Morbid schrieb:
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> The movement of the tread doesn't have to be big,
> it just has to be enough to cleverly both exploit
> surface tension and to break it. The problem with
> water is that it IS a liquid. This means it is
> constantly generating surface tension everywhere.
> So, if you slow things down enough, it acts like
> syrup.
>
> A contact patch is just that, actual contact
> between tyre and tarmac. So there is no need to
> drain water away from the patch itself, as if
> there was water between the contact patch and the
> tarmac, you would already be riding on water, and
> be aquaplaning. This means, that due to contact
> between tyre and tarmac, water is constantly
> pushed away, and that is in FRONT of the tyre.
>
> You can replicate this, with a bit of water on a
> table and your hand. If you move your finger
> towards the water, exposing the length of it, you
> will push it in front of your finger, even though
> there are wedges below your joints where it could
> escape between. Move that finger really fast, and
> you will fling the water in along in front of you.
> Even if your finger is not in full contact with
> the surface of the table, you will STILL be
> pushing water in front of your finger, even though
> some of it escapes between your finger and the
> surface.
>
> Thus, the quicker the tyre is moving forwards,
> even IF you constantly break surface tension with
> the tread, the more water will be pushed in front
> of it and it will build up a larger and larger
> wave in front of it. This wave if allowed to grow
> too big, will induce aquaplaning, when the tyre
> lifts up over it. That is when you are literally
> "riding on water".
>
> When the tread is "open" before contact, and cuts
> surface tension, some water will be forced into
> the tread from the wave. When the tyre hits the
> tarmac and comes under weight the treads come
> together, narrowing the groove. Since the water
> cannot go down, it can only go where there is room
> to do so. That is, following the tread pattern, or
> deeper into the grooves.
>
> Example: if you have a straw and you dip it in
> water, and then place a finger on top, and lift it
> out, you have water trapped inside the straw. If
> the water was to drop out, it would make a low
> pressure area in the straw below your finger. Due
> to your finger, air cannot enter from the top. It
> is surface tension of the water, that prevents air
> from entering at bottom of the straw and
> equalizing that low pressure at the top, and hence
> the water dropping out. How can we manipulate
> this?
>
> Well if you grasp the straw at a part below your
> finger and mash it where there is still air, you
> use the air pressure to break the water tension
> and push water out. If you put a finger at the
> bottom of the straw, remove the one on top, and
> then mash the lower part of the straw, you are
> pushing water UP the straw. With enough of the
> straw collapsing, water will eventually escape at
> the top. If the straw had a trumpet shape in the
> bottom, the effect would be much more pronounced.
> That is what the action of the
> expanding/contracting tread is doing.
>
> So, to explain, there are basically two types of
> treads on a wet tyre (oversimplification). You
> have treads that run around the circumference of
> the tyre, and you have treads the run lateral to
> the tyre. The treads that run the circumference of
> the tyre drain the wave made in front of it, and
> also acts as storage and transportation system.
> When that tread narrows the groove on contact with
> the tarmac (due to load weight+downforce), it
> pushes water DEEPER into the groove, and along the
> route of the groove. This brings us to the lateral
> treads, where the water is displaced too.
Yeah, that's what I had in mind as well, maybe my wording was a bit too sloppy. But yes, agreed. (except for the water / syrup comparison: this property is called viscosity and not really related to surface tension, but not important here, I get your point)
> When the
> tyre rotates enough that a certain section does
> not act as a contact patch any more, it is not
> under load. Then the groove opens up again - THAT
> PULL along the surface of the water in the groove
> helps break the tension, letting centrifugal force
> sling it away from the tyre, and thus not only is
> spray created, the tyre is drained and ready for
> another cycle.
This is the only thing that I do not see. Imo the draining of the tread is purely centrifugal force. Surface tension is not broken here, it just dictates the shape of a water droplet. The area of the water/air interface is minimized due to surface tension. If I understand correctly what you're saying the tread would have to pull the water surface in such a way that it would shrink the water/air interface if the water transforms into a drop. I can't see this happening but I haven't found any numbers on that so who knows. Imo it's just centrifugal force, nothing more. But it's a minor point really.
>
> You can see this in action on the pictures below.
>
>
> [
i68.tinypic.com]
>
> [
i68.tinypic.com]
>
> Notice the fact, that these are cars that both use
> downforce and do not use downforce. Both are
> making spray, and you can clearly see the action
> of the tyres flinging the water into the air. You
> can even see the flinging action from the FRONT
> tyre of the non downforce car. And you have to
> agree, that these wet tyres are probably a lot
> worse than what F1 cars have today.
>
> While it is true, that undercar downforce of any
> kind, and especially the diffuser, and even just
> the low pressure area behind a car that creates
> drag will create spray, they are NOT alone in
> doing this. In the wet though, this massive
> vacuuming action will help a lot to dry a track
> for each lap run.
Maybe again my wording is at fault here but I did not try to convey that only the undercar is creating spray, I'm aware that most of it is caused by the tyres. My point was that the spray caused by the wheels will acutally slow the car down and that a wet track will decrese the efficiency of the diffusor.
used to be GPGSL's Nick Heidfeld