Can I Install Tern Handlepost/Fork on Dahon Frame? Part 1: Introduction

As discussed in the previous blog post, I have always worried about the strength of the special 31.8mm stem on my Dahon Boardwalk. In fact, the clamps have broken before, thankfully not during a ride. That was the reason why I decided to get the better Controltech Stem to replace it.

The Controltech Stem requires a T-shaped handlepost for mounting a handlebar, similar to the setup shown in the picture below.

Syntace Stem used on the Tern Verge X18, but the clamp size is for 25.4mm handlebars, not 31.8mm.

As I am already using the Fnhon 4 bolt handlepost, this means that it is not directly compatible with the Controltech Stem, which requires a T-shaped handlepost. I could use the bar section of the stem (as seen below), and clamp that section in the 4 bolt handlepost. This will create a T-shaped handlepost for the Controltech Stem to fix onto.

The bar section of the stem (on the left) that I can use to convert a clamp type handlepost to T-shaped handlepost.

However, I don't really like this setup as it means multiple joints, which causes lower stiffness and is not an elegant setup. There will still be many bolts at the handlebar area as the 4 bolt handlepost is still there.

The only way to install the Controltech Stem elegantly is to use a T-shaped handlepost. The Controltech Stem will then join the handlebar to the handlepost, clean and simple. The problem here is that neither Dahon or Fnhon makes T-shaped handleposts in such a short length. In order to maintain the handlebar height at about the same level, I will require a handlepost that is approximately 29cm in length (from top to base). The shortest T-shaped handlepost from Fnhon is about 34cm in length which is way too long.

During my search for a suitable handlepost, I found that Tern handleposts are actually shorter, and are quite easily available from www.premiumbikegear.com. There are a few choices available, with different lengths, tilt angle and colour.

The problem is, a Tern handlepost cannot be fitted directly onto my Dahon Boardwalk. This is because the Tern handlepost requires a longer section of the fork steerer tube for clamping, as compared to a Dahon handlepost. In other words, to have a chance of using a Tern handlepost on a Dahon bike, I will also require a new Tern fork with a longer steerer tube. Since this is the only option I have, I decided to get both a Tern handlepost and a Tern fork. The only way to find out if a Tern handlepost will work on a Dahon bike is to try it out myself!

First, I need to choose the handlepost. For most bikes, the tilt angle should be 12 degrees. This will put the handlepost pointing straight up when mounted on the bike. Checking the Tern Bicycles website will show the different bike models that uses 6 or 12 degree tilt angles. As for the length, I went for the shorter 290mm (29cm) version as that is exactly what I need.

Tern handlepost is available in Black or Silver colour, with 2 different tilt angles and 2 different lengths.

Tern Physis 3D handlepost, in the specifications I need.

Looks very sturdy!

Measures 29cm from the base to the centre of the T-shaped portion. I found that a good way to measure the handlepost length is to set the base flat on the floor, and measure the height from the floor.

T-shaped top portion is machined separately, and press-fitted onto the top of the handlepost

Metal pin used for hooking onto the rubber strap on Tern bikes when the handlepost is folded down. I will remove this pin since it is not required.

Very tall clamping section with 2 clamp bolts. You can see the rubber seal at the base of the handlepost.

3D forged profile is strong and seamless, with no welding lines to be seen anywhere on the handlepost.

Base of the handlepost, with the rubber seal removed. This base profile is special as it replaces the Upper Cover of the headset. More details in the next blog post.

Inside of the handlepost base. Note the tall clamping portion.

External locking mechanism, used on earlier versions of Dahon bikes before the clamp mechanism was changed to internal. Although the external clamp looks bulky, it still works very well.

Note the distance between the base hinge and the lever hinge. This gives a really wide joint interface which is good for ensuring high stiffness.

Safety catch on the locking lever which prevents the lever from opening on its own. It does not take any load when the handlepost is adjusted and operated correctly. Therefore, the handlepost can function normally even if the safety catch is broken.

Weight of the Tern Physis 3D handlepost. Weighs 710 grams, a whole 200 grams heavier than the Fnhon 4 bolt handlepost which weighs 511 grams. Hopefully the additional weight is worth the improvement in stiffness!

Now that I have introduced the new Tern handlepost, it is time to look at the new Tern fork. For 20" Tern forks, there is only Black or White colours to choose from. All other specifications are the same. As stated above, the reason for getting a new fork is because I need a fork with a longer steerer tube to be compatible with the Tern handlepost.

Brand new Tern 20" fork!

Unwrapped and ready to go

Main difference from Dahon fork is that the V brake bosses are at the rear of the fork instead of at the front...

...and the mount for the Magnetix plate is on the right side of the fork leg instead of the left. This is due to the different folding method.

The steerer tube area and the inside of the fork is similar to Dahon forks. Can still use the Elosix front brake adaptor for caliper brakes.

Weighs 438 grams on its own, comparable to the Dahon fork.

The key part of this Tern fork is the steerer tube, which is 140mm long. For reference, the Dahon fork has steerer tubes of 2 different lengths, 111mm (for Speed/Boardwalk/Vitesse frames) and 123mm (for Mu frames).

Another new discovery for me is that the inside of the fork is not threaded. Rather, it has a starnut inserted in the steerer tube, same as standard road bikes or mountain bikes.

Although there is no problem in dealing with a starnut, the problem is that neither the fork nor the handlepost comes with a top cap to be used with the starnut. As shown in the handlepost installation manual below, a top cap is required to pre-load the headset bearings during installation.

Installation manual for the Tern handlepost

Luckily, the missing top cap is just a standard top cap, which is the same as those found on road bikes or mountain bikes. It is easy to find a top cap to use with this Tern handlepost and fork.

Standard top cap used for pre-loading the headset bearings.

A standard M6 bolt of suitable length is used with the top cap.

The M6 bolt will thread into the starnut during installation of the handlepost.

Total weight of the Tern fork + top cap is 454 grams, lighter than the Dahon fork + steel compression bolt at 488 grams.

With a new Tern handlepost and fork in hand, I will be able to do a proper comparison between the handleposts and forks of Dahon and Tern. By doing so, I can see how to make the Tern handlepost and fork fit my Dahon Boardwalk frame. Is it possible, and is it easy? To be continued in Part 2!

Click here for Part 2!

Controltech Stem for Dahon (25.4mm to 31.8mm handlebar)

On my Dahon Boardwalk, I have been using a special stem as an adaptor, to convert the 25.4mm handlepost clamp to use a 31.8mm handlebar. It is a good idea as I get to use a 31.8mm dropbar which is more common nowadays, and has many more choices than a 25.4mm drop bar.

However, one thing that I am concerned about is the strength of the stem. Ever since I detected the broken clamp on the stem, I always worry that the stem might not be strong enough. Even with the replacement clamps from a PRO stem, the base body of the stem might not be strong enough.

Also, although there is no problem with the function of the stem and handlepost, it does not look too neat as there are so many bolts at the handlebar area.

Up to 10 bolts at the centre area. 4 from the handlepost clamp, 4 from the stem, 1 from the Cateye Bar Fly and 1 from the handlebar extension mount.

If I can change the stem, I will be able to reduce the number of bolts around the handlebar area. Also, I can stop worrying about the strength of the stem, if I use a good, strong stem from a reputable brand. The difficulty is finding a good stem that converts a 25.4mm clamp to use with a 31.8mm handlebar.

Most stems that are available only extends the reach, but maintains the clamp size at 25.4mm. An example would be the popular LitePro stem.

There is also an alternative stem for 31.8mm handlebars, the Ridea stem. This also converts the 25.4mm handlepost clamp to use with a 31.8mm handlebar. However, this stem extends rather far forward through multiple joints, and thus will not be as rigid. It also takes up a lot of space on the handlebar which leaves very little room for accessories. Lastly, there are even more bolts and holes on the stem which will look even less neat.

Ridea stem. Gets the job done, but is not an elegant design.

This does not leave me with many choices. Luckily, Controltech has such a product that can satisfy my requirements. It will convert a 25.4mm clamp size to a 31.8mm clamp size. The difference is that it only comes with the clamps, and thus you will need to find a way to attach it to the handlepost.

Controltech 25.4/31.8mm aluminium stem. It also comes in a carbon version, but it is more expensive and also heavier...

Aluminium Controltech 25.4/31.8mm stem, with a weight of 96 grams.

Recommended max tightening torque on both sides are set at 8 N.m Best to use a torque wrench to get the correct torque.

2 separate clamp bolts for the 31.8mm and 25.4mm section. Looks very strong with plenty of material around the clamp bolt areas.

Centre to centre distance is about 33mm, which is smaller than the distance for my other stems.

A very short centre to centre distance. Main function is not really to adjust the reach, but to convert 25.4mm clamp to 31.8mm clamp.

Comes in a pair for use with handlebars. Works exactly like a LitePro stem.

The first piece of this new project is in place! Stay tuned to see how this project progresses, and how I plan to install this new Controltech stem onto the Dahon Boardwalk.

Lezyne Power Drive XL Front Light

At the recent grand opening of the bike shop The Bike Settlement, I came across a great deal for a Lezyne light. As the distributor for Lezyne and many other brands (such as Minoura, Cateye, American Classic, Lynskey), they do offer great deals from time to time when some old stocks need to be cleared.

Although I already have too many front lights, I could not resist a good deal when I saw one. At 50% off the original retail price, it was too good a deal to pass up. Here is the new front light that I got!

Lezyne Power Drive XL, 2014 version. There is a newer, brighter 2015 version.

The list of features that this Power Drive XL front light has.

With a max brightness of 475 lumens in Overdrive mode, it is more than plenty for normal commuting use. For commuting, I will use either the Economy mode or the Flash mode, which gives a really good runtime.

Contents of the Lezyne Power Drive XL Front Light. 2 different sized clamps for different handlebar diameters.

The two rubber shims of different thicknesses, to cater to all handlebar diameters.

You may notice that this Power Drive XL front light is very similar to another Lezyne light which I have, the Lezyne Super Drive XL front light. Comparing the two side by side, they look very similar. The biggest difference is probably only the brightness and runtime of the different lighting modes. This first generation Super Drive XL front light has a max brightness of 500 lumens. At that time (Year 2012), the Power Drive XL has a max brightness of 400 lumens.

Lezyne Super Drive XL on top in silver colour, and the new Lezyne Power Drive XL in black.

The lens and power buttons look exactly the same

Similar rubber flaps at the bottom to protect the charging port

Even the laser etched markings at the cap are the same

The only difference in appearance are the profile lines at the side of the main body.

Weight of Super Drive XL

Weight of Power Drive XL. Slight weight difference is probably only due to the difference in side profile of the main body.

Together with the handlebar clamp, the Power Drive XL weighs 170 grams.

Both the lights use a 18650 sized lithium ion battery. However, I had previously upgraded the capacity of the Super Drive XL light from 2400 mAh to 3400 mAh, boosting the runtime by a theoretical 40%.

Although the lights themselves are very similar, the light mounts are quite different! The Super Drive XL uses the first generation of mounts, while the newer Power Drive XL uses an improved mount.

Old mount on the left, new mount on the right

Old mount on the left looks much smaller than the new mount on the right

One of the complaints that I had about the previous mount was that it was quite difficult to slide the light onto the mount. The plastic lever was really tight and I was always afraid of breaking the mount. The other problem that I saw was that the old mount had a plastic thread for the bolt to tighten into.

I was surprised and quite glad to see that both of these problems have been addressed in the new mount. The new mount is wider and also more secure than the old mount. The snap fit design has been modified such that it is easier to insert and remove the light from the mount.

As for the plastic thread issue, there was a risk of stripping the thread on the old mount if the bolt is overtightened. This has been solved by inserting a steel nut into the mount, which is unlikely to be damaged.

New mount on the right is more user friendly as it is easier to insert and remove the light from the mount.

Instead of a plastic thread on the old mount, the new mount has a steel nut insert to prevent thread stripping issues.

I also tried swapping the lights around with the mounts (Eg. old light with new mount and vice versa), but they did not seem to fit very well. It was either slightly loose or too tight to install. Although the mounting design and mounting points look similar, there are probably slight dimensional differences between the old and new mount.

This light will go onto my Avanti Inc 3 commuting bike, replacing the Blaze Laserlight that I have been using previously. With a black colour finishing, this new Lezyne Power Drive XL front light also matches the stealthy black colour scheme of the Avanti bike.

New front light on the commuter bike! 

Matches all the other black accessories and colour of the bike

With this new light, the battery runtime is good, and I can also bring along a spare battery to swap in just in case the battery runs out. Overall, it was a good deal for a new front light!