Hello and welcome to Simplified on PowerDrift where we take complicated automotive ideas
and break them down into something you can use in your life with motorcycles.
Today we're talking about tyre tread, what it is, what it does, and why you should really
pay attention to it?
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So tyre tread, the word tread on a tyre refers to the part of the tyre which is usually in
contact with the ground where you normally see a pattern.
But it doesn't always have to be a pattern, right?
Because if you see racing slicks on one side, they have no pattern at all whereas on the
other side, racing wet tyres have a lot of patterning going on and off-road tyres have
a completely different kind of pattern altogether.
But 99% of the time, the job of the tread is just one which is to eliminate as much
water as possible between the tyre and the road surface.
Any water that gets in there can A) sort of work like a lubricant and reduce the amount
of grip you've got,
or B) if there's enough water between the tyre and the road it will remove the contact
entirely, a concept we call aquaplaning, which I can do a Simplified about, if you'd like
to know more about aquaplaning, leave us a comment, but aquaplaning is a situation where
the tyre no longer touches the ground and at that point, you have no control over the
vehicle at all and the tread's job is to delay the onset of aquaplaning as much as possible.
How does it do this?
If you look at the pattern on the tread, we're going to primarily talk about two surfaces,
the one on top which touches the road actually, and the one at the bottom, which doesn't ever
touch the road until the tyre wears out.
Let's call these the positive surface and the negative surface just for convenience.
Now the positive surface's job is effectively what the tyre is supposed to do, which is
transfer your control inputs to the road so that the vehicle responds in the way that
you want it to.
Which means I accelerate, the positive surface actually bends, hysteresis is the official
word and the hysteresis and the friction allows you to move the vehicle forward when you open
the throttle.
When you use the brakes exactly the reverse of this happens, where again, the positive
surface in contact with the ground will deform and that will allow your braking input to
be turned into retardation.
It's the same when you turn the vehicle's handlebar as well, it's the same when you
turn a steering wheel in a car as well, that's what the positive surface does.
What the negative surface does is give a channel to the water so that the pressure of the positive
surface diverts the water into the negative channels and these channels allow the water
to exit the scene rather than get between the
positive surface and the road that it is touching, in essence, that's what a tread does.
But, tread designs can be optimised so that they make less noise because treaded tyres
do make a lot of road noise and if you design them badly, you'll hear it as a drone and
a lot of off-road tyres on the road will make a lot of noise because noise is not a criteria
that is used to design tread for off-road tyres, right?
So quietness is one function of the tread, if you make the negative channels too big,
and the positive channels are in very, very small blocks, then these blocks can bend and
if they bend, then you'll also feel it as a little bit of an instability on the vehicle
because every time you put a control input, that block is actually twisting around a little
bit and not giving you a feeling of stability, right?
Tread can also have sipes which are extremely narrow channels, you'll usually see them on
really low performance vehicles because they have the time to use the sipe to evacuate
water, whereas a fast moving vehicle will just not give the sipes enough time to do
anything, therefore high performance tyres will have some amount of tread, but they may
not have a lot of sipes at all.
Also, as you go up the performance ladder and the vehicles get faster, the presumption
is that the wetter it gets the less chances that you will be outside with those tyres
and those tyres on the edges of the tyre where you're doing very serious cornering will not
have any tread at all because the presumption is you will not use the motorcycle at that
lean angle in the wet at all, so it doesn't need tread there.
But it will have some tread in the middle area of the tyre where you're going more or
less in a straight line or at relatively modest lean angles and there is some amount of work
needed to get water out from between the road and the tyre.
Why we need to pay attention to the tread is because when a tyre is new, there is quite
a difference in the height between the top of the positive surface and the bottom of
the negative surface.
This channel is the amount of volume there is into which water can go and exit the situation.
As the tyre wears out, the positive top and the negative bottom come closer and closer
together, which means that the size of the channel is reducing the amount of water that
the tyre can remove from the situation, starts to reduce as the tyre wears out.
This is why you have TWIs or tyre wear indicators which are slightly raised ribs
that sit at the bottom of the negative channels and the idea is when the rib and the top of
the positive surface come to the same level you need to get rid of the tyre and usually
this rib will be about 1mm from the bottom and that's why they also say if you take a
one rupee coin, stick it in the tread and the top of the positive surface touches the
bottom of the number one you need to get rid of the tyre because at that point, the negative
channels have reached a point where it is no longer possible for this tyre to do its
job in the wet.
So, first reason to pay attention to the tread is obviously from the perspective of tyre
wear and if you're out in the wet then this tyre needs to do its job and support you as
you try to brake, as you try to accelerate and as you try to turn, and a worn tyre will
not be able to do this for you.
When you go to the off-road situation, the job that a tread has to do actually changes quite a bit.
Remember, a road doesn't deform, right, so the tyre is sitting there on top of the road
deforming and allowing you to perform the acceleration, the deceleration and the turning,
but an off-road surface presumes that the surface itself is not stable and now the tread's
job is literally to dig into that surface and then propel you forward, which is why
off-road tyres have knobs which are effectively like hooks, and these hooks are supposed to
penetrate the surface and push the motorcycle forward, allow you to turn and give you grip.
These tyres will always make a lot of noise because of the design of the tyre and here
you will see that the negative channels are larger, because here the job is not to evacuate
the water, but give a chance for the positive blocks to actually dig into the surface and
move you forward.
Even there, once the difference comes smaller and smaller and smaller, the hook is not going
as deep into the surface anymore, and therefore the amount of grip that you're going to enjoy
from the off-road tyre will fall and in both cases, what I'm fundamentally saying is, the
less tread depth you have, the worse your tyre will feel either in the wet or off-road
depending on what kind of tyre you're using.
Now let's talk about the one thing we've not talked about, which is, why does a racing
slick not have any tread pattern at all?
Now remember, the tread's job is only to evacuate water from between the tyre and the road and
a dry racing slick presumes that you're in a dry condition going as fast as you can,
there is no water in this situation so it doesn't need tread because the larger the
positive surface is, the more power I can transfer, the more confidently I can turn
the motorcycle and brake the motorcycle.
When you maximise this, you get a tread pattern that has no negative channels at all, a racing slick.
But the presumption and the reason why you will never use a racing slick out on the public
road is because when a racetrack gets wet, a racer will simply drive two or three kilometres
back into pit lane and get a completely different kind of tyre and go back out again.
And in most cases, in racing applications, the difference between a racing slick, no
tread at all, to a wet racing tyre, which has a lot of tread is only the arrival of
the tread pattern itself, the compounds usually don't differ too much.
These compounds, the wet compounds do have to be a little bit stronger because now you've
weakened the positive surface by creating a lot of negative channels, but that's literally
the only difference there is.
When I rode my first wet laps at the Jerez circuit on the Panigale V2, we were given
a wet tyre for the first time and I was really uncomfortable with it, but the Pirelli engineer
said if you've used a SuperCorsa, effectively you're using a SuperCorsa with a lot of tread
added so the grip levels should feel something similar and that was how it was three or four
laps later once I got used to the feel of the tyre.
So in sum your tread's job is to remove water from between the tyre and the road so that
you can continue to perform acceleration, deceleration and turning on a motorcycle.
The reason to pay attention to tread depth is because as the depth gets less, the amount
of water we can remove becomes less which means the amount of grip you will have available
starts to become less and less and less to the point where it'll becomes zero and the
reason why we say you change your tyre when 1mm of tread depth is left is because you
never want the situation to hit zero.
Thank you so much for watching.
That's all you need to know about tread depth really.
This is Simplified on PowerDrift where we break complicated ideas into small bits that
you can use in your life with motorcycles.
If you'd like to discuss this in more detail, leave us a comment.
If there's other aspects of a tyre that you'd like us to talk about, leave us a comment.
We already have a Simplified on how to read the numbers on the side of the tyre for example,
please do go see that and if there's other topics, anything at all automotive that needs
to be discussed, leave us a comment and we'll get right on it.
Thank you so much for watching.