Thursday, July 6, 2017

Brompton M6R: Imperium Cycle Hinge Clamps

After getting a Brompton M6R for myself, my upgrading instinct has kicked in. As with all bikes, I will identify areas that are not up to my standard and see if it can be upgraded. On the Brompton, there are a few areas that do not seem to belong on a premium bike. The parts that I am referring to are the injection molded resin parts that belong more to a supermarket bike than a bike that has a starting price of around $1800.

There are a few of these parts around, such as the shifters, the chain tensioner, the hinge clamp knobs, the roller wheels, and a few clips here and there. Although they function well, they do not provide the premium feeling that a Brompton should have. Imagine a premium Mercedes car with plasticky interior trimmings, that is the feeling I got.

The very first component that I want to upgrade are the hinge clamps. I have always been a fan of Dahon's folding clamp mechanisms, which are well engineered, easy to operate and nicely designed. If the Brompton has Dahon's clamp mechanism, that would be the best of both worlds.

Brompton uses a very simple clamp that basically holds both sides of the hinge together, using a simple but cumbersome rotating knob to press the clamp against the tapered surfaces of the frame. This removes any free play between the joints and does not need any adjustment over time, since you are basically adjusting it every time you use the clamp.

One annoying aspect of this hinge clamp design is that when you loosen the knob, you have no idea how far you need to rotate to loosen it sufficiently to free up the joint. Loosening it generously only encourages the clamp to rotate after becoming loose, causing it to be misaligned against the frame. All this creates the cumbersome feeling as I always need to fiddle with the clamp position to align it, before tightening the knob.

After loosening, the clamp will rotate and not be lined up with the frame. Also, there is no stopper to let you know when the clamp is loose.

Plastic knobs on a premium bike? Rather disappointing...embarrassing even.

Same for the hinge clamp on the handlepost

I wanted to get rid of the plastic knobs which do not belong on a premium bike such as the Brompton. After looking at a few aftermarket hinge clamps, I found that there is actually a solution to prevent the self rotation of the hinge clamp after loosening. This is exactly what I am looking for.

One downside of upgrading a Brompton is that the components cannot be found cheaply on Taobao, unlike those for Dahon or other folding bikes. Seems that the supply of these aftermarket parts are strictly controlled to maintain the higher prices that Brompton owners are willing to pay.

Anyway, I found the hinge clamp set from Imperium Cycle that look good and has the self aligning function.

Hinge clamp set in all black colour, made of aluminium

The various parts of the hinge clamp set and what they do

The pair of hinge clamps, for the frame and also the handlepost

They are virtually identical, except for the silver bolt at the end which has slightly different lengths. The silver bolt with the step is for the handlepost.

Machined lever for lightweight image. Feels much better than the plastic knobs.

One side of the clamp is longer than the other, and this is what keeps the clamp aligned after loosening the knob.

Comparing the new clamp with the stock clamp. The clamp plate on the stock clamp looks quite a bit thicker.

New hinge clamps weigh 62 grams a pair

Stock Brompton hinge clamps weigh 105 grams a pair

The silver bolt at the end is reversed (left hand) threaded, to prevent self loosening when operating the clamp.

Using a size 4 Allen key to tighten the silver bolt into the black bolt.

One problem I found during installation is that the frame hinge will get in the way of the Allen key when I am tightening the silver bolt. Even with the ball end of the Allen key, I am not able to engage the silver bolt properly to tighten it. To solve this, the next version should have 2 flats on the silver bolt, so that we can use a wrench to tighten it instead of an Allen key.

The silver bolt acts as a stopper during loosening, which is designed to stop when the clamp has retreated far enough to free up the joint.

At this point, the shorter side of the clamp has cleared the frame, while the longer side is still engaged to prevent self rotation of the clamp. Ingenious design!

Both hinge clamps installed!

All black aluminium hinge clamps and levers look more befitting of the Brompton

This upgrade is a must for me, as it solves the two main issues of the stock hinge clamps. First, there is a stopper which stops the knob when the clamp has been fully loosened. This makes it easy as I just need to twirl the lever until it stops, without thinking how many turns is required.

Second, the long-short clamp design ensures that the clamp is aligned with the frame or handlepost at all times. When I need to tighten the joint, I just close the joint and tighten the knob. No need to fiddle with the clamp to align it. Much faster and fuss free than the stock design.

If you are a Brompton owner who folds and unfolds the bike a few times a day, this is a highly recommended upgrade as it makes operating the hinge clamps much easier, and you will wonder why did you put up with the original clamp design for so long.


  1. Would the clamp bolt prevent usage if the in frame Brompton toolkit?

    1. No it does not interfere with the Brompton Tool Kit. I also checked that out when I bought the tool kit, will show it in a later blog post.

  2. tylsteve, I discovered your blog less than a week ago and already it has me reaching into my pockets. You offer great insight, and some terrific close-up photos in addition.

    Can you tell me if you were able to solve the frame hinge Allen key problem, and if so how? I have not yet ordered my hinge clamps, but am sure to do so quite soon (I started with the BikeFun Suspension Block upgrade you recommend...waiting patiently for it to arrive from Singapore).


  3. Aluminum bolts to secure a bike frame??! I would not dare to ride this improved bicycle.


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