Tyrell IVE - Folding Mechanism and Design

Having done the brief introduction to the Tyrell IVE, here is a more detailed look! For today, we shall focus on the folding mechanism and folding design used on the Tyrell IVE. After all, this is a folding bike, and the folding design definitely matters a lot.

The Tyrell IVE is an interesting bike, as it combines the folding design from different brands, creating its own unique folding method.

For example, the rear triangle folds below the frame, similar to that used on the Brompton. The handlepost design is similar to the Tern design, with a long clamping length for extra stiffness. Handlepost clamp lever is a quick release type like Dahon's design, which is far easier to use than the Brompton type which needs to be turned. Finally, the Tyrell front fork also folds, which I think is a Tyrell original design, first seen on their Tyrell folding mini velo, the Tyrell FX.

Let's check out each of the folding components in detail!

Big red lever mounted on the left side of the handlebar, which is used to release the rear triangle from the frame. 

I have never seen a remote lever used as part of the folding mechanism, so this is new to me. If you press the lever during riding, nothing will happen as your weight still keeps the rear triangle and frame together. However, if you lift up the bike and press the lever, the rear triangle will detach and swing downwards.

Red lever activates the inner cable which runs to the rear triangle. This releases the latch that holds the rear triangle to the frame.

View of the metal latch on the rear triangle, which catches onto the frame. Activating the red lever moves the latch.

The part which the metal latch hooks onto. Although the black part looks like a rubber suspension (like on the Brompton), it feels quite stiff and probably does not flex much.

Roller wheels on top of the rear triangle, which supports the bike when the rear triangle folds below the frame. Design borrowed from the Brompton.

Metal rear fender with a small roller wheel mounted on top, which will also support the bike when the rear triangle is folded.

Small roller wheel in use. Small clearance between the fender and the ground, might have problems rolling if pushing the folded bike over uneven ground.

Initially, I was skeptical of the idea of having a remote lever activate the rear triangle folding mechanism. Is it worth mounting a lever, running an inner cable and outer casing all the way from the handlebar to the rear triangle, just to activate the folding mechanism? Not only does it add weight and complexity, it also adds additional cabling which will clutter up the bike's appearance. It could easily be replaced by a lever on the folding mechanism itself, similar to the Brompton design.

However, after using it for a while, I find it quite useful. For example, when I am rolling the bike along (unfolded), and I need to stop and park the bike, I just need to press the red lever and fold down the rear triangle. Since my left hand is already on the handlebar, right hand holding the saddle, it is super convenient to press the red lever and swing down the rear triangle in the same motion. There is no need to bend down and look for the folding lever, like on the Brompton.

Convenient? Definitely yes. Unnecessary? Maybe. A more low profile remote lever will probably appeal more to me. I will be fine with no remote lever at all.

After folding down the rear triangle, this is how it looks. Parking mode.

As seen from the picture above, the front wheel needs to be turned to the side to avoid the rear wheel. This direction is opposite from the Brompton, so I was initially confused until I figured it out.

Also, you can see that the the rear wheel actually ends up beside the frame, instead of directly under the frame like on the Brompton. This is partly limited by the triangular mainframe which cannot accommodate the rear wheel directly underneath it.

How does the rear wheel, which is initially aligned with the frame, end up beside the frame when you fold it? This is made possible by a rear triangle hinge that is angled towards one side, as seen below.

The special rear hinge that is angled to the side, allowing the rear wheel to swing to the side of the frame.

Although it is ingenious, I don't think it is an elegant design. From an engineering point of view, it is difficult to control the angle during manufacturing. Straight profiles are always easier and cheaper to manufacture, compared to special shapes or dimensions. That said, Tyrell does not do things the easy way, that is what makes them special.

Moving on to the front fork, I think the Tyrell folding front fork is an original Tyrell design. The Brompton has a folding main frame, just behind the head tube. With a folding front fork, the length of the folded package can be shortened. Let's see how it works.

Loosening the clamp will allow the bottom half of the fork to swivel down, with the pivot located at the rear as shown here.

There is a secondary pin that passes through both the upper and lower part of the folding fork. This prevents accidental folding if the front clamp loosens, which can be catastrophic.

After loosening the clamp, the pin must be pulled out, to allow the fork to fold.

The safety pin has a button at the end, which must be depressed to allow it to be pulled out or inserted into the fork.

Having the safety pin is a reassuring safety feature, however it can be quite easy to lose the pin, especially if you forget to insert it back after removing it during folding. Another problem is that the pin tends to rattle within the fork, as there is some free play. I had to use a rubber band to put some tension on the pin, so that it does not rattle when I cycle.

There is a plastic catch on the non-drive side of the rear triangle, which will be used to hold the front fork when folded.

Front fork folded, but not placed onto the plastic catch yet (located on the rear triangle).

Top down view. As you can see, the front fork rests on the plastic catch which is located on the rear triangle. This holds the front fork to the frame, preventing it from swinging open.

Handlepost design, with a chunky base that looks very similar to the Tern design. The lever design is something different from Dahon or Tern though.

The black block holds the upper part of the handlepost to the lower part when the lever is closed, by pressing it down firmly. It can be adjusted by turning the lock nuts on top and below of the black block.

One major advantage of having a tall clamp portion is that there is a larger interface between the handlepost and the steerer tube, which will improve the stiffness of the handlepost. Is it effective? This will be revealed in a later post on Ride Quality.

There is a small little metal stub on the other side of the handlepost. What does it do?

When the handlepost is folded down, the metal stub goes into the black plastic catch, which prevents the handlepost from swinging open. Similar in design to the Brompton.

With the front fork and handlepost folded, the fold is almost complete!

The final part of the fold is to lower the seat post, which works the same way as other folding bikes. Release the seat post clamp, and push down the seat post into the seat tube. For this bike, the fitting between the seat post and the seat tube is rather tight, therefore it takes a bit of force to push it down.

What is the purpose of this little plastic knob, and the strange semi-circle frame design?

The semi-circle frame design is to avoid the seat post when it is lowered. Some may call it clever, but I feel that it looks more like a workaround.

As for the plastic piece, it will rest against the seat post. This holds the rear triangle in place, instead of having it swing down when the bike is lifted. Similar to the Brompton design.

Final folded package. Quite wide and long, and looks quite untidy to me.

Side view of the folded size. Still looks OK.

As you can see from the folded package, the fold is not compact like the Brompton, neither is it neat like the Dahon. It has a relatively wide size, which also makes it harder to carry around. The folded size comparison will be done in the next post.

Although there are roller wheels under the bike, it is difficult to roll it around as it seems too wide, while steering it is also difficult. It is much faster and easier to carry the folded bike around using the top tube.

There are many little cutouts and special frame designs on this Tyrell IVE, with the purpose of enabling the fold without interference. Some people may like this kind of design, calling it clever, but I personally don't like it.

It feels like "since there is interference here, let's just create a depression on the frame to avoid the interference". This is done many times on this frame as I will show in more detail below. Not only is this not elegant, the special design also spoils the clean aesthetics and increases the production cost.

Depression on side of front fork. This is for fitting into the plastic catch on the rear triangle (shown earlier). Comes with a thick rubber patch to avoid scratches.

Depression on right side of down tube, behind the chainring. This is to avoid the rear tire when the rear triangle is folded down.

As shown here, the depression on the down tube is to avoid interference with the rear tire.

Another depression on left side of the down tube, near the headset.

This is to avoid interference with the front mudguard stays when the front fork is folded.

With all these special designs on the frame, the fold is made possible, although it is still not compact compared to the Brompton. Anyway, it works, although not in an elegant way that I would prefer.

The final thing that annoyed me is that the bottle cage bosses on the down tube is practically unusable. Although there are two threaded holes, and you can mount a bottle cage on it, you can't fold the bike!

When a bottle cage is installed on the down tube, folding is not possible as the rear wheel will interfere with the bottle cage.

Even if I just install the portable pump, the front mudguard stays will still hit the pump.

In summary, the bottle cage can only be used if the bike is not folded! You basically need to choose between folding the bike, or having a bottle cage BUT cannot fold the bike. This is quite ridiculous to me as this is a folding bike, and if you can't mount a bottle cage AND fold the bike, you might as well leave out the bottle cage bosses.

If the bottle cage prevent the full fold, but still allows the half fold (swing down rear triangle to park the bike), then it might still be acceptable. However, the bottle cage interferes with even the half fold, meaning that I cannot even swing down the rear triangle to park the bike.

Therefore, in the end I am forced to remove the bottle cage and pump mount as it just cannot be used together with folding the bike. The two bottle cage bosses are practically useless to me as I cannot use them. Do take note of this if you plan to mount a bottle cage on the Tyrell IVE.

With that, the folding mechanism and design has been shown. The next post will compare the folding design and geometry of the Tyrell IVE with my other folding bikes, the Dahon MuEX and the Brompton M6R.