ambodach wrote:Brucey’s point about the snap ring should be noted. Getting it off is easy when replacing sprockets but I could not get it back on. Ended up going to my local garage and one of the mechanics got it on immediately with no problem.
It's not difficult, but you need a flat screwdriver to help it back on, or very strong fingers
you then need a friction thumb shifter for the handlebars, and the braze on front mech of course and a long outer cable, make sure the fold is OK and the outer is not too short, tight. The pit falls are the double chain rings, the chain wheel bolts can foul the chainstay when you fold the bike and then it wont unfold! so you would then as I did need to fit a longer BB, in my case 4mm longer. Don't expect the change to be slick, it works well for what it is. Always fold the bike with the chain on the outer, big ring.
currently I have 74 inch and 52 inch, but the first day in Cornwall/Devon (and possibly further north) will require something smaller. One practical solution would be to carry a spare chainring, to switch between say 48 T and 54 T for different days... it only takes 5 minutes to replace a ring... the question is whether the tensioner will cope with a chain too long by 6 links... folding not an issue as I can do without folding it en route.
since the chain wraps around only half of the chainring changing by -6T makes only 1.5" of extra chain slack; this ought to be within the capacity of the tensioner, unless you fold the bike.
S2L » 27 Feb 2019, 11:12am Back to gearing, with a LeJoG in mind
currently I have 74 inch and 52 inch, but the first day in Cornwall/Devon (and possibly further north) will require something smaller. One practical solution would be to carry a spare chainring, to switch between say 48 T and 54 T for different days... it only takes 5 minutes to replace a ring... the question is whether the tensioner will cope with a chain too long by 6 links... folding not an issue as I can do without folding it en route.
Stupid idea?
Have you tried fitting 2 chainrings as a double ? No shifter required, just push the chain over with a toe or a hedgerow stick when necessary; it takes about 20 seconds. Think of it like high or low range on a tractor gear box. There is a photo of our bikes further up this thread. We are using 42/28 doubles, so the chain tensioner can handle a 14 tooth difference, probably more. Some people reckon that having the smaller ring on the outside makes the shifter-less change slicker. Alway fold the bike with the chain on the bigger ring.
S2L » 27 Feb 2019, 11:12am Back to gearing, with a LeJoG in mind
currently I have 74 inch and 52 inch, but the first day in Cornwall/Devon (and possibly further north) will require something smaller. One practical solution would be to carry a spare chainring, to switch between say 48 T and 54 T for different days... it only takes 5 minutes to replace a ring... the question is whether the tensioner will cope with a chain too long by 6 links... folding not an issue as I can do without folding it en route.
Stupid idea?
Have you tried fitting 2 chainrings as a double ? No shifter required, just push the chain over with a toe or a hedgerow stick when necessary; it takes about 20 seconds. Think of it like high or low range on a tractor gear box. There is a photo of our bikes further up this thread. We are using 42/28 doubles, so the chain tensioner can handle a 14 tooth difference, probably more. Some people reckon that having the smaller ring on the outside makes the shifter-less change slicker. Alway fold the bike with the chain on the bigger ring.
Have fun.
I did think about it, but wasn't sure whether the rings would be far apart enough for the (rather wide) chain to fit... now that I know it does, it seems by far the best option... maybe 44T and 54T, which would give me a smallest gear of 42 inches... good enough to go up 10-15% inclines if they are not too long
It occurs to me that we are using a double chainring in conjunction with the the single drive sprocket on a 3 speed hub, which is a different chain tensioner to the Brompton rear derailler. I don't know what the effect might be of a big change in the angle of the rear derailler caused by the use of a big gap between front chainrings, but presumably if they are within the range offered as standard Brompton chainwheels (44t to 54t, I think) then it is likely to work. Please let us know how you get on.
Gattonero wrote:Find a sprocket from an 8 or 9sp cassette, also you need to indent the Rh chainstay for anything over 17. It's not rocket science but if done wrong it may wreck the rear triangle...
I suspect that'd be the end of any warranty claim... not to speak about resale value... I'll probably stay with the 17, seems to be OK...
You are not meant to take a 5lb sledgehammer and bash the frame with it, all you have to do is do "indent" the inside of the tubing by the size of half a chickpea. Even in the the worst case scenario, you can replace the rear triangle only, but the tubing used is ductile and will not cause any problem for such a small mod. In fact, resale value won't be affected because the indentation is so small that is very unlikely to be spotted.
It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are...
I provisionally re-fitted the 16 T original sprocket, as the 17 T got jammed a couple of times trying to shift back to the 12T... think it's too narrow, but I can't find anyone who has an old 8 speed cassette with a 17 T loose sprocket.
On the plus side, my first Brompton commute at 30+ km/h yesterday
