just custom cycling wheels that
will make a difference to your performance on the bike; it’s the gears too.
Three decades has seen a huge progression in terms of the number of gears on
bikes and we’re now at the point of 22 gear groupsets, thanks to the
combination of two chainrings and 11 sprockets. What’s more, the variety in sizes
of chainrings and sprockets has also evolved as well, therefore offering a wide
range for riders to hit the sweet spot in terms of gearing options on their
With such a generous number of gears on offer, riders
might think that they should just stick instead of twisting, but they’d be
wrong. Without trying different setups, riders may well not ever know if
they’re riding on the ideal combination for their body. After all, there is a
finite amount of power on offer and the efficiency of the system depends upon
maintaining a consistent cadence (~80rpm), irrespective of the riding conditions.
Every road cyclist should know that the size of the
chainrings and sprockets command the gearing of a bike, but there’s more than
just the volume of teeth involved. Essentially, the key here is the ratio and
the way the sprockets multiply the effort made with the chainring.
Doing the Numbers
You can work out the number of wheel revolutions produced
by a bike’s gearing through knowing the ratio of the chainring to the rear
sprocket, for example:
A 54T chainring is paired with a 13T cog; it has a ratio
of 54:13, or 4.15. Making a simple complete rotation of the crank will cause
the rear wheel to rotate 4.15 times.
Comparing Gear Ratios
Okay, so we’ve established that there are options galore
at your disposal. Now we need to know how to compare them so you know what’s
best to get you blowing up the sprints like Andre Greipel, or steaming up the
climbs like Chris Froome.
Roll-out, or meters of development, is worked out by
multiplying the gear ratio by the circumference of the wheel (measured in
meters). This is basically the distance the bike will travel after one crank
revolution. For example; using 53 x 12T gives you a return of 9.28 meters of
roll-out for a road bike fitted with 25C tyres compared to 3.28 meters for 39 x
For this method, you have to relate the gear ratio to
wheel size by multiplying the gear ratio by the diameter of the wheel. Take a
27-inch road wheel, for example; using a high gear ratio such as 54 x 13T is
comparable to riding a penny-farthing with a front wheel that is nearly 10 feet
tall! In contrast, a low gear ratio like 38 x 26T is equal to a 42-inch wheel.
Of the two, roll-out is a little more informative, if only
because it is more tangible than a theoretical wheel diameter. Nevertheless,
either value can be used to easily calculate the expected speed for any given
Speed (miles/h) = Gear inches/63, 360 x Pi
(3.14159) x cadence (rpm) x 60
Speed (km/h) = Roll-out/1000 x cadence (rpm) x
What’s more, it’s these kinds of considerations that could
mean the difference between killing it in a fixed gear (e.g. track and Red Hook
crit riders), in particular. All it takes is a negligible difference in gear
ratios (0.1m/1 gear inch) to alter the ease that you can accelerate and the
maximum speed you can hit. For road riders, these differences won’t be felt,
and it’s the larger increments (0.5m/5 gear inches) that are more meaningful
for you guys and girls.
For those riders that like to spin and can maintain a high
cadence for long periods, compact chainrings are likely to suit them better
than a standard combination. In contrast, riders that can push bigger gears at
a lower cadence are more likely to prefer bigger chainrings.
Choose Your Gearing
The only way to decide how any of these effects on the
gearing of a bike translate to the road is to put them to the test. This can be
a costly exercise, especially when considering a change of chainrings, so the
best time to explore the issue is when one or all of the parts of the transmission
are due to be replaced.
If you’re thinking about heading to the French Alps, you
can make some assumptions around the range of low ratios that are currently in
use. Worst case scenario is wishing you had a lower gear, so it is well worth adding
at least one extra low ratio so you can pedal without feeling like you’ve just
ridden into setting concrete while breathing directly fire into your lungs.
For these kinds of rides, you won’t see much use in having high gear
ratios, mostly because the descents will be unfamiliar, so you won’t be
attacking them full on. Here’s where you can say bye to a couple of high ratios
without affecting the utility of the bike. Even today, egos ride high and there
is still far too much focus around the preservation of high gear ratios on road
bikes. it’s nothing personal, but the majority of riders just don’t have the
horsepower to push these gears unless you’re descending, but you can let
gravity do its thing then anyway. So, be humble and get the right setup for
your riding, not what looks closest to a pro ratio.
Any good local bike store will be able to help in your quest for the
perfect ratio, but hopefully, this has given you some inspiration to try and
find the ratio that best suits you…!