i have a 2016 subaru outback. thought i didnt need snow chains but now being told i need cables. is this true & if so what size do i need for 22560R18 tires

All depends on the driving you do. If you go over mountains, you should have some chains with you. Sometimes they will not let you over unless you chain up. If you live in a area with lots of snow it is good to have chains to get around. The only place that I know of where you have to have chains is getting over a mountain pass. When look for chains/cables, it will say on the packaging what tire size they fit. So bring your tire size along, you never know when you need them but it is nice to have them when you need them.

Read your owners manual but I believe it will tell you that you can use type "S" low clearance cables on the front only.

The cable size is the tire size.

I'd try spare wheels with dedicated snows first, as the Mich X- Ice3, new Conti SI and Bridgestone WS80 are superb. Get 18's for best handling, but if it's just for snow/ice cheaper 17 (225/65- 17) will do...but be sloppy at higher speed or in the twisties, as this Subie OE 17 size is a truck/SUV one unfortunately. If I were doing it I 'd stick with the 225/60-18 for decent highway winter use as well as slippery stuff. Sorry, but no experience with cables. (Indeed, to my knowledge, NONE of my 1900 or so Subie AWD clients over the past 1/3 century (gulp!) have ever needed chains/cables here in New England.) That said, adding crutches to your all-season stuff is cheaper than the $1k needed for a decent wheel/snowtire setup. If your need is based on snow depth then maybe you need deeper shoes, but if it's about ice traction I'd try these high-speed snow tires first, as they'll be better than chains/belts on ice.

Unfortunately people like me who live in snow county but then drive nice dry roads 90% of the time don't really have the option to buy those fast wearing dedicated snow tires.

Yeah, I get it. That's why I've sourced snows for only 1-2% of my clients too! Unless it's a chariot dedicated to their winter chalet or au pair use the two-set solution is unnecessary. I have found, however, that at least the Mich Ice2...and maybe 3, didn't seem to wear quickly through dry winter highway use...even on a heavier G37x. Can't say the same for the WS80 nor the newest Conti SI.