Winfried

Hello,

A folding bike with 20" wheels I'm looking at ships with a seven-speed, 11-28T cassette + Shimano Acera derailleur, and a 52T chainring.

To use it for touring, I'm thinking of replacing the single chainring with a dual chainring, and replace the cassette with a wider alternative.

i've never done this.

Provided it's even possible, I guess I'll need to change the whole transmission:
- in the rear, build a wheel with a new hub, replace the derailleur (low cage because of the wheel size) and lever, and possibly the derailleur hanger
- in the front, find the right dual chainring + bottom bracket to get a good chainline + derailleur + lever

Is that correct?

Thank you.

ScottCommutes

One additional concern is that you would be attempting to mount a front derailleur and cable on a (folding) bike that was never meant to have one.
Another concern is that the tone of your post suggests that you want to have all this planned out before you even get the bike.

Bill Kapaun

If you look at "conventional" bikes with FDER's, the seat tube is directly above the crank and the FDER is attached to it.

On your bike, the seat tube is offset a couple inches or so and the FDER won't be in the correct place.

Andrew R Stewart 

One solution was to use a rear hub with both a cassette splined driver and an internal gear system. Sachs had two versions of their Dual Drive that Bike Friday (among others) used to expand the range without adding a double crank and ft der. I believe these hubs are no longer offered. Andy

KerryIrons

Wouldn't it make more sense (and save money and effort) to buy a bike that has the gearing you want? They are available from several manufacturers. As others have noted, the diameter and angle of the seat tube might make fitting and using a front derailleur highly problematic.

70sSanO

You need to address this in terms of gear inches and what is needed not necessarily gear choices that might be duplicates and used rarely.

You might end up sacrificing some top end for climbing low end.

And gaps are less of a concern if you need to get to point B from point A.

Figure out what the lowest gear inches you need and go from there. If you have ridden similar terrain, regardless of the type bike, you can determine the lowest ratio.

Worst case, if you can get cassettes with full cogs and not spidered, you can build a custom cassette. Personally I would never consider a cassette with an 11/12/13 if I were in your position because you are wasting a more usable ratio. And touring on a folding 1x makes each ratio gold.

John

icemilkcoffee 

Just get a 12-32t cassette and forget about changing to 2X in the front. With the 20” wheel 32t is very low already

base2 

I am a big fan of these type of hack/bodge type of projects.

One possible option is a Shimano E-type derailleur. It is a version of a standard front derailleur that has it's own mounting bracket that affixes to the bottom bracket as if it were a standard 2.5mm spacer. Only the spacer is a few inches tall and has a derailleur on top. I don't think it could accommodate a 52 tooth chainring. But knowing such a thing exists opens up possibilities. I had one and ended up manufacturing by hand a less flexy bracket for it out of a much higher grade of aluminum. there is no reason you couldn't do the same to accommodate the height of a taller chainring. Mounting a suicide shifter on the seat tube with a pulley to convert to a down pull derailleur could be easy or hard depending on the tubing diameter

Also in the style of the SRAM Dual-Drive, but minus the easily broken plastic clickbox and unobtainable shift rod, there is also a Sturmey-Archer CS-RF3 and it's disc brake brother the CS-RK3 to give you the range of a triple but the 3 "front" gears are located inside the rear hub. The hub is inexpensive but you'd have to build a wheel around it. It is operated by a standard mountain triple shifter.

Another option is a Schlumpf Drive of some variety. I own 2 and have installed them on various projects. They are not cheap but they too provide the range of a triple in a self contained 2-speed crank set. Speed change is accomplished via a kick of a button with your heel.

The Sturmey-Archer wheel is probably the cheapest/easiest solution.

70sSanO

I'm revising my original suggestion of a custom cassette after a 20" wheel size duh moment.

I'd probably swap the 52t chainring for a 48t and run an 11-40 cassette (9spd?).

You'll need a rear derailleur that can handle a 40t max cog, but your capacity is only 29t so you don't need an SGS.

This gives you 22 GI to 81 GI. For folding bike touring I'm guessing that should be enough.

John

Edit added: Just noticed you are looking at a 7 speed. Your first step is to not buy a 7 speed if you want to tour with a wider gear range 1x.

veganbikes

I would recommend getting a bike more suited to your needs. If a bike comes with so many parts that are low end or not suitable then I wouldn't even bother with it in the first place. If I had the bike it could be one thing but a theoretical bike I would just move on quickly and not even consider it.

First question to ask yourself is do I need a folding bike, if not your world opens up to a load of awesome touring bikes and plenty of other bikes that can be used for touring. If you do need it to fold there are still options out there for quality bikes with quality parts that would better fit the bill or at least be better candidates for upgrades.

Anytime I see new 7 speed stuff I run away, far away unless it is maybe an IGH 7 speed is old 80s and early 90s stuff is is 2024 we have 12 speed as the new stuff and we have had Rohloff for a while as well so we can go 14 speed IGH, any derailleur stuff that is 7 speed (minus a few odd ball DH gruppos) is pretty well outdated and at the bottom of the barrel or under it. If the drivetrain of that low spec the rest of the bike cannot be far from it and that usually doesn't make for a good touring bike. Less reliable lower initial cost parts are just not what I want for touring or really most any riding but very infrequent riding because I can only ride that bike infrequently.

Winfried

Thanks for the infos.

I've been touring with a Brompton for years with a dual chainring + derailleur, and a Shimano gear hub in the rear. It works fine (several after-market, braze-on clamps are available), but I'm looking for a more efficient folder and possibly disk brakes — not a regular bike because folders are so much easier to take on train/bus.

If possible, I'd rather avoid going back to a gear hub à la (RIP) DualDrive, and only use derailleurs for maximum performance.

Although less compact once folded, the bike I showed in my OP rides better than a Brompton, and costs half the price of a Birdy.

2_i 

An interesting idea. I pulled out an E-type mount Shimano FD from storage, and it is heavy at 270g because of that mounting plate, which is thick steel formed into a wavy shape to make it more rigid. The weight is of concern for a folder. I did not check precisely the largest chainring it can take, but it looks like low 40s, maybe 42T. If you wanted to go higher, the FD would need to be heavier. I am not sure about the aluminum idea - if you wanted to make it withstand the torques acting, it would need to be quite thick, and then the chainline comes in. I presume that grabbing a seat tube mount ends up being more sensible. Incidentally, that E-type mount also grabs the seat tube, but to aid in positioning, I suppose.

base2 

Admittedly not the best pics in the world. But well enough to show what can be done with a hole saw, a hack saw, a flat file, and box I'm miscellaneous hardware. It actually worked quite well.

I'm not sure exactly what happened to this project. I think I maybe may have donated it back to the Co-Op after deleting the smallest chainring and replacing the rear wheel since the extra torque afforded by the low gear and additional braking force by the Arai drum was more than the shoddy Schwinn hub on the drive wheel could handle.

2_i 

If this were optimized, I expect it could become a commercially viable solution for folders and other bikes where the seat tube does not follow an axial direction from the bottom bracket.

hokiefyd 

Depending on your gearing range needs (I apologize if you listed them, Winfried, and I just missed them), don't overlook the Microshift Advent SS (SS for Super Short). It's designed for small-wheel bikes, to offer a pretty good amount of capacity while not having a long cage that might hit the ground. Its maximum sprocket spec is 38t, and capacity is 27t. Microshift have an 11-38 cassette to go along with this derailer. That'd give you a 345% range without having to fit a front derailer and 2x crankset. If that's enough of a range, just adjust your chain wheel size to get the gear inches you need.

I don't know if that's enough range, but it's a possible solution.