Hi, all: I may have a choice between an older (like ten years) six-speed Brompton or a couple years' old three-speed Brompton. Any reason to pick one over the other? Thanks a lot.

6 speed 10 years old, would be a SRAM/Sachs 2 by 3 speed hub,
the external sprockets, 13/15T
half step the 3 internal hubs ratios.
same internal hub ratios as the 9 by 3 dual drive.

2 years old the 3 speed would be the Aluminum shell version of the AW3
.75/1/1.33 gears.

Math :https://sheldonbrown.com/gears/internal.html

Depending on the year of the newer one it will have a longer wheelbase(better ride and if your tall it helps stretch out a bit more),better brakes and quite a few other upgrades that the older one doesnt have. Buy newer,nothing wrong with a 3 speed.

If you buy the old one you will be able to upgrade it to a 6speed BWR hub for about £140 but if you get the new one and want to upgrade to 6 sp..BWR hub it will cost more because you will also need the rear derailleur so it will cost about £200 plus ..However you will have better brakes on the newer one..perhaps a clip to stop the rear triangle falling down when you pick it up..maybe a left hand crank with a stop on to stop the folding pedal scratching the paintwork..Hard choice..

Personally I think any six speed is far better than a 3 speed..

Check out this thread https://www.bikeforums.net/showthread...light=brompton

If forced to give an answer, I would have said that the six speed option only came with the "new" model. That is, the one with the longer wheelbase ... not unless there is a third generation of Brompton that I missed. Just to be clear, I really could have missed a third generation frame since I have not shopped for one in several years.

ref : Brompton Book , in print.

New is Mk 4, SRAM made the hubs for Mk3, UK sturmey AW3 or a few 2 cable 5 speed. is Mk2.
1st generation looked a lot different..
my Mk 2 has forged hinges, butt fillet brazed on, newer ones use a cast hinge, tubes fit inside
brass flows inside the space between. those got the extra inch of wheelbase.

OK. From memory the Merc was an imitation of Mk2 then. And we rode an Mk3 for a long time and there was a bump in the wheelbase there.

So is the wheelbase for Mk3 = Mk4? I've only casually seen "new" ones ... say made in the last two years ... and didn't notice anything different. Assuming that Mk4 isn't brand spanking new, what is the practical difference between Mk3 and Mk4?