40T sprocket, same chain?

Hello,

Considering a 40T sprocket but my chain and front sprocket are only 5k miles old. Will a 40T fit without having to replace the chain?

Inquiring minds want to know,

Flip the adjusters if the chain is stock length.

I'm doing the same soon

Bit tight but works fine. You do have to reverse the chain adjusters though

Can I ask why 40t in the rear when you could go -1 on the front and get the same for a lot cheaper?