Actually, 1200 and 1500 have same final drive RATIO ... but they are not identicle parts, but since the 1500 rear wheel and 160/80-16 tire is taller than the 1200's 150/90-15, you'll see a slight RPM drop at speed as engine drives rear wheel, speedo registers off front wheel (speedo doesn't work) . You can use a 150/80-16 tire on the 1500's wheel bringing overall "MPH<->RPM ratio" back closer to OEM.
The 1500 rear disc is larger (315mm) hence the need to use 1500 caliper bracket which gets narrowed (to ~.51") some when the shock lower bolt gets shortened on end. This will result in slightly more rear brake due to increased "leverage" of larger disc and greater swept area. Same caliper. yup, got 93 caliper on it now, same as 84. didn't change til the 1800's.
The 1500 wheel has more meat in hub area supporting it's OEM double row drive side bearing. that is what a person needs, if going to be at or OVER Max capacity of bike. 84 is 380#.... 1800's are 430# and that isn't even a LOT of weight, with 2 HEALTHY Ppl/gear and trailer tongue load... that is going to be at or over max load for most MC tires @ ~834#.
Shinko 230 Tourmaster is ~1100# but delaminated in 5 years and <~4000 miles? too much weight? not enuf air pressure (36, my aching back/blown shocks doesn't like rough roads)? cheap tire? for $81 shipped, just... 5 years... abt the max a person shd run a tire anyway... some say 2 years? or less? Ur mileage may vary. $100/hr shop time now, wow. last I was there, $75 for HD's, and $65 for "others"
195 55 16 car tire instead of the 160 80 16 bike tire... is about an inch shorter in OD, yes? and 35mm wider, over an inch (25.4 mm to an inch... fit in the swingarm? I looked for a 175 80 16... one left for $225? sort of negates the "cheaper car tire" thing when other car tires are $56. some say yet the 195 55 16 will fit in swingarm.... others say NO; it wont fit in the swingarm. seems like a LOT of extra wide tire to fit in the swingarm? I tried to stick my finger tween stock 150/90-15 MC tire and there isn't enuf room for my portly finger.
I do like the idea of using 1500 NO AIR shocks on back. I put on aftermarket e bay NO AIR shocks, they fit/work, but they are at/over their max capacity even adjusted for max load. do the 1500's have... air shocks or coil spring shocks? air? yes? just saw ONE coil spring shock "for 1500" online. hummm, all in all, figure the new MC tire I put on is good for 5 years, regardless of mileage and ... I doubt I will be able to ride in x yrs. thx for input, appreciate the knowledge. Still got the 165/80-15... just got to take off .056" material off the 1200's wheel all around the wheel and whittle down the "safety bead" that's necessary if blowout to keep tire on the wheel? the 16.5" 4x4 wheel does NOT have ANY safety bead and when the tire is LOW, bead pops easily and on the rim. not going to limp it anywhere, unless don't care about the tire/wheel. ... that is probably ruined anyway if going faster than 10 mph when it happens.