Dahon MuSP: Frame, Fork and Handlepost

Time to start another bike project! This time, it is to build a bike with drop bar, so that it is more efficient for riding fast. Once again, it is not for my own use, as I already have too many bikes.

Main requirements:
1) Blue wheelset
2) Drop bar setup
3) Geometry for shorter rider (1.55m)
4) Di2 electronic shifting
5) Folding bike is preferred for easy storage and transportation

Although these requests does not seem to be restrictive, it is actually not easy to build a bike with all these requirements. Some requirements are easy to fulfill on its own, but if you combine it with another requirement, it becomes much more challenging.

For example, a drop bar setup is easy to fulfill. However, requiring a geometry to suit shorter riders (shorter reach, lower seatpost height, lower stand over height) would usually also mean a folding bike is required, as even small-sized road bike frames have a relatively long reach and stand over height.

The requirement for Di2 electronic shifting is because the rider's hands are small, and it is difficult to push the lever to operate the shifter. Using Di2 electronic shifters would solve this issue, as shifting gears only involves pushing the buttons.

Secondary requirements that result from the main requirements also makes it more challenging to find a suitable frameset. For example, using a drop bar road shifter will mean that the most suitable brakes to use would be standard road caliper brakes or disc brakes. Although disc brakes are nice to have, they add weight and are more difficult to set up. OK for full sized bikes but not for folding bikes.

Most folding bike frames use V brakes, but these are not directly compatible to road shifters due to different cable pull ratios. Although there are adapters such as the Travel Agent, they are not ideal as you can read from my previous experience.

A table which I created long ago to summarize the compatibility

Previously I have also used long reach caliper brakes, so that I can use caliper brakes on 20 inch folding bikes that were not originally designed for caliper brakes. Even if I use 451 wheels on 406 frames, standard reach road caliper brakes cannot reach the rims without a brake pad adapter.

Also, I want to use a frame that can use standard reach road caliper brakes, without needing to use any adapters which will decrease the braking power. Ultimately this means that I need a folding bike frame that is designed to accept standard reach road caliper brakes. This type of folding bike frame is surprisingly rare, but I managed to find one in the Dahon MuSP.

Stock Dahon MuSP9, comes in red or black frame colour

The Dahon MuSP comes stock with a Shimano Sora 1x9 speed setup, with 451 wheels and flat handlebar. Most importantly, it comes stock with a standard road brake caliper setup, which will match perfectly with a drop bar with road shifters.

However, the stock components are not what I am looking for, as I will be installing a 1x11 speed Ultegra Di2 groupset. Therefore what I need is actually just the frameset, without almost all of the components. After buying the whole bike from the bike shop and getting all the components removed, what I have is just the frameset! It is kind of expensive this way, but it is the only way to get a genuine Dahon MuSP frameset.

Dahon MuSP frameset in black colour! Stripped of all the stock components.

This model has all the welds smoothed out as seen here. Hand polished after welding to remove the characteristic overlapping scales of aluminium welding. 

Same for the centre frame joint area. Welds are polished to be smooth.

At the seat tube junction, where the rear seat stays are welded to the main frame.

Model name of this frame is MuSP

Smooth welds even at the bottom bracket junction area

This frame design does not have traditional chain stays, and so it has two large "arms" to act as support for the two seat stays.

Another interesting characteristic of this frame, other than the smooth welds, is the internal cable routing! This is not common among folding bikes, due to the need for the cables to move during folding. Although internal cable routing has the potential to make the cabling look neater on the bike, it will also make it more difficult to set up the cable routing.

The cables enter the main frame near the head tube area, through the centre frame joint, and out to the rear brake caliper and the rear derailleur. In this case, the biggest challenge is routing the cables through the centre frame joint, as it will open up and fold. How does Dahon prevent the cables from getting overstretched or bunching up during folding and unfolding respectively?

By encasing the cables in a metal coil, it helps to protect them during folding and unfolding, as shown below. This metal coil is actually just a metal spring that guides the cables internally across the centre frame joint.

Metal coil running across the centre frame joint, with the cables enclosed inside.

Frame weight (inclusive of headset cups, seat post clamp, rear dropout hanger, seatpost shim)

Strictly speaking, the weight of the headset cups should be deducted from the frame weight. That means the main frame weighs exactly 2400 grams. For comparison, the carbon Java Freccia frame only weighs 1060 grams...

The stock Dahon MuSP aluminium fork does not have smooth welds. However, the road caliper brake mounting hole is special and not found on other forks.

Front fork weighs 480 grams

Weight of the steel compression bolt weighs 45 grams

Although the Dahon MuSP already comes stock with a handlepost, I think it is not suitable for mounting a drop bar. First, the stock handlepost uses a quick release clamp, which means that it is difficult to get sufficient holding torque on the drop bar. Second, the stock handlepost is relatively tall (around 31.5cm from my estimate), which puts the handlebar quite high up.

Since this bike needs to be sized for a shorter rider, the saddle height will also be lower. It will be strange and not ergonomic if the handlepost was tall, while the saddle position is low. Therefore, a shorter handlepost will work better to follow the lower saddle height.

Other than reducing the handlepost height, the reach from the saddle to the handlebar also needs to be reduced. My idea for reducing the reach for this folding bike is to follow the example that I used on the Dahon Vitesse last time, which is to put the handlebar behind the clamp on the handlepost. This means that a stem is required to offset the handlebar position behind the centre of the handlepost.

To do that, I decided to get a shorter handlepost with a T-shaped top, similar to what I had for the Dahon Vitesse, but shorter. This was because when I previously used the 31.5cm T-shaped handlepost, I had to position the stem angled downwards, to put the handlebar in a lower position.

Previous setup used on the Dahon Vitesse, to reduce the handlebar reach.

Comparing the stock Dahon handlepost (left) with the new T-shaped Fnhon handlepost (right).

Measuring the length of the handlepost, starting from the joint line at the bottom clamp area.

This T-shaped Fnhon handlepost is 27cm in length, which is exactly what I wanted.

It was not easy to find this handlepost on Taobao, as it has a rare combination of features.

1) T-shaped
2) Short (27cm or so)
3) Inward folding

Most handleposts (Dahon or Fnhon or otherwise) can fulfill 2 out of 3 of these requirements, but not all 3. The inward folding requirement is so that I can fold down the handlepost and handlebar in a special way, to reduce the folded size even though it has a drop bar. This method only works if you have an inward folding handlepost.

This handlepost is the lightest that I have used, at just 494 grams. It is even lighter than the 4 bolt, 27cm Fnhon handlepost that I previously used on the Dahon Boardwalk.

With the frame selection complete, we can now move on to the other components. The difficulty is not over yet, as I need to run a Di2 setup on this Dahon MuSP frame, which was not designed for Di2, plus the challenge of internal cable routing!

As for the blue wheelset requirement, we shall take a closer look when we study the wheelset.