Wednesday, March 25, 2015

Can I Install Tern Handlepost/Fork on Dahon Frame? Part 5: Adjustments and Accessories

This is the 5th and last part of the project, "Can I Install Tern Handlepost/Fork on Dahon Frame?". Continuing from the previous part of the project, where I completed the installation of the Tern handlepost and fork onto the Dahon Boardwalk, this final post will wrap up the whole project.

As stated at the end of the previous post, I encountered a steering problem when I test rode the bike after installing the Tern handlepost and fork. It is kind of difficult to describe the problem clearly in words, but I will try.

Normally, a small wheeled bike such as my Dahon Boardwalk will have a more nimble steering feel as compared to bikes with standard wheel sizes. However, test riding the newly upgraded Dahon Boardwalk felt really strange. I found it difficult to keep the bike travelling straight even on a straight and smooth road. The bike tends to auto-steer to the sides, and it was taking a lot of effort to keep the front wheel pointing straight.

Having rode a folding bike regularly since 2008, I have a few years of experience riding small wheeled bikes, and I am familiar with the steering feeling. Although some bikes are naturally more twitchy, this felt different and wrong.

It got so bad that after a while, I could not steer properly while riding! Upon steering to the side, the handlebar stayed to the side and did not want to return to the centre. Luckily, I was going slow and only test riding around the estate, so there was no great danger. At that point I knew that something was seriously wrong with the steering.

My first suspicion was that the headset may have been tightened too much, causing the headset bearings to seize and stop rolling properly. However, even after I loosened the top cap inside the handlepost, the steering still felt stuck.

The next step to troubleshoot this problem is to remove the handlepost, and see if I can spot any anomalies. Upon removing the handlepost, I noticed some wear on the gold coloured headset bearing cup.

Signs of wear at the front of the gold headset bearing cup

Metal shavings can be seen between the headset bearing cup and the base of the handlepost

Abrasion marks and metal shavings found along the inside edge of the handlepost base

From the signs of wear that I spotted, I found that the edge of the handlepost base was rubbing against the headset bearing cup. This meant that the clearance between the handlepost base and the headset bearing cup is not sufficient to allow for smooth rotation. When there is no load on the handlepost (Eg. in the workstand), the handlepost can rotate smoothly. However, during riding, the load from my weight on the handlebars will close up the tiny gap, causing intermittent rubbing. This excessive friction eventually caused the handlepost to jam up and stop rotating properly.

One way to solve this would be to grind away the bottom edge of the handlepost base, to create more clearance. However, since the handlepost is already assembled with the rest of the handlebar, it is too troublesome to remove the handlepost for grinding at the workshop.

The other way is to add a spacer above the headset compression ring, so that the handlepost rests slightly higher. This will create more clearance between the base of the handlepost and the headset bearing cup. This spacer diameter is the same as a standard headset spacer, but they usually come in 5mm or 10mm thicknesses, which is far too thick. Therefore I sourced for thin headset spacers from Taobao.

Set of thin headset spacers

3 x 0.3mm spacers, 1 x 1mm spacer, 1 x 2mm spacer, 1 x 3mm spacer

From what I see, adding just one 0.3mm spacer will create sufficient clearance to avoid rubbing. However, I took the chance to add back the rubber seal that was on the base of the Tern handlepost. Therefore, I chose the 1mm thick spacer and placed it on top of the headset compression ring.

1mm headset spacer on top of the headset compression ring. This will reduce the clamping length by 1mm.

Rubber seal that comes with the Tern handlepost. It was previously removed due to insufficient clearance.

Rubber seal re-installed to the base of the Tern handlepost

After putting the Tern handlepost back onto the steerer tube. Slightly shorter clamping length, but it will have to do as there is nothing else I can do to increase the clamping length.

Rubber seal can be seen between the base of the Tern handlepost and the gold headset bearing cup. This minimises the amount of rain and dust that enters the headset bearings.

After making these adjustments, the steering feel of the Dahon Boardwalk is back to normal! The front wheel is now able to auto centre itself as designed, making steering much easier and natural, instead of me having to try so hard to keep the front wheel straight.

Now that the Tern handlepost and fork has been mounted successfully on the Dahon Boardwalk with no issues, I can now add on more accessories to the handlepost and handlebar. One accessory that I want to add to the Dahon Boardwalk is the Shimano Sport Camera.

The camera has previously been installed on the Merida Scultura 5000 road bike, using the K-Edge Go Big GoPro handlebar mount. If I want to mount the camera on other bikes, I would need to get additional mounts to allow quick and easy transfer of the camera from bike to bike.

However, the biggest problem here is that the K-Edge mount is really expensive! From Taobao, I found similar GoPro mounts at a fraction of the cost. They may not look as nice as the original K-Edge mount, but they have the same function and are much cheaper.

GoPro handlebar mount from Taobao. Looks almost the same as the K-Edge version.

Same as on the K-Edge mount, I moved the mounting piece to the top of the mount.

As there is no more space on the top of the handlebar for mounting this GoPro mount, I mounted it sideways on the Tern handlepost. Although the camera will be tilted to the side, the camera is able to auto rotate the video to the correct orientation.

As seen from the front. Loads of accessories!

The Controltech Stem is tilted slightly forward to put the handlebar at the correct reach. This is because the vertical part of the handlepost is further back as compared to Dahon/Fnhon handleposts, due to the taller handlepost base.

Tern handlepost locking lever with the green protective sticker removed. Looks very glossy and elegantly designed!

Final view of the upgraded Dahon Boardwalk with the Tern handlepost.

Yet another project completed successfully!

Through this project, I have learnt much about the design, construction and installation of the Tern handlepost. As for the ride quality, I have not detected any large improvement in handlepost stiffness, as the previous Fnhon 27cm 4 bolt handlepost is already very stiff. In fact, when I pull hard on the handlebar, I can feel some flex coming from other parts of the bike, such as the long seatpost and the main folding joint on the frame. The stiffness of the bike frame and handlepost is probably as good as it gets with this Dahon Boardwalk frame.

Tuesday, March 24, 2015

Can I Install Tern Handlepost/Fork on Dahon Frame? Part 4: Installation

In the previous part of this project, I have completed the measurements and considerations for fitting a Tern handlepost and fork to my Dahon Boardwalk frame. The conclusion is that I will need to cut the steerer tube as it is too long for my Dahon Boardwalk frame.

Before cutting the steerer tube, it is important to calculate and measure how much to cut. The ideal length is when the steerer tube rests just below the top edge of the handlepost base. This will maximise the clamping length for best stiffness and strength.

The tricky thing about this modification is that the starnut is already in the steerer tube. As the starnut cannot be removed without damaging it, the only way to continue using the starnut is to push it further down into the steerer tube, before cutting the steerer tube to the required length.

Starnut comes pre-set in the steerer tube of the fork. Standard depth is about 10-15mm.

My plan is to cut about 12mm off the steerer tube, as shown by the marking here.

Marking on the inside to show the initial position of the starnut.

Special starnut setting tool by Park Tool. Used to set starnuts to a depth of 15mm.

As I needed to set the starnut even deeper than 15mm, I swapped out the pin at the end of the tool for a longer pin. This pin will not thread into the starnut, but will be inserted through the hole to help centre the tool on the starnut. Washers are also added to control the depth of the starnut during the hammering of the tool.

Washers are used to control the depth of the starnut, and also to ensure that the thread of the starnut is not damaged.

The gap between the tool and the steerer tube before pushing the starnut further in. Upon proper setting of the starnut, the tool will rest fully on the edge of the steerer tube.

Before hammering the tool, the fork is set on a sturdy workstand for proper support. This method prevents damage to the fork ends.

After pushing in the starnut. It has been pushed deeper by about 10mm.

Now that the starnut has been pushed down, away from the area that will be cut, it is now time to shorten the steerer tube. My preferred way of cutting a tube is to use a proper tube cutter as shown. This is the same tube cutter I used when I shortened the handlebar of my Avanti Inc 3.

To cut the steerer tube, tighten the cutting blade onto the marking (12mm) made earlier.

Turn the tool around the cutting line, and tighten the tool after every 1-2 turns. Eventually the cutting blade will cut through the thickness of the steerer tube.

After cutting, the steerer tube is now 12mm shorter than the original length of 140mm.

New crown race from the LitePro headset for the new Tern fork.

Installed the crown race onto the Tern fork. For more info on installing headset for Dahon/Tern bikes, click here.

Now that the Tern fork has been modified, it is ready to be installed onto the Dahon Boardwalk! Before that, I double checked the instruction manual that came with the Tern handlepost to make sure that I am installing the Tern handlepost and fork correctly.

Instruction manual for installing the Tern handlepost

Before installing the new Tern handlepost and fork, the old handlepost and fork first needs to be removed from the Dahon Boardwalk.

Amount of steerer tube that protrudes from the top of the headset.

From my measurement, the length of steerer tube that protrudes above the headset is about 36mm. This is 3 times more than the 12mm of steerer tube with a Dahon handlepost and fork! With this large increase in clamping length, the interface between the handlepost and the fork will be a lot stronger and stiffer.

After installing the Tern handlepost on the Tern fork, this is how it looks. The steerer tube could have been about 1-2mm longer, but it does not matter too much.

Using the top cap to pre-load the headset bearings. The bolt of the top cap threads into the centre of the starnut in the steerer tube.

Two clamp bolts at the base of the handlepost tightens the handlepost securely to the steerer tube.

Tern handlepost and Tern fork installed onto the Dahon Boardwalk

In order to install the Controltech Stem, it needs to be slid on from one side of the drop bar. This means removing the bar tape, shifter and accessories from one side of the drop bar.

Installing the Controltech Stem onto the drop bar

As the stem and handlepost design is different from the previous Fnhon handlepost, the Di2 wires will need to be adjusted to account for the different length and location.

Controltech Stem installed onto the T-bar of the Tern handlepost. Note that the gap between the handlebar and the handlepost is very small!

Found a new place for the Di2 Digital Gear display! Also, the stem area is much neater with only 5 visible bolts, as compared to 10 previously.

With all the accessories mounted on the handlebar again

Finally, the Tern handlepost and fork have been installed successfully onto the Dahon Boardwalk. However, this project is not over yet. As I found out later on during test riding, there is some problem with the steering, which makes the bike quite difficult to ride.

In the final part (Part 5) of this project, I will reveal more details about the steering problem and describe how I finally managed to solve it. Also, I managed to find space to install a mount for the Shimano Sport Camera!

Part 5 is now up! Click here to continue reading.

Friday, March 20, 2015

Can I Install Tern Handlepost/Fork on Dahon Frame? Part 3: Considerations

Continuing on from Part 2 of the series, "Can I Install Tern Handlepost/Fork on Dahon Frame?", this is the third part of the series. In this post, I will be checking for the compatibility of the new Tern handlepost and fork with the Dahon Boardwalk frame.

In Part 2, I compared the Tern and Dahon/Fnhon handleposts side by side, and the differences have already been highlighted. The same comparison was also done for the Dahon fork and new Tern fork.

In summary, the critical differences between these components are:
1) Tern fork has a longer steerer tube than the Dahon fork, as the Tern handlepost requires a longer steerer tube to clamp onto.
2) Tern fork uses a starnut for pre-loading the headset bearings, different from the threaded compression bolt used on the Dahon fork.
3) Tern handlepost has an integrated headset Upper Cover shape at the bottom of the handlepost, which eliminates the need for the headset Upper Cover.

Based on these observations, the items which I needed to check and confirm in response to these findings were:
1) Is the Tern fork steerer tube long enough for the Tern handlepost, or is it too short?
2) With a starnut system, is the installation method different or still the same?
3) How will the whole headset and handlepost assembly look like without the use of the headset Upper Cover? Will the base of the Tern handlepost be compatible with my current headset and Dahon Boardwalk frame?

I started by studying the assembly of the headset and the Upper Cover. This was done using a spare LitePro headset that I had.

From left to right: Upper Cover, compression ring, headset bearing inside the bearing cup. The lower headset assembly is not shown.

If assembled without the Upper Cover, the headset assembly would look like the stack on the right.

When the Upper Cover is placed on the compression ring, it provides a flat platform for the base of the handlepost to rest on. There would be a small gap between the bottom edge of the Upper Cover and the bearing cup to allow for movement during steering.

If the Tern handlepost is to be installed, the Upper Cover will no longer be needed. This is because the base of the Tern handlepost will also fulfill the role of the Upper Cap, which is to press onto the compression ring. In other words, the Tern handlepost will rest directly on the headset compression ring.

Comparing the bottom profile of the headset Upper Cover with the base of the Tern handlepost. They look quite similar! 

When the base of the handlepost is placed on the compression ring, there should be a small gap between the handlepost and the bearing cup. There is a very small gap here, not sure if it is sufficient for smooth rotation.

It seems that the Tern handlepost can be installed onto the LitePro headset, although it can only be confirmed upon actual installation. Note that I had to remove the rubber seal at the bottom of the handlepost as it was rubbing against the headset bearing cup.

Next, I checked the height of the headtube for the Dahon frames, as the headtube height directly affects the length of the steerer tube that protrudes above the headset. If the headtube is tall, there would be less steerer tube sticking out from the top of the headset.

Dahon Boardwalk frame with a headtube height of 89mm.

Dahon Vitesse frame with a headtube height of 89mm. Similar frame design as the Boardwalk and Speed frames.

Dahon MuEX frame with a headtube length of 101mm. This is 12mm taller than the Boardwalk/Speed/Vitesse frames.

After measurement, I found that the Mu frame has a taller headtube than the Boardwalk/Speed/Vitesse frames. This extra height is 12mm, which corresponds to the different steerer tube lengths. As stated earlier, the Mu fork has a steerer tube that is 123mm long, while the Boardwalk/Speed/Vitesse fork has a steerer tube length of 111mm. This difference in steerer tube length is solely due to the difference in headtube height.

Other than the headtube height, the clamping height of the handlepost base is also important. This is directly related to the length that the handlepost wraps around the steerer tube. By logic, a taller clamping length should give a stiffer and stronger interface between the fork and handlepost.

Dahon/Fnhon handleposts have a base thickness of around 26mm. This is not exact as the base is sloped.

However, upon actual measurement, the clamping height of the Dahon/Fnhon handlepost is only 12mm.

The Tern Physis handlepost has a base thickness of 53mm, twice as much as the Dahon/Fnhon handlepost. This means that the clamping height of the Tern handlepost is likely to be twice as much as a Dahon/Fnhon handlepost.

As you can see from the base thickness, the Tern Physis handlepost has a much thicker base, which requires a longer steerer tube to clamp onto. This is one of the factors that will give greater stiffness over the Dahon/Fnhon handlepost and fork design.

Next step is to find out the length of the headtube that is normally required to install the Tern handlepost and Tern fork. This is done by inserting the handlepost onto the fork, and aligning them such that the handlepost base is at the optimal clamping height.

When the Tern handlepost is at the optimal clamping height on the steerer tube, the headtube length required is 101mm. This is 12mm too long, as the Dahon Boardwalk headtube length is only 89mm.

This is how it should look like if the headtube length is 101mm long. The end of the steerer tube should rest just below the circular surface for the top cap.

From this, we can conclude that the steerer tube for the Tern fork is too long for my Dahon Boardwalk headtube. Before we go any further, let us just try out the Tern fork and Tern handlepost in the Dahon Boardwalk frame.

Tern fork in the Dahon Boardwalk frame, without the headset Upper Cap. The Upper Cap is not installed as the Tern handlepost does not need the Upper Cap.

The exposed steerer tube length is far too long at 49mm! I will need to cut away the steerer tube to shorten it for this frame.

With the Tern handlepost installed onto the Tern fork. As you can see, the steerer tube is too long as it protrudes quite a bit above the base of the handlepost.

The extra length of the steerer tube is measured to be about 9mm. To be safe, I will cut away about 12mm of the steerer tube, so that the steerer tube is just below the top edge of the handlepost base.

By now, it is quite clear that the Tern fork steerer tube is too long for my Dahon Boardwalk frame. It will be necessary to cut short the steerer tube to ensure that it is compatible with the Tern handlepost. From the calculations and measurements shown above, cutting away 12mm seems to be about the right amount.

As a side note, you may have noticed that from the measurements above, the ideal headtube height to suit the Tern fork and Tern handlepost is 101mm. This is exactly the headtube height on the Dahon MuEX frame!

In other words, if I wanted to install a Tern fork and Tern handlepost on a Dahon Mu frame, it would go on perfectly without needing to cut the steerer tube! This is something worth considering for those who has a Dahon Mu frame, and want to install a Tern handlepost.

Now that all the considerations and measurements have been done, the next step would be to do the actual modifications required. The main task would be to cut the steerer tube, but it is not so straightforward as the starnut is still in the way.

In the next part of this series, I will show how I did the modifications and installation of the Tern handlepost and Tern fork onto the Dahon Boardwalk.

Part 4 is now up! Click here to continue reading.