TonyBurns

iTrader: (3)

You cannot have understeer or oversteer if you cannot steer, if you travel in a straight line your not doing either of the above because your not incontrol (if you try steering), and to be in a skid you dont have to actually steer anything, but you can get into a skid from understeer, but not always. 2 different things though SOME people do call it the same thing, its not.

Tony

M3 Compact

Tony, are you not getting a sh*g or something?

Your persistent repeating of your ridiculous argument is rather worrying.

With 7000+ posts, obviously you can write/type, how is it that you can't read?

No I didn't. If it's not steering at all, it is still steering less than the amount of steering input and it is understeering.

If it is steering at an amount under/less than which the input is requesting, it is understeering.

And it's input, not imput.

Understeering to any extent is a front wheel skid, even if it's understeering 100% (losing all of the input) and you're going in a straight line, it's still understeering and skidding.

As before (yawn) if you're not trying to steer (no input) and you lock the front wheels, that is a front wheel skid only. It's you're (as in you are).

Due to the accuracy of the rest of your judgement here, I'll take that as a compliment.

Thanks.

john banks

The guy still does have control though Tony, not that that is actually the point.

Whilst he may not be able to apply more steering lock and keep the same or improve his slip angle, he could take off steering lock and reapply, or feather the throttle if he is on it, or as Simon mentioned if brave and skilled, or on a loose surface or where there is run-off, the handbrake. All remedies for understeer, which, if as I have said, you have the space, can be done here.

I did exactly this in a roundabout the other day, the roundabout was greasy and my line was compromised as I had to go 180 degrees around a reasonably tight roundabout and I deliberately went in reasonably swiftly and gradually increased the power as I went round, at one point I was also tightening the line. The combination of more lock and gradually increasing throttle gave a fair pronounced understeer which I just let it scrub off a few feet whilst lifting the little throttle I had and being ready to apply any opposite lock required - none was required, not surprising since there was not much weight transfer as I had not been using much throttle and it was mainly steering induced. I could also have taken lock off and reapplied as I had deliberately taken a bit of a tight line to provoke it. In the wet at Knockhill I've tried both methods for dealing with understeer. Just because it happens relatively suddenly and you drift quite dramatically off your line because of a combination of factors - surface, camber, steering and throttle input all against you at once, does not mean that it has turned into a skid rather than just being understeer. If just one factor was changing more slowly such as slowly increasing speed on a constant radius skid pan, the breakaway would be more progressive. It is still understeer whether it happens quickly because of circumstances or being hashy with the controls, or whether it happens smoothly whilst deliberately finding the edge.

Tony, do you maintain that during your "front end skid" that you can't simply reduce the slip angle and regain control?

It is still understeer, everyone else except you agrees this. I think you've absorbed another's idiosyncratic nomenclature. But I also think you've missed an opportunity to correct a situation you see as irrevocable by removing steering lock and reducing slip angle to regain lateral adhesion?

Gear Head

iTrader: (2)

Here here John!

TonyBurns

iTrader: (3)

John,
agree 100% what your describing is understeer, just read below though, this is the point im making.
Now also describe "slip angle".
You will eventually see what im getting at (also still have lots of ammo left on this one )






Tony

john banks

I direct you to Simon's definition of slip angle in the glossary thread in this forum.

Are you saying that it is not understeer for James' roundabout which was smaller than mine because he says "it doesn't actually turn"? Still misguided if that is the case IMHO.

You'd be well advised to let it rest and put your ammo away in case you shoot yourself in the foot

TonyBurns

iTrader: (3)

Yup read that

Slip Angle
The difference as an angle between the direction a tyre is travelling in and the direction the wheel is pointing. In order to create a lateral force, a tyre must exhibit a slip angle. "Slip" does not necessarily indicate "skidding" / loss of grip.


Yup that looks good to me also
BUT then your looking at aquaplaning, driving on snow/ice/oil with no grip in a straight line, which is what is indicated in the first post, BEFORE the turn in, and the above can indicate loss of grip on the front before you also turn the wheel, which is also as indicated in the first thread otherwise you have to state that aquaplaning in a straight line is understeer, which its not, as its a skid....
But i do agree that when the car is actually turning and then looses grip, this is understeer, its just when it isnt turning and carries on in a straight line i dont agree on

Tony (now off down the pub for a couple of pints )

TonyBurns

iTrader: (3)

John,

This ones for the mappers
Guy wants to know the sort of boost levels on an STi8 with tek3?

http://bbs.scoobynet.co.uk/showthrea...85#post4268285

Tony

john banks

Doesn't sound to me like James had a problem before he turned the steering wheel?

On a low mu surface there isn't a huge problem until there is an unintentional differential between road speed and rotational speed, but the longitudinal or lateral grip available when demanded is low, to the point where at relatively low speed the car appears to simply not turn in, the slip angle at the front exceeds that at the back and you have understeer by definition.

I hope your pints improve your reasoning I'm staying sober and thinking about how to make my car faster tonight

mutant_matt

As a small aside, just to counter the "all front wheel skids are understeer" argument: If the front wheels loose traction whilst in a straight line, like aquaplaning or jamming on the brakes on a non-ABS equiped vehicle, it's a skid, NOT, understeer, even if after turning the wheels it still goes straight.

If though, the car was understeering (i.e. turning but not to the degree as asked by the driver) and *then* lost all traction, whilst that technically becomes a loss of control/skid, that would probably be fair to be called understeer, no?

Matt
<not down the pub but got nothing better to do (babysitting), but getting nicely pished anyway >

TonyBurns

iTrader: (3)

Agree with you Matt, this is the point i was trying to make
If you read what is said on the first post, the guy doesnt actually turn, the car just skidded, when he tried to turn, which was what i was trying to get across.

Tony

Fat Boy

Jamesmt posted at the start of this thread :

"So whats it called when you go into small slow wet roundabouts and just lose the front because it doesn't actually turn and you start sliding - is this also understeer/sliding or just me driving like a tw*t?"

So the order of events is he "loses the front because it doesn't actually turn", and then "you start sliding".

To me that suggests that he is turning his steering wheel (as, for some strange reason, most people prefer to go round roundabouts rather than over them or into the bushes on the outside ) but his car is still going straight on. That's understeer.

No mention of I locked up and slid into a roundabout, etc. Keep drinking the Calpol Matt

Tony " the car just skidded when I started to turn" - that's still understeer.

Do you need a larger shovel?

CTR

Understeer

M3 Compact

LMFAO.

Understeer.

Quote:

Originally Posted by mutant_matt

As a small aside, just to counter the "all front wheel skids are understeer" argument: If the front wheels loose traction whilst in a straight line, like aquaplaning or jamming on the brakes on a non-ABS equiped vehicle, it's a skid, NOT, understeer, even if after turning the wheels it still goes straight.

You appear to have acquired Tony's reading deficiencies.

Quote:

Originally Posted by M3 Compact...If you're travelling in a straight line without ABS, and you stamp on the brakes, that's a front end skid only.(Ignoring the rear wheels for the purpose of this explanation). If you then try to steer, obviously it won't and that is then understeer. (Albeit caused by muppetry with the brakes)

If you're applying steering lock and the front tyres don't steer the car as much as they would if they were on rails, then that's understeer. No matter what the degree of 'slip' or severity.

In actual physical terms, all cars are understeering all the time when the rear wheels are 'in line' and any steering is applied. Some linear input is always lost through the tyres when applying a steering adjustment.

Mild understeer or severe understeer, is all understeer.

Simon.

BMW Rallying.com

Steer is a verb (to steer), if you're applying a steering input/request that the car isn't transferring in to actual steering, it is 'understeering'.

The cause/extent/speed are all irrelevant, as is the question of an already skidding front end.

You could try seeing it Gramatically, I'm not an English Grammar expert/instructor, but try thinking of the verb perform.

If your car has a mechanical fault (eg clutch is slipping), when you're applying a power increase that is lost through the fault/slipping clutch, your car is not performing as it should be, so it is 'underperforming'.

Understeer.

mutant_matt

I think a few of you mis-interpreted my post

I believe in this case he had understeer. The point I was making though was that not all "front end skids" are understeer, it depends on the circumstances!!

If you lock up in a straight line, that's a skid! If you are still locked up and start turning the wheel, it's still a skid, not understeer. If you were to take your foot off the brakes and regain traction, turn and the car carries ploughing straight on, it becomes understeer (though the definition at this point is a little blurred and in this set of circumstances, I think skid or understeer is a reasonable definition )

If you go flying into a roundabout, turn the wheel and it ploughs straight on, it's understeer.

If you go flying into a roundabout, turn the wheel and the car turns some but not enough, it's understeer.

Matt

P.S. Fat Boy,

TonyBurns

iTrader: (3)

No its not understeer, its a skid, otherwise aquaplaning, driving on ice, driving on snow would also in your opinion be understeer, straight line, no grip on the front when trying to turn (note that the car didnt turn when the wheels did, ie carried straight on, not understeer but a skid).
Now if that doesnt get though ill put it in laymans terms

Skids only happen in straight lines, understeer happens when turning (ie you have to be turning and the car following the turn for it to happen).

Tony

PS, you also dont have to lock your brakes up to have a skid

john banks

The definition of understeer specifies that you have a greater slip angle at the front than at the back. It is a relative definition, not absolute. It doesn't require embellishments or complications So you don't need a certain slip angle at the back to qualify. You create the slip angle by turning the wheel, it doesn't need a high mu available to create a slip angle, and in fact you will more easily create a slip angle with a low mu given the same input.

I most agreely with you Matt, but I can't follow some of it or do I misunderstand? :

"turning but not to the degree as asked by the driver"
does not equal...
"If you go flying into a roundabout, turn the wheel and it ploughs straight on, it's understeer."

Do these statements contradict each other in that in the first one you are defining Tony's understeer, and in the second one, Tony's skid and everyone else's understeer?

"If you are still locked up and start turning the wheel, it's still a skid, not understeer."

Now you've made the slip angle at the front greater than the rear, so unless we change Bosch's definition of understeer, you've just added understeer to your skid?

In reality, I very much doubt on most surfaces that cars are not turning in at all, just that on a low mu surface things happen a lot quicker in terms of the avalanche of slip angle.

Note on the below dry vs wet that the mu available is obviously less, but notice that the wet trace peaks earlier? That is why in the wet modes of traction control they run closed loop around a smaller slip angle as optimum mu is found there. For a given steering or torque input at a given speed, the mu achieved is lower, and the breakaway will be quicker. Behave like you do in the dry and what would have been a nicely controlled understeer will avalanche quickly, pass the peak of mu and have a lurid slip angle difference between front and rear. "I just went straight on".

M3 Compact

Rubbish. You're asking it to steer via an input, but it's not. Therefore it's understeering. Absolutely agreed/correct.

Simon.



BMW Rallying.com

StickyMicky

agreed from me as well

non of this front end skid mush, sounds like sumthing a detail-tefal-spec c driver would say

TonyBurns

iTrader: (3)

LOL, really?!
So everything a car does is understeer?
Well according to you it is
If there is no grip OR maximum grip on the front end of a car, it will travel in a straight line, simple fact, turning the wheels will do nothing until you reach a point where traction is usable and the car can turn, either by slowing down or releasing the brakes.
This is a SKID, not understeer, you can turn the wheels all you want in a straight line and you will continue to travel in that direction when the car is in a skid, for understeer to occure, the car HAS to be able to steer.
Basically, if you think that a skid is understeer (which it is not, but thats what your saying), then you have just changed motorsport forever

Tony

john banks

Do you agree that the slip angle at the front is greater than that at the rear?

M3 Compact

Please don't incorrectly quote me Tony, at no time have I stated that "everything a car does is understeer".

If we're not Understeering, or Oversteering, then we are steering accurately, agreed?

So your example of a car travelling in a straight line with full lock applied to no effect is a car that is steering accurately is it?

It's Understeer.

Gear Head

iTrader: (2)

Come on Tony, I see your point, believe me I do, but does it really matter? Both arguments seem to hold some truths. When over-steer occurs, the driver is able to reduce its effect be reducing the steering angle, I believe the same applys for under-steer. What i'm trying to say is that, 'skid', in both cases, occurs when the driver goes beyond the extreme of over or understeer. You have to go through the stage where the tyres begin to loose grip in order to experience any kind of 'skid' effect.

It does seem fair then to call the effect, understeer skid, or oversteer skid.

john banks

It does matter because Tony is peddling confusion and inaccuracy that clouds the question that the poster was asking. Without it we could have been done within a few posts. He doggedly clings to erroneous ideas that have no reference to back them up and will not be corrected. It is the same in countless other posts he makes, misinformation is spread as fact. On the other hand, I've brought data and quality references to the party, along with some practical ideas for solution to the poster's problems. But I am always ready to be corrected when clearly wrong.

Keep it simple, understand what a slip angle is, and then you have an accurate, all encompassing definition of understeer and oversteer. Consider the grip available in two axes at 90 degrees to each other and all is clear. Understand the basics of how tyres work, and read up on the causes and cures of understeer and oversteer, then go and practice in a safe place. Always be prepared to accept new solutions and to be corrected.

I would be delighted to be accurately corrected on any matter by any poster on this thread, including you Tony, if you produce a proper argument backed up by references where necessary, preferably not to the dictionary or your own pet ideas. You'll have to work pretty hard on this one, you could start by answering my question:

"Do you agree that the slip angle at the front is greater than that at the rear?"

If you accept it is (and I don't see how you can't unless you don't understand slip angles) then you would have to dispute Bosch's definition of understeer to conclude that understeer is not being experienced. I am not prepared to consider the second possibility in my mind given your lack of credentials to do so.

Gear Head

iTrader: (2)

I think anyone with a any sense will read this thread, and work out what the majority think.
FRONT END SKID IS UNDERSTEER (EXTREME)

M3 Compact

Well said John.

Agreed, and it makes no difference which leads to which.

All understeer is a front end skid of some degree.

All front end skids with any steering applied are understeer.

Simon.

BMW Rallying.com

Paulo P

iTrader: (42)

I can't believe you lot are still banging on about this It's understeer FFS

StickyMicky

no its not its a front end skid

(dohh forgot which side im on )

scoobyDAZZA

2000STI7

Come on guys, 3 pages, 4 months and nobody has got it right!!!!

It’s Called….PUSH

Juan Pablo