Brompton is a folding bike company that builds around
80,000 bikes per year out of their factory in London.
These are some of the smallest folding bikes available,
and their ingenious design allows them to fold down in just a handful of seconds.
The bikes are somewhat light, very durable, and quite comfortable to ride,
plus you can push them around very easily in their folded state.
They are a great bike to combine with public transport, store in an apartment,
hide under your desk, or take with you overseas.
But these folding bikes are far from perfect,
and there is a large aftermarket industry that aims to make your Brompton better.
For example, you've been able to find the components required to build ludicrously
lightweight Bromptons for many years. I'm talking folding bikes absolutely
dripping with carbon and titanium, and weighing under 5 kilograms.
Just this year, Brompton released their own lightweight titanium model, a 7.5 kilogram
bike that might not have come about if the aftermarket industry hadn't paved the way first.
In this video, I'll be explaining some of the aftermarket features available for Bromptons,
including bigger wheels, wider tires, gearboxes, belt drivetrains, and disc brakes.
These popular upgrades might give us a glimpse into the future of Brompton bikes.
Let's start with the wheel diameter. Brompton bikes use 16-inch wheels with
35 millimetre wide tires. This wheel size is key for providing the famous small fold,
but it also compromises the performance of the bike in some situations.
Studies conducted by Schwalbe tires have shown that rolling resistance
losses are inversely proportional to the tire radius. This means that
larger diameter wheels have a lower rolling resistance than smaller diameter wheels.
Some quick maths suggest that switching from 16-inch wheels to 20-inch wheels could increase
a rider's speed by one kilometre per hour, lopping about three minutes of an hour-long ride.
In addition, larger diameter wheels have a smaller angle of attack over bumps and depressions on
the road surface, allowing a rider to maintain higher speeds if the surface is less than ideal.
Brompton tires are often just 35 millimetres wide, which is a touch
wider than you'll find on modern road bikes. These tires are great on smooth surfaces,
but on less than ideal surfaces, higher volume tires can float over bumps much better,
with only a minor increase to the rolling resistance.
Ultimately, folding bikes trade between folded size and performance.
Based on the aftermarket options available, it seems lots of people
are seeking a more versatile Brompton. Let's take a look at the aftermarket wheel options.
There are two common wheel diameter upgrades for Bromptons:
18-inch and 20-inch. In order to complete a wheel and tire upgrade,
you'll also need a new fork and rear triangle to match. Kinetics in Scotland manufactures steel
forks and stainless steel rear triangles that will suit 18x2.0" tires or 20x1.3" inch tires.
The number one reason to use 18-inch wheels is to fit tires with significantly more
air volume. Two inch wide tires deform more over cobblestones and dirt paths,
which improves both your comfort and speed on these surfaces. This wheel upgrade is likely
the perfect balance between folded size and mixed surface bike capability. There are some
great 18-inch tire options too, as Birdy folding bikes are built around this spec.
If you want to achieve the highest average speeds on the road, the 20-inch option is about as fast
as it gets for a small folding bike. You can even get Schwalbe's top-of-the-line road bike tires in
the 20-inch size, which literally halves the rolling resistance of a typical Brompton tire.
On the opposite end of the spectrum, Vincent at Eerder Metaal in the Netherlands goes a step
further and offers custom Brompton builds with 20-inch wheels in a 2.6 inch width.
To make these large wheels work, Vincent uses a custom fork and rear triangle,
and he even shaves down the head tube of the frame.
The Xplorer is the ultimate dirt road Brompton. Vincent has tested his bike
on lots of mountain bike trails and has found that it's surprisingly
capable. He has built up Xplorers with both derailleur gears and internal gear hubs.
The folded size is 14 centimetres longer, 4.5 centimetres taller,
and eight centimetres wider than a regular Brompton,
which is still a very manageable size for an apartment or public transport use.
Another interesting aftermarket wheel dimension is 16x3.0". This is actually
a smaller rim diameter than what is found on stock Bromptons, but it allows for the
super wide tires to fold into a very small package. The advantage of this width is that
you can run especially low tire pressures to float over sand, mud or cobblestones.
Brompton bikes have a few different drivetrain options. You can opt for
no gears, two or four-speed derailleur gears, a three-speed internal gear hub,
or a combination between a derailleur and the three-speed hub - providing six gears.
The gear range that Brompton offers on these drivetrains is between 133%
and 302%. This simply means that the biggest gear ratio is 1.33x bigger than the smallest
ratio on the two-speed bike, and it's 3.02x bigger on the six-speed bike.
With bigger gear ranges, we can pedal our bikes across a broader range of speeds,
which is especially handy for hill climbing or pedalling downhill.
In comparison to other bikes, the Brompton gear ranges are quite small. Road bikes typically have
more than 400% range, and mountain bikes more than 500%. To increase the capability of a Brompton,
the aftermarket is producing custom rear triangles that fit all of the best internal gear hubs.
Rohloff and Kindernay are considered top of the crop,
and offer 14 gears that are spread across a 500%+ range.
Alfine 8 and 11 speed hubs are popular thanks to their lower cost,
and I've seen a few bikes with Enviolo CVT hubs too.
A company in Germany even customized a Brompton frame to house a Pinion gearbox. This gearbox
has an incredible gear range of 636% and 18 individual gears, which gives this Brompton
owner the ability to write up the steepest Hills and still have gears for the strongest tailwinds.
When you add a gearbox drivetrain to a bike, you can also switch to a belt drivetrain. Belts are
a particularly good fit for Bromptons because they're ultra long-lasting,
grease-free, and require almost zero maintenance. For these reasons,
I would not be surprised if we saw a belt drive Brompton rolling out of the factory soon.
With the aftermarket providing new forks and rear ends to house bigger wheels, gearboxes,
and belt drive - this gives them the opportunity to add disc brakes too.
Disc brakes aren't an essential component by any means, although they are nice in wet conditions,
and are generally very reliable given that grit cannot work its way into the hydraulic lines.
But with fat tyre bikes, the regular Brompton rim brakes do not offer enough
clearance for wide tires, so in most cases, disc brakes are a necessity.
Brompton frames come in only one size. That's whether you're 150cm
or 200cm tall. While you can get them to fit taller riders by swapping a few components,
best practice bike fitting requires frames to get longer as they get taller.
This is not the case with a Brompton, as the distance from the saddle to handlebars
remains almost the same, no matter the height of a rider. I might be a bit biased here as a
2-metre tall cyclist, but I would love to see a new Brompton that's scaled up for tall cyclists.
Frame modifiers such as Junik-HPV have successfully extended the length of
Brompton frames to appropriately accommodate tall customers. There
is no reason why Brompton couldn't offer an extra large frame size.
Sure, it would fold a bit bigger, but you can bet that tall cyclists would
take a bigger fold over a cramped riding position.
Brompton is in a unique position where they can draw experience and design
from the extensive knowledge of the Brompton aftermarket community. Perhaps, the ultralight
titanium Bromptons today would not exist if the product wasn't created by the aftermarket first?
There is clearly demand for Brompton models that sacrifice folded size for slightly larger
wheels. The 20x1.1" wheel spec would be a great option for mile munchers,
and the 18x2.0" size would be perfect for those who want to take their bikes on
bumpier roads. The frameset to accommodate these wheel sizes could even be the same!
It'd be great to see premium-level internal gear hubs as an option on Bromptons. These drivetrains
are reliable and long-lasting, and are already available on other folding bikes such as Bike
Friday, Tern and Birdy. If Brompton wanted to be a bit different to the rest, the 6, 9,
12 and 18-speed Pinion gearboxes are very much an option they could pursue. And belt
drive would be the perfect drive option for any of these gearboxes.
Now it's time to pass a question on to you. Do
you think Brompton will expand its bike range in the future?