Spacer query for new cog

[lucifuge]

I have a Giant Seek S, which is running the stock 45/20 = 2.25. I want to change the 20T to a 18T to make 45/18=2.5. Now, i've found a 18T cog (Chris King) which i'm planning on getting.

My question is, do I need to also source spacers?? or is it not required if the bike was originally a SS?

[BRLVR.v2]

No, just replace the sprocket and use the original spacers. Make sure the chain line is aligned the same way.