Jamesemt

I always presumed understeer to be when you go into a corner, but the car doesn't want to turn...

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?

Can I do anything to the car which will help it grip in these situations - I don't want to alter the suspension too much as I am used to its predictable handling...blob eye WRX...

Any ideas?

john banks

Sounds like understeer. I'm no expert, but try some of the following:

Driving techniques...
Go slower into the roundabout and smoothyl apply power as the front wheels straighten out, can do this earlier by choosing your line
Smoothly apply the steering and throttle
Try using less steering if you understeer
Be wary lifting off too heavily unless you are ready to catch the back end

On the car...
Check/correct geometry, tyre pressures, consider different tyres
Stiffer rear anti-roll bar
Consider a front diff if happening under power, also an "anti-lift" kit can increase the castor angle and reduce understeer under power even though it doesn't actually reduce lift
Some swear by solid drop links and strut braces as well

Driving style, geometry, tyre compound and a Suretrac front diff reduced the understeer dramatically on mine.

TonyBurns

iTrader: (3)

I think your confusing understeer with a front end skid.
With understeer, you still have grip and can still turn in, what understeer will do is pull the nose out more, so you have to turn in tighter, but it is also a warning that your loosing/edging towards the maximum grip on the front, so backing off slightly whilst still keeping power on should keep you safe(ish).


Different tyre choice is the best bet, not being overly agressive going into corners, slow in, fast out is better than fast in, hit wall/hedge/tree.... and gives you better feel for the grip on the front.

So to recap:-

Understeer, when the cars nose pulls out slightly, ie in a left hand bend, the car will edge further out to the right.

Oversteer, similar to the above but..... instead of the nose pulling out, it turns in more, so, left hand bend, turn corner, nose pulls towards kurb more.

Hope that helps

Tony

john banks

Tony, I don't understand the difference between a front end skid and understeer.

"so you have to turn in tighter"... I find that makes the situation worse as you are increasing the slip angle further? It does scrub off speed, but I think it slows you down more? I try to feather the throttle whilst taking off some lock if it is excessive.

TonyBurns

iTrader: (3)

John,
A front end skid is when you loose traction on the front, turn the steering wheel and you still carry on in the direction you were going, understeer is when the nose runs wide, you can still pull it back in though, thats the biggest difference.
Personally i try not to go into corners full throttle, half seems to suffice most of the time and as you state, gentle adjustment on the throttle is adviseable, you shouldnt get the car stepping out on you though, unless you really mess up, then you have a big oversteer problem

Tony

jfrf

sound like understeer to me

i found that changing the geometry definitely helped
cost 150 quid.
was more noticebale on roundabouts. better turn-in

wider front tyres on my car also helped as this gave the front a bit more grip

john banks

Still not sure I understand the difference between a front end skid and understeer Tony, what you are calling a front end skid - isn't that just severe understeer?

Maybe I misunderstand, but I consider that lateral grip and longitudinal grip are in two different axes at 90 degrees to each other, and the slip angle is a marker of the severity of understeer (when considering the front tyres) - ie how many degrees away from the direction the tyres are pointing you are actually travelling. If you demand too much longitudinal grip you more easily overcome the tyre's lateral grip and understeer results if this occurs at the front. Understeer can be severe so that you have no lateral grip at all resulting in the car ploughing straight on.

Are we using different terminology to discuss the same phenomenon? If so, why the need to differentiate what appears to be the same process (degrees of understeer) and call it a front end skid, or do I miss the point? Is there something different about what is causing your front end skid or how to correct it?

TonyBurns

iTrader: (3)

John,
Its just basically the difference between grip and no grip.
Understeer means the car is understeering, so adjusting the steering by turning in more, you should still have control, a front end skid is when you have no grip, you can turn the steering wheel in any direction, the wheels move but you carry on in a straight line.
Easiest way to describe it

Tony

john banks

Still sounds like severe understeer to me, with the same causes and solutions. You have a big slip angle, so you let it scrub off speed if you have space (if you went in too fast), reduce the power progressively (if you gave it too much throttle), or take off some lock to reduce the slip angle and regain control?

TonyBurns

iTrader: (3)

John,
What is being described here is a front end skid, the car has no grip on the front and cannot be controlled until grip is gained again, understeer isnt like this, you get understeer in corners but the car doesnt go the line you want, but by adding more steering you can still make the manouvre, this described above is beyond steering, as there is no control of the steering so its now a step further, loss of traction, so not understeer.
Remember, with understeer or even severe understeer, you still have control of the car, with a front end skid you have no control what so ever.

Tony

john banks

You mentioned loss of traction, in that case you can reduce the demand for longitudinal grip (reduce throttle) or reduce the slip angle (reduce lock) and influence lateral grip - with enough time and space of course.

I don't think understeer ceases to be understeer simply because the slip angle becomes so great that increasing it further doesn't help, it is indeed quite expected.

I don't think that with severe understeer that you necessarily still have control of the car by means of the steering in the space you have available.

I don't see any need to complicate it by calling it something else implying that there is a different tyre dynamic going on, a different cause or a different cure, it is all part of the same process.

TonyBurns

iTrader: (3)

John,
If you cannot steer, you cannot have either under or over steer.
The loss of traction, either due to damp conditions or trying to break the laws of physics will cause you to have a front end skid.
At this stage, you have no control of what the car does, even braking will only regain that control when the grip returns, but outside of that, your not in control of the car, thus the correct term is a front end skid.

John,
the other way of thinking of this is when you brake hard in an none abs equipped car, you brake, the brakes lock up, you turn the wheel and nothing happens, your in another front end skid. Its exactly the same principle except this time you have maximum grip, but you still cant turn.
Once beyond the limits of grip/or maximum frontal grip (locking wheels up), the car will skid, it may take some time to regain control but whilst your not in control your in a skid.
Skid, no control
under/oversteer, control.

Tony

Jason Knowles

try replacing the rear plastic drop links with solid ones helped my 03 car

john banks

I don't agree with your definition of understeer then. I also don't agree you that have no control - just because you can't keep your line by adding more lock doesn't mean you might not be able to redeem the situation by for example removing lock, otherwise I would have binned it many times, just needs a bit of space, but I find that if you keep the excessive lock on you end up using more space to scrub off the speed passively and sort it out than if you removed some lock and then gently reapplied some when grip resumed, although it is easier to keep a level head if you triggered it deliberately in the first place and were expecting it.

I quote SDB's old Driving Techniques guide:

"Understeer, generally thought of as the bane of the lives of most motorsport participants, is when the front wheels lose grip in a turn and in effect just carry straight on or the car turns much less than the angle of the wheels would normally dictate."

An alternative definition (Bosch) is that the slip angle at the front exceeds the slip angle at the rear.

From Simon's definition, it does include carrying straight on (your front end skid) or steering less than intended (your understeer).

The second definition of understeer also includes your front end skid.

Simon quotes three solutions to understeer:

"There are generally three methods of recovering from understeer.

Slow Down
If you have the time and road left, you can simply hold the steering where it is and let the car slow down to a point where the front wheels grip. In this situation it is important to remember 3 things. 1 - Less is more with regard to steering, the front wheels are more likely to grip if they are pointing more in the direction of travel. 2 - Brakes are the food of understeer. If you stand on the brakes you are likely to lock up the front wheels and create even worse understeer than you had already. 3 - When the front wheels grip it can suddenly snap into oversteer due to the sudden change of direction which can occur.

Feather Steering
As discussed, the front wheels will grip much quicker if the front wheels are pointing in the direction of travel. It requires a serious amount of mind over instinct but can be very effective if you straighten the front wheels and try to gently edge them round again. The idea is, you straighten the front wheels to regain grip and then ease the steering back to the point where it is about to lose grip again which gives you maximum steering.

Handbrake
This is a bit of a last ditch attempt and should be well practiced off road before attempting it on the road. The only thing which has less grip than an understeering wheel is a locked wheel. If you whack on the handbrake and and lock up the rear wheels, the front wheels will automatically have more grip than the rear wheels. This will almost certainly throw the car into oversteer, which is infinitely more controllable than understeer."

I've used the first two, particular on track (although I'm no expert as I said, I don't have anything like the natural car control some people have) and been surprised at the recovery of the second one compared with the first.

Your braking scenario is different, you have maximised longitudinal grip at the expense of lateral grip, so it is not at all surprising that you lose directional control, the solution is to reduce the demand for longitudinal deceleration (lift off the brakes) and then steering control resumes very quickly.

I've never seen a well written driving techniques guide bother to define "front end skid" as a phenomenon different to understeer, but happy to be corrected. In the absence of this I think it is just adding confusion. The guy had understeer, the three techniques listed by Simon can help to sort it out, and by extension help to learn how to prevent it.

I think we'll have to disagree on this one!

TonyBurns

iTrader: (3)

Probably best to john
But as the book says, if you cant steer, you cant have under or over steer.....

Tony

john banks

Which book? Not any of the ones I've read....

Not in Bosch's or SDB's definitions, but is in Tony's definition LOL

Try taking some lock OFF next time and tell me what you think

TonyBurns

iTrader: (3)

Found this for you John

Oversteer and Understeer
Fortunately, a well designed car does not suddenly break into a skid. As the tyre approach their traction limits, they tend to slip sideways across the road. The angle between the tyres actual path and its natural path is called its slip angle. This gives the driver advance warning that the front/rear of the car is in danger of breaking loose and starting a skid.

If the rear tyres approach their traction limit more rapidly than the front, then the effect is for the rear of the car to steer a wider path than the front wheels. This rotates the car more than the driver intended and, if nothing is done, leads to the car turning a smaller radius corner. When this occurs the car is said to oversteer.

If the front tyre approach the traction limit more rapidly, the effect is that the front of the car takes a wider radius curve than the driver intended. The car is said to understeer.

Understeer is safer than oversteer. If the car understeers, and no correction is made the result is a wider corner than intended, but the car remains stable. If the car oversteers, the turn made has smaller radius than intended. The smaller radius produces higher cornering forces bring the required traction even closer to the limit of the rear wheels, and thus causing even more oversteer. The situation becomes worse until the rear wheels lose grip completely; the car spins and all directional control is lost.



Tony

john banks

http://www.google.co.uk/search?hl=en...ine:Understeer

How many definitions of understeer that include your front end skid here? How many definitions of the vague "front end skid" can actually be found? I couldn't find any. You're using odd terminology that makes no sense at all. Nowhere does the above text differentiate between a skid and understeer. Perhaps they are the same thing ?

john banks

The most technical definition is "Where the slip angle of the front wheels are greater than that of the rear wheels." This definitely includes your front end skid. There is simply no need to complicate it. The causes and cures are no different. End of story.

Gear Head

iTrader: (2)

Could 'front end skid' just be the extreme effect of understeer, just as the back end completely stepping round is the extreme effect of oversteer?

john banks

I think so. There is nothing in the accepted definitions that includes the ability to get it back with more steering lock, otherwise that would not be warned against with "less is more" in Simon's decription. Other way of putting it is, I don't think it just becomes a "front end skid" when further additions to slip angle produce a plateau or even less lateral g.

If I understeer so badly that I go into the roadside furniture even though I'm still putting more lock on, it's still understeer IMHO. Tony says if you can't steer it isn't understeer, but you can steer - you can take lock off, it really works given enough space like all these things.

AvalancheS8

I'm with John 100% on this. What was described is understeer. Severe understeer certainly, but understeer none the less.

There is a continuous progression between very slight understeer and a slip angle so big that the car just goes straight on, there is no need to call it by two different names.

After all, even after the front end is going straight on and you can wind on more lock with no effect, you can still steer, just not by winding on more lock. The options you have to control, and therefore steer your car at that point are to wait for it to slow down, to back off gently if you have throttle on or to wind all the lock off and start again, feeling for the limit of grip. So you never have "no control", you never have no ability to steer, or control the car, so the definition of a "front end skid" is redundant.

Certainly, sometimes, the control that you do have to steer the car can't be exercised by winding on more steering lock, and sometimes it will be beyond the skill of the driver to salvage the situation, or there won't be space on the road to save it, buy the fact remains, it is understeer.

Beastie

iTrader: (2)

I agree also with John, if the frictional coefficient of the road is reduced then understeer is induced earlier, but nonetheless this has to be understeer. As the friction of the road is common for back and front wheels then the back end would come round before the front is ploughing on thus oversteering. I believe this is referred to sometime as plough on understeer by motoring journalists and the like.

The fact is that on a wet road understeer can be induced earlier than on a dry road, speed can be less than on a dry road but understeer does not need to be recoverable.
If the vehicle is set up to oversteer then the back of the vehicle should step out before the front loses grip. The exceptions to this would be on snow/ice or oil where the frictional co-efficient may be so low that grip cannot be found.

IMHO

TonyBurns

iTrader: (3)

John,
This is a front end skid, you still cannot have understeer if you cannot steer, you need traction to steer, here you dont have any traction, and turning the wheel wont make one bit of difference if the tyres aint gripping.

You have gone beyond under and oversteer, you may as well take your hands off the steering wheel as you have that much input on the car, and you may as well call a spin extreme oversteer, but it isnt as you cannot steer.
For the time you are beyond traction, you have lost control, so you will either have a skid or a spin, both are extremeties where you can do nothing until you regain grip.

Tony

Pavlo

It's understeer

Gear Head

iTrader: (2)

Agree with John. The term itself 'understeer' perfectly desribes the effect. The car is not turning to the desired angle of lock. It is UNDER STEERING. Understeer itself is when the front tyres are sliding and not gripping 100%. As this rate of grip decreases, what else can it lead to other than a complete loss of grip and hence, front end slide?

DaveD

iTrader: (2)

Is this not terminal understeer?

I agree that if you are trying to turn, then it must be understeer - the wheels aren't locked, so it can't be a skid??

I used to get this when I first got the Scoob. I have now learnt to approach corners more slowly in the wet, and apply the power much more smoothly - that way the amount of understeer can easily be controlled.
The other option open which I sometimes used when the steering wheel wasn't doing anything (at slow / roundabout speeds) was to snap off, and then back on the throttle. This normally transferred enough grip to the front to get the car to turn, but would only be attempted with a shallow steering angle!

Slower in / less throttle is the best route!

Gear Head

iTrader: (2)

I understand how to correct and get around understeer, the question here is, is front end skid understeer? Is a 'donut' classed as oversteer? If it is then it is just the extreme end of oversteer, just as front end skid is the extreme end of understeer.

Fat Boy

John's correct, Tony's definition is incorrect. A front end skid is still understeer in the same way that a rear end skid is the terminal stage of oversteer.

Anyway, the methods detailed above are correct, less early power, less entry speed, less steering deflection, plus mechanical aids, more caster, stiffer rear end, more weight transference ( ALK), geometry, tyres can all help.

ozzy

I'm open to the suggestion that an analy boring text book full of handling dynamics will state the difference between a front-end skid and the definition "understeer", but it sounds like splitting hairs to me.

I'm more surprised that Tony's gone through a thread and not mentioned his Spec C

Stefan