Hi, this is Pam and Gilbert from 2Bikes4Adventure. We've been touring on small wheels for
more than a decade. We've cycled on 20 inch, 18 inch as well as the 16 inch wheels on our Bromptons.
Those 16 inch wheels make possible Brompton's compact fold
and make them distinctive among folding bikes which more commonly used 20 inch wheels.
This unique size however limits our choice when it comes to tires.
Until the introduction of the Primo Comet tire in 1996, the Brompton was plagued with poor pneumatics.
Soon after, Primo inspired house brand tires became the norm, first the Brompton Yellow
then the more robust, but slower, Brompton Green which was eventually renamed Brompton Kevlar.
Over the last 20 years, Schwalbe has consolidated a kind of monopoly on the 16-inch
tire market, culminating with the retirement of the venerable Brompton Green or Kevlar
in 2018 which was replaced by the Schwalbe Racer as the default tire on new Bromptons.
But in 2020, Continental entered the market with his excellent Contact Urban, a refreshing
development that will challenge Schwalbe and offer a viable alternative to consumers. In this video
we will compare the most common tires available to help identify the best one for your adventure.
Over the life of a Brompton, tires are the accessory most likely to be replaced,
whether from normal wear and tear or an unforeseen road hazard. They can also be a cost-effective way
to improve your cycling performance and add to your comfort and peace of mind. It's important
to note that not all so-called 16-inch tires are compatible with Brompton wheels. 16 inches
refers to the outside diameter of the tire and doesn't guarantee a proper fit on a Brompton rim.
To prevent confusion, we recommend using the European Tire and Rim Technical Organization
or ETRTO designation, especially when ordering online. This two-part number system identifies
the tire width and rim diameter as measured in millimeters. Selecting a 349 millimeter tire rim
will ensure proper fit on your Brompton. As for the tire width, it varies depending on the model selected,
most tires being between 30 and 35 millimeters. Aside from purchase price, some of
the main attributes in selecting a tire are tire: weight, puncture protection and rolling resistance.
The weight of the tire is the easiest of these attributes to compare. Fast cyclists will likely
prefer the lightest tire for its promise of a faster ride while commuters will appreciate the
weight saving when carrying the bike onto metro and buses. Some tires are available with a folding
bead, like the Kojak. These tires are usually lighter than a comparable non-folding tire.
As a matter of interest, the Brompton Kevlar was lighter than the Racer that replaced it.
Notice the significant weight difference between the Marathon Plus and the Schwalbe One. This would
add as much as 600 grams to the total weight of the bike, 300 grams per tire. So how would this
affect the rider's performance? Accelerating a wheel while cycling involves two forces:
rotational force, to turn the wheel and translational force to move it forward.
Consequently, each 100 gram saved on wheels is equivalent to reducing the bike frame weight
by 200 grams. To put this into perspective, Replacing Marathon tires with Schwalbe One
would improve acceleration performance equal to replacing your regular steel
Brompton fork and rear triangle with titanium parts, at a fraction of the cost.
Alternatively, you would be able to carry an extra one liter water bottle with no extra effort.
There are no recognized standard ratings for puncture protection,
each manufacturer claims to have superior solutions and rates them using their own
in-house scale. While this works to compare different tires of a particular brand,
it remains unreliable when comparing between different manufacturers.
Fortunately, independent third parties have performed control tests to evaluate puncture protection.
One such test consists of slowly moving a one millimeter plunger into a tire tread,
in this example, a Marathon Plus. As the force increases, the plunger initially deforms the tire then
starts perforating the various layers until it reaches the inner tube. The force indicated is in Newtons,
so you can divide by approximately 5 for reading in Pounds or 10 for Kilograms. The point of
maximum force occurs just prior to puncture, after the plunger is moved by 13 and a half millimeters.
A similar test on a Marathon Racer indicates a higher force was required to puncture the inner
tube but with half the plunger displacement. To understand this difference in behavior, we have
to see how each tire is built. The Marathon Plus has a thick and soft puncture protection belt
between the tread and the casing while the Racer has a thinner but stronger nylon one.
So, which solution is better? In stress-strain tests like this one, the protection level is
reflected by the area under the curve, the bigger the area the more protection the tire provides.
In this case, the Marathon Plus beat the Racer by about 33 percent.
similar tests are repeated a few times and also performed on tire sidewalls
The results are averaged and combined into a total puncture protection factor.
This graphic illustrates the relationship between puncture protection and tire weight.
Not surprisingly, the lightest tires are most prone to puncture
and the heavier ones are more robust. Better protection often means a heavier tire.
Note that Contact Urban data points have been extrapolated based on data available online.
Besides the usual flats due to foreign object punctures, another problem that affects low
volume tires is the pinch flat caused when the wheel hits a curb or pothole at speed.
It is a particular concern for small wheels like those on Bromptons, especially when they're under inflated.
Published test results simulating this type of incident are difficult to find.
The test usually consists of dropping a weighted metal wedge from increasing heights until the
inner tube eventually fails. The height of the final drop indicates the robustness of the tire.
The Marathon Plus is once again the winner, but it's interesting to notice that the Racer
provides a similar pinch flat protection as the regular Marathon but at a much lower weight.
We could expect the Urban Contact to perform as well as the Racer. Next to installing
an airless tire, the Marathon Plus is the best bet for those who want peace of mind.
The regular Marathon and Continental Urban tires remain a very good choice for most casual riders.
To better understand the principle of rolling resistance, let's consider
a 12 kilo Brompton carrying a 73 kilo cyclist. When pedaling, the rider applies power
to the bicycle crank in order to propel the bicycle forward. This is commonly measured in watts
It will be proportional to the pressure on the pedal and the size and rpm of the crankset.
A casual rider would normally be able to generate 100 watts without feeling tired.
This power is transmitted to the rear tire via the chain and a Sturmey-Archer internal hub.
This setup causes a loss of seven percent through mechanical friction which is, incidentally, twice
the loss than with a high quality derailleur. So, of the 100 watts generated, 93 watts remain to move
the bicycle forward. The bike will accelerate until the aerodynamic drag and rolling resistance equals
93 watts, at which point the bicycle speed will stabilize. In our example, at 20 kilometers per hour.
The rolling resistance represents slightly more than half the effort spent by our Brompton rider,
about 53 watts. As we can expect, rolling resistance is directly proportional to the weight carried.
Adding a 20 kilogram touring setup would increase the rolling resistance accordingly and reduce the
speed to 18 and a half kilometers per hour. Road conditions can have significantly more impact
than payload. Riding on a gravel road for example could drop the speed by a further 30 percent.
And what causes rolling resistance? As the tire rolls on a hard surface, the leading
edge deforms the tire casing. The trailing edge of the tire restores some of the energy back
while retaking its normal normal shape as it rolls forward. The difference between the
energy absorbed and then restored is the main principle behind rolling resistance.
Furthermore, if the ground is permanently deformed behind the wheel
or vibrations are transmitted to the rider while riding on gravel roads, additional energy is lost.
Assuming we ride on a smooth hard surface, we can decrease the rolling friction by reducing the
contact size between the tire and the ground. We do that by increasing the tire pressure.
The exact relationship between rolling resistance and tire pressure for any given
surface and tire is based more on empirical data than a mathematical model. Here's the total power
loss measured as a function of tire pressure for our Brompton rider equipped with Marathon tires.
Notice the previously mentioned 53 watts at 100 psi.
As the pressure is reduced, rolling friction starts to increase slowly at first then gradually worse
as the pressure drops below 60 psi. Note that the minimum pressure suggested for Marathon tires is
65 psi. Each tire has its own characteristics but retains a similar curve shape. Now let's compare
two cyclists of equal fitness level one riding on regular Marathons and one with Schwalbe One tires.
Both sets of tires are inflated to 100 psi. The Schwalbe One would complete a 60 kilometer course
in two hours 43 minutes which would be 17 minutes ahead of the Marathon competitor.
The difference in performance between lightweight slick tires like the Schwalbe One and the heftier
Marathon is clearly visible and could mean the difference between winning and losing in a race.
For long distance tours or city commuters, this difference may not be important.
For us, the reassurance of a puncture-free journey is worth arriving a few minutes later.
In addition to weight, puncture protection and rolling resistance,
other factors may come into play like durability, on and off-road grip and cost.
The range of tires that fit our Brompton is still limited compared to that for regular
sized bicycles but there's enough performance overlap among the available models to give valid
choices whatever our intended use. A long distance traveler will be willing to sacrifice speed
for a more robust tire like the Marathon Plus while a faster cyclist will offer slick tires like
the Schwalbe Kojak or Schwalbe One, at the risk of more frequent punctures. Casual riders may settle
for a more cost effective solution, somewhere in between, like the Racer, the Marathon or the new
Continental Contact Urban depending which one has the best price at the time and place of purchase.
We hope that the tires you select provide the optimal compromise between comfort
efficiency and reliability for whatever small wheel adventures that you are
planning.