Downforce (not drag) and its effects on fuel consumption

[raymondu999]

With the fuel limits next year, a large part of the competitive advantage will come from fuel efficiency, and measures such as cutting drag so less fuel goes into countering drag. L/D ratios will probably come to the fore over sheer downforce figures as that could be for nought if you need to fuel save every lap of the race.

Assuming two cars A and B where both have identical amounts of drag at any given speed, but Car A has more downforce (ie a better L/D ratio) then how does that affect fuel consumption?

Car A, in effect, would be on throttle for longer distances (shorter braking & traction phases) but then it wouldn't have to accelerate as hard anyways as it's carrying more speed.

On the other hand, the one with less downforce will have to accelerate harder on exit as it carries less speed.

I can see that if you're at a track like Hungary then Car A will dominate Car B, but will they use more fuel thanks to having to maintain a higher average rpm through the lap? Of course if the difference is more extreme they could in fact end up going a gear higher but on similar (or slightly lower) revs than Car B

Any and all guidance appreciated.

[flynfrog]

L/D drag ratios have always been important over sheer DF. Every time they save some drag that is more DF they can crank on the car. The ratio might shift to a different target but the goal has always been to maximize L/D ratio for a given target lap time.


Maybe one of the sim guys can give us an idea of what this means for lap time.

[raymondu999]

L/D drag ratios have always been important over sheer DF. Every time they save some drag that is more DF they can crank on the car. The ratio might shift to a different target but the goal has always been to maximize L/D ratio for a given target lap time.


Maybe one of the sim guys can give us an idea of what this means for lap time.

And... this relates to the topic (fuel consumption) how, exactly?

[flynfrog]

nothing changes except they have a new target ratio.

[flynfrog]

I should rephrase that. They have a new max drag figure and will try to as much df out of it.

[raymondu999]

I'm not asking "what they should do" - I'm asking how downforce affects fuel consumption in a circuit-racing series.

[Diff-user]

Good topic!
I believe we'll see a change in setup philosophy. Right now Red Bull for instance, knowing that their car has more downforce, set it up biased to perform better in medium to high speed turns at the expense of pure top speed on long straights. However, if fuel economy is the need of the day, then keeping the required downforce and thus having less drag than the competition (Thanks to better L/D) might be the way to go as far as set up is concerned.

So car A might shed some of its downforce may be? A draggy car in a fuel economy run will be slower than a car that can lower its downforce to the levels of the competition and thus save fuel at the same speed.

[Kiril Varbanov]

Good topic with many parameters and IF's. As soon as I get back from vacation and off the mobile device, I will be chiming in.

[hollus]

Ray, Flyn is right, I hope it wasn't you with that downvote: If car A has the same drag as car B but more downforce, what would happen most of the time is that on friday they would turn down downforce a tad, and then have a bit more downforce and a bit less drag than car B.

But assuming that come the race the situation is as you proposed:
Car A will be faster. It's lap time (and race time) will be reduced linearaly with the increase in average speed. Its drag increases quadratically (I believe I have often heard cubically?) with speed. So a larger amount of fuel goes to overcome drag in car A both per lap and during the race as a whole. Note that this is because car A chose to be faster that way. It could slow down a bit and match the average drag of car B by being faster than B in the slow bits and slower than B in the fast bits (end of straights, etc), which would still result in a lower lap time than car B.
A different factor is tires. More downforce should result in larger rolling resistance. Bow big a factor is this?

[Blanchimont]

If both cars are absolutely identical in weight, tyres, engine, etc. and the only difference being the downforce, then for me it's clear that the higher downforce car will use more fuel.

For an exact analysis you could create a histogram that shows how much time is spent for different engine power output regions. The more time is spent under 100% throttle and at high power numbers the higher the potential fuel consumption.

And higher downforce will allow a driver to earlier push the throttle down and brake later, which means that more time is spent under 100% throttle.

[hollus]

But that car is as likely to use higher RPM as to maybe stay a gear higher in certain corner, or to have longer gears. I would think in average, engine load is, on average, more or less constant no matter what. The car with higher downforce would accelerate earlier and brake later, but would also have a higher speed through that straight, hence spending less time in it. I am not sure the engine is a big factor here.

[Blanchimont]

But that car is as likely to use higher RPM as to maybe stay a gear higher in certain corner, or to have longer gears. I would think in average, engine load is, on average, more or less constant no matter what. The car with higher downforce would accelerate earlier and brake later, but would also have a higher speed through that straight, hence spending less time in it. I am not sure the engine is a big factor here.

The cars are absolutely identical, the gear ratios are the same for this comparison.

As the engine is responsible for the fuel consumption, for me it is the most important thing to look at regarding this question! As i pointed out above, a histogramm of engine power will probably give the answer. This histogramm is not dependent on the chosen gear, it's only about engine power. And as you agree that average engine power seems to increase with downforce the fuel consumption should also increase.

[Tim.Wright]

L/D drag ratios have always been important over sheer DF. Every time they save some drag that is more DF they can crank on the car. The ratio might shift to a different target but the goal has always been to maximize L/D ratio for a given target lap time.

I have done some simulations on this a few years ago. I can say that in F1 L/D ratio is not important. You always want as much downforce as possible. The increase in performance from downforce is always more than what you lose from drag. For that reason F1 cars are very draggy.

Therefore, back on topic, the teams seem to accept the fact that the downforce comes with an extra fuel consumption penalty because of the extra drag.

[silente]

i would say that car A would anyway use more fuel, since its average speed is higher.

Anyway, i think a reasonable way to tackle the problem would be to do a very basic lap simulation calculating then the energy required for the two configuration to complete a lap in a certain track.
Assuming the same fuel features, the car requiring more energy would definitely use more fuel.

You could try to do a similar (basic) simulation yourself using Optimumlap, from OptimumG.
It´s a very basic free lap time simulation software (car as a point mass, but for this kind of study i think it is ok). I think they also have a basic F1 car model you can download, to try and change L/D parameters quite quickly to see which configuration leads to the highest fuel consumption.

Still, maybe then you could want to investigate the effect of an higher/lower fuel consumption not only on a single lap, but also on a full race distance...

[andylaurence]

Whilst a higher average speed results in a higher average power, it also results in a lower time spent at that average power. I would expect that there is a point where increasing downforce increases fuel economy as well as where increasing downforce decreases fuel economy.