25 replies to this topic

[eoin]

This started in the RC live forum during qualifying so I thought I would bring it here....

I am under the impression that a cars aero is less important in the wet. Everyone else was under the belief that aero is more important in the wet. I believe that as the cars are traveling slower they won't be penalised as much for running more wing to get the optimum DF levels as they would in the dry.

Thoughts?

[FCYTravis]

Aero becomes important in the wet because available grip is reduced dramatically. You're right in that the cars run more wing, but it's not that there's necessarily less of a penalty - it's just that downforce becomes the only option available to improve road-holding.

In rainy conditions, grip is everything and teams won't hesitate to sacrifice straight-line speed at the altar of increased downforce and potentially higher cornering speeds.

[eoin]

But doesn't DF just increase mechanical grip? When it is dry there is alot of grip available, more that the tyres can use, hence DF to increase mech. grip. However when it is wet the track just doesn't offer the grip, so increasing the DF doesn't help after you reach a certain level.
As an example rub your finger lightly along a table. Now press down, DF, and rub the table. You will find it hard to move. Do the same with an icecube and you will see that no matter how much pressure you put on the icecube the grip doesn't increase.

[Ben]

Originally posted by eoin
As an example rub your finger lightly along a table. Now press down, DF, and rub the table. You will find it hard to move. Do the same with an icecube and you will see that no matter how much pressure you put on the icecube the grip doesn't increase.

I think this is a bit confusing.

The ice cube doesn't feel like it's gripping more because the force hasn't increased by a noticable amount. I suspect it is larger. Also in this case you will almost certainly have a lubricating layer of melted water, hardly the same as a tyre on road.

Originally posted by eoin
When it is dry there is alot of grip available, more that the tyres can use, hence DF to increase mech.

I think this is also misleading. Friction coefficient only makes sense when we consider two materials in contact and undergoing relative motion. It is true to say that the friction coefficient between the tyre and the road drops when the road is wet, but this doesn't change the fact that increasing the normal load on the tyre will give you more lateral force.

You can't think of the tyre and the road as two separate 'grips' as you seem to be saying. They are interacting together.

It may be that the optimum downforce level (and corresponding drag level) is different in the wet, but I don't think you can say that downforce is any more or less important in the wet. Downforce is a fundamental part of a Formula One car whether it is wet or dry.

Ben

[eoin]

It is true to say that the friction coefficient between the tyre and the road drops when the road is wet, but this doesn't change the fact that increasing the normal load on the tyre will give you more lateral force.

On a dry track the level of grip offered by the track is such that the limiting factor is the car, so the cars with more downforce and mechanical grip will go faster.
When the track is wet, the grip offered by the track is lower, and this becomes the limit of adhesion. Increasing the downforce won't offer more grip as it isn't available.

Now I am not saying that DF doesn't help in the wet, just that a cars aero effiecency isn't tested as much in the wet. If Williams have to run a little more wing that Ferrari to get the optimum DF levels, they won't penalised as much as in dry as the drag levels will be lower.

[indigoid]

Originally posted by eoin
Now I am not saying that DF doesn't help in the wet, just that a cars aero effiecency isn't tested as much in the wet. If Williams have to run a little more wing that Ferrari to get the optimum DF levels, they won't penalised as much as in dry as the drag levels will be lower.

eh, how does that work? The atmosphere doesn't magically get thinner when the track is wet. The drag levels will be the same, surely?

[Dragonfly]

Originally posted by eoin
But doesn't DF just increase mechanical grip? When it is dry there is alot of grip available, more that the tyres can use, hence DF to increase mech. grip. However when it is wet the track just doesn't offer the grip, so increasing the DF doesn't help after you reach a certain level.
As an example rub your finger lightly along a table. Now press down, DF, and rub the table. You will find it hard to move. Do the same with an icecube and you will see that no matter how much pressure you put on the icecube the grip doesn't increase.

Such example is irrelevant.
Ice melts proportionally to applied pressure thus providing a water cushion . Threaded tyres push water to the grooves and outside the contact spot so more pressure means less water there. There was a good article in formula1.com where Pat Simons explained the physical and even chemical processes taking place in the tyre and surface interaction.

[dosco]

Originally posted by eoin
When the track is wet, the grip offered by the track is lower, and this becomes the limit of adhesion. Increasing the downforce won't offer more grip as it isn't available.

I disagree. A wet track will have a lower coefficient of friction, thus for the same downforce there is less friction.

But increasing the normal force will still increase the total friction. It's just that the coefficient is lower so the total friction force is less.

To complicate things, though....aquaplaning is a problem, and downforce isn't going to "fix" that problem.

Now I am not saying that DF doesn't help in the wet, just that a cars aero effiecency isn't tested as much in the wet. If Williams have to run a little more wing that Ferrari to get the optimum DF levels, they won't penalised as much as in dry as the drag levels will be lower.

That's only because the drivers are driving slower.

So why is it "important" that the cars' "aero efficiency" be 'tested' in the wet?

I have to concur with Ben in that downforce is just part of the deal. It is a variable that must always be managed.

[Spunout]

dosco,

I have to (partly) disagree - IF you meant downforce doesn´t help with aquaplaning. Otherwise you can ignore my post, because IMO everything else you wrote was spot on. As we know, aquaplaning means a wedge of water being build up between the tyre and the road, causing tyre(s) to lose contact to the road, dropping friction to almost zero. Using non-scientific terminology you can say the tyres "rise on water" How easily aquaplaning begins depends on amount of water, speed, tyres contact patch to the road, and weight of the car (and other factors like suspension, shock absorbers, etc). As a rule light car with wide slicks is worst (without downforce F1 cars would be dead slow on wet). Grooves help because they displace the water and because the contact patch to the road is smaller. The reason downforce helps with aquaplaning is because it "artificially" increases the weight of the car by pressing it to the track, creating more pressure (per cm2 or mm2 or whatever) to the road, and therefore helping the tyres to displace the water more effectively. In fact, the most important reason F1 cars can travel 300+ kph at soaking wet track IS downforce (aquaplaning). If you think about it, putting 500 kgs of led weights to any car would make it more resilient to aquaplaning on straights. With downforce you can achieve the same effect without all the cons of added weight in corners (higher tendency to continue travelling towards the current tangent). Of course, one has to separate aquaplaning and wet grip in general. When it comes to grip on wet in conditions where aquaplaning is not an issue, I agree - in context of aerodynamics, there is no principal difference between wet and dry track, the level of grip is simply lower. But in both cases (aquaplaning vs wet grip in general) downforce allows the cars to go faster without spinning off

[dosco]

Originally posted by Spunout
I have to (partly) disagree. As we know, aquaplaning means a wedge of water being build up between the tyre and the road, causing tyre(s) to lose contact to the road, dropping friction to almost zero. Using non-scientific terminology you can say the tyres "rise on water" How easily aquaplaning begins depends on amount of water, speed, tyres contact patch to the road, and weight of the car (and other factors like suspension, shock absorbers, etc). As a rule light car with wide slicks is worst (without downforce F1 cars would be dead slow on wet). Grooves help because they displace the water and because the contact patch to the road is smaller. The reason downforce helps with aquaplaning is because it "artificially" increases the weight of the car by pressing it to the track, creating more pressure (per cm2 or mm2 or whatever) to the road, and therefore helping the tyres to displace the water more effectively.

Fair enough.

Isn't this highly dependent on tread pattern?

And isn't there an upper limit on speed independent of tread pattern?

Of course, one has to separate aquaplaning and wet grip in general.

Exactly what I was trying to get at before I stuck my foot in my mouth.

Happy happy joy joy. D'oh!

[Spunout]

"Isn't this highly dependent on tread pattern?"

Yep.

"Exactly what I was trying to get at before I stuck my foot in my mouth."

[McGuire]

Originally posted by FCYTravis
Aero becomes important in the wet because available grip is reduced dramatically. You're right in that the cars run more wing, but it's not that there's necessarily less of a penalty - it's just that downforce becomes the only option available to improve road-holding.

In rainy conditions, grip is everything and teams won't hesitate to sacrifice straight-line speed at the altar of increased downforce and potentially higher cornering speeds.

Exactly. The penalty remains the same, as to the square of the speed, but is less important as grip becomes more valuable relative to speed. The other part of wet setup is building some mechanical feel back into the car for the slicker surface, typically by decreasing the roll and wheel rates (soften the springs, unhook the antiroll bars, especially the rear). In many cases, moving the brake bias forward usually doesn't hurt either. Not being British I'm no expert on wet setup, but that is what I know about it.

[eoin]

Originally posted by indigoid


eh, how does that work? The atmosphere doesn't magically get thinner when the track is wet. The drag levels will be the same, surely?

Drag rises proportional to the square of the velocity of the car.

But increasing the normal force will still increase the total friction. It's just that the coefficient is lower so the total friction force is less.

Yes but as the coefficent is lower the effect of increasing the DF will also be lower. If you double the DF in the wet the drag on the longer straights will remain similar to dry drag levels, however in the corners the grip levels will still be 30-40% less than in the dry.

Thanks for the input, even if I am somewhat more confused that when I started!

[dosco]

Originally posted by eoin
Drag rises proportional to the square of the velocity of the car.

Yes.

Yes but as the coefficent is lower the effect of increasing the DF will also be lower. If you double the DF in the wet the drag on the longer straights will remain similar to dry drag levels, however in the corners the grip levels will still be 30-40% less than in the dry.

I'm not sure what you're trying to understand.

If the coefficient of friction of the pavement is lower when wet, the teams generally dial up more wing angle. Why? Because the cars are going slower, they need more wing angle to try to compensate for the lower speed in an effort to maximize frictional force. More DF equals more friction force.....in the end, depending on the Cf of the pavement, the frictional force may or may not be the same as when dry (I'd assume that the wet friction force is less than dry since wet laptimes are larger than dry laptimes).

How is the drag affected? The car's Cd will be increased due to higher wing angle(s), but the car is going slower so the drag may be about the same or less than in the dry.

What are you confused about?

[Greg Locock]

I'd have thunk this was an ideal case for those of you who play with Lapsim, or equivalent, to figure out the likely correct direction.

Reduce the grip values to those typically obtained in the wet

At low levels of alpha the grip curve is unchanged. The peak level is reduced by 10-15%, and then it falls off very rapidly as alpha increases, so by 20 degrees you'lll be down to 33% of the maximum grip in the dry.

I suspect that the load sensitivity of the grip will be increased, that is, it will fall off faster with increasing vertical load. I have no data to support that, I'm just guessing.

then retune the aero for minimum lap time.

[ivanalesi]

do you guys remember what was changed to MS car on the grid of the 97 Monaco GP, the entire rear engine cover, he was the only one to have a lot more downforce and the result was a victory to be compared with Donington 93:)

[Fat Boy]

There's 2 things we just have to accept about wings.

1. The more wing we have in a given car, the slower it will go down the straight.
2. The more wing we have in a given car, the faster it will go everywhere else.

Once we accept that, we just have to find out timewise if 1>2 or 1<2.

The area on the track where downforce is most apparent is under braking, particularly high speed braking. It does matter in the corners as well, but since most corners in the rain are at relatively low speed (as opposed to the dry) the gain in the corners is somewhat less.

The next time you're running a car in the wet, put the guy out with whatever aero package you started with in the dry. Then go to a low-downforce configuration for a session. Then go to a maximum downforce configuration. I guarantee that the high downforce configuration will be the fastest. The side benefit is that the driver will have more of a margin of error to slide the car around and will more than likely not go agricultural.

Offensive side note:

I've heard a lot of weird ideas from European racers concerning rain. Considering how much it rains over there, you'd think they'd have it completely figured out. Some want to stiffen the car (from dry settings) and others want to pull wing. I don't know where these ideas come from. They cannot be the product of actual testing. If you are doing a full wet change-over you will want to soften the springs and dampers, go maximum wing angle (balanced with less front % than the dry), stand the cambers up, a lot of rear toe-in, no anti-roll bars, and high tire pressures that the dry tires (aids in water evacuation). Once you do that, it's all up to the man behind the wheel to go out and find the grip. In most cases, the rain line will bear little resemblence to the dry line.

[wegmann]

Originally posted by Greg Locock
At low levels of alpha the grip curve is unchanged. The peak level is reduced by 10-15%, and then it falls off very rapidly as alpha increases, so by 20 degrees you'lll be down to 33% of the maximum grip in the dry.

I'm sorry, what exactly does alpha mean here?

[Ben]

Originally posted by wegmann


I'm sorry, what exactly does alpha mean here?

Slip angle.

Ben

[Chickenman]

I think the most revealing truth about downforce is in a report at GP2004 on cornering speeds recorded at Spa this year.

Quote: "The most impressive thing about driving in the rain in Spa is the lap times and the speeds. With Michael’s time of 1:53.755 in his first qualifying run ( Edit: 2004 SPA wet qualy ) he would have been on pole in 1992, where they qualified in the dry. In 1997 Eau Rouge was taken at 287 kph in the dry. This year Coulthard did 291 kph there in the wet. In the race the fastest flew over the crest at 321 kph. It is all about tyre grip and aero. "

JV did an interesting interview on TSN some years ago, talking about aquaplaning, specifuaclly at Spa. One of the most interesting comments was that you absolutely could not slow down on the straights. Referring to the Kemmel straight, he commented on the problem of aquaplaing at high speeds. The problem is that the natural reaction is to slow down. This ( JV said ) you absolutely cannot do because as soon as you slow, the car loses downforce and the car will aquaplane even worse.

It is a vicious circle....The driver wants to slow down because of lack of visablity andor aquaplaning...but he can't slow down because to do so would reduce downforce which would cause instant aquaplaning.

Aero downforce is an absolute wonderful thing in the wet....for cornering. On high speed straights it can be a double edged sword.

[Deepak]

Originally posted by Chickenman
I think the most revealing truth about downforce is in a report at GP2004 on cornering speeds recorded at Spa this year.

Quote: "The most impressive thing about driving in the rain in Spa is the lap times and the speeds. With Michael’s time of 1:53.755 in his first qualifying run ( Edit: 2004 SPA wet qualy ) he would have been on pole in 1992, where they qualified in the dry. In 1997 Eau Rouge was taken at 287 kph in the dry. This year Coulthard did 291 kph there in the wet. In the race the fastest flew over the crest at 321 kph. It is all about tyre grip and aero. "

JV did an interesting interview on TSN some years ago, talking about aquaplaning, specifuaclly at Spa. One of the most interesting comments was that you absolutely could not slow down on the straights. Referring to the Kemmel straight, he commented on the problem of aquaplaing at high speeds. The problem is that the natural reaction is to slow down. This ( JV said ) you absolutely cannot do because as soon as you slow, the car loses downforce and the car will aquaplane even worse.
It is a vicious circle....The driver wants to slow down because of lack of visablity andor aquaplaning...but he can't slow down because to do so would reduce downforce which would cause instant aquaplaning.

Aero downforce is an absolute wonderful thing in the wet....for cornering. On high speed straights it can be a double edged sword.

Exactly what i thought as i went thru this topic.

I think the trouble begins when you brake hard and the tyre suddenly loses grip due to loss in downforce which directly reduces the efficacy of the water displacement by the treads which results in aquaplaning.

Maybe this is the reason why the most number of spins in the wet happen under hard braking.

[Chickenman]

Originally posted by Deepak



Exactly what i thought as i went thru this topic.

I think the trouble begins when you brake hard and the tyre suddenly loses grip due to loss in downforce which directly reduces the efficacy of the water displacement by the treads which results in aquaplaning.

Maybe this is the reason why the most number of spins in the wet happen under hard braking.

Yep...I agree 100%. I think that is exactly what happens.

[McGuire]

Originally posted by Fat Boy
I've heard a lot of weird ideas from European racers concerning rain. Considering how much it rains over there, you'd think they'd have it completely figured out. Some want to stiffen the car (from dry settings) and others want to pull wing.

Why on earth would one want to go up on the springs and bars? What is the reasoning behind that, do they say?

[Big Block 8]

Originally posted by Chickenman

Quote: "The most impressive thing about driving in the rain in Spa is the lap times and the speeds. With Michael’s time of 1:53.755 in his first qualifying run ( Edit: 2004 SPA wet qualy ) he would have been on pole in 1992, where they qualified in the dry. In 1997 Eau Rouge was taken at 287 kph in the dry. This year Coulthard did 291 kph there in the wet. In the race the fastest flew over the crest at 321 kph. It is all about tyre grip and aero. "

Although it's already related in "tyre grip" and "aero", I'd also still like to point out what's missing, and that's the increased engine power from 92 and 97. More power in the engine, the more of it you can convert into downforce. So, if the mills were pushing 1800 hp instead of 900, we'd see today's cars going into corners much faster - with the very same tyres and the very same aero (except the wing setting of course).

[RDV]

Fat Boy-I've heard a lot of weird ideas from European racers concerning rain. Considering how much it rains over there, you'd think they'd have it completely figured out. Some want to stiffen the car (from dry settings) and others want to pull wing. I don't know where these ideas come from.

..the fact that they race in Europe does not exclude incompetence... we have our fair share!

Given winged cars and the possibility of increasing downforce for the wet, the need for as much grip as you can get for braking (cornering gain will be less as at a lower speed , therefore not as much gain) plus shifting the car to a more confortable (i.e. understeering ) balance for the wet, go for downforce.

I have some curves on tire performance in wet/dry conditions from testing... interesting reading.
Breakaway is more abrupt, and we have to cater for aquaplaning.

Sometimes on flat bottoms , you have to lift the ride heights (thus loosing downforce) to avoid surfing the puddles with the plank!... basic fiddles would be two (at least notches of rear wing... brake balance to rear (due to reduced tire grip you cannot achive the same weight transfer forward), softer dampers and bars, to make car a bit sloppier and less reactive, thus more controlable... stiffer springs?, methinks not...

[Fat Boy]

I'm not saying that I agreed with the 'stiffer' thing. It was mentioned and I said, "No". It's highly possible that some of the guys that are shipped over here are shipped over for a reason.

I will say that in N.A. in general, we don't race when it's sloppy wet or pouring rain, so you can go too far in the change over and then have a car that is too soft for intermediate conditions.

Not sure on the downforce/straight line aquaplaning theory. I've always thought that aquaplaning was more a function of the tire/tread block design. You can aquaplane a bus, even though it has a huge normal load on the tire. It's just a matter of setting up a hydraulic wedge between the tire and the track. Having said that, I've never done any scientific testing on it.

I don't run flat bottoms, so I don't have to deal with raising the car for that reason. Having spent time on a surfboard, though, I can see the potential problem!

End of the day, I've never gone slower in the wet by adding downforce at any track on any car. YMMV.