Rear Tyre / Tire sizes for a Gen 2

I'm sure someone else has asked this nut couldn't find any posts.

Can the Gen 2 run a 190/55 rear rather than the 190/ other bike runs the /55 so it would be nice to only need to keep 1 size spare.
If its OK to use a /55 does it make the speedo read nearer true as i've read that as with the Gen 1 its a bit optimistic with the speed.

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