- There is often much discussion during Grand Tours
about how much time the so-called climbers
need to put into the time trialists,
or vice versa, to secure the lead.
And this years Giro d'Italia is a particular good example
because Tom Dumoulin, defending champion in the Giro,
is also time trial world champion.
He is chasing Simon Yates in pink, who has made his lead
on climbs and in bonus seconds.
So, why is the time trial on stage 16 so crucial?
Well, no one could possibly call Dumoulin a poor climber.
He's just not quite as good on the steep climbs
as the pure climbers.
And the so-called climbers are bloody strong
at time trials, as well.
They're just not as strong as the time trials specialists.
This is pro cycling after all,
and the riders are all very, very strong.
But a time trial on stage 16 of the 2018 Giro is seen as
Dumoulin's big opportunity to make time
for the GC on the smaller climbers.
But why is a flat time trial
different to mountain stages anyway?
And why is it so often assumed to be due to body size,
which riders are stronger on climbs versus flat time trials?
Well, let's try the simple answer.
Of course, it seems obvious initially,
I mean, power to weight is
the main determining factor on a climb.
Which means that smaller riders can drop
taller, heavier riders even though the threshold power
of the smaller rider might be lower.
But in a flat time trial, your mass is largely irrelevant.
As once you're up to speed,
it does not decelerate you at all.
Except of course, every time you go up a hill
or you have to accelerate after the corner.
But the time trial we're talking about
from Trento to Rovareto is largely flat and un-technical.
But on the flat, in a straight line,
mass makes no difference.
So it's just pure power that counts.
And smaller climbers with lower body mass,
but also lower threshold power, simply cannot compete
against larger, heavier, more powerful time trialists.
Simple.
But, it's not quite simple as that, of course.
Now speed in the time trial is largely determined
by the ratio of your power to your aerodynamic drag.
And small riders are smaller and therefore,
one would think they would have less drag.
In cycling at race speed, roughly 90% of the total
resistance posing your motion depends
on aerodynamic drag of air which is
directly proportional to the effective frontal area.
The other 10 percent is lost in
rolling resistance and friction losses.
So here we've got the equation for drag force
where F D is the drag force, C D is the coefficient of drag
A is your frontal area, that's a half,
Rho here is your air density
and U is the relative wind speed.
So you can see that your drag force
is directly proportional to your frontal area.
Now, clearly, a smaller rider can make themselves smaller
on a time trial bike so they have a smaller
effective frontal area and thus less drag.
So why don't the smallest riders always win
flat time trials?
Well, that's because it's a little bit
more complicated even than that.
It's due to a non-linear relationship
between body mass and frontal area.
So in general, and I want to stress that
this is a gross generalization, and of course
every human body and every cyclist is different
which is why the sport is exciting,
but in general there is a non-linear relationship
between the muscle mass and the effective frontal area
by which I mean that as a rider's size increases,
their muscle mass increases and I mean,
I'm talking about lean pro cyclists here
you know, when I put on a bit of weight
it's normally due to more chocolate
rather than my muscle mass increasing, sadly.
So their frontal area also increases,
but not by as much as their muscle mass.
This is because frontal area can be approximated
as having roughly a squared relationship with your height.
While muscle mass can be approximated as
having roughly a cubed relationship with your height.
So if we're given increase in effective frontal area
for a bigger rider, their threshold power
actually increases even more relative to a smaller rider.
Now this is a cubed versus squared relationship.
So basically that means that a larger cyclist's
power to drag ratio really should be better
than that of a smaller cyclist
if those riders are well matched on a climb.
And that is why size does matter and why Yates
will have his work cut out to hold off Dumoulin
in stage 16's time trial.
Okay, now for the caveat, so clearly I have made
some major assumptions here, and I expect a flurry
of comments objecting to what I've said.
And yes, the success of some smaller cyclists at time trials
does seem to totally disprove this
but it's meant to be a generalization
and of course it doesn't hold true in every case.
Let's think about some things that change the equation.
Firstly, position.
Now frontal area, effective frontal area is as much due
to position, and thus the equipment and the flexibility
and the physiology of a cyclist as to their size.
I'm assuming that small and tall riders
can scrunch themselves up into exactly
the same time trial position but it's a personal thing
on a rider by rider case.
Secondly, body shape.
Now body shape is about much more than just height.
So some riders have wider shoulders, for example,
and thus a larger effective frontal area.
And that's not necessarily dependent on height
although it might coelect.
Thirdly, you've got your drag factor,
the drag coefficient actually.
The frontal area is not the only direct correlation
with drag force as you can see from this equation.
The drag coefficient which describes the
aerodynamic efficiency of a body independent of its size
or shape is actually really hard to predict.
In fact the only way to measure it for a complex shape
like a cyclist on a bike is really through
direct testing in a wind tunnel.
Now some cyclists just have better time trial positions
and thus a lower drag coefficent.
That's a separate consideration
from their frontal area and size.
Next we come to weight.
Now weight is actually important in a time trial
at every hill and every corner
that requires the rider to slow down.
So whenever the rider has to reaccelerate.
Next we come to pacing, and of course,
there's a very different way of riding a time trial
to riding a long climb at grand tours.
So in a race a climb is never ridden steady.
It's a very different physiological load to a time trial,
especially a flat time trial
where the pace should be fairly steady
so it's a very different physiology required for the two.
Next, I think most importantly,
to be honest, we come to mentality.
So some cyclists are simply better at time trialing
in terms of their mentality and some are better
at suffering and attacking on climbs.
That's a very complex issue to do with,
sort of self confidence, focus, targets,
what people think they're good at
so that's a really complicated one to deal with.
Now I hope this video equips you to predict
the results of the 2018 Giro d'Italia
although I doubt it given all the caveats
and expect that the time trial on stage 16
will totally stuff up my very generalized analysis.
So if you want to check out a much better video
about time trials, why not look at Tom Dumoulin's
World Champion Stripe time trial bike
which Dan caught a glimpse of at the Abu Dhabi tour.