Actually i think thats a mattress.

But yeah, cheese with wheels on.

Quote from richy :

Actually i think thats a mattress.

But yeah, cheese with wheels on.

If the front came up even a tiny bit (which it would due to massive drag and weight at the rear) it would just flip over at decent speeds really. When think about aero, don't just think about the physical air hitting the surface of something, but you have to think about how the air around the shape will act and what effects it will have on the object.

Quote from richy :

Just technically the term downforce is incorrect and shouldnt be used.

What planet are you on? Lift is up. Less lift is real, as it's just less up force. Downforce is real and perfectly acceptable, and is used to describe when a vehicle has a downward aerodynamic force. It's simple. Yes, they might have a wing, or a £30 splitter, that might give 6N of downforce at 150mph (and it is correct to call that force downforce, as you are considering the influence of one bit). But when you look at the car as a whole it will [probably] still suffer from lift.

It's like talking to a child. A dim one. How old are you?

5 weeks older than you, apparentely. He does admit to being a white van driver though, so what do you expect.

Awesome. You guys actually made dynamics and fluid dynamics more confusing than my professors did.

Good job!!


Alls I know is that to make a street car work better in the wind, you need to restrict its flow under the car, as well as provide an efficient way to evacuate what does manage to get under there. If you can reduce the pressure under the car, you reduce lift.

As far as power and torque, just get a bigger cam. If you aren't blessed with cubic inches, low end torque is going to be hard to come by. Your only hope it to try to maintain manifold pressure as rpms increase. With enough air, you can keep torque from falling off too fast. At some point though, you still need to shift.

More food for thought: http://g-speed.com/pbh/torque-and-hp.html

Quote from Ball Bearing Turbo :

That's not very nice :sadbanana:



Actually, it's very simplified but not as stupid as first glance would indicate. Power IS directly related to top speed, actually, since it's really just an indication of torque delivery at higher rpms. All other things being equal, a higher HP engine will push the same car to a higher top speed - so that's not really "stupid" to say.

Also, to say torque affects acceleration is also not stupid, unless you think F=MA (or A=F/M) is stupid, and most people don't think that. For a given set of gears, the greatest acceleration numbers occur at the engine's peak torque area. So, that's not really stupid either is it? Incomplete, yes, but not stupid.

Since you have such a great understanding of this simple topic (by your own profession), please answer me in detail the following question:

The definition of 1HP = 550ft/lb per sec
Take a power curve, and plot the HP values at various places on the curve. Of course, the most amount of work is being done at the horsepower peak. Say the engine makes 300hp at 6000 rpm, that's 165,000 ft/lb/s of work being done, whereas for example at 4000rpm, the engine makes peak torque but only say 270hp which is 148,500 ft/lb/s. So we can see that more work is being done at peak HP, BUT, the problem is that max wheel torque is experienced at 4000rpm, where the engine's torque peaks. This is all, of course, in the context of a single gear ratio.

Please explain why this seeming dichotomy exists, and specifically why work is a useless concept in this situation, in terms of how fast the car would accelerate. Since it's so simple, and everyone else is a moron, and you hate us, please oblige with the all encompassing truth about the matter.

damnit

I'm always too late to come in and call people stupid and prove them wrong with solid proof and math by my side.

Torque is simply twisting force, and the only pure number coming from an engine. All other ratings are calculated from torque. When someone gives you an indian burn you don't sit there and calculate how badly it hurts over time; you just know that the harder they twist, the more it hurts.

Onto the downforce vs lift debate.

Downforce is rated as the amount of force beyond -weight at a certain speed.

If a car weighing 1000 pounds is going 500 miles per hour (your guys' cars were boring as hell), and produced 1000 pounds of lift. If you add a wing that makes it only produce 500 pounds of lift at 500 miles per hour, you are not able to say it produces 500 pounds of downforce (technically). If that were the case, when they rated a car that HAD downforce, they would have to figure out how much lift the car would have at a certain speed, and then add that to the amount of downforce it makes.

Say adding 3 wings makes the car squish down to the ground with 500 pounds of weight at 500 mph. If you all are trying to argue that any force that negates lift is downforce, then technically you would have to say that the car is producing 1500 pounds of downforce because at 500 mph with no wings, it produced 1000 pounds of lift.

Not only is that bulky to figure out, but impossible in real life situations. You can't just remove all anti-lift devices off of an f1 car and tell it to go drive 200 mph so they can figure out how much lift it produces.

Its also impossible to wind tunnel a wing and say it produces X amounts of "downforce" because it will be different on every car.

I tried to explain it more simply than I read it in the other posts, although I had no problem understanding the syntax that is the most correct way of talking about it. Before reading this thread I would have considered any negative lift downforce as well, but now i can be elitist and say anti-lift devices and such

Nice thread,very interesting to read.

About the downforce on normal cars,i wonder if someone can remember the problem of the first AudiTT version.

Audi corrected that with a really small wing and it worked well.

Then i assume it should be usefull on some bad designed cars?But it is such a small wing,i can t understand how it could resolve the complete problem.I will google this a bit and see if they are some good stuff to read about that.

It's not a wing, but a spoiler, and was designed to keep the flow attached further along the car, thus reducing lift at the rear (relative to the front).

Unfortunately it didn't make an ugly push-me-pull-you car attractive.

Does it produce lift or downforce?

is that a spoiler or a wing?

Looks like it could be a manufacturer badge (I'll use it if I ever start one ), so I'd say it produces drag, but no appreciable vertical component.

It would also probably whistle when air passed through it. And would be banned for hurting pedestrians stupid enough to walk into roads without looking. As if a car without such a badge might just ruffle their hair.

yeah its the Maybach badge for sure

Quote from tristancliffe :

It's not a wing, but a spoiler, and was designed to keep the flow attached further along the car, thus reducing lift at the rear (relative to the front).

Sorry in our country a spoiler means something else.

I agree with your answer but that s pure logic,my point was more about the size from the wing and how it can affect so much the car even more since it is only a road car.

It's basic aerodynamics. Keep the flow attached (vaguely laminar, higher pressure that turbulent) and you'll decrease lift. A wing that size wouldn't work - it doesn't even have airflow both sides of it.

What do you call a spoiler? If it's wing, then what do you call a wing?

maybe they profit and loss example can help :

When you start a business, you have to invest some money in it. That money you lose. It's your loss. Later when you start selling your product, you start to get some money back until eventually you will have gotten back your investment and after that you start to make a profit.

Now imagine lift is loss and downforce is profit.

Your normal road car produces lift (loss). You can decrease that a bit by modifying the road car with bits that produce downforce (profit).

That's like investing 1000 euro and earning back 250 euro. Have you made a profit at that point? No you are still at a loss

Your car produces lift - you can decrease it a bit, but it'll still produce lift, not downforce.

Now of course in the world of Car Marketing, they will not say "did you know this car produces less lift that it's rival?" That's stupid. They'll use the cooler terms that you hear in F1 - downforce!

Talk to car engineers and you will probably hear something else.

Tristan is more interested in looking at these things from an engineers POV. I think Richy is more the marketing type

edit - oh wow, i replied at page 3 - i think i missed 2 :P Sorry if my post is outdated heh

Quote from Victor :

maybe they profit and loss example can help :

When you start a business, you have to invest some money in it. That money you lose. It's your loss. Later when you start selling your product, you start to get some money back until eventually you will have gotten back your investment and after that you start to make a profit.

Now imagine lift is loss and downforce is profit.

Your normal road car produces lift (loss). You can decrease that a bit by modifying the road car with bits that produce downforce (profit).

That's like investing 1000 euro and earning back 250 euro. Have you made a profit at that point? No you are still at a loss

Your car produces lift - you can decrease it a bit, but it'll still produce lift, not downforce.

Now of course in the world of Car Marketing, they will not say "did you know this car produces less lift that it's rival?" That's stupid. They'll use the cooler terms that you hear in F1 - downforce!

Talk to car engineers and you will probably hear something else.

Tristan is more interested in looking at these things from an engineers POV. I think Richy is more the marketing type

edit - oh wow, i replied at page 3 - i think i missed 2 :P Sorry if my post is outdated heh

Still a bit too simple... You have two ways of decreasing your loss (lift): One selling more (adding downforce), the other optimizing your costs (optimizing airflow, adding spoilers = no downforce involved)...

Quote from Victor :

edit - oh wow, i replied at page 3 - i think i missed 2 :P Sorry if my post is outdated heh

Noob! Bet you didn't even search!

Well actually torque is important and different from horsepower.A 6l V8 will accelerate from let's say 200-250 km/h faster then a 2l v-tech or a 1.2l rotary engine and it will have a bigger top speed because of the superior torque. That's why some slakers prefer to have they're daily driven cars powered by a diesel engine instead of a petrol engine. Because you don't need to change gears so often because of the high torque that it has.Of course some people buy diesel cars because they prefer economy to power and speed, the slaker thing was just a comparison to show high torque advantage.

A question I thought of a long time ago and haven't satisfied myself with an answer. Does a 20 tonne lorry have more grip than an F1 car? The grip comes from the weight of the vehicle (static mass + whatever lift/downforce is created) in combination with the properties of the tyres and the suspension. Current F1 cars will produce a maximum of around 2 tonnes of downforce at 220mph, so their total weight will be about 2.5 tonnes, give or take a hundred kilos. The 20 tonne lorry won't have nearly as good tyres (obviously), but it does have a lot more weight pushing them into the ground. Now...obviously I'm not suggesting that a truck is quicker than the F1 car, but does it have more grip?

Quote from amp88 :

A question I thought of a long time ago and haven't satisfied myself with an answer. Does a 20 tonne lorry have more grip than an F1 car? The grip comes from the weight of the vehicle (static mass + whatever lift/downforce is created) in combination with the properties of the tyres and the suspension. Current F1 cars will produce a maximum of around 2 tonnes of downforce at 220mph, so their total weight will be about 2.5 tonnes, give or take a hundred kilos. The 20 tonne lorry won't have nearly as good tyres (obviously), but it does have a lot more weight pushing them into the ground. Now...obviously I'm not suggesting that a truck is quicker than the F1 car, but does it have more grip?

Depends on what you want 'grip' to mean. if you want to define it as the maximum lateral g-forces that the vehicle can produce around a race track. F1 wins. This is considering the idea that grip involves the geometry and physical size of the vehicles. If you calculate the max frictional force in a stationary position, the truck wins. Consider that at rest, the frictional force required to begin movement will be the weight of the vehicle times the coefficient of friction for the tires.

I think that you are actually thinking about the scientific definition of traction/grip/friction, and that is good. The answer is a matter symantics.

Quote from AndroidXP :

Of course it does. If you look at an airplane wing and a car from the side, they have the same basic form. Air can pass unhindered below, but has to take a detour around the top, creating a low pressure area on top which pushes the car/wing upwards.

Thankfully the shape of a car is far from an ideal wing and the amount of air that goes below it is limited, so the car doesn't take off at 60mph.

This is also the reason why F1 cars change from turned-down noses to turned-up noses a few years ago, to stop the body of the car acting so much like an aerofoil. If you look at modern F1 cars the body is shaped so it tends to 'cut' the air to either side instead of above and below.

'Ricer' wings do create a tiny bit of downforce at normal roads speeds, but not so much that you'd notive. I imagine if you got one on a track and was ablt to take it up to 130mph or so you night notice the effect, however as they are designed more for looks than actual aerodynamics, any extra grip would be offset by the extra drag.

Quote from amp88 :

A question I thought of a long time ago and haven't satisfied myself with an answer. Does a 20 tonne lorry have more grip than an F1 car? The grip comes from the weight of the vehicle (static mass + whatever lift/downforce is created) in combination with the properties of the tyres and the suspension. Current F1 cars will produce a maximum of around 2 tonnes of downforce at 220mph, so their total weight will be about 2.5 tonnes, give or take a hundred kilos. The 20 tonne lorry won't have nearly as good tyres (obviously), but it does have a lot more weight pushing them into the ground. Now...obviously I'm not suggesting that a truck is quicker than the F1 car, but does it have more grip?

It's an effect called load sensitivity. A tyre has a higher coefficient of friction (for want of a more accurate term) when the load approaches zero. As you increase load, the CF falls off. So whilst more load + lower CF = more grip, the load (being a bigger vehicle) means that cornering abilites are lower.

A light car uses a high CF, and can generate a high cornering force despite 'low grip'.

A downforce car (e.g. F1) has the high grip (high tyre loads from aero but a lower CF), but doesn't have much mass to go round corners = F1 wins.

It's a tad more complicated than that, but if you can understand what I wrote you know enough for now You've just got to differentiate between grip and CF, and consider where the load is coming from.

With regards to the F1 car vs the truck; say the truck had a downward force of 10000N and the F1 car (including downforce) had the same net force of 10000N. In a straight line they would be exerting the same force downwards, but at a corner the greater mass of the truck acts sideways, the F1 car has a much smaller sideways force due to its smaller mass.

For Richy; imagine a wing ON IT'S OWN moving through the air at 100mph, say that wing generated a downwards force of 100N. That 100N would be downforce.

Now imagine a car, when it moves at 100mph say it generates an upwards force of 1000N. That 1000N is lift.

Now attach the wing to the car. The wing is acting downwards with 100N, but the car is acting upwards with 1000N.

This gives a total force of 900N LIFT.


Now imagine the wing generates a downwards force of 1000N and the car generates 800N of upwards force.

The total force is 200N DOWNFORCE

Quote from spookthehamster :

With regards to the F1 car vs the truck; say the truck had a downward force of 10000N and the F1 car (including downforce) had the same net force of 10000N. In a straight line they would be exerting the same force downwards, but at a corner the greater mass of the truck acts sideways, the F1 car has a much smaller sideways force due to its smaller mass.

Same point that I made, from a different point of view, and ultimately a much better way of explaining it, without confusing the issue with tyre load sensitivity stuff. I'm rubbish at explaining things to people - always have and always will be. It's why I'm not a teacher. Unfortunately, it's also why a lot of teachers shouldn't be teachers

For another example:

You can ignore coefficients of friction (and therefore tyre dimension, number of tyres, and tyre load sensitivity) and working simply from lateral gs for the purposes of this question (or longitudinal, it doesn't matter, so long as you are consistent).

Without downforce (or just when moving very slowly), your F1 car is going to pull ~1.5g in the bends. It has a mass of 600kg, so on earth your total grip will be 600*9.81*1.5 = ~8800N.

With downforce, and travelling ~200mph, it can now pull ~4.5g in the bends (despite a reduced coefficient of friction, but we'll not go into that now). Thus using the same formula, the total grip now becomes 600*9.81*4.5 = ~26500N. Which is a lot. But is it more than a truck?

Trucks don't have (appreciable) lift or downforce, I'd say could only pull 0.6g in the bends, but are rather massive. So that makes it 8500*9.81*0.6 = ~50000N. Twice as much as an F1 car, even at 200mph. Ergo truck wins. And that was just taking the mass of the cab. Add your trailer and 20 tonnes of payload and grip is massive.