I've recently bought a second hand Brompton for my commute and day to day riding around town, but the gearing feels a bit off to me. I'm used to riding a 700c fixed gear bike, running 48t x 17t, and I guess ideally I'd want the middle gear on my Brompton to be roughly equivalent to the gear I run on my fixed gear bike. The brompton has a sturmey archer 3 speed hub, which is labelled 'SRF3', and is currently running 50t x 14t. Is this going to be possible? What sort of sizes of sprocket/chainring do I need to get my middle gear roughly equivalent to the 48t x17t on a 700c?