- Crank length is an aspect of our bike
that we very often overlook.
In fact, it's entirely possible
that many of you watching this
might not even be aware of the crank lengths on your bike.
And understandably so, because we're quite happy to ride
whatever comes fitted to the bike in the first place.
And yet crank length can affect
how effectively we generate a pedaling force.
Plus, it could be argued that crank length
is one of the most important factors
of a comfortable and efficient bike fit,
behind, say, the very obvious of, say, our saddle height.
And despite this, many of you might not even be aware
that cranks do come in varying different lengths.
So perhaps we should be paying more attention.
And today I'm going to discuss
why shortening our cranks could be important,
and delve into the benefits
of having that shorter crank set on your bike.
(upbeat music)
Right then, lets start with the basics.
The crank length is measured
from the center of the pedal axle
all the way through to the center
of the bottom bracket spindle here.
Now these come in a range of size
from as little as 160 mils
and can go up to as much as 185 mils.
But if I'm honest, they are mostly in a narrow band
between 170 and 175 mils, always in increments of 2.5 mil.
So if we take an average of that narrow band as 172.5 mils,
sold as an average to most bikes here in the UK,
which are pitched as suitable for a UK average height male,
which would be five feet 10, or 177 centimeters,
then we can deduce in simple proportional terms
that our crank length could be 9.7% of our height.
So, using this as a guide, and assuming
average leg length proportion relative to your height,
we can see that crank length should probably alter
dependent on your height,
and yet, referring back to that standard 172.5 crank
that I talked about, which comes fitted as standard
to effectively all bikes
from as much as a 58 centimeter frame
down to as little as a 52 centimeter frame,
with only something like a 165 millimeter crank
perhaps being found on very small female bikes,
we can kind of see that the cycling industry
has perhaps got stuck in the past,
and effectively a lot of us are riding cranks
that are perhaps too long for out bodies to cope with.
So on the basis that our cranks
could very well be a little too long,
what can we expect to find as a benefit
to shortening our cranks?
Well first and foremost, most riders feel
a general improved comfort from a shorter crank,
and as a general rule, by shortening our cranks,
there's usually a more powerful, smoother pedal stroke
that comes from the crank and that improved comfort too.
Indeed, this is a good place to point out
that the crank length doesn't actually have
any direct impact on our power output.
Unless of course you are riding a single speed.
And in that case, the crank length,
or the longer the crank length,
will help to generate more torque.
But this is where gears come in,
and they can offset any affect that that lever length,
which is our crank, will have.
And I don't really know any triathletes
who are racing on a single speed bike.
Indeed, the improvement in hip range
is possible the biggest advantage that shorter cranks
brings to the table.
The effect of crank length is felt the most
at the top of our pedal stroke, or the 12 o'clock position
when our knee's at the tightest of angles,
and therefore the knock-on effect is that
the shorter the rider or the longer the crank,
the tighter our knee is going to have to bend.
So by default, the shorter the rider
and the longer the crank,
the less ideal a combination this is
for the range of motion in our hips.
More knee bend means the potential
for knee pain, hip impingement,
and even some lower back pain too.
Plus, producing our peak power becomes more difficult
the tighter that hip angle becomes.
So, the longer the crank, the bigger the potential there is
for us to have a dead spot in our pedal stroke
between 11 o'clock and two o'clock.
Now a further benefit to the shorter cranks,
which a lot of triathletes are now becoming receptive to,
is the fact that we can have some improved aerodynamics.
Now this is because, and is widely accepted
by a lot of bike fitting professionals now,
that the shorter crank can allow us to get
our lower torso position
due to our hips being in a more open angle,
all because of those shorter cranks.
Our saddle height is generally guided
by the maximum leg extension we have
at the bottom of our pedal stroke.
So shorter cranks mean that we're going to have
less extension by the value
that we've shortened our cranks by.
So hopefully that means you'll understand
that we need to compensate for the shortening of our cranks
by increasing our saddle height by that same value.
However, all that being said,
an ideal saddle height generally falls
in a sweet spot or narrow window
that can be a little bit too high or a little bit too low.
Now hopefully you've found this sweet spot
either by trial and error, or a proper bike fit.
And the chances are that initially you wouldn't need
to alter your saddle height because you're in
this narrow window or sweet spot range anywyay.
So a good suggestion would be to
get a good few long rides in first,
before you even start to think about
perhaps nudging your saddle up or down
by small increments of say two to three mils.
And finally, it has to be remembered
that bike fitting is as much of an art as it is a science,
and doesn't really need to be rigidly stuck to.
More guidelines to work from.
So, what are the benefits to be had
from having a shorter crank?
Well, our pedal stroke is going to be smoother,
and therefore hopefully more efficient.
They'll also help us to maintain a higher cadence, too.
Plus, they're going to help us avoid that dead spot,
which can be found at the top of our pedal stroke
between 11 o'clock and two o'clock.
Plus, if you're suffering any knee, hip, or lower back pain,
this could be an indicator that your cranks are too long.
So that could be a quick fix to that problem as well.
Plus, there's little if not any evidence
that taller riders are suffering injuries
due to switching down to these shorter cranks.
It really just comes down to a comfort thing
or that perceived notion I talked about earlier
that a taller rider necessarily needs
to have a longer crank.
Now, I don't know about you,
but as someone who's always ridden
a standard 172.5 mil crank
just because they've always been fitted to my bikes,
I for one feel pretty sold on this notion
that the most logical decision
is always to opt for a shorter crank.
Now, if any of you have got any experiences,
or have shortened your cranks,
please drop them in the comments below.
I'd love to hear about that.
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