F1technical.net

### Gedankenexperiment warning ###

Just wondering if, theoretically, a F1 car could simply run out of grip to compensate drag in the wet, and what would then happen.

I am not talking about aquaplaning here. The theoretical situation (Charlie would never allow it ) is an extremely wet track with a straight long enough the the cars can still approach their normal terminal speed. Say China in super extreme wet weather tires that won't aquaplane even in a lot of water. These tires would of course be very slow for cornering, with such extreme threads, but if they were used...

In the dry an F1 car brakes at about 5G max. Roughly 1G comes from aero braking, that is, drag, and does not go through the tires. 4G go through the tires, though.
Now, in my theoretical extreme weather, the tires would only support 1G of acceleration. This corresponds roughly to the point where cornering speeds are halved compared to dry cornering speeds.
This car, approaching the end of the straights, would need 1G of grip just to stay at 300+ km/h and compensate for drag. This all has to go through the tires.

So what happens when this car runs out of grip to make up for the drag?

I can imagine that the first thing is that the car stops accelerating, it simply can't accelerate anymore. But the real question is what happens in conjunction with this magic moment when drag overcomes the longitudinal grip capacity. Is it a smooth event? Does the car simply stay in the edge at constant speed? Or do the wheels suddenly start spinning and lose even more grip? What happens to lateral stability when there is no more longitudinal grip to provide directional stability? Could a driver simply lift and regain grip, or would the car spin laterally?

I can speak to this in a real word situation. If you ride dirt bikes on gravel fire roads you can hit a point where you aero drag is greater than the traction, more throttle just spins up the rear tire. Its noticeable but predictable. You get an rpm gain with no speed gain and you can feel the tires spinning more.

I doubt an F1 car would run out of grip.

1) In addition to drag, an F1 car also has downforce
2) L/D ratio is greater than 1: As velocity increases, lift (downforce) will increase more than the corresponding drag.

Drag formula:

Lift formula:


Both are essentially the same formula and increase with the square of the speed. The ratio between the two will remain constant (ideal formula) at any speed. But as downforce is really the aerodynamic downforce plus the (constant) car weight, drag can slowly overcome the effect of downforce at speed. Doubling your speed will quadruple the drag and will quadruple the aerodynamic downforce but it will not quadruple the total force on the tires (aero downfoce + weight). This is assuming tire grip does increase linearly with vertical force, which sounds optimistic. So I think the scenario still holds.
But agreed, a current F1 car in current tracks in current tires will probably never come close to the situation.
Hence the "thought experiment" warning.

Even a thin film of water wetting the surface after the tire pumped most of the water in to thread channel would compromise traction. The small openings in the pavement would be water filled compromising keying of the tire compound into such openings. Only the longer tire and pavement asperities would project through the water film. And the water would function as thin film boundary lubrication, as opposed to gross hydroplaning (largely but not entirely redundant to the aforementioned).

So tire spin would be more likely but really not knowable.

tim away, sorry your second point is unhelpful. do the maths

More generally in wet weather your acceleration is limited at low speed by tire slip, so it would feel like that -a sudden breakaway in wheel rpm.