Could lap times be maintained with half the downforce?

[barnettracing]

Originally Posted by S14

Indeed. The only way to add to its mass, other than adding more mass, would be to make it travel much, much faster.

Yep, a car traveling at 3.00x10^8m/s would be so heavy it wouldn't be able to move without an astronomically powerful engine. It'd be pretty hard to see the races happening too. E=mc^2 and all...

[barnettracing]

Originally Posted by luke g28

Genuinly curious here.

What is the difference in max cornering speed (at a set radius) for a 500kg car with 100kg downforce and a 600kg car with 0kg downforce?

To my mind the loads experienced by the tyre are the same in both situations?

Hypothetically, downforce acts as an exponential. Therefore, the arbitrary figure of 100kg downforce can be considered as dMax. dMax is the level of downforce produced at vMax (maximum velocity). Therefore, whilst accelerating the downforce of the car would be less, meaning that the total weight (not mass) of the car would be less than 600kg (I know this figure is actually a mass, not a weight). Because F=ma, a car with less F (weight) will have an effective lower mass. This will cause it to accelerate faster if both engines produced the same power.

The lighter car with downforce will therefore be able to accelerate both laterally and longitudinally than the heavier car without downforce. It is this principle that makes a 500kg FRenault faster than a 1300kg GT car.

[luke g28]

Originally Posted by Adam43

I they have the same grip then the 500kg car will corner quicker as the tyres only have to change the direction of a smaller mass.

F=ma. The F is the same by definition of your example. The m is lower for the 500kg car so the a, the rate of change of velocity, is higher.

I dont think it is that simple as you have ignored any contribution from downforce.

Another example to show my meaning, this time two 500kg cars, one with 100kg downforce and the other with 0kg. Using the same F=ma logic the acceleration would be the same for both cars.

I would suggest that F must increase, by applying more vertical load to the tyres, you achieve more max grip from them. This is why squat can aid acceleration.

For overall simplification I would suggest that the original 500kg car makes its 100kg downforce at its max cornering speed. Simplistic I know but it is very easy to over complicate.

[Dave Brand]

Originally Posted by barnettracing

Therefore, the arbitrary figure of 100kg downforce can be considered as dMax. dMax is the level of downforce produced at vMax (maximum velocity). Therefore, whilst accelerating the downforce of the car would be less, meaning that the total weight (not mass) of the car would be less than 600kg (I know this figure is actually a mass, not a weight). Because F=ma, a car with less F (weight) will have an effective lower mass. This will cause it to accelerate faster if both engines produced the same power.

Downforce is just what it says, a force, so it doesn't have any effect on the mass/weight of the vehicle, so it has no direct effect on acceleration. There will, however, be two factors which will have some effect. Firstly, any aerofoil produces both lift & drag, so the drag component will add to the total drag; secondly, increased tyre loading will increase rolling resistance. Without any data I don't know just how significant these effects will be - negligible, no doubt, at low speeds.

Originally Posted by luke g28

I dont think it is that simple as you have ignored any contribution from downforce.

He did say "if they have the same grip", which allows for the effect of downforce.

Simplistic I know but it is very easy to over complicate.

It's also very easy to over-simplify. It's a very complicated subject; as with any complicated subject it can be broken down into simple components, but the complex manner in which those components interact means that considering them in isolation doesn't give a true picture of what's happening.

[alc]

Originally Posted by luke g28

Genuinly curious here.

What is the difference in max cornering speed (at a set radius) for a 500kg car with 100kg downforce and a 600kg car with 0kg downforce?

To my mind the loads experienced by the tyre are the same in both situations?

To a first approximation, the 500kg car will be about 9.5% faster. (square root of 600/500)

[luke g28]

Originally Posted by alc

To a first approximation, the 500kg car will be about 9.5% faster. (square root of 600/500)

Please expand on your logic

[barnettracing]

Originally Posted by Dave Brand

Downforce is just what it says, a force, so it doesn't have any effect on the mass/weight of the vehicle, so it has no direct effect on acceleration. There will, however, be two factors which will have some effect. Firstly, any aerofoil produces both lift & drag, so the drag component will add to the total drag; secondly, increased tyre loading will increase rolling resistance. Without any data I don't know just how significant these effects will be - negligible, no doubt, at low speeds.

Drag is also a force, hence my reasoning that downforce (which does have an effect on weight, but not mass) would have an effect on acceleration. My physics is a bit rusty and I'm pretty sure that I went horribly wrong in the middle of my reasoning.

[Adam43]

Originally Posted by luke g28

I dont think it is that simple as you have ignored any contribution from downforce.

The consideration of downforce was a major part of my reply.

I made an assumptions about the example given. The 100kg (or 1000N) of downforce was at the particular corner in question. My answer differs from barnettracing two posts later as this user assumed the downforce was a maximum downforce.

Another example to show my meaning, this time two 500kg cars, one with 100kg downforce and the other with 0kg. Using the same F=ma logic the acceleration would be the same for both cars.

I don't see how you get the acceleration being the same in this example. m is the same for both (by your definition 500kg). If you claim a is the same for both too then F has to be the same for both too. This can't be the case as the downforce will give one car more grip.

I would suggest that F must increase, by applying more vertical load to the tyres, you achieve more max grip from them. This is why squat can aid acceleration.

Yes. F increases due to the downforce. In your second example the car's m = 500kg in both, so a must be higher for the downforce car.

In the first example, the veritcal load in the example is the same for the downforce car (500+100) and the non downforce car (600). I thought keeping the vertical load/grip the same was the point of the example you gave?

For overall simplification I would suggest that the original 500kg car makes its 100kg downforce at its max cornering speed. Simplistic I know but it is very easy to over complicate.

That is what I did!

I'm sure you can't be, but the 100kg of downforce can't be considered as m. Said just in case.

Also for clarification we should just be considering acceleration and force as vectors. Acceleration is the rate of change of velocity. In this case it is the change of direction, not magnitude of velocity. Again said just in case.

Originally Posted by Dave Brand

... There will, however, be two factors which will have some effect. Firstly, any aerofoil produces both lift & drag, so the drag component will add to the total drag; secondly, increased tyre loading will increase rolling resistance. Without any data I don't know just how significant these effects will be - negligible, no doubt, at low speeds...

I suspect the tyre loading/resistence part ruins a lot of this simple model.

[Adam43]

As a random comment I wouldn't really describe F=ma as "logic" more a law of physics. Newton's second law of motion.

[Dave Brand]

Originally Posted by barnettracing

Drag is also a force, hence my reasoning that downforce (which does have an effect on weight, but not mass) would have an effect on acceleration.

Downforce doesn't affect weight.

A simple analogy:

Put a 1 kg bag of sugar on your kitchen scales; the scales will show a weight of 1kg. Now press down on the bag of sugar until the scales indicate 1.5kg. Now how much does the bag of sugar weigh? The scales are actually adding two forces - the force exerted by the mass of the bag under the influence of gravity, & the force exerted by your downward pressure.

Maybe a little bit pedantic, but downforce should be quoted in Newtons, not Kilograms - that would actually remove a lot of the confusion.

[Adam43]

Yes, while using kg for forces is often done it doesn't aid understanding.

Good analogy about the scales measuring the total force.

I am quite enjoying this conversation, so while we are at it. I would consider 'weight' a force. It is the force of a mass caused by a gravitational field. Ie the weight of an object is less on the Moon than on the Earth, but the mass of the object is the same.

Of course downforce does not add weight!

[barnettracing]

Originally Posted by Dave Brand

Downforce doesn't affect weight.

A simple analogy:

Put a 1 kg bag of sugar on your kitchen scales; the scales will show a weight of 1kg. Now press down on the bag of sugar until the scales indicate 1.5kg. Now how much does the bag of sugar weigh? The scales are actually adding two forces - the force exerted by the mass of the bag under the influence of gravity, & the force exerted by your downward pressure.

Maybe a little bit pedantic, but downforce should be quoted in Newtons, not Kilograms - that would actually remove a lot of the confusion.

Okay, downforce won't affect the weight (only a change in gravitational acceleration will be able to do this). However, it will affect the total vertical force vector that said object experiences. That is why a car with downforce has more grip. If a car has a mass of 500kg it has a weight of c.5000N (rounding gravitational acceleration up to 10m/s^2). If it then created downforce equivalent to the weight of 100kg that would add an extra c.1000N of downward force, pushing the car into the road. This extra 1000N would only be present when the car is moving though.

Therefore, if you measured the weight of the car when at vMax it would weigh more, but it wouldn't have an increased mass (ignoring the minute increase caused by its extra kE). Because it would weigh less than the 600kg car, it would be able to accelerate faster for the same amount of force provided (engine power) and it would also be able to change direction quicker. (I know I'm not really arguing with you now David). However, the extra downward force created by the wings would provide the car with even more 'grip' as it is effectively being squashed into the tarmac.

For this reason, the 500kg car with '100kg' downforce will be quicker than the 600kg car. It will accelerate (and decelerate) faster and will be able to change direction quicker. Furthermore, the faster it goes, the more downforce it generates, enabling it to go faster, enabling more downforce etc. At this point, the limiting factor becomes the force that the tyres are able to create through their chemical interaction with the tarmac.

Again, this is all off the top of my head, but I believe my reasoning is less flawed than last night.

And yes, forces should be in Newtons (N) rather than kilograms (kg).

[Adam43]

Look at us all trying to say the same thing in different ways!

On the go quicker, more downforce, means you can go quicker, more downforce, means...
I don't think this ever over rewards. For example I don't think there is ever a situation where a corner isn't possible at 100mph, but is possible at 110mph! Don't tell Gilles that though

[luke g28]

Good discussion.

Regarding earlier posts I think I got confused as everybody is suggesting different meanings for "F"

Any excuse to post this



When you resolve all the vertical forces it doesnt matter whether the 600kg (or 6,000N if you prefer) comes from mass or downforce, the vertical loads on to the tyres will all be the same. Therefore the friction generated by the tyres will be the same.

If all the forces are the same then the car is going at the same speed.

Using the earlier reference to pushing down on a sugar bag, I dont see why it matters whether you add extra sugar to the bag or push down on it, as long as the vertical load sums to the same figure, it will require the same force to push it along the floor.

I feel like I am missing something obvious because nobody else agrees

[Adam43]

Originally Posted by luke g28

When you resolve all the vertical forces it doesnt matter whether the 600kg (or 6,000N if you prefer) comes from mass or downforce, the vertical loads on to the tyres will all be the same. Therefore the friction generated by the tyres will be the same.

If all the forces are the same then the car is going at the same speed.

I suspect the problem here is the concept around speed, velocity and acceleration. Acceleration doesn't just mean going quicker in a straight line. Changing direction is also a form of acceleration. The faster you are travelling the more acceleration (and force) is needed to change direction. That is a clunky sentence, but I hope it gets my point across.

The force is the same. Yes.
The mass is lower for the downforce car in this example. 500kg v 600kg.
So the change of direction is quicker for the lower mass car. The rate of change of direction is the acceleration. It can have a higher corner speed (the magnitude of velocity) as it changes direction quicker.
500xa1=F1=F2=600xa2 therefore a1>a2
(Sorry can't do proper subscripts)

Cool old diagram

[miatanut]

Originally Posted by Adam43

I don't think this ever over rewards. For example I don't think there is ever a situation where a corner isn't possible at 100mph, but is possible at 110mph! Don't tell Gilles that though

I'm not at all sure that is true. I've heard of vintage racers driving aero downforce cars that saying there is a zone where a car feels very uncomfortable on a turn but taking it faster it felt more planted. It's a situation that comes up on high speed sweepers.

It may also be that vintage racers, and their crews, don't have the right height, rake, etc. right, and a car property set up by a professional team wouldn't experience that.

Anybody know?

[wnut]

Once you have figured out your downforce and the ability of the tyres to resist sideways motion i.e. Centripetal Force

The magnitude of the centripetal force on an object of mass m moving at tangential speed v along a path with radius of curvature r is:[5]
where is the centripetal acceleration. The direction of the force is toward the center of the circle in which the object is moving, or the osculating circle, the circle that best fits the local path of the object, if the path is not circular.[6] The speed in the formula is squared, so twice the speed needs four times the force. The inverse relationship with the radius of curvature shows that half the radial distance requires twice the force. This force is also sometimes written in terms of the angular velocity ω of the object about the center of the circle:

from

http://en.wikipedia.org/wiki/Centripetal_force
(Good instructive article)

Downforce generates grip, but does not add to mass, so all the grip is available to overcome the forces generated by a smaller mass in the above equation.

[luke g28]

I see now

A plane has so much lift that it flies but the kinetic energy is a property of the mass of the object so it still takes force to accelerate it.

duh.

lol.

[Marbot]

So, can lap times actually be maintained with half the downforce?

It seems as though it's not an easy question to answer. Not even if you only apply it to the current 750 bhp F1 cars. There's also the question of refueling and tyre changes, which could have a significant effect on an F1 car being able to 'maintain' lap times over the course of a race distance.

[IndyDonut]

Originally Posted by Marbot

So, can lap times actually be maintained with half the downforce?

It seems as though it's not an easy question to answer. Not even if you only apply it to the current 750 bhp F1 cars. There's also the question of refueling and tyre changes, which could have a significant effect on an F1 car being able to 'maintain' lap times over the course of a race distance.

Give em fatter tires, more mechanical grip, less weight (Keep strenght), lower CoG, and more power. I mean, it would depend on which track, though. Monza just needs raw power. A place like Spa or Malaysia needs lots of grip.

[Oldtony]

Of interest would it be easier to achieve at a slow circuit like Monaco or a high speed circuit like Monza/
Monaco, more torque less wieght out of slow corners. Greater mechanical grip from wider tyres. Less appendages to knock off on kerbs or barriers.
Monza, More power, less drag to achieve higher terminal velocity.

[wnut]

Originally Posted by wnut

But the power required to overcome the aerodynamic drag is given by:
Hence note that the power needed to push an object through a fluid increases as the cube of the velocity.

At the end of the day brute force and maximum downforce are king, but the challenge was to try and maintain the lap time with half the down force.

The F1 Lap record for Silverstone is 1:30 odd and the F3 lap record is 1:53. So the question I guess would be what would a 50 kg underweight F3 (F3 min weight 550Kg) with 650 bhp instead of 200 bhp run?
Also better gearbox, tyres and brakes than the F3s.

What do you reckon that would get down to?

Your post above gets us back to here Oldtony.

Still a very interesting question in my book.

[Marbot]

Originally Posted by Oldtony

Of interest would it be easier to achieve at a slow circuit like Monaco or a high speed circuit like Monza/
Monaco, more torque less wieght out of slow corners. Greater mechanical grip from wider tyres. Less appendages to knock off on kerbs or barriers.
Monza, More power, less drag to achieve higher terminal velocity.

If a track just had two very long straights with a hairpin at both ends with which to join them together, then it could be that no downforce might be the best answer. It certainly wouldn't be the best answer for Monaco.

It was interesting to note that the HRT cars, despite having engines with competitive bhp figures, were pretty much hopeless everywhere. Having not that much less downforce than their contemporaries, they suffered from every handling flaw under the Sun, whether it be Monaco or Monza. Brake problems and 'locking up', through lack of downforce going into the corners, was also a big issue for them.

[Oldtony]

Originally Posted by Marbot

If a track just had two very long straights with a hairpin at both ends with which to join them together, then it could be that no downforce might be the best answer.

Bring back Avus

[Marbot]

Originally Posted by wnut

Still a very interesting question in my book.

Those 23 seconds to find don't seem a lot. But what is the downforce of an F3 car compared to an F1 car? Are F3 cars also considered to be too reliant on aero for grip? I don't know.

A 650 bhp, lightened F3 car with half of the downforce of a current F1 car. Sounds interesting.

Later versions of the 4 cylinder turbocharged 'Offy' Indy car engines produced 800 bhp. One of those in an F3 car would be interesting just by itself. Also very interesting to drive, I shouldn't wonder!