13 replies to this topic

[Ali_G]

Now that I thnk of it at low speeds it would be better for an F1 car to be heavy as at low speeds centrafugal force is small but the overall weight of the car is just pressing it on to the track.

Could anyone therefore come up with a speed where weight does not matter to the cornering speed of an F1 car.

It would be the speed where at the forces of Centrafugal and Normal Reaction from the weight of the car minus downforce would be the same.

Niall

[TommyBoy]

I can't agree that a heavier car is better, even on slow corners, weight transference would negate any "downforce" advantage. Also you've still got to brake and then accelerate that weight.

If heavier cars were better how come it's really light cars like Westfields and Caterham's that corner quicker on track days?

[IndyIan]

Ali_G,
It is always better for a car to be lighter, because even in slow corners because more mass would increase the centripidal force more than the friction force from the tires with more mass on them. This because tires don't generate more grip at the rate that downforce is added to them. The reasons for this are hard for me to explain but if you get some race car fundementals books from the library they will show why.

[Wolf]

Mass comes into equation, but for hight speed turns (where cars get much downforce) it looses significance. The centrifugal force is proportional to weight of the car (m*v^2 /R), but the downforce produces grip (in F1 more than three times the weight of the car). So the car with more weight would have greater centifugal force pushing it out, and the same amount of grip (mu*(Fa+m*g)), where Fa>>m*g, Fa-being downforce being created by aerodynamic devices.

[Ali_G]

I was just thinking that when a car is cornering at very low speeds that the centrafugal force is tiny and that normal reaction is much much greater than it. Therefore in that case weight would be an advantage.

Niall

[blkirk]

If the cornering force is tiny, then the car is nowhere near the limit. If the car is not at the limit, it's time to get a new driver.

[PDA]

The lateral force on the tyres is directly proportional to weight. Higher weight means higher force means breakaway at lower speed. therefore, lighter is ALWAYS faster.

[Ali_G]

Ya I was just running it over in my mind there again. Yer thinking does make sense. I just though that at low speeds that Normal Reaction would be greater than Centra-Fugal.

Niall

[Xan]

When i was racing go karts with my friend, who is 20kg lighter than me (im 90kg, he is 70gk). We noticed that in fast corners, particularly one which was a little bumpy that I would be able to take the corner flat, and not lose traction, and in contrast his car was unstable and would lose traction easily.

I dont agree that lighter is always faster, particularly when the power of your car is very low and there is no downforce. In this case, maintaining cornering speed is more important than braking late and powering out.

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I will try to explain this;

F(centripital) = m V^2 / r

thats is, the centripital force is directly proportional to the mass times the square of the velocity and inversly proportional to the radius of the corner.

This centripital force is the force which is pushing the car off the track, and will cause it to break traction if V is too high.
------------------------
now, the frictional force, or grip is equal to

F (normal) = u m g

(u = frictional coefficient of rubber on road)
(m = mass of car)
(g = gravitational constant)

so if we can say that the car will skid and lose traction
when the centripital force exceeds the normal force we have...

umg = m V^2 / r

therefore mass cancels!

ug = V^2 /r
ugr = V^2
V = sqroot(ugr)

and thus in this case,
the maximum cornering speed depends only on u and r
that is, the tires, the radius of the corner.

(Tommy boy is right, exactly, the increaed centripital force does negate any grip advantage of the car)

Using this, i seem to have proven that weight dosent matter, (extra weight will create exactly enough grip to balance the increaced centripital force) if it is a closed system, and aerodynamic effects, tyre wear, and temperature can be ignored.

Now, we can say that any advantage of a lighter or heavier car must only come from other variables, such as aero, bumpy track, engine power...etc.

Maybe in the case of a go cart hitting a small bump, the heavier car will be more stable and recover its grip faster?

In the case of a road car at very high speed, you may notice the handling become "floaty" and unpredictable? (I know i have!!! in my '72 torana, which is only 1100kg). In this case a heavier car is better and more stable through a fast corner, due to the fact that at high speed, road cars in fact generate some LIFT!

This dosent mean to say that is it great to make your car as heavy as possible! since you have to brake and accelerate too! As Ali_G suggested at the start of the thread, there will indeed be an ideal weight, which not too heavy, not too light, but i think it will only apply to poorly powered go-karts and poorly powered road cars.

In the case of formula one, the lighter car will ALWAYS be better, but not because of PDA's reason, but because of the downforce being such a significant factor (as wolf explained) and the engines being so powerful.

[westendorf]

Zero.

[danut]

[QUOTE
V = sqroot(ugr)

and thus in this case,
the maximum cornering speed depends only on u and r
that is, the tires, the radius of the corner.

Well, there are a few observations to be made regarding this formula, which will show that it does not necesarily apply to racing cars.

Firstly, the equations describing motion are designed for a so called "material point" - maybe this is not the correct term in English, as I am translating it from romanian - anyway, the ideea is that in order to serve the purpose of these equations any object is considered to have its mass concentrated in one point. So as the equation is certainly valid for any point of any given mass it will not stand in real life, because it does not include the position of the center of gravity, which will affect the way weight is transfered during cornering/braking/accelerating.

Secondly, these equations describe the motion of points in vacuum, so aerodinamic behaviour of the car is also not included here.

If it the equation woul be true for the real world it would mean that through any given corner you coud pass at the same speed with different vehicles - you don't even have to try this to see it's not true.

dan

[Ali_G]

I never took into account that there are different angles of corners and other things.

Niall

[Powersteer]

I think some of you got your calculation wrong in many areas. Ciao

[goGoGene]

The word centriFUGAL makes me cringe. It is a pseudo-force, which can be used in a non-inertial referance frame. But you need to be careful not to mess up your math.

ggg