The effect of the temperature on the car's performance

[BalazsSzabo]

Temperatures have a massive effect on the performance of the car, mainly on the engine, but also on the aerodinamics of it.
I heard from Ferrari the best ambient temperatures were around 20-25 Celsius for the engine, because that is the best for the oil.
I would like to know how much does the downforce alter according to the change in the temps? Is it better to have a cooler temp out there? If yes, why?
Other question: when does the engine give its biggest performance, the most horse power?

[Lycoming]

downforce is generated by the equation F = Cl * .5 * p * v^2 * A.

Cl is the lift coefficient, it essentially depends on the shape of the wing and its angle of attack. A is planform area, essentially how big the wing is. v is the airspeed, the speed of air relative to the wing, which changes with wind.

p is the interesting one, it is air density. This is the only variable in that equation that is related to temperature. There is a linear relation between downforce and density; as p increases, downforce increases proportionally, though drag does as well. Generally speaking, cooler air is more dense, and at the 24 hours of le mans, some teams opt to switch their aerodynamic packages during the night as the temperature drops.

The same sort of thing applies to engines; more density means more oxygen available for use in combustion and more air for cooling. However engine performance with respect to temperature is more difficult to explain, as it depends on many more factors.

[ajaxtheprince]

A number of factors like altitude, pressure, temperature and humidity influence the air density. A higher altitude, low pressure area, higher temperature and high humidity all have one result: they lower the density of the air.

When air density decreases both engine and aerodynamic performance decreases. The reason being that air molecules are further apart from each other. In other words, less air molecules in a single intake stroke of the engine and less air molecules hitting the front airfoil surfaces creating less downforce.

Hope this helps:http://www.rscycles.com/tech_articles/air_density.htm

[marcush.]

temperature is ambient ,but track temp as well! so a hot track and low ambient still has an aero effect and an effect on tyre performance.

No doubt the less dense air does also affect the vertical component you generate by using a wing so you got less downforce as well -you are shedding drag but losing downforce with temp .
The track is uusally hotter than ambient so everything close to the track is more affected and the rear wing lesser ...as it is mainly in higher up airstream methinks ...so one could expect to losse downforce coming from front wing and underfloor ...in sum that would be a shift to more rearward bias for the aero cop..and a loss of aero balance..?

electronic components don´t like temps a rule of thumb is for every 10 degrees higher temps you expect a hlving of component life ...so with uncontrolled heat input formerly safe components may reach the end of their life very quickly...

[BalazsSzabo]

Thanks for your answers. So, generally, a car is quicker in the winter test due the he air density. This is one of the factors why times from winter testing can't be reached on a proper race weekend during the season.

[BalazsSzabo]

Staying at the topic: Which temperature window do the tyres and thy engine (water and oil temp) work in?

[Lycoming]

Don't quote me on this, but I believe that the slicks operate ideally at around 100 degrees C and the treaded tyres are around 80. Not sure about water oil.

[pipex]

I remember that water temp for a F1 engine was around 125ºC, oil temp I forgot...

[olefud]

Water/oil temps cut two ways. Too high and the engine suffers. Too low at peak and the delta T relative to ambient requires large heat exchangers with greater weight and drag. Most race radiators run with a high vent release pressure to allow high water temps without boiling.

I agree with the previous comments relating to mass density and down force. However, there is an odd idiosyncrasy of air that could cut the other way. Air becomes more viscose at high temps. More viscose air forms thicker, more stabile boundary layers that yield greater lift/down force. Of course the temps would have to be rather greater than ambient to do much. More like, say, exhaust temps.

[dj_mixmaster_2000]

I completely understand how temperature can affect engine performance. Generally speaking what they say on t.v. is that colder track temperatures turn into faster speeds; but my question is about the tires. If the track temperature is cooler, wouldn't the tires have a harder time reaching optimal temperature? Thus giving the car a harder time to transform its grip into movement/speed for the car, which then slows the car down. In other words, the less sticky/grippy the tire is, the slower the car would go? I don't know if I am wrong or right; which is why I am asking this question.

Or is it because of the cooler temps, the engine performs better, producing more speed, which allows the tires to reach optimal temperature faster? Or am I just thinking too hard and that track temperatures don't really affect tires and their grip as much as I think?

With the new tire rules in F1 and having the big "unknown variable" for F1 engineers, this really got me thinking about temperature, how the tires grip and transform movement for the car, and how they all really relate.

[Lycoming]

In le mans, they run their fastest laps during the night. Michelin brings 3 compounds of slicks and to counter the fact that the tyre becomes harder to warm up, most teams switch to a softer compound as the sun sets and track temp drops. In F1, they can't really do that, and it can be a problem. Track temp dropped a bit between Q2 and Q3 in China this year, suddenly everybody was running 5 tenths slower that they were in Q2.

If temp drops too far though, there isn't much you can do. I remember being at a formula student competition where the track temperature was around 7 degrees C. I can't remember whether anybody was running the Hoosier LC0 compound (which to my knowledge is the softest available FSAE tyre) but people were struggling with poor traction all day. the front would wash out on turn-in, then the back would kick out when they tried to get back on the power. Lap times plummeted when the track warmed up a bit later in the day to about 13 degrees C. This is what happens when you try to run a formula student event in Canada.

So as for how temperature drops affect tyre performance, it cuts both ways, but it is definitely significant, probably much more so than the effect on engines in most cases. Besides, in most cases, the engine plays a relatively small role in lap times provided its running reliably. the corners is where you gain time in almost all racing series; the only obvious exception is drag racing, and even then, getting the tyres to work perfectly so you can get a good launch is crucial. Also, if you had a more powerful engine, you wouldn't put that much more energy into the tyres. You would heat them up a bit better under braking, but the changes in power that we are discussing right now would have a very small effect.

Finally, remember that there is a big difference between ambient and track temp. On sunny days, the delta can be on the order of 15 degrees C.

[Robbobnob]

Another point that hasn't been mentioned is the amount of air that's required to cool the cars as they travel from climate to climate. In winter testing as the dT is comparatively large compared to Malaysia or Bahrain they make use of smaller more discrete cooling, when compared to the larger sidepod exits and gills that often appear at the warmer races.
With these larger openings, less energised air flow is entering the air stream where ever it exits. As the two flows mix it will increase the vorticity of the flow out the back of the car. Depending on each cars specific aero characteristics this will create more drag than its smaller cooling options.

The other system that is temperature dependant is the KERS. Resistance in metallic materials increases proportionally to the temperature. Therefore the warmer it gets the higher the loads on the electrical components for a given power output. Batteries and Capacitors also vary with temperature but I am not knowledgeable on that.

Not to mention the drivers ability to concentrate. Push him hard in a warmer environment and he'll perspire quicker, therefore needs to carry more water to compensate, increasing the overall weight of the car.

[dj_mixmaster_2000]

So what we're basically saying is that there are still enough variables to keep F1 interesting for a very long time. Score one for Science!!!