Originally Posted by
pacificcyclist
I have done this upgrade to my Dahon Mu SL and a person I know who has a D7 had done exactly the same upgrade.
Basically, most Dahons come with a double crankset. If you can remove the bolts from your crank that hold the chain ring, you will have a chain guard on the outer crankset and the actual chain ring which is usually a 52 or 53T on the inner. What you can do then is replace your 53T with either a 44T or 46T and place it where the chain guard sits now.
Then for your climbing chain ring, you would go with a 39T chain ring, since this is the smallest ring they make for 130BCD crankset and put it in place of where the 53T or 52T sits now. You will now have a 46T/39T setup. You have 2 options. You can either shift between the 2 rings using a tire lever or your finger or install the ThorUSA deraileur adapter and buying a braze-on front derailleur and a friction lever shifter. The advantage of the having a front derailleur is to keep the chain from falling. I've done all I could to prevent the chain from falling, but decided that the derailleur is the best option. Do not get the index shifter for the front on this mod. I'll tell you why.
For my Dahon Mu SL, I have a 11-34 rear cassette mated to a SRAM X9 rear derailleur so I have low gears. Not sure if Neos can take 34T, but if it does, you'll have to be sure you do not CROSS SHIFT too much.
So what's the downside?
Well there is a downside to this. You can not ride CROSS SHIFTING too often. Which means, you can not cross a big chain ring to a big cogset on this setup all too often. You have to treat the gears as a 2 by system. Due to the shorter than usual wheel base of the Dahon folding bike, you can not cross a smaller front chain ring to a small cogset (11T) without rubbing the outer big chain ring next to it. You will wear out the chain a bit faster than if you're not crossing by causing a slight bend on the chain thus no longer hitting the bigger chain ring next to it as the chain wears. With this in mind and if you plan to install a front derailleur setup you would probably be better served with a friction lever shifter so you can manually trim the derailleur without having the chain rubbing against it. Actually, I will be in the process of installing this to my Dahon soon and all I need now is to order the adapter from ThorUSA.
Having said that, having just 2 chain rings is enough to tour really. You'll just have to coast down a steep hill.
I too tried to use the existing crank on a pre-Neos rear derailleur Speed P8 as part of a dual crank upgrade ; however, I encountered two problems: 1) the existing Speed P8 bottom bracket square taper spindle is too short (as I recall, it’s 103mm) for a front derailleur (mounted to a front derailleur mount) to shift inward enough towards the inner front chain ring to cause a proper shift, and 2) when I bolted two chain rings to the existing crank, there wasn't enough space between the two front rings, at least on my bike, to shift properly unless I added spacers. However, even if I added spacers, problem number 1 is not solved. To solve problem number 1 requires a new bottom bracket with a longer spindle and a compatible crank to position the inner chain far enough from the seat tube so that the front derailleur can shift inwards far enough to derail the chain from the outer ring to the inner ring and vice versa. Thor sells the front derailleur mount along with a 3mm spacer to move the spindle out to the right. I tried the spacer and was able to attach both crank arms. But again, 103mm plus the 3mm spacer didn’t move the chain ring far enough out for the derailleur to shift from the outer to the inner front chain ring. I’ve posted in detail elsewhere what parts I used to complete a successful and relatively cheap dual crank upgrade.
As far as using a friction shifter is concerned, I used a Sram "microshift" grip twist shifter for the front derailleur. It’s cheap and effective and matches the twist grip shifter for the rear derailleur. Two versions of the Sram grip twist front shifter are available: one is the "microshift" version and I don't recall the name of the other version. It's the closest thing to a friction shifter because it requires several small intervening "micro" clicks to move from the "1" marked on the grip shift to the number "2." The small incremental clicks allows me to trim the front derailleur. I learned about the microshift version from Sheldon Brown’s site.
Regarding cross chaining, I run a 32t (for touring with heavy loads and primarily to start the bike rolling) and a 48t chain ring on the front. On my large front chain ring, I don't shift beyond the 4th rear cog (out of 8), and on the smaller front chain ring, I don't shift beyond the 4th rear "center" cog either.
Thor sells the front derailleur mount, as does Gaerlan.com. I’ve searched the internet for any useful instructions Thor might have posted relating to the selection of bottom brackets, cranks, shifters etc… for the front derailleur mount he sells and I have found nothing. I emailed him and asked him a few questions relating to spindle length etc... and never got a reply. If Thor has posted any information, please point it out to me.