Why cars understeer?

[Azon]

I was just wondering why certain cars understeer more than others? It relatively simple with oversteer but I have no idea why understeering occurs and how different suspension geometry may affect it. I am really interested in the technical side of the problem. How hard will it be to eliminate understeer?

[whiteballz]

the more a car weighs the more kinetic energy it has to move around. higher speeds effect this too. same with the amount of grip on tires.

[Matra et Alpine]

Where the centre of mass is on the vehicle matters too.
FWDs have most of the mass at the front wheels so that mass wants to keep going in a straight line
There are many rasons why the front tyres approach the traction limit more rapidly, the effect being that the front of the car takes a wider radius curve than the driver intended.
Think in terms of tyre contact and forces - all varied by suspension and steering geometry, tyre compliance and weight.

[Azon]

the more a car weighs the more kinetic energy it has to move around. higher speeds effect this too. same with the amount of grip on tires.

Sorry, but I don't quite understand what you are trying to say there - whatt do you mean higher kinetic energy "to move around"?

Where the centre of mass is on the vehicle matters too.
FWDs have most of the mass at the front wheels so that mass wants to keep going in a straight line

That's what I thought, but I wanted a beat more specific answer. Thanks anyway.

[Matra et Alpine]

Sorry, but I don't quite understand what you are trying to say there - whatt do you mean higher kinetic energy "to move around"?


That's what I thought, but I wanted a beat more specific answer. Thanks anyway.

To what level of detail and why ?

If you want to know ALL the reasons and variables then you have to go to university to one of the recognised automotive deisng course and in 4 years you'll knwo them ALL

There are also numerous books on race car setup and design which go through most of the basics of suspension design. BUT theses are heavy reading without a strong engineering/technical background.

The simple answer is the one given, everything which alters the tyre contact to the road and alters the polar moment of the vehcle affects the hadling. THEN add the dyanmics of weight transfer front to back AND side/side - ie corner weights AND then the compiance/rebound on the suspension and the driver input. There isnt' a simple answer. it woudl take many 10s of thousand sof words to go through each of them and lots of math to calcualte and understand it.

Sorry it's not the asnwer you're lookign for but sometimes there are no easy answers orquick shortcuts.

If you start out with a fixed car configuration the BIGGEST difference you can make is in the tyres and the camber of the wheels. But even that varies significantly between different suspension - macpherson, wishbone, anti-roll, etc etc.

Why not give soem background and we can mayeb give you more focussed information. I'm afraid we can't write the complete treatise on it in the time avaialble

[Azon]

To what level of detail and why ?

If you want to know ALL the reasons and variables then you have to go to university to one of the recognised automotive deisng course and in 4 years you'll knwo them ALL

There are also numerous books on race car setup and design which go through most of the basics of suspension design. BUT theses are heavy reading without a strong engineering/technical background.

The simple answer is the one given, everything which alters the tyre contact to the road and alters the polar moment of the vehcle affects the hadling. THEN add the dyanmics of weight transfer front to back AND side/side - ie corner weights AND then the compiance/rebound on the suspension and the driver input. There isnt' a simple answer. it woudl take many 10s of thousand sof words to go through each of them and lots of math to calcualte and understand it.

Sorry it's not the asnwer you're lookign for but sometimes there are no easy answers orquick shortcuts.

If you start out with a fixed car configuration the BIGGEST difference you can make is in the tyres and the camber of the wheels. But even that varies significantly between different suspension - macpherson, wishbone, anti-roll, etc etc.

Why not give soem background and we can mayeb give you more focussed information. I'm afraid we can't write the complete treatise on it in the time avaialble

Ok looks like it really is very comlex but thanks for trying.

[Cotterik]

jesus matra is there anything you DONT know you should be the prime-minister

[scottie300z]

Why do cars understeer?
Physics.

there you have it.

[BlueSubaruSTi]

the easiest way to put this...

oversteer-rear tires lose grip first
understeer- front tires lose grip first

I remember someone saying, if you see the tree before you hit it its called understeer, if you only hear and feel the tree its oversteer.

[KnifeEdge_2K1]

to understand under and oversteer the concept of slip angle must be applied

when turning the contact patch is distorted slightly and is actually moving in a direction not parrelel to the direction of the tire, tye more this direction varies from the direction of the tire the bigger the slip angle

generally the direction of the contact patch is away from the direction of the turn, when the front wheel's have a slip angle larger then the rear wheels, understeer occurs, when the slip angles are equal neutral steer occurs, when the rear wheels have higher slip angle then the front oversteer occurs

the things that affect slip angle most as mentioned bofore are weight distribution and tractive force, since fwds are heavily forward biased in weight, the front tyres have to apply a much greater force (compared to a mid engined car of equal weight) towards the inside of the turn, this increases slip angle, the previous condition applies to all front engine machines, but the additional fact that a fwd drives the front wheels only increases understeer because tractive force (the force the engine applies to the wheels) increases slip angle at the front even more

changing suspension geometries can easily change the ammount of slip angle of each tire at certain speeds, but ultimately the original configuration (weight distribution and drivetrain) will determine the maximum handling capacity of the car well ... assuming all other factors are equal

[drakkie]

Sorry, but I don't quite understand what you are trying to say there - whatt do you mean higher kinetic energy "to move around"?

Every moving object has a so called kinectic energy (also known as movement energy). if the amount of this kinectic energy gets more, it will take more energy to move the direction of it, and it goes understeering, cos the energy will try and remain working on the same angle.only by using enugh force, it will turn.if the amount of kinetic energy is too high, the car will keep on going in a straight line.

[KnifeEdge_2K1]

um ... energy really has nothing to do with it since its a scalar quantity, momentum is prolly what you're talkin bout, that takes work to change, amount of work needed to turn the car is related to the slip angle bla bla bla

[Tuscan666]

I remember someone saying, if you see the tree before you hit it its called understeer, if you only hear and feel the tree its oversteer.

I think those was the words of Mr Clarkson.

[Jack_Bauer]

I think those was the words of Mr Clarkson.

I think that was actually Richard Hammond plagiarising Walter Rohrl.

[Indyrs500]

Because someone hasn't thrown the front wheel drive trollies into the north sea and gone and bought 'Real' cars that drive from the back end and therefore handle properly.