I have a standard 2s Brompton from 2018 (I think?) but the gearing should be 54T x 12/16. It's been fine but I think I'd like to make it a little speedier. Generally what are the pro/cons of switching out the chainring vs replacing both cogs? I think the ratio between the two is about right but I just want a slightly faster gear than 12 and 16.

12 is the smallest so you have to go up on chainring. I have heard that 60 is the largest.

There are third party cogs with 11t for the Brompton.

There is also a 3 speed conversion with 11-14-17t https://www.bikegang.co.uk/bikegangh...-9S-p194768178

The problem is that you need to get again those special cogs every time you replace the chain. An issue with chainrings, when going with non-Brompton, is the potential lack of a chainguard.

You could turn that 2s into a 6s with a BSR/BWR three-speed gear hub.

Hub Gear Calculator

the question is how fast would you want it to be, 20mph, 25, 30? In your current setup (54x12t) at 90rpm, you can go as fast as 20mph already. If you replace your 54t with 60t, you could hit the 25mph mark.

I have a 2sp Brompton Lightweight with a 60 chain ring and I believe a 12/16 rear set-up.
I use the bike for training (fits in the car to work and inside home 17-20 miles) I’m finding I could do with a higher gear, so would it be better to go 61-62 on the front or try an after market 11 on the rear ?? Tia.
FYI I’m a low cadence rider.

Moving from 60 to 61 or even 62t won't change a lot, 1.66% or 3.33%.

But moving from 12 to 11 will increase the gear inch by 8.3% which is a bigger increase.

BTW, you can do both!

For the chainring, you must check that it is compatible the hook that attach the folded front frame to the rear triangle.