Dahon Boardwalk vs Merida Scultura 5000: Frame Geometry

One of the primary reasons for me to get a road bike is to compare it with my drop bar Dahon Boardwalk. This Dahon Boardwalk has been modified thoroughly, and it is now more of a road bike than a mere folding bike. It is interesting to ride these two bikes and compare them, to see if the common assumptions between road bikes and folding bikes are true or not.

Nowadays, I try to alternate my rides between the Dahon Boardwalk and the Merida Scultura 5000. By doing so, I can detect and appreciate the differences and similarities between these two types of bikes. As this testing is still on going, I am unable to write a comparison of the ride quality yet.

However, what I can do now is to compare the frame geometry of the Dahon Boardwalk with the Merida Scultura 5000. By placing the bikes side by side and taking some measurements, the similarities and differences can be seen clearly.

What are the geometry differences between the Dahon Boardwalk and the Merida road bike? How do they affect the riding posture and feeling? Read on to find out!

In order to have a fair comparison on the frame geometry, we will first need to set a datum to compare the bikes. In this case I chose the centre of the BB or crankset to be the datum. This will allow me to compare the other dimensions such as the saddle height, handlebar reach and such.

Using the centre of the crankset as the datum. I placed the bikes such that the centre of the cranks are aligned with each other.

When the kickstand and bike stand are used to set the bikes upright, the rear wheel is unable to touch the floor. In this case, both rear wheels are set at the same distance off the floor for best accuracy. 

Comparing the seat tube angle. The Dahon seat tube is slightly steeper as the seat tube ends behind the BB, and not on top of the BB. Does not affect the final saddle position though.

Saddle height is practically the same!

Both saddle's fore-aft positions are also about the same. This also means that the saddle position relative to the crankset is the same across these two different bikes.

Comparing the rear axle positions to determine the chain stay length. They differ by a bit. The Dahon chainstay length is 400mm, while the Merida chainstay length is about 410mm. A shorter chainstay length will give a more nimble ride.

Different gap between the rear wheel and the seat tube, due to the different wheel sizes. Does not affect the ride quality.

Comparing the front axle positions. The Dahon front axle is about 20mm further forward of the Merida. This can affect steering feel, but this is not the only factor. The head tube angle and handlebar position also affects the steering feel of the bike.

So far, the frame geometry is quite similar between the Dahon Boardwalk and the Merida road bike. With a similar saddle height, the pedaling feel will be the same across the two bikes. 

The difference in chainstay length cannot be felt due to the small difference of less than 10mm. For comparison, trekking bikes have longer chainstay lengths of around 440mm for better stability and rear wheel clearance (for fenders and front derailleur). A short chainstay length gives a agile and nimble feel to the bike, and steering feels sharper due to the short rear end. However, it can be less stable at high speeds as the rear end tends to move around more compared to a bike with a longer chainstay.

Next, let us move on to the position of the handlebars and the road shifters. There is a much more obvious difference in positions for this area, due to some frame and handlepost limitations and certain preferences. Both handlebars are FSA compact drop bars of 400mm width, and thus the drop bar dimensions should be the same.

Overview of the handlebar positions. Generally, the Dahon handlebar is higher up and further back compared to the Merida handlebar.

Top view of the handlebars. The Dahon handlebar is about 30mm further back compared to the Merida handlebar.

Front view. The Dahon handlebar can be seen to be higher than the Merida handlebar.

Comparing the shifter positions. Since the shifter positions are related to the handlebar positions, the shifter on the Dahon can be seen to be further back.

Close up view showing the different shifter positions. As can be seen, the shifter on the Dahon is both higher and further back comparatively.

Another view of the shifters from another angle. Note the different hood shapes. Ultegra 10 speed 6770 Di2 shifter on the Dahon Boardwalk, and the new Ultegra 11 speed 6800 mechanical shifter on the Merida Scultura 5000.

By a rough estimation, the shifter hood position on the Dahon Boardwalk is about 30mm higher and 30mm further back. This gives the Dahon a shorter reach and a less bent-over position compared to the Merida road bike. It is exactly what I wanted, as the Merida road bike is supposed to put the rider is a more aerodynamic position for fast riding.

The difference of 30mm in the height and reach makes a big difference to the steering feeling. With the Dahon Boardwalk, there is a more relaxed feel when holding the shifters, due to the shorter reach and more upright position. As for the Merida road bike, the lower position and slightly longer reach creates the perfect geometry for a road bike, and makes me want to ride faster.

If I wanted to fully replicate the feel of a road bike on the Dahon Boardwalk, I can rotate the stem forward to give a similar handlebar position as the Merida road bike. However, I much prefer to keep the current handlebar position of the Dahon Boardwalk, as it is more comfortable and great for more relaxed riding.

In summary, the major frame geometry differences between my Dahon Boardwalk and the Merida Scultura 5000 are at the handlebars. The different shifter positions give a different feel to the ride. Even so, the positions are not that much different and can be adjusted to be the same if desired.

Finally, a picture showing the two different Ultegra shifters! Ultegra 10 speed 6770 Di2 shifter on the Dahon Boardwalk, and the new Ultegra 11 speed 6800 mechanical shifter on the Merida Scultura 5000. My favourite picture of this blog post.

Avanti Inc 3: Modifying the Gear Range

A simple question to all the cyclists out there: Do you use all the gears on your bike? Or are some gears rarely/never used? If that is the case, that means that your gear range is not optimised to your cycling ability or usage.

Modern bicycles have many gears, from the 3x10 gearing of a MTB to a sleek 2x11 gearing of the latest road bike drivetrains. Even entry level bikes with 7 speeds are also able to cover a reasonably wide range of gear ratios. The reason for gears is to vary the gear ratio of the bike, so that the human legs can pedal comfortably at various speeds without spinning out or exerting overly high torque.

The optimal gear range is when you can expect to use most of the gears (>80%) on a regular basis. Except for perhaps 1 top gear for downhill pedaling and 1 low gear for exceptionally steep slopes, you should be using all the other gears during your regular trips. Of course, the actual gear range will vary from bike to bike and rider to rider, depend on your pedaling style (spinner or masher), the terrain (flat or hilly), and fitness (casual or pro rider). Some people can get by perfectly with just 3-4 gears, or even single speed.

For my bikes, I try to optimise the gear range for my usage, by using the appropriately sized chainring and cassette, so that >80% of the gears are used regularly. As an example, my Dahon Boardwalk has a rather narrow gear range (28" to 88") as shown below. The top gear of 88 gear inches is considered low, compared to other 20" folding bikes with 53/11T (96") or even 56/11T (102") gear combinations. But this gear range is perfect for my riding style, as I prefer to spin rather than mash, and I don't cycle as fast either. On a normal commute, I will typically use gears 2-9, while in the large 53T chainring. The small 39T chainring is reserved for special hill climbing trips.

Optimised gear ratios for myself, on the Dahon Boardwalk

Now, back to the main topic, which is the gear ratio on my Avanti Inc 3. As previously shown, the Avanti Inc 3 has a gear range that is comparable to that of a normal full sized road bike.

Comparing the gear range of the Avanti Inc 3 with a full sized road bike

Unfortunately, this means that the original gear range of the Avanti Inc 3 is too high for me. Let's focus on the gear range of the Avanti Inc 3. Using the stock gears of front 50T and rear 24T, together with the Alfine 11 internal hub, the gear range is as shown below.

Stock gear range of the Avanti Inc 3

On a typical commute on the Avanti, I will typically only use gears 2 to 8. This is (not coincidentally) similar to the gearing that I use on my Dahon Boardwalk. Gears 9 to 11 are too high and never used. My target is to lower the overall gear ratios, so that the higher gears become usable, while I get even more low gears for slope climbing.

I have been researching on the various ways of reducing the gear ratios on the Avanti, but it is not as straightforward due to the belt drive system. On a normal chain drive system, all it takes to lower the gear ratio is to use a smaller chainring or larger rear sprocket, and modify the chain length accordingly. However, on a belt drive system, changing the chainring or sprocket size will mean a new belt is needed. This is because belts comes in fixed lengths, and the length cannot be altered.

Due to the belt length restrictions, changing the sprocket or chainring size will also involve changing the belt, which is additional cost. Therefore it is best to change out as few parts as possible.

The options for lowering the gear ratio are listed below:
1) Same rear sprocket, smaller chainring, shorter belt. (New chainring and belt required)
2) Larger rear sprocket, same chainring, longer belt. (New rear sprocket and belt required)
3) Larger rear sprocket, smaller chainring, same belt. (New rear sprocket and chainring required)

Thanks to the Gates belt drive calculator, I can calculate the required belt length, rear sprocket size, front chainring size, or chainstay length required. With 3 out of 4 of these factors entered into the calculator, the value of the last factor can be calculated. For example, using the original setup of front 50T, rear 24T and a nominal chainstay length of 444mm (as provided on the Avanti website), the required belt length is about 118T.

Original belt drive setup on the Avanti Inc 3.

Note that the calculated values are before belt tensioning, so there should be at least 2-5mm of adjustment length required for tensioning the belt.

During the research, I found that the largest rear sprocket size available for the Nexus/Alfine 3 spline design is only 26T, which is hardly bigger than the stock 24T. This means that even if I change the sprocket from 24T to 26T, it will only result in a drop in gear ratio of about 8%, which hardly makes an impact as the approximate gear steps between the Alfine 11 gears is about 13-14%.

This rules out Option 2 as the impact to the gear ratio is not big enough.

Option 3 is to keep the same 118T belt, but to change to a larger rear sprocket and a smaller front chainring. This will lower the overall gear ratio.

Using same 118T belt, but with larger rear sprocket of 26T and smaller front chainring of 46T.

This will lower the overall gear ratio by about 15%, which is good as it shifts the overall gear ratios by at least 1 gear. Although this setup is theoretically possible, the required chainstay length of 449mm seems to be a little too long. Even with the eccentric BB, I am afraid that there will not be enough adjustment range for proper belt tensioning (default chainstay length is about 444mm, so 449mm may be at the limit already).

That leaves us with Option 1, which is to keep the same 24T rear sprocket, but to change to a smaller chainring. In order to lower the gear ratio sufficiently to make a difference, the chainring should be changed from 50T to 39T (22% lower) or 42T (16% lower).

Using a 39T chainring will really drop the gear ratio by a lot, but what I was concerned about was the gear ratio of the internal hub. It seems that there is a recommended gear ratio for the Alfine 11, which is about 1.9 (Front chainring / Rear sprocket). The original setup of 50/24T gives a ratio of 2.08, which is a little higher. Using a smaller 39T chainring will give a ratio of 1.625 (39/24T), which I feel may be too low, and there is a possibility of damaging the internal hub.

Just to be safe, I went with the safer option of a 42T front chainring size. Although the gear ratio is not lowered as much, it is still a good decrease of 16%. The gear ratio of 1.75 (42/24T) is also closer to the recommended 1.9.

Using the Gates belt drive calculator once again, we can check the belt length required for this setup.

With a 42T front chainring and 24T rear sprocket, the new belt length required is either 113T or 115T.

In this case, it is possible to use either a 113T or 115T belt, as both chainstay lengths required are either side of the nominal 444mm chainstay length. Due to the possibility of insufficient adjustment distance for belt tensioning, I decided to go with the 113T belt instead of the 115T belt.

As you can see by now, changing the gear ratio on a belt drive bike with internal hub is not easy, as there are many more factors to take note of, such as the chainstay length, the available sprocket/chainring sizes, the available belt lengths, the belt tensioning, etc. But finally I decided to get the 42T chainring to try, together with a shorter 113T belt.

Well this is just the start of the challenge, as the 42T Centertrack chainring is only available in the 4 arm, 104mm BCD type (MTB crank arm). This means that I will also need a new 4 arm MTB crankset to replace the previous Sora road triple, 5 arm 130mm BCD crankset.

Gates Centertrack Belt, with a length of 113T

Gates Centertrack 42T chainring. 4 arm, 104mm BCD type

In order to change out the belt from the original 118T to the new 113T belt, the frame needs to be split, as the belt comes in a complete loop. This is when the frame joint on the right side seat stay comes into play. As shown below, the joint can be opened for installation/removal of the belt.

 Unscrew the 2 bolts at the bottom of the joint, and the 2 pins can be slid out

Frame joint with the 2 pins removed

The frame joint

Frame joint + 2 pins + 2 bolts

The split in the right side seat stay

Just realised that the right side fender and rack stays have to be opened up too, to allow the belt to pass through

Now, for the new MTB crankset, the eccentric BB shell width is already at 73mm, which is a suitable width. In fact, a 2.5mm spacer is required on the right side to get a proper chainline. Without this spacer, the spindle will be too long on the left side.

Standard Hollowtech II MTB Triple Crankset setup, on a 73mm BB shell width

The BB is already a MTB Hollowtech II BB, so all I need to do is to remove the right side BB cup to install the 2.5mm spacer. However, I found that no matter how hard I pushed the BB tool, the BB cup just would not budge. Luckily, I had an idea to use a Dahon seatpost to get extra leverage on the tool. In fact, the large diameter Dahon seatpost fits onto the BB tool like a glove! With the extra leverage of the "cheater bar", the BB cup could be removed easily.

Using the Dahon seatpost for extra leverage! Very useful to loosen tight BB cups from the frame.

MTB SM-BB51 BB with the 2.5mm spacer installed under the right side BB cup.

The next step is to install the new crankset and chainring! As the MTB crankset has an even wider chainline compared to the road triple crankset, chainring bolt spacers will be required to adjust the position of the front chainring. A straight chainline is very important for belt drive systems, to avoid premature wear and noise issues.

Long chainring bolts, plus spacers of various thickness for chainline adjustment.

To cut the long story short, my calculations showed that in order to maintain the same chainline on a MTB crankset, I will need to use a 4mm spacer to shift the chainring inwards. Just to be safe, I also got spacers of different widths for chainline adjustment if required.

Final setup, with a 4mm spacer in between crankarm and chainring to get the correct chainline. The other 5mm spacer is necessary due to the chainring bolt which is too long.

Using a 4 arm Deore MTB crankset for the new 4 arm 42T chainring

Perfect chainline! I am glad that the calculations are correct.

To make it easier to adjust the eccentric BB, I got this new Park Tool Pin Spanner for adjustment. This pin spanner is special as it is adjustable to fit holes of different sizes and distances.

Park Tool Pin Spanner SPA-6

Hardened, replaceable pins for adjustment

Spanner can be closed...

...or opened to suit different hole dimensions and distances.

This is how I use the pin spanner for the eccentric BB. Hook the pins into any 2 holes on the eccentric BB and turn the spanner to adjust the belt tension.

Finally, the upgrade is complete! The gear range has been shifted downwards, to a more appropriate and usable range for me. The gear that I usually cruise in has been shifted from gear 6 to gear 8. The lowered gear ratio of gear 1 will be very useful for steep slopes!

New gear ratios with a 42T front chainring. Top gears are now more usable, and the lowered gear 1 will be useful on steep slopes.

Final front crankset setup

The exposed chainring bolts look quite OK. But the hole in the centre of the spindle might collect dirt inside...

New belt drive system! The front chainring now looks much smaller compared to the previous 50T chainring.

 

Previous image of the bike, with 50T front chainring and 5 arm road crankset

New image, with a 42T front chainring and 4 arm MTB crankset

This upgrade has not been easy, as a lot of research was needed to learn more about the belt drive system and the limitations. Gathering the required components was also not so straightforward, especially for the chainring as it is not easily available online.

However, all this effort is worth it as the gear ratio on the Avanti Inc 3 is now optimised, and I can use most of the gears on a regular basis. The other benefit is a lower bottom gear for tackling those steep slopes. Another unintended benefit is the slightly lighter weight drivetrain, due to the smaller chainring and shorter belt.

Road or MTB Components for Dahon / Tern Folding Bikes? - Part 3

For this third and last part of this series, we will discuss the remaining components on a typical folding bike. These are the drivetrain components that are closely interlinked, and must all be compatible in order to work well.

Do check out the first and second parts of this article in order to get the full story!

The drivetrain components are:
3) Crankset + BB
4) Cassette
5) Chain

3) Crankset + BB

The crankset and the BB are integral parts of the bike. The power that you apply through your legs needs to pass through the crankset before it goes to drive your rear wheel. The BB needs to be smooth spinning to minimise resistance. Therefore, choosing a good crankset and a smooth BB is important for efficient power transfer.

For folding bikes, the most commonly used cranksets are road bike sized cranksets. These usually come as a standard front double of 52/39T or compact 50/34T. However, most folding bikes come stock with single chainrings, as they are not designed for speed or touring and don't need a wide gear range. Most well designed 20" folding bikes come with the standard 52 or 53T front chainring. 

Dahon Mu P8 with a standard front single 52T chainring.

Other performance-based folding bikes such as the Dahon Vector X20 or the Tern Verge P18 come stock with a front double road crankset. The chainring sizes are usually a standard 53/39T or the larger 55/44T. The larger chainring offers higher top end speed for stronger riders, while the small chainring gives you the low gears required for steeper slopes. This wide gear range makes the bike a very versatile bike with the ability to go almost anywhere.

Tern Verge P18 with a larger 55/44T chainring to compensate for the smaller 20" wheels.

As you can see by now, Dahon / Tern folding bikes come with either a front single chainring of about 53T, or a front double chainring of 53/39T or 55/44T. Why don't we see MTB cranksets on Dahon / Tern folding bikes?

The answer is because of the gear range. Small wheeled bikes have a natural lower gear range due to their smaller wheel diameter compared to MTB or road bikes. Comparing to road bikes or MTB, even with the same drivetrain setup (cassette and chainring), the gear range will be about 20%-30% lower due to the smaller wheels.

For most riders, using a standard 53/39T crankset with an 11-28T cassette on a 20" folding bike will be sufficient for almost all terrain. Although the gear range is not as high as that on a road bike, it is sufficient because:

1) Most folding bikes don't go as fast as road bikes. In short bursts it is possible, but it cannot be sustained without greater effort than road bikes.
2) Small wheeled bikes are less stable at high speeds (>40km/h), thus the highest gears are seldom used.
3) The top gear combinations on the road bike (53/11 and 53/12 on 700C wheels) are too high for normal* usage anyway.

*My definition of normal refers to an average rider that rides mainly for leisure, with a cruising speed of 35km/h or below on a road bike.

Shimano 105 5700 road crankset, 53/39T. A popular choice for folding bike upgrades due to the affordable price and good performance.

If a MTB crankset is used, the gear range will be quite a bit lower. Using a front triple crankset as an example, the typical Trekking crankset is 48/36/26. The low end gear range is very good, especially on a small wheeled bike. However, the top end gear range will probably not be sufficient. If a Shimano Dynasys MTB crankset is used (optimised for 26/27.5" MTB), the front triple combination of 42/32/24 is definitely not enough for flat ground pedaling.

Deore Trekking crankset, 48/36/26T. Not quite enough top end speed for flat roads or downslopes. Great for touring though.

Deore XT MTB Dynasys crankset. Typically 42/32/24T, good for large wheeled bikes but not enough top end speed for small wheeled bikes.

Due to gearing limitations, road cranksets should be used on Dahon / Tern 20" folding bikes. MTB cranksets will also fit, but the gearing will not be ideal as there are too many lower gears and not enough high gears. The ideal gear range is where all the gears have a chance to be used on normal flat roads and slight up/down slopes. Having too many unused low gears or high gears means a gear range that is not optimized.

Another reason to use road cranksets is to facilitate the installation of a front derailleur (FD) if required. For Dahon / Tern folding bikes, an FD can be installed on the frame, either on the frame FD hanger itself or through the use of an FD adaptor. In either case, the FD type that can be used is only the braze-on type, which needs to be attached to the frame/adaptor directly. Only road FD come in braze-on models; MTB FD don't come with braze-on models, thus MTB FD cannot be installed on Dahon / Tern folding bikes. Since only road FD can be used, naturally only road cranksets should be used if front shifting is desired.

Braze-on road double FD mounted on Dahon Boardwalk using a LitePro FD Adaptor

Even for loaded touring on 20" folding bikes, there is no need to use a MTB crankset. A better choice would probably be a road triple crankset. A typical chainring combination for a road triple would be 53/39/30T. The 53T large chainring will give you some speed if required, while the 30T small chainring will get you up most slopes. Any steeper and you are probably better off walking!

4) Cassette
The choice of cassette has a very big impact on the riding characteristics of the folding bike. Cassette sizes can vary greatly, especially between road and MTB cassettes. As stated, there are two types of cassettes, road and MTB.

Road cassettes are characterized by the smaller gear range and closer gear ratios across the whole cassette. The common sizes for a 10 speed road cassette would be: 11-23, 11-25, 11-28, 12-27, 12-30. The advantages of a road cassette would be the smaller difference in gear ratios between the gears, which allows better cadence control. This in turn enables more efficient and comfortable pedaling at the preferred cadence. Another advantage is the lighter weight of a road cassette, due to the smaller sprocket sizes and thus lesser material.

On the other hand, the disadvantage would be the limited gear range. Due to the smaller spread of gear ratios as compared to a MTB cassette, there would be times where you have an insufficiently low gear when going up a steep slope. This is less of a problem on small wheeled bikes, as the smaller wheels already mean a lower gear range.

Shimano 105 CS-5700 12-27T cassette

A MTB cassette is noted for its wide gear range, in order to tackle all sorts of terrain and slopes. MTB cassettes typically have a size of 11-32, 11-34 or 11-36. The advantages of a MTB cassette is definitely the wider gear range, as provided by the large low sprocket of 32, 34 or even 36T. This large sprocket will give you a low gear ratio that can help you climb up steep slopes.

However, the disadvantages are that they are quite a bit heavier than road cassettes. Depending on the actual cassette combination and grade of cassette, a MTB cassette will be about 50% heavier than a road cassette. Another point to take note is the larger steps between gears. Due to the need to achieve a larger spread of gear ratios across the same number of sprockets, the jump between each gear is quite big. This is OK for off-road riding, as there is no steady cadence anyway. However, it will be more difficult to maintain a comfortable cadence on the road, as the next gear is usually too low or too high, making it difficult to find the perfect gear and maintain the optimum cadence.

Shimano XTR CS-M980, 11-36T cassette

Comparing the sprocket sizes for road and MTB cassette:
10 speed road 12-27T: 12-13-14-15-16-17-19-21-24-27
10 speed MTB 11-36T: 11-13-15-17-19-21-24-28-32-36

Using these two cassette sizes for comparison, you can see that the MTB cassette has a larger difference in gear ratios between gears.

 Larger jumps in gear ratios on the MTB cassette. Close ratios on the road cassette is important for cadence control, especially for the higher gears.

 

 The gear steps between each gear on the MTB cassette is larger than the road cassette

From what I have observed, Dahon / Tern bikes with front single chainrings (Eg. 8, 9, 10 speeds) usually use a MTB cassette in order to achieve the gear range required. For example, the Tern Verge X10 uses a wide range 11-36T MTB cassette. This gives it a wide gear range that can cover most terrain. However, it suffers when riding on the road for longer distances, as the big jumps between gears will make it difficult to maintain a comfortable cadence. 

For 8 or 9 speed folding bikes, the gear range will be smaller. For example, the Tern Link D8 uses an 8 speed 12-32T cassette. The gear range is not as large as on the Verge X10, as the gear steps will be too big if we try to achieve 11-36T on an 8 speed cassette.

Tern Verge X10 with 11-36T cassette for a wide 10 speed gear range

As for folding bikes with a front double chainring, such as the Dahon Vitesse P18, they are equipped with a road cassette (11-28T) for better cadence control on the road. Although the cassette itself does not have the super low gear of MTB cassettes, the front double crankset with the small chainring will do the job of providing the lower gears.

Dahon Vitesse P18 with 11-28T road cassette, and front double crankset. Together, they enable better cadence control and also a wide gear range.

For Dahon / Tern folding bikes with a front single chainring, I recommend a MTB cassette for a wider gear range. This will enable the bike to be used even for steeper slopes. Of course, if you have powerful legs, or don't climb slopes, you can probably get by with a close ratio road cassette and a front single chainring.

As for Dahon / Tern folding bikes with a front double chainring, the best option here is to use a close ratio road cassette. The road cassette will give you the optimum gear at all cadences, and the front double crankset will give you the gear range required for flat road or slopes.

Note that the choice of rear derailleur (RD) needs to match the type of cassette used. A road cassette should use a road RD for best shifting performance. A MTB RD will work with a road cassette, but the shifting performance will suffer.

On the other hand, a MTB cassette must use a MTB RD. A road RD cannot reach the larger sprockets of a MTB cassette and thus cannot be used.

Indirectly, this also affects the choice of shifter, as MTB RD should go with MTB shifter, and road RD should go with road shifters...which brings us back to Part 1 of this article.

5) Chain

Lastly, the chain! The only purpose of the chain is to transmit the rotation of the crankset to the rear cassette. Although the role of the chain may seem simple, it is at the heart of the whole drivetrain! Without the chain, the bike is practically useless.

There are many different chains out there, but the main difference is the width of the chain. 8 speed chains are wider than 9 speed chains, which are again wider than 10 speed and 11 speed chains. Chains should always match the speed of the cassette and chainring, in order for rear or front shifting to work properly.

Even for chains of the same speed, there are also road and MTB chains. The differences are minor, which means that using a MTB chain on road drivetrain components or vice versa is likely to work normally.

The differences are the shape of the chain links, such as the chamfers on the edges of the links. The surface finishing of the chain links are also different. Road chains are normally more shiny due to the plating on the surface, while MTB chains are usually less shiny. High end chains are also differentiated from normal chains by the use of cutouts in the chain links for weight savings.

Of course, whenever possible, use road chains on road drivetrains, and MTB chains on MTB drivetrains for best shifting performance.

Dura-Ace CN-7900, with cutouts in the chain links for weight savings. It is also very shiny and corrosion resistant due to the Ni plating.

CN-HG73, a normal 9 speed chain. No cutouts in chain links or Ni plating.

For Dahon / Tern folding bikes, there is nothing special to take note for the chain. Just ensure that the correct speed of chain is used and the shifting should work fine.

Conclusion

Now that we have come to the end of the 3-part article, let me summarize the key points:

Shifter + RD/FD
- For front single folding bikes, either road or MTB components (shifter + RD) will work equally well.
- If you want to use MTB shifters and MTB RD on your folding bike, I would suggest using a short cage RD, such as a Shimano Saint or Zee RD.
- Avoid mixing road and MTB shifters + RD.
- For a folding bike with a front double drivetrain setup, a road setup is the only way to go.
- Only road double FD will fit on Dahon / Tern folding bikes.
- If you want to have a front double drivetrain for your Dahon / Tern folding bike, use standard road double components.


Brake Calipers + Brake Levers 

Crankset + BB
- Due to gearing limitations, road cranksets should be used on Dahon / Tern 20" folding bikes.
- The ideal gear range is where all the gears have a chance to be used on normal flat roads and slight up/down slopes. Having too many unused low gears or high gears means a gear range that is not optimized.
- Only road cranksets should be used if front shifting is desired.

Cassette / Chain
- For Dahon / Tern folding bikes with a front single chainring, I recommend a MTB cassette for a wider gear range.
- For Dahon / Tern folding bikes with a front double chainring, the best option here is to use a close ratio road cassette.
- The choice of rear derailleur (RD) needs to match the type of cassette used.
- Chains should always match the speed of the cassette and chainring, in order for rear or front shifting to work properly.
- Using a MTB chain on road drivetrain components or vice versa is OK.

With this knowledge, you should now be able to choose the correct type of road or MTB components for upgrading your folding bike!