When selecting a new Brompton, one major decision is the number of gears to go for.
Now that Brompton has introduced its four-speed drivetrain, there are even more options.
Which one to choose? Hi we're Pam and Gilbert. We've been touring on folding bikes for more
than a decade. In this video, we'll review the gearing configurations offered by Brompton
and help you identify which is right for you. Some basic explanation first: A typical bicycle
drivetrain consists of a chain ring at the front attached via the chain to a sprocket at the back.
As the chainring rotates, it makes the bicycle move forward. The distance traveled after a full
rotation of the chainring is measured in meters of development. It can be computed
using the size of the chainring, the number of teeth in the sprocket and the tire diameter.
For bicycles with an internal hub, the hub ratio is also factored in. In some areas of
the world, the term "gear inch" is preferred, which measures a similar attribute in different units.
On a flat road, a commuter would commonly use a 50 to 60 gear inch or 4 to 4.8 meters of
development range. For hill climbing, the low gear setting should be around half that value.
Alternatively, high speed rides would require gears in the 100 gear inch
or 8 meters of development range. Therefore a 400% ratio between the lowest and highest gears makes
an excellent range for a multi-purpose bike. For example, a typical full-size hybrid bike
the Trek FX3 with its 40 teeth chainring and 10 speed cassette has a range of 418%.
A road bike like the Specialized Allez Sport has a similar range, but skewed toward higher speeds.
Its dual chain ring and 9 provide a narrower gap between gears, ensuring better cadence optimization
than a hybrid bicycle. In comparison, a similarly priced city bike like the Gazelle Chamonix with
its eight-speed Shimano internal hub has a narrower range at 307%, which misses
the lower and higher gears found on bikes that focus on speed or climbing. Let's look at how the
ranges available on various Brompton options compare to these hybrid, road and city bikes.
Brompton offers three basic chain ring sizes: 44T, 50T and 54T.
As well as five different gearing configurations: 1, 2, 3, 4 and 6 speeds.
The only single speed Brompton now offered is the T-Line.
With its specially designed carbon 50T chainring, it has only one chainring
configuration. With 69 gear-inches or 5.6 meters of development, this premium ultralight bicycle is
particularly appropriate as a quick multi-modal commuter in a relatively flat environment.
The two-speed brompton or C Urban is offered with the 50T and 54T chainrings although
a 44T could be installed as an aftermarket upgrade. The gearing range is quite narrow at 133%,
but as the name implies, it will do a good job in an urban environment.
The Brompton 3-speed uses a Sturmey- Archer standard range internal hub.
It's less efficient and heavier than a derailleur- based system, but is more robust. The gears are
equally spaced at 33%. The A-Line, the less expensive bike, is only offered with a
44T chainring while the C-Line Utility is offered with all three chainring options,
the 50T being the default value. Both offer a total range of a 177%.
The newly introduced derailleur based 4 speed is available in both P-Line
and T-Line. While only the 50T chainring can be ordered for the T-Line,
a 54T option is available for the P-Line. Surprisingly, its 164% range is smaller than
the 3 speed models. It's lighter and more efficient however and has smaller increments
between gears. It's an interesting option for a high performance Brompton if money is no object.
Finally, the 6 speed C Explore is built around a hybrid drivetrain combining a
proprietary wide-range internal hub and 2 rear sprockets. It provides a wider range 302%
with increments of 22% and 27% between gears. While the standard chainring is 50T,
those planning on long distance touring would appreciate the 44T chainring option instead,
which provides an acceptable 29 gear-inches or 2.3 meters of development in first gear.
This is the configuration that we selected for our 6-speed Bromptons.
When making the Brompton gear decision, a couple of important questions are: How fast can it go? and Can
it climb hills? Ultimately, it's more the rider's fitness than the gearing that determines speed.
Assuming a rather casual cadence between 60 and 80 rpm, here's the associated speed
for each gearing configuration. For example, our Brompton's 5th gear would translate to
24 km/h at 70 rpm, a similar speed and cadence to the T Line's one speed.
Also notice how the 4 and 6 speed ranges slightly overlap,
enabling the rider to better adapt the preferred cadence to road and weather conditions.
To evaluate climbing performance, we need to factor in the slope gradient and the maximum sustainable
power a cyclist can generate. Slope gradient is usually computed in percent (%), it's basically the
elevation gain divided by the distance traveled. The famous French Tourmalet for example is about
20 kilometers long with an elevation gain of 1400 meters, for an average 7% grade.
Of course, the maximum power generated varies from one cyclist to another.
According to research performed by NASA, an average fit man could be expected to generate a maximum of
200 watts for one hour. This can increase to about 500 watts for 30 seconds effort.
Therefore, a 70 Kg rider cycling at 60 rpm could expect the following results:
A cyclist riding a T-Line one speed up a 10% hill would be exhausted after only 30 seconds.
The same rider on a 6-speed C-Line Explore would be able to sustain a similar cadence for more than 25
minutes. Replacing the 50T chainring with a 44T would almost double that time to 45 minutes.
By staying in first gear, our typical cyclist using a C-Line Explore should be able to climb
a 30 km, 4.5% grade in about 4 hours, for a total of *1350 meters elevation gain.
If the bicycle is fully loaded, the expected elevation gain after four hours
would be reduced to about 1000 meters. Climbing power, like speed, will vary significantly
depending on fitness level, but the mechanical advantage provided by lower gears is a key factor.
Is there a simple answer to which gearing configuration to choose?
Well, it depends on intended use as well as budget. If you plan to climb hills or
do long distance touring, the 6-speed Explore with a 44T chainring is the ideal choice.
If price is the principal motivator, the A-Line offers the best deal. The commuting cyclist with
a large wallet will focus on the T-Line whose lightweight makes for ideal multi-modal use.
The C-Line Urban offers a better price to weight ratio for those who cannot afford or justify a T-Line.
For performance riding, we give the nudge to the P-Line - although it is heavier than the T-Line, it
offers a better chainring selection and is thus better suited to a faster rider. Finally,
the C Utility with its robust 3-speed Sturmey Archer internal hub will likely require less
maintenance than the other models, but because it's only 300 grams lighter than the 6-speed, we would
probably suggest an upgrade to the Explore. Either that or save 33% and go for the A-Line.
We hope that your gearing decision gets you the best cycling experience that your money can buy.