What forces work on a racing car?

NobodyImportant

Hi all, total noob question and will be no bother to you all!

Im writing an article at the moment trying to show that the best way to improve a racing car is to reduce its weight. Improving Horespower only makes it faster in a straight line, where reducing weight makes it corner faster, accelerate faster and it can brake later.

What Forces apply to a racing car?

Gravity? Inertia? Friction? What else?

Thanks a million in advance.

EL_Loco

http://www.science-of-formula1.com

Delphi91

NobodyImportant wrote: »

Hi all, total noob question and will be no bother to you all!

Im writing an article at the moment trying to show that the best way to improve a racing car is to reduce its weight. Improving Horespower only makes it faster in a straight line, where reducing weight makes it corner faster, accelerate faster and it can brake later.

What Forces apply to a racing car?

Gravity? Inertia? Friction? What else?

Thanks a million in advance.

I would suggest that you have:

1. Force forwards (due to the engine)
2. Force backwards (due to friction between car tyres and the track surface)
3. Force backwards (due to wind resistance)
4. Force downwards (due to the weight of the car + driver)
5. Force upwards (often called the normal reaction - the force provided by the surface the car is on at the time)
6. Aerodynamic downforce (acting downwards)

There may be one or two others, but the above are the basic ones (I think/hope!)

grimreaper1001

->
engines force
<-
Friction due to ground

Then you have air resistance, which you should resolve into i and j components, one will act against the engines driving force, one will act down, which is also known as downforce.

And of course, weight which is m*g.

note this is for straight line. you don't want to go into cornering.

phelixoflaherty

If you tape money onto the car. It improves aerodynamics

Fringe

Reducing the weight will reduce the friction. Friction can be calculated by F = uR where u is the coefficient of friction and R is the normal reaction which will decrease with less weight.

Professor_Fink

There are two sets of forces you need to consider here: Forwards-backwards forces and side to side forces. You want to increase forwards acceleration (and presumably top speed) while minimizing sideways motion in corners.

The engine determines the torque on the wheels, but it is the friction between the tyres and the road which determines how much of this is transfered to the road. This combined forwards force is countered by air resistance (which typically scales as v^2).

The sideways force is determined by the centrifugal force, which is m a_centrifugal, which is opposed only by friction from the tyres.

The friction from the tyres scales as mg + aerodynamic downforce. The constant will depend on where it is side to side motion or forwards motion, and will depend on tyre material, temperature and surface area.

By reducing the mass of the car, m, we reduce both side to side motion (since aerodynamic downforce is the only term not linear in m), and increase forwards acceleration (since a = F/m).

Note though, that a small change in m will not make a large difference. The best way to increase performance is actually to improve the friction with the ground. The simple way to do this is to a) use good tyres, and b) increase the surface area of the tyres. The small increase in mass will be more than countered by the ingreased grip.

So, there are a few points:
1) Better tyres improve everything. Top speed, acceleration and better cornering. for forwards motion the grip will saturate, and so the top speed can only be pushed towards a limit set by the engine power (although you will never reach it). The acceleration is equally limited. You can push towards a maximum acceleration set by the engine (although you will never reach it). However, better tyres always improve cornering.

2) Less mass improves acceleration and cornering, but not top speed. In fact, by reducing friction at the wheels it can even lower top speed.

3) Increasing engine power improves acceleration and top speed, but doesn't help with cornering.

4) Better aerodynamics will help top speed, acceleration and cornering, but again these have fundamental limits, and only at high speeds.

Since we want to improve three parameters, this problem has no simple solution in general. Better tyres and aerodynamics always makes sense, but eventually you reach a limit where your money is better spent on a bigger engine or reducing mass. If money is no limit you push all of these! Hence the look of F1 cars: Huge tyres, extremely honed aerodynamics, very low mass and large engines.

There is no one feature of a VW Golf that you could improve arbitrarily to make it out perform an F1 car around a track.

NobodyImportant

Thanks for all the help, people, much appreciated.

I have modified and help built and setup a race winning car, currently writing an article about it, to show that the car, while having much less BHP than its competitors, because it was light it was still faster.

So we have Gravity pulling the car down and affecting its speed up and down a hill, which is related to mass. Friction, which is also related to mass, Centrifrugal Force? What about momentum? Am I miles away? Like if a car is doing 80mph towards a bend, it wants to go straight on, rather than turn, is that a physical force acting on the car?

Thanks again,

Pgibson

Don't forget: LOW centre of gravity.

Can't have it rolling over on corners!

(Loved the way my ancient Mini used to take tight corners at full speed...... as though it were glued to the road.)

.

Professor_Fink

NobodyImportant wrote: »

So we have Gravity pulling the car down and affecting its speed up and down a hill, which is related to mass. Friction, which is also related to mass, Centrifrugal Force? What about momentum? Am I miles away? Like if a car is doing 80mph towards a bend, it wants to go straight on, rather than turn, is that a physical force acting on the car?

The acceleration due to gravity isn't mass dependent. Actually it is the fact that the force generated by the engine isn't mass dependent that makes a difference. Depending on the aerodynamics friction may be either dominated by downforce due to gravity (which is mass dependent) or by aerodynamic downforce (which scales as velocity^2, andis not mass dependent). The momentum isn't really the relevant quantity for cornering, but rather the rate of change of momentum (which is equal to the force applied).

Mahatma coat

Power to Weight ratio is one of the most important calculations in a race car
http://en.wikipedia.org/wiki/Power-to-weight_ratio

P/W

so any reduction in W leads to an increase in overall power

from what I remember its easier to alter the ratio by reducin the weight as its takes 4 times the increase in power to gert the same result

but I expect someone will correct that with the proper ratio

Delphi91

Mahatma coat wrote: »

Power to Weight ratio is one of the most important calculations in a race car
http://en.wikipedia.org/wiki/Power-to-weight_ratio

P/W

so any reduction in W leads to an increase in overall power

...

This is only true if the power-to-weight ratio remains constant. Otherwise they are not connected.