After talking to Iain (mcwrx) the other night about the advanced drivers day he had it got me thinking about this. His car is a Honda S2000, which as we know seems to be fussy in the geometry department, with I think the rear being the main problem?

I watched a video of Iain driving the car or should that be spinning it around some of the corners, yet the instructor didn't! If it was going to break away he corrected it with no problems...he also said the car handled fine for him.

So, could it be the geometry is actually ok, it's just that the average road driver doesn't know how to respond when it feels like the car will spin and take control.

Discuss?

Nice topic ER... If pursued this will be a nose bleed of a read for members ... Your question knocks on the door of the darkest area of chassis/ human calibration...we have...
* Chassis indexing
* Chassis frequency
* Human frequency
* Chassis calibration

Where to start......

The driver needs to understand the physics of whats happening around him/her, be able to detect it through various inputs, visual, audible, (I nearly put Aural, the passenger screaming!) tactile through the steering wheel and seat of the pants. They also need to know the reactions of the car to their inputs. (Weight shift etc.)
Finally they need to be able to decide what is the correct course of action to take and have the speed of response to take that action. (I fail on both counts!)

Your average Joe driver never takes their car to the limit, only finding it when they have exceeded it and they become a passenger. Your instructor with his skill and experience is tuned in to the car and can anticipate the response of the car by feeling the inputs the car is feeding him.
Time, experience and training will give the majority of people improved handling skills, being able to read the car and respond correctly.

A good driver should be able to get the best fron their car regardless of the geometry set up. The better the driver the more they will be able to get from the car, a poorer driver would be losing it all over the place.


h

I will probably struggle to digest it but will give it a shot...it's an interesting subject. As for starting how about number 1 in your list...Chassis indexing, what do you mean by this?




Good post...things like weight shift are one to look into.

I know the majority of the public will not push their cars to the limits, but as you say if they do end up finding it, what's going to happen?

I was driving round a roundabout last week (right hand turn). I was halfway around it and started to accelerate away when I felt the car was going to oversteer (turn more than it should?). The road was a little damp though but I also feel this could be down to how my camber/caster is setup. However, my point is that I could feel it was going to happen so I got off the throttle and let the car straighten up naturally.

I'm not sure if this was the correct way of doing it but it worked for me and has in the past when the back end has swung out (crap tyres!)! I'm sure there would be some drivers who would try to accelerate out of it, try and stop by braking hard or steering the opposite way...would all of these make the problem worse?

Dynamic indexing....... Sam@ TDi summed this up perfectly in a previous post...
.............................
Option one would always be to shed some weight! having a DI soo far above 1.00 can really only be caused by a mis-match in wheelbase to the mass, basically the chassis has far too much yaw inertia for the short wheelbase to influence easily. If we could take just 10% weight out of our demo car we'd have a DI of 1.39, much better!

Unfortunately to take 10% weight out we'd have to seriously comprimise the car's very comfortable characteristics so for some (most) people this would defeat the object.

The other option is to simply accecpt that the car will as a result of it's high DI always make poor use of it's rear axle in terms of producing lateral acceleration and then to try to work around it.

A good example would be the Mitsubishi Lancer Evo-5, it's actually a car with a DI of 1.35 so this would make it pretty vectra/modeo'ish to drive... But Mitsubishi's chassis dynamics team have cunningly swerved this potential marketing disaster by employing an overly pointy geometry and suspension sollution giving the car the ability to change direction light a housefly, then in order for the average joe customer to be able to control and exploit this very odd and naturally quite unbalanced set-up they've been forced to add an active yaw control system in the form of an electronically controlled torque biasing center diff. This solution works so well that not only is the car acceptable to it's intended market it's actually now considered as one of the worlds best handling cars.

Going to read that a few times and digest it overnight!

Still learning about this stuff, and how to react when the back end goes.
A novice driver might turn into the slide and slam on the anchors, throwing the weight forward off the rear wheels, increasing the slide. Wrong thing to do, but for a novice on a circuit it may be the best thing to do rather than power into a barrier.
An experienced driver will turn into the slide and keep the power on, to keep the car balanced and use the steering to drive out of the slide. The reaction for the untrained driver is to slam the brakes on, learing not to do that is very difficult, and not a skill I have achieved! Will keep trying tho'!

h

Controlling an unstable vehicle requires actions at rates that are too high to respond to an intellectual approach. i.e. if you have to think about what to do, you are probably too late.

At the action rates required, we are dependent largely upon reflexes. Reflexes are developed and maintained by practice (think about learning to ride a bicycle) and most of us simply do not get the practice.

I can think of a few winters when there have been icy conditions for long enough to develop my "slippery conditions" skills to the point where I was driving really competently. Even an hour on a skid pan will make a big difference, but if we don't practice, we lose it. A simpler example would be the balancing of clutch and accelerator when starting off. We all do it without a moment's thought, but I'll bet there are few who did it naturally from the beginning when learning to drive.

Similarly, those who get the chance to drive "on the limit" for significant periods of time develop control skills that most of us do not. Understanding the physics of what is happening may help us to recognise what we ought to do, but doing it quickly enough to really be in charge demands practice.

It is a perverse truth that the improvements in vehicle stability resulting from clever engineering (and the introduction of speed limits?) actually make it less likely that most road users will develop and maintain the higher skills of vehicle control.

As an old man, I am certainly not complaining about it, but I doubt if I am nearly as competent at vehicle control now as I was in the days when I drove the less sophisticated vehicles of 50 years ago.

One small example of car vs. driver...

I went to a gravel play-area near me the other day with a friend.

In a Mazda MX5.

Started showing him how to drift etc and he keeps spinning out when he tries! Same thing happened to him in the snow/ice in february, causing him to have an accident.

I thought things felt a bit perculiar when in the car with him driving, so had a closer look at what he was doing.

He was slamming on the brakes when the car started to slide, taking his foot off the accelerator completely (ie, not left foot braking).

After a bit more instruction and very expressed "Don't touch the foot brake for what we're doing here!" (was just teaching him how to kick the back end out under power... no weight shift, not even handbrake)... plus a lecture on why to never slam on the brakes when you're sliding like that (we're both physicists, heh).

Talked to him about it and got the response "was i?"... he didn't even realise he was touching the brake... he said he thought it must have been instictive.

I really didn't understand lol... I've never had a problem like that, my instinct is to control the car (probably due to my racing experience... although I don't remember ever having a problem like that).

I think it might also have something to do with the age you first get in a car or drive something with four wheels.

He had never driven anything on 4 wheels until after his 17th birthday... I, on the other hand, started driving full size cars when I was 3 (steering or pedals, lol) and started karting when I was 6, progressing to gearbox karts further down the line, along with rallying etc etc.

So his instinct is to do perhaps what he was tought by his driving instructor to pass his test and was never really given a chance to push the limit of grip... the person the op is mentioning might be similar?

... just an idea

You're oversteer instincts are probably from your karting days

Don't you mean oversteer "control" instincts? hehe

You're most likely correct... have to react a lot quicker in a kart than you do in a car... hence going in to a tyre wall from 109MPH once (thankfully it was multi-layered!)

Was really pushing for a good lap time & by the time the front left locked up, it was too late to correct... oopsie!

For anyone who has been reading my blog will know I've got the interior stripped out at the moment. Well want can I say, the difference it has made to the handling of the car as well as acceleration has surprised me! The car feels much more responsive now.

I've always been confused with what yaw inertia means, done some 'googling' and I found this...Yaw inertia is a measure of how far weight is from the centre of gravity...do you agree with this? Would the centre of gravity change for each chassis though and would it be the centre or nearer the front/rear?

I have both front seats in my car at the moment but all of the rear and carpet/underlay is still out...the rear weighs quite alot on it's own, plus I only have 1/4 tank of diesel. Unfortunately as it's been raining I can't try the car properly on any corners to 'feel' the difference it has made, but the difference is noticable when driving normally.

Depends where your noticing the change in handling.... I think it would be the polar moment of inertia rather than the yaw.

It's definitely helped with the castor issues I'm having, the front isn't as nervous now, even in the wet! I'm tempted to leave the seats out until the weekend, but put the carpet back in so I can test it some more!

I agree.... It's good to experience a change in the handling and to know why it's changed.

Tony,
can you define please?
I don't understand the definitioins that come up when I google.
h

I'll explain in bits... and then add it all together

Acceleration / braking / turning causes a torque moment... for example, when accelerating, the front of the car gets "lifted" off the ground and the rear gets pushed in to the ground... understand that bit?

Torque is a tendancy for a force to cause a rotation around an axis... the axis in the case of acceleration, would be wherever the centre of mass in the car is & would be lateral (from left to right)... dependant on the exact weight distribution. So, it would pivot about a lateral line through the car.

Torsion is how an object can twist due to an applied torque... ie, the metal in a car isn't strong enough to never bend under torque... when cornering/accel/braking there will normally be a little bit of warping of the chassis.

A polor moment of inertia is a prediction of a certain objects ability to resist torsion. ie, it gives a rough idea of when the chassis will start to bend/twist/warp & helps predict when it will change shape so much, it actually affects the handling/behaviour of the vehicle etc

Such predictions can be used to help set up a car to take in to account this warping of the chassis and do the best to compensate for it.


Hope that makes sense to you bud, ask if it doesn't

Makes sense to me, I've always struggled to understand it as well

Problem is none of these predictions help after the design stage. It's the definition of the handling problem that suggests the type of correction required, or if it's an enhancement what type of materials needed to perfect the chassis past the design limitations.

Your cars weight reduction proved a poor DI but in truth what manufacturer would design a sedan with a naked interior

Changing even one part of the design, i.e. lowering, will throw their hard work designing the chassis out of the window then? Or if you're mazda and raise the car when it's been designed with a lower ride height that messes everything up?

If I had the space I could be tempted to buy another mondeo and strip it properly to use on the track, see how it handles then

Your spot on there mate..... An undressed Mondy would handle much better without question.

do the competition cars not have the active yaw feature then?

No... not to my knowledge..... I suppose it's like saying do they have ABS?.... Most track cars are bare in the enhancements meaning the driver.. drives not the technology.

I think the RS model, which most rally efforts are based upon, has a conventional centre diff. I imagine it's like vTec; a good compromise between everyday use-ability and high performance.

Yep i have to agree mate.

Well, as it was dry today I thought I would see how well the car handled going home. This is not a comparison with the seats in but just a summary of how the car 'felt' today.

The back felt very planted, didn't feel like it was going to break away and stuck to the road, plenty of grip there! This has surprised me though as I've always thought on a 2WD car the back wouldn't be as grippy as the front?

The front when pushed felt like it was going to turn in too fast and the steering feels quite light. I was taking a left turn at a roundabout, going round the bend was ok it was when I started straightening up that the front wheels felt like they still wanted to turn left! I backed off the throttle and all was fine.

Rear seats are going back in tomorrow after work so I will see how the car behaves then.

Oversteer

Knew there was a name for it!

Would taking the rear seats out of caused this?

Yes.... Look at most modified road cars intended for the track.... they strip the interior to reduce weight but this also changes the final weight distribution and DI.... Your car is now nose heavy.

I'll take it easy going home tomorrow then, it wasn't a nice feeling! There's not much fuel left so I'd imagine it's very nose heavy!

So I've experienced oversteer but what was the right way to correct it?

Counter-steering slightly... or... I take it you're talking about the mondeo - so that will be a FWD car right? If so... more power can also minimise oversteer (but only in a FWD car, generally not a RWD car - albeit there are exceptions).

Too much power to the front though & you'll get understeer... something which I think is ALOT more dangerous than oversteer.

Not too easy to explain really - it's the kind of thing you could do with someone who knows what they're doing sitting next to you / showing you how it's done.

Understeer is desireable amongst OEM because if you understeer off the road you'll hit whatever stops you head-on, rather than sideways. More bodywork between the driver and the tree/lampost/etc see ?

So what's better under or oversteering? I've understeered a couple of times and that was scary...I went to corner and the car carried on straight ahead and then turned so I ended up on the other side of the road!!

At least when I oversteered I still felt I had some control and there's less chance of crashing into an oncoming car? The rear seats are back in now so will test it again tomorrow and Friday, see what happens now...

For safety on the road "under", for fun and track "over".

Why do you think I prefer understeer then?

Cos it feels safer?

Sorry I meant I prefer oversteer from what I've experienced, I didn't like understeer at all

And that's why so many manufacturers are going FWD

I would much rather avoid the tree/lampost/etc... which is possible (and quite simple) to control with oversteer... whereas understeer is very hard to control... ie once you've gone, you've gone... unless you're keen enough to left-foot-brake.

Unfortunately... it's evident that most people seem to (slam on the) right-foot-brake when they feel the back end out... from my experience of teaching people how to drift anyway... just comes naturally to them.

Whereas any person who knows how to drive will tell them it's the last thing they want to do!

So certainly in their interest... FWD/understeer is alightly preferential in a tough situation.




For me... oversteer is better... it's very simple to control & very easy to naturally react quickly without too much input needed. The main thing is, if you react quick enough - you will (almost) always be able to control it...

Whereas understeer, once you're at that limit... you're travelling in a straight line and that's the end of the story until you slow down enough to turn or balance the car with left-foot-braking.



Really depends on how the driver is trained...



Because you can control it

Yes I think you're right, oversteer is easier to control than understeer. As you say, once you're going in a straight line it's difficult to correct it. When it happened to me I was only doing 30mph so could slow down quickly enough to get around the bend!

I have never slammed on the brakes if I lose or feel I'm going to lose control of the car...that's something I knew not to do before I started driving so I think it just comes naturally to me to ease off the throttle and let the car sort itself out

I'm just wondering why understeer is deemed safer for road use though?

Because when you get it all wrong for whatever reason the car understeers and hit's whatever it's going to hit head on.

What happens when you oversteer and fail to control it...which way does the car go? Same direction as understeering only sideways/backwards?

"Saturation limits"....... The car will oversteer if driven within the normal parameters, it's only when you push beyond these parameters it (i nearly said she) will understeer.

Yeah - more likely to have a side-impact with oversteer... which is obviously a weaker point with less crumple zone... so bad

I just prefer to avoid the crash all-together and control the oversteer.


Having said that though... the majority of drivers gut reaction is to hit that brake as soon as anything starts going wrong... which is quite often helpful on FWD cars as it shifts the weight back to the front (generally), where it's needed.

Obviously there are lots of exceptions to these circumstances... just general rules.

Weight transition and moment of inertia to speak of a few.

Well since I've had the rear seats back in the oversteer has been reduced alot although I've not pushed it too hard yet. I don't think my car is the best one to test this weight transfer on as the suspension has been modded alot plus I have the castor issues.

Shall we try Chassis frequency?

Would need to know the DI first.

How do we find that out then? Can't we just talk about what Chassis frequency is referring to/what it means etc?

Also back on to the oversteer quickly, I've noticed my car wants to oversteer more when going left compared to right...I take it that's down to the castor?

99% of the time handling complaints are because of the driver rather than the car/ chassis. Nevertheless for now let's go down the comparison route.

By compassion what difference would you expect between driving a....
1: Lada Riva
2: Evo 10

Is that in answer to my oversteer question? I thought it might be how you set the car up due to the castor issues I was having making the car unstable? The left side has more camber than the right and the right side more caster than the left.

Lada is over 20 years old and the Evo 10 obviously a new car so there would be a big difference in the suspension/chassis plus other parts. I would imagine the Lada has thin ARB's, small rims/tyres, standard suspension at normal ride height so the ride wouldn't be great...alot of body roll and not much grip when pushed hard? The Evo has been made as a fast road/track car so would be pretty much planted motor?

Forgetting the handling differences, which one of the two would be harder to drive in your opinion?