I actually am not too sure about understeer anymore!

If I want to enter a corner, steer into it, and find myself sliding straight on towards the outside of the corner, am I understeering? I used to think so.

Or am I just being silly trying to enter the corner at the speed I was trying? Hmm if I would go slow enough, even with tyres made from soap I could enter the corner without alledged understeer.

My question is basically, if a car can pull near its maximum lateral (cornering) G forces at any time when turning the steering wheel, can you call that car understeery? If my car does 1G in the turns, I enter a corner too fast and end up in the gravel traps after 'understeer', yet the telemetry shows that I did 0.99G laterally until I left the tarmac.. Then really the *CAR* wasn't understeering was it?

Or was it? Lateral G forces are just that, forces in a line from the left door keyhole to the right, 90 degrees from the rolling direction of the car. The greater the yaw angle of the car then, the more the lateral force will try to slow down and corner your car.. But I'm not quite sure on this..

What would a TRUE definition of understeer be!?

The difference between the circle the wheels are currently tracing and the direction in which they are pointed is the slip angle. If the slip angles of the front and rear wheels are equal, the car is in a neutral steering state. If the slip angle of the front wheels exceeds that of the rear, the vehicle is said to be understeering. If the slip angle of the rear wheels exceeds that of the front, the vehicle is said to be oversteering.

Indeed, what thor says, at least, that's what it says in my racing books.

I'd say understeer is ANY TIME the car wants to take a wider radius through a corner than the driver intended or the race track demanded.

It can be caused by excess speed - better drivers tend to cause this less, newbies more so. Watch an LFS rookie attempt BL1 T1 at 120mph to see the extreme. Watch me at 55mph to see a subtle version - I'll make the corner but I'll be later on the throttle and on the wrong line to be quick out of the corner.

It can be caused by too much steering - the tyres can't cope with the slip angle requested, provide less lateral grip than needed, and so the front of the car will not go where you wanted it to (unless the rears have a high slip angle too, which is why saving oversteer with MORE steering can be possible, if a little inelegant.

To little tyre loading from weight transfer (accelerating) or too much (coasting/braking) can cause it too.

The REALLY hard bit is working out whether the cause of the understeer is the driver (going to fast or not using the controls properly) or if it's the car (poor car setup, mechanical problems etc). When the F1 guys say the car understeers they mean that no matter what they do they can't get through a corner without understeer (except by going REALLY slowly), and in such cases you might reasonably assume it's the cars fault. But when I say my Reynard understeers it's more likely to be a driver problem (inexperience leading to too high an entry speed or steering too much or not being smooth...) than a car problem. Having said that I want to try a slightly softer (one click) front ARB and one 'blob' more front wing (we've put a random scale on the wing adjusters so we can easily compare settings, but they don't mean anything).

Edit: I guess what you are saying is when does 'too much speed' understeer become 'a car problem' understeer? If Alonso says it understeers at T2 why doesn't he just go a bit slower or is the understeer NOT caused by 1mph too much speed and something else. And how sensitive are drivers? I might think my F1 car is gripping like mad by Kimi might think it's the worst understeer he's ever had... It's a VERY subjective answer if you ask me, and the only scientific explanation is simply to say the front slip angle is greater than the rear. Why that is is almost impossible to pinpoint (but more front wing might help!).

Agreed, but that doesn't rule out the driver. I don't think you can rule him/her out completely but with LFS, some will find a car to understeer where others say oversteer, even with the same car setup..

I'm still thinking somewhere towards yaw angle. How easy the driver can change the 'heading' of the nose of the car, with any combination of wheel/pedal input..

Edit: not in response to Tristan

a well balanced car can be made to understeer or oversteer, depending on driver inputs, allowing the driver to control the attitude of the car not just in the corner it's in, but also setting it up for the next corner.

if it's easier to cause understeer, but requires more radical driver inputs to cause oversteer, then it's probably safe to call the car understeery, and vice versa.

I think I'd put it a different way. I would forget about slip angles and just say if the front tyres 'break traction' before the rears then the car is understeering. If there rears break traction before the front then the car is oversteering. To say a car is oversteery or understeery you have to say at what time it is oversteery or understeery as all cars can oversteer and understeer in different circumstances.

Quote from Gentlefoot :

I think I'd put it a different way. I would forget about slip angles and just say if the front tyres 'break traction' before the rears then the car is understeering. If there rears break traction before the front then the car is oversteering. To say a car is oversteery or understeery you have to say at what time it is oversteery or understeery as all cars can oversteer and understeer in different circumstances.

Agreed, one end of the scale is obvious oversteer, other end is obvious understeer. The grey area happens in the middle where driving style starts to have an effect on how the car handles.
As already stated understeer is all to do with slip angles etc. How much understeer there is partially down to set up and driver but the optimum is different for every driver. Which means the only available explanation of understeer is the tyre model one of slip angle.

Quote from Niels Heusinkveld :

Agreed, but that doesn't rule out the driver. I don't think you can rule him/her out completely but with LFS, some will find a car to understeer where others say oversteer, even with the same car setup..

Well I basicly agree with Tirstan, if the car takes a wider line than you intend then it's understeering, or your sleeping.

As for the thing on the same setup, that's nothing to go by. Me and Jonesy have this conversation all the time (Had it more when doing the MoE) because I would find a FZR set of his extremely oversteery but he would find it nice and balanced, the differnce in styles affects the way the car reacts massivly....and I wouldn't say the styles were that much differnt.

Quote from Thorvertonian :

If the slip angle of the rear wheels exceeds that of the front, the vehicle is said to be oversteering.

i know thats the usual definition but doesnt that mean that a (properly trail braked) car is always understeering all the way to the apex ?

best definition of under / over steer i ever saw was (not word perfect) -

understeer - you see what you crash into

oversteer - you don't see what you crash into

Quote from Shotglass :

i know thats the usual definition but doesnt that mean that a (properly trail braked) car is always understeering all the way to the apex ?

Why would it if done properly. Trail braking when braking hard, turning in and coming of the brake pedal softly to be off the brake pedal by the apex. Why would this understeer? The tyre produces a maximum force whether this is used in braking, steering or both the total cannot exceed the maximum force. So as you start to turn in you lift of the brake, meaning there can be a force for turning the car.

because at turn in the front slip angle is always greater than the rear on or else the car wouldnt turn in in the first place

You are explaining a situation in which you are forcing understeer. You're asking the front tires to do more than they can.

The whole understeer vs. oversteer thing varies greatly from driver to driver, as each one has a different style. For example Alonso (quick turn in) vs. Hamilton (smooth turn in).

But, like others have said, if the back slips its oversteer, if the front pushes, its understeer.

- oh yeah, keep this in mind as well; a lot of newer drivers complain of oversteer when that isn't really their problem. They are turning in far too rapidly and entering the corner too fast, which causes understeer, the car then slows down by scrubbing speed from the excessive steering angle, then the car reaches a speed at which the front tires regain grip. This sudden transition flicks the back end out and can, by the untrained eye, look like oversteer.

If you turn in really fasst, and exit the corner really fast, you're creating a big yaw angle. A big yaw angle doesn't automatically mean understeer or oversteer, it just depends which side of the car has a bigger slip angle.

Quote from mikey_G :

If you turn in really fasst, and exit the corner really fast, you're creating a big yaw angle. A big yaw angle doesn't automatically mean understeer or oversteer, it just depends which side of the car has a bigger slip angle.

yaw eh

Well a positive yaw value=understeer and a negative yaw value=oversteer.

Quote from Shotglass :

i know thats the usual definition but doesnt that mean that a (properly trail braked) car is always understeering all the way to the apex ?

Again it depends on style. When I trail brake it's not to get the car understeering, it's to avoid understeer while I am slightly over the target apex speed during the time between turning in and hitting (or missing lol) the apex.

Quote from Gentlefoot :

Again it depends on style. When I trail brake it's not to get the car understeering, it's to avoid understeer while I am slightly over the target apex speed during the time between turning in and hitting (or missing lol) the apex.

the point is at turn in you need more lateral force from the front wheels than form the rears and you achieve that by a mix of load shifting to the front and higher slip angles at the front ... so by the usual definition cars would understeer all the time at turn in

Quote from Shotglass :

the point is at turn in you need more lateral force from the front wheels than form the rears and you achieve that by a mix of load shifting to the front and higher slip angles at the front ... so by the usual definition cars would understeer all the time at turn in

Surely by increasing load over the fron tyres will result in less understeer. You always have higher slip angles at the front because the front wheels steer. It doesn't necessarily mean understeer.

Quote from Gentlefoot :

It doesn't necessarily mean understeer.

it does by definition thats the whole point im trying to make

Understeer is easy to define.. But I don't think we can find a unanymous (sp!) way to define when to call a *car* understeery...

As much as this may sound wrong or right, I just define understeer as:

The front wheels have a larger turning radius potential than the rear wheels.

:zombie: Or, basically, the RAC.

Because you cannot say it is entirely due to just loads on the tires or whatnot, it is tons of other things that can cause it. And understeer will always be evident, no matter how hard you try to get rid of it (well you can't get rid of it).

I would define it as such:
Imagine the front outside and rear outside wheels as tangents of a circle (the outside wheels more so because they do most of the work in a corner). In order to follow that circle at the speed at which you are going, you need a certain torque created by the tyres. If the torque created by the tyres around the CoG is less than that, then you have understeer. If it's more, then you have oversteer.

Singularly, why would torque have anything to do with it?

Loads, aero, toe, camber, suspension, pressures, terrain, weight transfer, steering input... the list could keep going for just one factor of causing understeer. You could be at any level of so called "torque" and still get understeer with any one of those issues.

Not that torque. Torque as in the one causing the car to rotate around its CoG, which essentially is what makes you turn.