Hello everyone, this is my first post in the Technical Forum.
At deportes2000.com we are having a discussion about weight and downforce.
Some Colombians say that if the car has more weight it will create more downforce but some friends and I say that it is better to have the less weight possible so the car won't have as much inertia when the car is in a corner as the car that has more weight. I say that if the inertia is bigger you have less downforce because the car wants to go straight off.
This is my theory:
More weight = more inertia = less downforce = you have to slow down in a corner.
Less weight = less inertia = more downforce = you can take the corner faster.
They also say that static weight has to do with the amount of downforce that the car would have and that's why they're saying that even though a Formula One team creates a special car to run at a superspeedway the CART car would still win because of the weight of the car and their believe in more weight = more downforce which I think it's wrong (Champ cars weight is around 200 kgs more than a Formula One car).
I say that the Formula One car would win because it has a better weight distribution, less drag (cars are not as wide as Champ Cars) and a better weight/HP relation. (If they design a special Formula One to race in an oval)
What do you think about this?
Weight and downforce
Started by
MONTOYASPEED
, Aug 17 2001 20:58
10 replies to this topic
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#2
Keith Young
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Posted 18 August 2001 - 01:44
Weight shouldn't effect downforce. In a way it could because the car will sit lower on it's suspension, thus getting more ground effect. The tires will have more traction if the cars heavier, you try pulling around a 500 lb guy. But with the more weight you have worse handling in every aspect, except if you feel like careening off the circuit.
Also about the CART and F1 comparisons,downforce has little if any role in a superspeedway like Daytona, Talledega, and Indy. I agree the F1 car is much more efficient, but I'd put my money on the CART cars because they have fewer regs. For instance they can have turbos, but I think it would be kinda close.
Also about the CART and F1 comparisons,downforce has little if any role in a superspeedway like Daytona, Talledega, and Indy. I agree the F1 car is much more efficient, but I'd put my money on the CART cars because they have fewer regs. For instance they can have turbos, but I think it would be kinda close.
#3
jdowns
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Posted 18 August 2001 - 03:13
There's another thread going on this, look at http://www.atlasf1.c...&threadid=26764
Basically what you're after is acceleration (cornering is considered acceleration, only sideways). Acceleration is force divided by mass (weight). So you want more force, and less weight.
Force is the total of downforce from the wings, and the weight of the car. Weight is only the weight of the car. Tyres come in to it in that they apply the force to the road. I think tyres in performance cars would have a coefficient of friction of about 1.2. That means, if you have 1500kg's of force (downforce + weight), then the tyres would give 1500*1.2 = 1800 kg's of sideways force. If your car weighs 600kgs then you'd have 3 g's of sideways acceleration.
If you have 1000 kg's of downforce, and a 1000kg car (and to keep it simple, tyres with a 1.0 Cf), then you have 2000kg's of force against the road, / 1000 kg's for the car, = 2g's. If you keep the 1000kg's of downforce, but reduce the car weight to 500kg's, then you have 1500 / 500 = 3g's of possible sideways acceleration.
Weight doesn't cause downforce, but you add the car's weight to it's downforce, but then divide by it's weight - so weight is a bad thing for performance ;)
Jordan.
Basically what you're after is acceleration (cornering is considered acceleration, only sideways). Acceleration is force divided by mass (weight). So you want more force, and less weight.
Force is the total of downforce from the wings, and the weight of the car. Weight is only the weight of the car. Tyres come in to it in that they apply the force to the road. I think tyres in performance cars would have a coefficient of friction of about 1.2. That means, if you have 1500kg's of force (downforce + weight), then the tyres would give 1500*1.2 = 1800 kg's of sideways force. If your car weighs 600kgs then you'd have 3 g's of sideways acceleration.
If you have 1000 kg's of downforce, and a 1000kg car (and to keep it simple, tyres with a 1.0 Cf), then you have 2000kg's of force against the road, / 1000 kg's for the car, = 2g's. If you keep the 1000kg's of downforce, but reduce the car weight to 500kg's, then you have 1500 / 500 = 3g's of possible sideways acceleration.
Weight doesn't cause downforce, but you add the car's weight to it's downforce, but then divide by it's weight - so weight is a bad thing for performance ;)
Jordan.
#4
MattPete
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Posted 18 August 2001 - 03:42
Quote
Originally posted by rough_wood
Weight shouldn't effect downforce.
The more weight the more downforce there is. In this instance, weight is the downforce created by the interaction between mass and gravity
. Of course, increasing downforce by adding mass is a big no-no.So, yes, technically adding weight adds downforce, but the tradeoff from the extra mass wipes-out any added benefit (and then some!).
Of coure, this has nothing at all to do with aerodynamically derived downforce.
#5
MattPete
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Posted 18 August 2001 - 03:45
Quote
Originally posted by rough_wood
Also about the CART and F1 comparisons,downforce has little if any role in a superspeedway like Daytona, Talledega, and Indy.
Indy's a relatively flat oval. Take away the wings and tunnels, and I'd bet you'd see lap times drop by 20 mph.
#6
MONTOYASPEED
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Posted 18 August 2001 - 03:53
So basically by adding weight we would be adding downforce to the car when it is static but we would be adding more inertia and the car would have to take the corner slower, right?
By reading all you guys are saying I think I was right, aren't I?
By reading all you guys are saying I think I was right, aren't I?
#7
MattPete
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Posted 18 August 2001 - 04:01
Quote
Originally posted by MONTOYASPEED
So basically by adding weight we would be adding downforce to the car when it is static but we would be adding more inertia and the car would have to take the corner slower, right?
By reading all you guys are saying I think I was right, aren't I?
Yup, pretty much, but I would change your equations just a tad:
Quote
This is my theory:
More weight = more inertia = less downforce = you have to slow down in a corner.
Less weight = less inertia = more downforce = you can take the corner faster.
to this:
Quote
This is my theory:
More weight -> more inertia + more downforce = you have to slow down in a corner.
Less weight -> less inertia + less downforce = you can take the corner faster.
In other words, the extra inertia is so devastating that it completely overcomes the benefits of the extra downforce...and then some!
#8
jdowns
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Posted 18 August 2001 - 04:02
MONTOYASPEED,
Yes.
For simplicity's sake, I think most commentators and technical people seperate the 'downward force' into downforce, which is purely from the aero parts, which is something that can be adjusted in racing cars, and the force down due to mass/gravity, which can't be changed (in most racing formulae). Yes, inertia is caused by mass, so adding mass to increase downward force is counter productive.
I guess we're just arguing semantics (English). The idea perfomance car would have tons of downforce (that's just the force from the aero, wings, ets.) and no weight (hence no inertia).
Yes.
For simplicity's sake, I think most commentators and technical people seperate the 'downward force' into downforce, which is purely from the aero parts, which is something that can be adjusted in racing cars, and the force down due to mass/gravity, which can't be changed (in most racing formulae). Yes, inertia is caused by mass, so adding mass to increase downward force is counter productive.
I guess we're just arguing semantics (English). The idea perfomance car would have tons of downforce (that's just the force from the aero, wings, ets.) and no weight (hence no inertia).
#9
MONTOYASPEED
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Posted 18 August 2001 - 04:07
Thanks a lot guys!!!!
#10
Ben
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Posted 19 August 2001 - 11:07
An interesting point I was reminded of about oval cornering is the fact that the corners are largely power limited rather than traction limited.
You can actually lap quicker in some cases by reducing downforce.
This is because cornering saps huge amounts of power in induced drag (cornering force multiplied by the sin of the slip angle) increasing downforce obviously increases cornering force but it also increases induced drag and at a certain point the power absorbed by the induced drag leaves some lateral force that cannot be used, because there's no power to push the car quicker.
In this case you will lap quicker by reducing the downforce, cornering at the same speed and being quicker on the straights.
It's counter intuitive in many ways but interesting I think.
Ben
You can actually lap quicker in some cases by reducing downforce.
This is because cornering saps huge amounts of power in induced drag (cornering force multiplied by the sin of the slip angle) increasing downforce obviously increases cornering force but it also increases induced drag and at a certain point the power absorbed by the induced drag leaves some lateral force that cannot be used, because there's no power to push the car quicker.
In this case you will lap quicker by reducing the downforce, cornering at the same speed and being quicker on the straights.
It's counter intuitive in many ways but interesting I think.
Ben
#11
olschak
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Posted 23 August 2001 - 09:52
maybe one I'll sit down and work it all out for a one-wheeler... until then:
let's drive a straight constant speed first.( we're approaching start-finish-line with a comfortable lead ) air drag would slow you down unless you hit the throttle and keep speed up by using tire-traction alone. this does not depend on the weight( I'll use the word weight for mass because the situation is clear) of the car from the traction side. The fuel and tire consumption however will be higher for a heavier car.
Move your arm out, adjust your hand and you feel the downforce if you do it right. ( I try upforce sometime with my hand at 150mph with the t-tops out, it really pulls my arm up, very funny feeling)
Now there are two things happening: with the downforce from your hand you increase the traction limit because the downforce adds to the force of the car's wheight on the tires and on the other hand you need more of the traction to maintain speed because you do have more air drag with your hand out.
You are trading more traction needed for more traction available. The question is do you have more traction to spare? The downforce thing is only dependent on your speed ( given a specific aerodynamic setup you do not change during the drive ), the traction needed depends on speed and the car's weight. The idea is that at high speeds you win traction to spare provided the car is not too heavy.
What can you do with the traction anyway. The point is that the tires will consume the traction available with combined braking and cornering forces when going into a corner. this means if you brake to the limit you won't have any more steering and if you give it all the steering you can cornering at constant speed you won't have any brakes.
this is where the aerodynamics come in and give you more traction that enables you to brake hard and move the steering wheel at the same time.
the other benfit of downforce is more subtle. the downforce can be massive as compared to the car's weight. This way it changes the suspension of the car by pushing it lower into the springs.
let's drive a straight constant speed first.( we're approaching start-finish-line with a comfortable lead ) air drag would slow you down unless you hit the throttle and keep speed up by using tire-traction alone. this does not depend on the weight( I'll use the word weight for mass because the situation is clear) of the car from the traction side. The fuel and tire consumption however will be higher for a heavier car.
Move your arm out, adjust your hand and you feel the downforce if you do it right. ( I try upforce sometime with my hand at 150mph with the t-tops out, it really pulls my arm up, very funny feeling)
Now there are two things happening: with the downforce from your hand you increase the traction limit because the downforce adds to the force of the car's wheight on the tires and on the other hand you need more of the traction to maintain speed because you do have more air drag with your hand out.
You are trading more traction needed for more traction available. The question is do you have more traction to spare? The downforce thing is only dependent on your speed ( given a specific aerodynamic setup you do not change during the drive ), the traction needed depends on speed and the car's weight. The idea is that at high speeds you win traction to spare provided the car is not too heavy.
What can you do with the traction anyway. The point is that the tires will consume the traction available with combined braking and cornering forces when going into a corner. this means if you brake to the limit you won't have any more steering and if you give it all the steering you can cornering at constant speed you won't have any brakes.
this is where the aerodynamics come in and give you more traction that enables you to brake hard and move the steering wheel at the same time.
the other benfit of downforce is more subtle. the downforce can be massive as compared to the car's weight. This way it changes the suspension of the car by pushing it lower into the springs.
