Hi all

Because of the London congestion charge applying to EVs from Jan 2nd, I’m considering getting a Brompton for a ~40min each way commute leg by bike (the rest is another hour+ by car) in order to remain financially solvent.

The route is pretty flat, nothing over 5% and I want to be able to hit 20mph.

I can get a used Brompton 6speed (likely with all steel frame) for less than half the cost of a new C-12speed which I think would be maybe 1-2kg lighter?

Any reason not to go for the used one? It looks in good condition in the photos, just a few scratches.

It also has a rack with the extra wheels, does that have any downsides? Does it make it easier to wheel through a shopping centre or train station? The official video I’ve seen on youtube wheeling the non-rack one looks awkward.

The rack makes it a lot easier.

There is no significant weight difference between an steel 6s and a C-line 12s which has also a full steel frame.

Its the P-line with titanium fork and rear triangle that, with the same transmission, weight about 1kg less.

A 4s P-line without the heavy 3s BWR IGH weight less.

Difference between the 6 and 12spd is negligible,but with racks installed the 12 will be a couple oz lighter than the 6. As to the gearing,that depends on how strong of a rider you are. The 6 has a range of 33-100",the 12 is 28-114". You can swap the 50t chainring on either for a 44t to lower the gearing,but the 12 will still have a decent top end while the 6 will get much 'spinnier'. You can plug the numbers into Sheldon's gear calc to see how they compare to your current bike. Both have 50t chainrings,the 6 has 13/16t cogs,the 12 has 11-13-15-18t. Also note the 6's 8spd chain/cogs will last longer than the 12's 10spd.

https://www.sheldonbrown.com/gear-calc.html

Not knowledgeable about Bromptons per se. But in general:

With at least 6 gears, what matters more is the whole gear range, more than narrowing gear steps.

I live in a city with long hills, sometimes short steep ones. My folder originally had 7 speeds, 52x11-30, and with 20"/406 wheels, lowest gear was mid-30s gear inches, too high, I had to walk up many hills. My 2X crank conversion was a game changer, 50/34x11-30 gave me 21 gear inch low, adequate, and I can go lower for touring with a 34 low cog. High is 85 gear inches, which is enough to pedal down mild downgrades, and any steeper, I just coast. For me, that is the gold standard, 400% range, 21-85 gear inches, and this is on a 170mm crank arms. For shorter arms (more common these days), use Sheldon Brown gear calc to compare "gain ratio", as this also takes into account the crank arm length on gearing.

All except the 4 speed external gearing Bromptons (gearing too limited) have internal gear hub (IGH), this can increase cost if you don't know how to service yourself or have facilities; it is for the latter reason that I avoid IGH these days, unless it has the ability to drain and refill liquid lube, and good seals, no needing to disassemble and grease, so in that case, easy to maintain and if done, nearly never needing to pull apart. So if you are buying used with an IGH, especially if not a drain-and-fill lube, make sure it is functioning well and doesn't need a rebuild, which it might if ridden often in the rain and not given an annual teardown with plenty of grease on the outer bearings to keep out water.

Dahon had sold a 20" bike with a 3x7 IGH instead of going multi chainrings like mine; Every one I find for sale has had the IGH neglected from maintenance. Same for Bike Fridays set up same, which is why they sell a lot cheaper in used the market.

But I will also say, with the smaller (349?) wheels on a Brompton, you can't get enough high gear without an IGH, or BIG chainring, or a Schlumpf drive at the bottom bracket. So there's a reason Bromptons mostly have IGH setups. On a 20" wheel, one can get by without an IGH, unless you need a road-race top gear.