temperature and the top speed of cars

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dougboyy
I have been thinking about this for the past few days.

Will a car go faster in hot weather or cold weather?

Hot air is less dense than cold air so if a car is driven in a hot climate, then it has less drag which technically should allow it to go faster. But cold air is more dense so it packs more oxygen molecules so it should give the engine more power(intercoolers). But if it is driven in the cold, the surrounding air would also be more dense resulting in more drag.

i'm refering to high performance cars. Not your typical family car, but not those 700mph jet engine cars either.

thanks
 
In general, cold dry air gives you the most power, and the increased air density doesn't affect the drag noticeably. So your best runs are going to be in the 55-70 degF range with relative humidity around 50%.
 
F1 cars lap faster when it's cool. Obviously they get more power when it's cool, but I'd imagine they also develop more downforce in the denser cold air.

I'd imagine that in any high performance racing/road car, the top speed would be significantly higher in cool conditions than in hot conditions.
 
Like Duke and amp88 said, the engine is likely to make more power when it is colder out.

I was just thinking about the tires; they will probably have a lower drag coefficient when it is colder out and the compound is harder, improving the top speed a bit. My tires take about 5 minutes to warm up (or less, on the highway), so this effect probably won't last too long.
 
amp88
F1 cars lap faster when it's cool. Obviously they get more power when it's cool, but I'd imagine they also develop more downforce in the denser cold air.
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they develope more downforce in the cold, but downforce is bad for speed, its only good for cornering. Thats why they removes aero parts when racing in high speed circuits like monza or montreal.

i was also thinkin that in really cold weather around 20degF(not uncommon here in canada during the winter), the engine might not run in optimal form due to the liquids being more viscous and such as opposed to 90degF weather.
 
I know when drag racing is done, they take into affect the level of feet above sea level, due to the thinner oxygen/air levels the higher you go.
Can't really say much else on the topic other then that.
 
Bubble Bunny
they develope more downforce in the cold, but downforce is bad for speed, its only good for cornering. Thats why they removes aero parts when racing in high speed circuits like monza or montreal.
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:lol:

Ok, thanks for that info...

You'll note I said they lap faster, not that the top speed is higher... :)
 
SRV2LOW4ME
I know when drag racing is done, they take into affect the level of feet above sea level, due to the thinner oxygen/air levels the higher you go.
Can't really say much else on the topic other then that.
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Beat me to it, i was just about to say that altitude has more effect on performance in general than air temperature. Its the same with athletes, if they train at altitude, because they have to work their lungs harder, their cardio system gets stronger, quicker. If i remember rightly Interlargos in Brazil is the highest F1 circuit on the Calender, they have a noticable reduction in HP when they race there.
 
In general, a car will run better when it's cooler, but top speed is generally higher when it's hot (lower drag > power loss). I don't know if the greater drag in cool weather will offset the increased acceleration from denser air charge, though.
 
It depends on the car's powertrain and its aero. If it's very smooth, like a C5 Corvette, denser air won't make a big difference on drag, so it'd be good to go ahead and try to get that extra power by running in the cold. If you were driving one of those VW Omnibuses, I'd imagine it to be more beneficial to run in hot weather with less drag. That engine's not making much power anyways.

It also depends on the power curve of the engine and how easily the car can reach its top speed.
 
TheCracker
Beat me to it, i was just about to say that altitude has more effect on performance in general than air temperature. Its the same with athletes, if they train at altitude, because they have to work their lungs harder, their cardio system gets stronger, quicker. If i remember rightly Interlargos in Brazil is the highest F1 circuit on the Calender, they have a noticable reduction in HP when they race there.
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I'm going to respond to the athletic portion of this. Not exactly, the advantage of training at altitude (for runners at least) is that they can reach the same level of aerobic activity at a lower speed. This means that there is less stress on the body but the same stress on the aerobic system. This allows them train a bit harder.

For sprinters altitude is good. The reduction in drag more than compensates for the loss in air. I think the 400m is right on the threshhold, where altitude benefits and losses become close to equal.
 
I was under the opinion slightly colder conditions were better.

Basically think of it as a simple tubo/supercharger effect. The colder it is the more dense it is, so there is increased HP.

I don't think it effects aerodynamics so much. I think that is more to do with humidity.
 
On a side note, which has nothing to do with your question but might be handy to know:

Petrol is densest (most dense?) at 4 degrees C (39 degrees F), so if you fill up on a chilly day you're getting more fuel for your money than on a hot day.
 
Roo
On a side note, which has nothing to do with your question but might be handy to know:

Petrol is densest (most dense?) at 4 degrees C (39 degrees F), so if you fill up on a chilly day you're getting more fuel for your money than on a hot day.
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Veeeeeeerrrrrrrrrrrry negligibly. You'll get about 7-10 extra miles from that "bonus" :)
 
amp88
F1 cars lap faster when it's cool. Obviously they get more power when it's cool, but I'd imagine they also develop more downforce in the denser cold air.

I'd imagine that in any high performance racing/road car, the top speed would be significantly higher in cool conditions than in hot conditions.
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But usually the lap times are actually faster when it is hot because the tyres are much stickier, therefore more grip
 
There's a happy point for everything, such as drag racers wanting between 55-70 degrees... but they arent going top speed, so while they see a benefit from power, the drag plays much less of a factor, since it's mainly on the second half of their run, which only takes about 1/3, usually 1/4 of the whole time.
depending on the specific car's intake, intake temperatures may not hardly be affected by outside temp as well.
I'd put my money on hot, very hot. why? because it takes more power to accelerate from 190-200 than it does from 90-100, by a LOT. with every bit of speed gained, it becomes far more difficult to gain it again. whereas, air density, from temperature, changes on a proportionate scale.

in other words, it'll take between 3-5 hp (most cars) to get from 200 to 201 mph... and your likely not to gain more than 10 (stretching) hp, from the temp diff between 60 deg. and 100deg.

also note, land speed records (whether at 700mph or 226mph) are always set not only in the desert, but also in the summer heat as well.
 
Well today I was at the drags and it was about 85 degrees and funnycars were running 4.7x for the most part , but once the temp dipped to about 65 degrees.

HPIM0217.jpg


A world record for top fuel funny car.:)

I grew up around these cars but they always put a smile on my face.
 
Summer sunny dry day with average 60-90 degrees F and little or no wind would be perfect for top speed testing.

Soft compound tyres are always better but they should be inflated to the top end of the recommended pressure rating for top speed (for acceleration they should be inflated to the low end). Not over the recommnded rating so they don't blow.

Wings should be removed or if adjustable set to the lowest drag coefficient angle, only for top speed testing though. Track testing and 1/4 mile drag will require the wings or fine adjustments (if adjustable) depending on the situation.

Car washed and waxed would help a little.

Removal of window wipers also helps, as would removal of spare wheel, jack, tools, passenger seat, rear bench (if available) and anything else that that's easily removable and will save weight.

Run high octane fuel, 100-110RON should be more than adequate.

Obviously top up if convertible and all windows closed.:dopey:

Last but not least a fine check of the car before the run for safety, if you value your life.
 
On a factory car, it's debatable.

On a tuned street car, probably not, as top speed will be gear-limited and not power-related. My Impreza will top out at 155, whether it's 50 or 100 out, just because that's where it hits redline in 5th.
 
I can tell you how it is in my case :

300+ hp turbocharged Impreza WRX STi :

The difference is like night and day.
The performance is a LOT better on a cold day, could be comapred to driving alone and with 3 people in you car, I'm not kidding.

Also take NOS : all it does, is cooling down the air/gas mix.

EDIT : Oh I just noticed that you talk about TOP speed. Never tested that. But acceleration and engine performance increase at cold temperatures, but you tend to have less tire grip etc, but I'm talking about sheer performance.
 
Max_DC
But acceleration and engine performance increase at cold temperatures, but you tend to have less tire grip etc, but I'm talking about sheer performance.
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I agree, I notice alot of difference in engine performance with cold air in the hills then I do on a warm day, Alot of difference.
 
No appie17, hot air is not better cooler air is better. But cold weather isn't. The balance is somewhere in the middle.

Of course as Takumi Fujiwara said it depends on the car also. On a standard car the top speed may be limited by ECU or Final Gear. I have 2 tuner cars and they both have cold air induction racing intakes and cryogenic artificial cooling as well as straight-through exhausts. Also both cars have front and rear wings, fixed but removable. Most importantly they both have fully programmable ECU and that alows me to fine tune the combustion, timing, rev limiting, speed limiting, launch, etc. Both cars were chosen by me especially because they have taller than needed gear ratios which meant I din't have to replace their gear boxes, just clutch and flywheel.

Then for me, unless I'm facing a lot of REAL heat, above 90F, I'm running much better in 60-90F and dry, warm, grippy road surface. Yes very cold air does alow for more power in theory. Still, a LOT of power gets lost from flywheel to road. This especialy when there is loss of grip due to colder tyres and road surface. The cold air will also affect the friction with the car at speed, especialy at high speed. We're talking about top speed here not 0-60Mph or 1/4 mile.

VIPERGTSR01, air temperature and density are important and although colder air is at higher altitude the air is more rarefied also. This can negate any improvement gained.

Lastly, Max_DC, invest in a Cold Air Induction solution, Cold Air Feed (maybe even lower it's height, lower to the road, colder air), Cryogenics, NOS being the extreme. In your case acceleration is obviously what's important and grip in a straight line is problably not that important since you have drive on all wheels. I guess this means that the drive configuration is also important, maybe even the weight? My cars are very light in track configuration so I need the grip for traction, turning and braking.

These are just my opinions from my experience and my knowledge so far. If anyone knows better I hope they post and shed more light on the sugject.

Also remember the topic question: warm or cold weather. NOT warm or cold air. Meaning the air can still be cooled on warm weather.
 
Cobra_UK
VIPERGTSR01, air temperature and density are important and although colder air is at higher altitude the air is more rarefied also. This can negate any improvement gained.
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Yes obviously but these hills are not that high (hence not mountains) but very cool at night.
 
Cobra_UK
Lastly, Max_DC, invest in a Cold Air Induction solution, Cold Air Feed (maybe even lower it's height, lower to the road, colder air), Cryogenics, NOS being the extreme. In your case acceleration is obviously what's important and grip in a straight line is problably not that important since you have drive on all wheels. I guess this means that the drive configuration is also important, maybe even the weight? My cars are very light in track configuration so I need the grip for traction, turning and braking.
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Yes I thought about buying a Carbon Air Box from BMC, but before that I would invest my money in a ECU. Well apart from that there is obviously a lot I could do, as you said from better suspension/sports tires to reducing weight.
But the car is my daily ride to university, I don't earn money and that's why those projects have to wait.
 
I thought we were to assume a "true" top speed, with no gear or ecu infractions included. (i.e., Dodge Viper, M5, etc..)

I also think we're to assume temperaure difference ONLY, in other words, same pressure, humidity, wind, etc...

Also, a car that tops out at 125mph is going to have less air restriction to fight than a car going 220mph, therefore, since air/speed velocity differences are present, you will likely find a different temperature to be beneficial for each, colder being better for the slow car, and hotter being better for the fast car.

I'd still place my money with hotter air for top speed.
 
LeadSlead#2
I thought we were to assume a "true" top speed, with no gear or ecu infractions included. (i.e., Dodge Viper, M5, etc..)

I also think we're to assume temperature difference ONLY, in other words, same pressure, humidity, wind, etc...

Also, a car that tops out at 125mph is going to have less air restriction to fight than a car going 220mph, therefore, since air/speed velocity differences are present, you will likely find a different temperature to be beneficial for each, colder being better for the slow car, and hotter being better for the fast car.

I'd still place my money with hotter air for top speed.
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Honestly mate, I don't think the thread starter was being that specific.

Still, say I was to go with your assumptions. Let's say over 150Mph top speed and the ability to cool the intake air by artificial means, the best engine coolant, engine oil and super-tough engine internals. My money's on hotter rather than cooler weather also.:)

Max_DC don't mess with the suspension those cars have fantastic suspension anyway, and if you were to get better it would cost a LOT of money. If I may here is a list of things for your car that I would recommend. I'm assuming that's your car in the picture.

carbon fibre cold air induction
racing 10mm ignition leads
iridium spark plugs
highest yield/heavy-duty car battery your car can handle
remove catalytic converter and replace with straight stainless pipe
racing stainless steel cat back exhaust
dump valve
carbon fibre bonnet in blue weave
sports soft tyres
best synthetic oil available
front/rear upper/lower strut bars
custom ecu tuned on rolling road for more aggressive timing, turbo boost, top speed delimiting and more

This would class as a light tune and I'd say it would be the best option for you. I don't know in Germany, although from what I've heard it's much cheaper there, but here that would set me back about £2000 and would turn that Impreza into one mean driving machine!
 
Cobra_UK
Honestly mate, I don't think the thread starter was being that specific.

Still, say I was to go with your assumptions. Let's say over 150Mph top speed and the ability to cool the intake air by artificial means, the best engine coolant, engine oil and super-tough engine internals. My money's on hotter rather than cooler weather also.:)

Max_DC don't mess with the suspension those cars have fantastic suspension anyway, and if you were to get better it would cost a LOT of money. If I may here is a list of things for your car that I would recommend. I'm assuming that's your car in the picture.

carbon fibre cold air induction
racing 10mm ignition leads
iridium spark plugs
highest yield/heavy-duty car battery your car can handle
remove catalytic converter and replace with straight stainless pipe
racing stainless steel cat back exhaust
dump valve
carbon fibre bonnet in blue weave
sports soft tyres
best synthetic oil available
front/rear upper/lower strut bars
custom ecu tuned on rolling road for more aggressive timing, turbo boost, top speed delimiting and more

This would class as a light tune and I'd say it would be the best option for you. I don't know in Germany, although from what I've heard it's much cheaper there, but here that would set me back about £2000 and would turn that Impreza into one mean driving machine!
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I'll better answer your pm, since this would be offtopic :)
 

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