Fuel saving in the wet

[hollus]

No, this is not a question about the best driving technique to save fuel in a wet race.

Of course you do save fuel when it is wet because you spend less time at full throttle and more time at part throttle or even braking, that's common knowledge...

Q1: Is that right? Intuitively yes, but you also accelerate from a lower speed after the corners, so more on-throttle time there, plus the race lasts more hours, which has interesting implications in a fuel flow limited formula...

So I guess before Q1 would come Q0: Do you save fuel in the wet post-2014?

If Q0 and Q1 are answered positively, then:

Q2: How much fuel is saved? Assuming no Whiting-induced safety-car, is a race that normally would need 100kg without fuel saving now completed with 90kg? Or 80kg? Or 70kg?

Assuming that it indeed requires less fuel to complete the race and hence that cars can gamble on starting lighter for a 100% wet race:

Q3: How much lap time is saved by not carrying 10 kg of fuel in the wet? And if Q3 cannot get a straight answer, Q3b: Is it more or less than it would be in a dry race?

[Jolle]

I guess there is no conclusive anwser. All depends of the amount of rain, type of circuit.

There might be a strong correlation between the duration of the Grand Prix and the amount of fuel. The shorter time they need over the 300km (wet or dry), the more fuel they need to save. (With the exemption of Monaco, that falls short of the 300km)

[PlatinumZealot]

It is not all about time in the race.. the biggest factors are acceleration, top speed and number of fast corners. In the rain all of these get reduced. The engine simply spends most of its time at lower loads and requires less fuel over the distance.

[livinglikethathuh]

All races have a 2 hour time limit; this limit is approached quite a bit in some races(Singapore, Baku maybe) and less so in high speed circuits (Monza, Spa). Monaco is an outlier because the race distance is 260 km instead of the usual >305 km thing. So, rain at some places (Canada 2011, anyone?) can shorten the race distance. Very easy in Singapore. Very hard in Monza, as the average speeds are very high and the wet has to slow down the cars A LOT.

I'll divide the fuel usage into two; usage while accelerating (read: part throttle) and usage while cruising at near Vmax at 7th or 8th gear where acceleration is negligible.

Modern F1 cars are traction limited up until ~160 km/h in the dry, with the reduced downforce and all, cars can spin the rear wheels at probably up to ~220 km/h. This means less throttle at a given speed, and also slower acceleration, less average speed and thus drag. Less drag over a given distance means less energy used to bend and buck air, so; fuel saved. Note that with the same engine efficiency, it is impossible not to save fuel in this case, as the driver cannot apply throttle above a given amount.
Where traction is not a problem, the car will be WOT, consuming the same fuel per unit time (probably 100 kg/h) as in the dry case. It is enough to consider how much time the car spends at WOT.
As I mentioned, the cars accelerate slower, thus cover a greater distance before they are WOT. This reduces time at WOT.
AFAIK drivers change the engine maps to leaner modes in order to keep the wheelspin under control, which may contribute to fuel saving.
Also the car will brake earlier, also reducing time at WOT.
I'd thus say that the car would save quite a bit of fuel when the track is wet.

You can say that the cars run more downforce when wet, well yes, they do bolt on more wing but wet tyres lift the car off the ground and reduce the downforce (thus drag) of the car. I believe the loss of ground effect roughly cancels the added wing out.

Still; teams will be reluctant to half-fill the tanks; any clearing of weather would mean the resuming of full gas racing, and with the added wings and a normally working floor(drying weather; dry tires) the car will be consuming more power than in a fully dry race where a wet setup is not in question.



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[krisfx]

In the wet, if they still use less aggressive maps to control wheelspin, that would probably have an effect on consumption.

[Facts Only]

A wet race will be the same distance as a dry race but will be completed at a lower average speed so you will ultimately use less fuel. This would be true of any car but on F1 cars with large amounts of drag from the wings any decrease in speed will have a much greater effect on amount of fuel saved.

[SectorOne]

I guess it depends on wether the race is a full on wet race or not. If it is then teams will adjust fuel loads and some fuel saving is the optimal i guess?

Also since a lap in the wet is much slower, the percentage of time per lap you lose by coasting should be smaller no?

[WaikeCU]

I think the drivers brake and lift also alot earlier. Don't think they will start braking at 100m board, but earlier. Also, coming off corner, they tend to short shift to gain traction. So less revs = less fuel consumption?

[Monobloc]

Good discussion as I have also been curious.