Anyone try and fit a 170/80/15 tire on the rear with success?

size	diameter	width
140/80/15	23.8"	5.5"
170/80/15	25.7"	6.7"

Egore runs a 150 on a stock rim & it works for him, and I have run 3 150's on my cast 3.5'' wide rim, but it is really tight. Everything has to line up perfect. And one tire might be a little bigger than the last one.
Have you SEEN a 170 tire? There a BIG & HEAVY tire.
I stick with 140/15's now.

One of the thing you need to consider is the width of the rim.  Trying to squeeze a wide tire on a narrow rim results in a tire that has a "too round" tread cross section.....the tire ends up having a narrow strip of rubber that is in contact with the road.  The result is fast tire wear down the center of the tire, and a bike that handles very "skittery".

The Suzuki Savage has a rim that is 2.75" wide......that is pretty narrow for a modern cruiser - but at 30 HP it is far more than the power of the motorcycle requires.

https://www.motorcyclistonline.com/motorcycle-tire-width-and-traction-video/

For nimble handling I recommend a 130/90-15 (which is nearly identical in size to the original 140/80-15 tire) - for taller gearing and highway cruising I recommend a 140/90-15.

Here is a chart that shows Metzler 170/80-15 fits rim widths between 3.50 - 5.00 inch.  The chart shows the widest tire they approve on the Savage rim is a 140/80-15 or 140/90-15.