120 or 110 rear tire for 450?

Because of the handling characteristics of your particular bike, a 110 would certainly help. Im going to say stick with a 120 because its not a big enough difference for most of us to really notice after the first few rides. I also think that a 110 would just lose so much traction that a 450 rider is used to having.

when we rode Yamaha's (2013) my son preferred the 110 over the 120 for handling. we switched to Honda in 2014 and he prefers the 120 over the 110. it's all preference. try both and go with the one that feels best

Try a 120/90

I wouldn't run anything but a 120. Too much wheel spin with a 110. They just don't hook up the same

Would there be quicker tire wear on a 110 due to less tire?

If you ride soft tracks more run a 110. If you ride more hardpack then go with a 120. The 110 will work better in ruts while a 120 provides a larger footprint to aid in traction when there isn't a lot to be had.

I think you would be happiest with the 120. The 110 on a 450 will just not have the grab that bike can achieve with the 120.

120 I say.

On my yz450f(2013) I preferred a 110. Makes for better handling. 120 is good but on that bike It didn't work for me.

I'm wanting something wider than a 120, I might have to lace in an 18" rim for more options in wider tires. I run a 140 on my CR500 and notice the increased traction difference in mid to soft terrain.

I agree, except I would clarify that soft tracks meaning tracks that develop deep, firm ruts.

On a pure sand track, the ruts aren't as much of a factor. The 120 works really well in sand, especially when there is less moisture in the sand.

You should also check the tyre compared to others... My 404 rear 120 is the same width as a Dunlop 32 110... Alot of dudes down here having good luck with the flatter Pirelli 120 I think too...

You can get a bigger profile on a 450 using a 120-80x19 tire with a 2.50 rim. On a 250f, using a 2.15 rim with a 110-80x19 or a 110-90x19 tire will give a larger profile......

I think motocross action prefers a 110 on 450's. I run a mx-52 110 on my YZ-450 on tracks like Piru-mx (tight, hard packed, rutty), and prefer that over a 120, much better cornering in the ruts. But I like a 120 better at tracks like Zaca (sandy). Always a mx-32 on the front. (stock rims). Do a search on motocrossaction web site, they wrote a few articles on this subject.

120s on my 450 and 110s on my 250f.

Tireguy is on the right path, rim width dictates tire size. You do have choices....

I think it depends on the tracks you ride and what feel your looking. On my KTM 450 I have mainly run a 110. I have tried a 120 but lost the cornering feel if there were deep ruts and hook up. I have tried different brands of 110 and some seem to have a smaller footprint than others.
The one trick years ago in SX that I know was a wider rear rim with the smaller tire but a wider footprint. Lots of things to try but ask a top tire guy and then test yourself you will get it.