WELCOME to the Forums Mikek...
Not many ways to say this but the 170 is not a "high end" lawn tractor... There are not as many things you can do to that light mower to improve it's traction, without negatively effecting the trans axle...
The first thing to try is drop the air pressure in the rear tires, that will give you a larger foot print.
You could put wheel weights on the drive wheels, But I don't think those wheels have the mounting holes for weights... You could load the tires, but with small tires, that will not gain much weight... :smile:KennyV