the difference between the center of the wheel and where the wheel mounting flange is at. Zero offset means the mounting flange is dead center in the width of the wheel. Positive offset moves the mounting flange out toward the face of the wheel and negative is back toward the inside/hub side of the wheel. Positive offset wheels have less "dish" than negative offset.
There are several good threads on the forum here if you want to look into it further. They explain it better than I can. Or Google it and get explanations with diagrams.
Mine: 2018 Sportsman 850SP - 26" Bear Claw HTRs on OEM steel wheels(I really don't like the Aluminum ones)
Polaris Hand warmers, Mirrors.
Hers: 2019 Sportsman 450. 26" Bear Claw HTRs on Moose 427X Wheels.
2007 Sportsman 500 EFI, Polaris Winch, 25" Bear Claws QSC Clutch Kit, Hand Warmers
2001 Magnum 325 MOSE 12" rear wheel conversion. 25" Sedona Coyote tires
2017 Polaris Ranger 1000XP - Roof and front glass
2018 Kawasaki KLR650
2001 Magnum 325 Warn winch and Moose 60" plow-Sent to Daughter and Son-In-Law since his blew up
SOLD 2004 Sportsman 600 Twin