With this article, I hope to provide more information regarding the components that are suitable for a folding bike. Although the focus is mainly on Dahon or Tern folding bikes, this may well apply to other brands of folding bikes that have a similar setup or construction.
An empty Dahon Vitesse frame. What are the components that will be suitable? Read on to find out!
There are hardly any groupsets or components that are dedicated to folding bikes or small wheeled bikes (with the exception of Shimano Capreo), thus most folding bikes use Road or mountain bike (MTB) components. This works well most of the time, unless you mix and match incompatible components.
This article will compare and explain the differences between some road and MTB components, and the suitability for folding bikes. For a more focused and simple analysis, only conventional derailleur setups will be discussed. Other types of drivetrains such as single speed or internal gear hubs will not be discussed.
Before we go into the different components categories, some background information will be useful. For me, I feel that there is no need to get top level components, unless you are racing competitively. Of course, if you can afford it, by all means get the top end stuff if that is what you like! For the rest of us, second tier components are more than good enough, as they have most of the features of top level components but at a much more wallet friendly price. In fact, even mid range components will work well enough for everyday use.
The two major bicycle component makers are Shimano and SRAM, with Campagnolo, Microshift and a few other brands making up the rest. Again, for simplicity's sake, I will only be showing components from Shimano and SRAM.
Each of these two companies have two major types of components, road and MTB components. Some components may look and work very similarly, but others will differ greatly. Here are some second tier road and MTB components from Shimano and SRAM.
Shimano Ultegra 6800, 2x11 speed road groupset.
SRAM Force 22, 2x11 speed road groupset
Shimano Deore XT, 2/3 x 10 speed MTB groupset
SRAM X0, 2x10 speed MTB groupset
Listing down the groupsets, from top level to mid range,
(11s = 11 speed, 10s = 10 speed, 9s = 9 speed, 8s = 8 speed)
Shimano Road (2013): Dura-Ace (11s), Ultegra (11s), 105 (10s), Tiagra (10s), Sora (9s), Claris (8s).
SRAM Road (2013): Red (11s), Force (11s), Rival (10s), Apex (10s).
Shimano MTB (2013): XTR (10s), Deore XT (10s), SLX (10s), Deore (10s), Alivio (9s), Acera (9s), Altus (9s).
SRAM MTB (2013): XX (10s), X0 (10s), X9 (10s), X7 (10s), X5 (10s).
Before we continue, my stand on mixing and matching components between different brands is: Don't do it! There is no advantage to mixing components from different brands, as the cable pull ratios are different and will give poor shifting performance. Besides, the appearance of the parts will be mismatched. Always use components of the same brand, and preferably the same series/groupset for best performance and appearance.
RD = Rear Derailleur
FD = Front Derailleur
SS = Short Cage RD
GS = Mid Cage RD
SGS = Long Cage RD
DCL = Dual Control Levers, which refers to the drop bar road shifters / brake lever combo
BB = Bottom Bracket (bearing unit supporting the crankset)
FHB = Flat Handlebar, usually used to refer to MTB-style road shifters for flat handlebar road bikes
The different types of components will be discussed separately, and the suitability for folding bikes evaluated in each section. The gist of each section will be underlined for easy reference. For many components, the suitability will depend on other components used as well. For example, a wide range cassette is only suitable/possible if a MTB RD is used.
1a) Rear Shifter + RD (Front single setup)
1b) Shifters + RD + FD (Front double setup)
2) Brake Levers + Brake Calipers
3) Crankset + BB
1) Shifter + RD (Front Single Setup)
Front single chainring drivetrains are very common for folding bikes, as they are relatively easy to maintain and have sufficient gears for normal city riding. The number of speeds will then purely depend on the rear cassette. It can vary from 6 speeds for an entry level Dahon Eco 2 to 10 speeds for a high end Tern Verge X10. 11 speed Dahon / Tern folding bikes are not available (yet).
6 and 7 speed bikes have virtually no chance of a meaningful upgrade, as components for 6 and 7 speeds are rare nowadays. Even 8 speed drivetrains are becoming less popular as the price of 9 speed drivetrains drop.
As a front single drivetrain setup, there is a lot of flexibility, as the only components you need to match are the rear shifter and RD. Of course your chain and cassette needs to be of the same speed, but that is not an issue here. For front single folding bikes, either road or MTB components (shifter + RD) will work equally well.
1 x 9 road drivetrain on my Dahon Boardwalk about 2 years ago
In the recent couple of years, Shimano has introduced a series of FHB road shifters, in addition to the standard DCL road shifters. There is the 10s Ultegra-grade SL-R780, 10s Tiagra SL-4600, 9s Sora SL-3500 and 8s Claris SL-2400. The shifter should be matched with the RD from the matching groupset for best performance.
Shimano Sora SL-3500 9 speed FHB road shifter
If you like to use MTB shifters (with Instant Release and Multi Release features for high end models), it is also viable. 10s MTB Dynasys shifters are available from XTR all the way to Deore, while 9 speed shifters are available in the Alivio, Acera and Altus series. Once again, use the RD from the same series for best performance.
Shimano Alivio SL-M430 9 speed MTB shifter
The main difference between road and MTB shifters are the cable pull ratios, or pitch. The pitch for road and MTB shifters are slightly different. There have been many cases where a MTB shifter is paired with a Road RD, or vice versa, and it seems to work OK. However, tuning the drivetrain nicely will be nearly impossible as it is difficult to get all of the gears to work properly. Avoid mixing road and MTB shifters + RD.
As for the RD, there are more differences. The most obvious one is the cage length, where MTB RD have a longer cage than road RD. Road RD are available in SS and GS cage lengths, whereas MTB RD are usually available in GS or SGS cage lengths. Some MTB RD have short cage lengths, such as Shimano Saint, Shimano Zee, and a few other SRAM MTB RD.
Shimano Saint RD-M820, short cage. Looks very tough!
SRAM X9 MTB RD, short cage. Comes stock on the Tern Verge X10.
The other difference is the tilt of the parallelogram, where the MTB RD tilts more in order to reach the larger sprockets on a MTB cassette. This is the part that determines the largest compatible sprocket, and not the cage length. The cage length merely determines the chain capacity, which is dependent mostly on the choice of front crankset and the cassette size.
If you are using a close range road cassette, such as a 11-25T or 11-28T cassette, a road RD will shift better (although a MTB RD will also work). If you are using a wide range MTB cassette, such as a 11-32T or 11-34T cassette, you will definitely need a MTB RD (a road RD will not work).
There is no compatibility issues with using road FHB shifters and RD on Dahon / Tern folding bikes. As for MTB shifters and RD, the only point to take note is that MTB cages are long, and in some cases it will go very close to the rear tire in the 1st gear. Therefore, if you want to use MTB shifters and RD on your folding bike, I would suggest using a short cage RD, such as a Shimano Saint or Zee RD.
2) Shifters + RD + FD (Front double setup)
As for a front double setup, it is more tricky as we have to deal with the compatibility issues of the FD and front shifter. Folding bikes that come with a front double crankset are less common. It usually starts from the mid range price point, such as the Dahon D18 (2x9 speeds) to top end models such as the Tern Verge X20 (2x10 speeds).
My opinion is that for a folding bike with a front double drivetrain setup, a road setup is the only way to go. A MTB setup just will not work. I am assuming that you are actually using front shifting, to get 2x9 or 2x10 speeds. If you did not install an FD, it means that you actually have a front single setup (even if you have double chainrings), in which case you can just refer to the section above for front single drivetrains.
Before I explain why a MTB setup is not suitable, let us see why a road setup works. Almost all Dahon and Tern folding bikes have a 68mm BB shell width, which is the BB shell width of road bike frames. This means that a road double crankset will fit nicely onto the frame, using a standard 68mm road BB. The chainline will then be optimum for a road double crankset, which is required for good front shifting performance. A brazed-on road double FD will also fit nicely, either on the welded FD hanger or the aftermarket LitePro FD adaptor.
Front double road crankset, with a 68mm BB on the Dahon Boardwalk frame
It is possible to install a MTB front double crankset on a folding bike. With the appropriate BB spacers, you could install a front double MTB crankset (such as Shimano Deore XT FC-M785), but you will not be able to install the required front double MTB FD. This is because MTB FD does not come in brazed-on mounting, and the clamp band options will not fit (largest clamp size is 34.9mm, which is far off from the seat tube diameter of 40/41mm for Dahon / Tern folding bikes). Only road double FD will fit on Dahon / Tern folding bikes.
Now, you may ask, can I use a road double FD with a MTB double crankset? The answer is no, the road double FD is not compatible with a MTB double crankset. Not only is the cable pull ratio all different, the curvature of the FD chainguide is also different. A road FD chainguide is optimised for a chainring curvature of 50-55T, while a MTB double FD can only cover a maximum of about 40T. With the wrong curvature, there will be a big gap between the FD chainguide and the chainring, and the shifting performance will be very bad.
Shimano XT FC-M785, MTB double crankset. Not recommended for folding bikes as you cannot fit a compatible MTB double FD.
After a bunch of explanation (hope you understood at least some of it!), the moral of the story is, you cannot have a MTB front double setup for a Dahon / Tern folding bike. Some people will try to be clever and ask, can I use a road front double setup, but a MTB rear setup? This is actually possible!
You could actually set up the drivetrain such that the front and rear are distinct groups. MTB rear shifter + MTB RD, and road front double shifter + road double FD + road double crankset. As for the cassette and chain, either the road or MTB version will work (surprise! to be elaborated on in Part 2 of this article).
This would give you a truly hybrid drivetrain setup, with a MTB rear and Road front system. It would work, but it will look really weird! The appearance of the RD and FD will not match, while the shifters on the left and right side of the handlebar also will not match. You could probably try this if you have a bunch of spare components lying around, but it is not recommended if you are buying new components. Just get components from the same brand and series and everything will work and look so much better.
Tern Verge P20, upcoming new model for year 2014. Should be of great value, and is all ready for upgrades!
In summary, if you want to have a front double drivetrain for your Dahon / Tern folding bike, just get a standard road groupset. All the components (except for maybe the caliper brakes) will go on nicely. Of course, depending on the frame you have, you may need an RD adaptor and/or FD adaptor. The FD should be of the brazed-on type and not the clamp band type.
This article is getting rather long, which is why I have to split it into two parts. The compatibility of the remaining components will be discussed in Part 2. Stay tuned!
Part 2 of the article is now up!
Brake Calipers + Brake Levers