United Trifold: Extra Short Handlepost Modification (Unsuccessful)

It's been a long while since I wrote about the United Trifold, but here I am to continue it. The whole bike has been modified from the stock 7 speed internal hub setup to a lightweight single speed setup.

One of the upgrades that I did was to change out the stock handlepost to a Fnhon double bolt type. At that point in time, I could only use a handlepost with a double bolt tall base to replace the original one, as the single bolt type is not compatible with the steerer tube.

The height was lowered by just 3 cm, which is not enough for me. Therefore, I continued to find ways to lower my handlebar position.

Then, I found that it was possible to use a single bolt handlepost with a shorter base, although some additional parts are required. These kind of handleposts are much more common, and comes in many more lengths. This would enable me to use a shorter handlepost to achieve a lower handlebar position.

The stock handlepost was 42 cm tall, while the Fnhon 3D forged handlepost is 39 cm tall. This time, I decided to get an even shorter 35 cm type.

Elosix 35 cm handlepost

Difference in height with the 39 cm handlepost is significant.

Due to a quirk in height definition (from folding joint), the 39 cm handlepost measures 42 cm including the base.

The 35 cm handlepost measures 37 cm including the base.

This means a 5 cm lower handlebar position if I switch to this new handlepost. Will it be too low? Only way to find out is to put it onto the bike and try.

90 grams lighter than the longer Fnhon handlepost (657 grams), and 200+ grams lighter than the stock purple handlepost.

The way to fit this handlepost with shorter base, is to use spacers to take up the difference in base height. I managed to find spacers with inner diameter of 28.6 mm (to match steerer tube) and outer diameter of around 50 mm to match the handlepost base. I was not quite sure which thickness would be most suitable, so I bought some of every thickness.

Spacers of various thickness!

The thicker spacers have a hollowed out section.

The spacer goes under the handlepost base, to take up the difference between this and the tall base handlepost.

Here is the amount of exposed steerer tube, too long for the short base handlepost to fit on. Note that this is the upgraded Litepro headset.

With the Litepro headset cover and without additional spacers, the steerer tube sticks out too far above the handlepost.

However, I found that using the spacer alone leaves a big gap at the side, even when it is pressed all the way down.

The inner ring on the Litepro headset cover is recessed, as compared to the spacer which is flush to the outer ring. That is why the spacer cannot fit directly on the headset compression ring.

Actually, the difference in base thickness is not that much. Only requires a 5 mm spacer.

The Litepro headset cover still has to be used, but with an additional 5 mm spacer on top. This height is just right.

5 mm spacer added under the handlepost. In hindsight, this is much easier than I expected. I did not have to go through all the trouble of getting the double bolt tall base handlepost.

With a much lowered handlebar position, it is now good for sporty riding!

Handlebar height from the ground is just 91 cm, even shorter than the Fnhon DB12 (95.5 cm).

How it looks with the shorter handlepost and lower handlebar position.

2-bolt type of clamp for a more secure clamping and also lower weight, since a quick release clamp is not useful for me.

So far, the modification is not an issue, every part can go on without any problem. However, during test riding, I noticed a strange phenomenon.

When riding with both hands on the handlebar, the bike steering is OK. However, once I take one hand off the handlebar, the steering becomes quite unstable. It becomes very sensitive, and it is nearly impossible to ride in a straight line when only using one hand on the handlebar. Once the handlebar starts turning to one side, it tends to keep turning, and does not self center to the straight position.

This is quite strange as I have not rode a bike like this before. To find out what was going on, I swapped back to the previous handlepost to compare. The stability became normal again, once the longer handlepost was used.

After more testing, I think I know what is the reason. When I changed to a shorter handlepost, the effective steering offset between the handlebar and the steerer tube became shorter as well. This is not an official term, just something that I use to describe this effect.

Imagine a horizontal line between the centre of the clamp to the ruler. A shorter handlepost will have a shorter horizontal distance.

This phenomenon is similar to changing to a shorter stem on a road bike or MTB. A shorter stem makes steering more sensitive, which is what happened when I changed to a shorter handlepost (with shorter effective steering offset).

Seems that there is a limit as to how much shorter I can make the handlepost, without affecting the steering stability too much. I tried adding a stem extension to put the handlebar in front of the handlepost clamp, to improve the stability. Although the steering stability is improved, there was too much flex in the handlebar and handlepost, due to the additional joints, so I decided against this idea.

In the end, I decided to change back to the Fnhon handlepost, which offers a good balance between steering stability, handlebar height and also weight. This modification to a shorter handlepost was not successful, but I did learn about how handlepost height affects steering stability.