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
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!
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.
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.
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!