[SPIKE ARRESTOR]

Originally Posted by Sutripta

@pratheesh: would you have searchable (ie not scanned) pdf's of Milliken, and Gillespie.

Unfortunately not, I have both these books, but in the form of scanned pdf's. Both are like Bibles to me, I am thinking of buying hard copies soon.

I know why you ask.

Spike

[shankar.balan]

Common sense would presumably dictate that one cannot expect to drive a tall SUV the way one would, a low slung sedan or hatch, especially around corners and on twisty roads.
However, for those hell bent on proving their decidedly phenomenal capabilities, in blatant defiance of common sense and/ or the laws of physics, their appointments with the dark side will probably come sooner rather than later.
I guess they all are, in some sense, 'seeking close and rapid contact with the almighty' and given the above circumstances, are bound to meet with unprecedented success in their stated aim as outlined in this sentence!

[venkyhere]

Originally Posted by shankar.balan

Common sense would presumably dictate that one cannot expect to drive a tall SUV the way one would, a low slung sedan or hatch, especially around corners and on twisty roads.
However, for those hell bent on proving their decidedly phenomenal capabilities, in blatant defiance of common sense and/ or the laws of physics, their appointments with the dark side will probably come sooner rather than later.
I guess they all are, in some sense, 'seeking close and rapid contact with the almighty' and given the above circumstances, are bound to meet with unprecedented success in their stated aim as outlined in this sentence!

i think the real problem is this word 'common sense' -> this is more connected with human 'psyche' than human 'thinking'. Here is why :
Why do we humans have this 'competitive' streak whether it be a case of making money, winning a game of chess, scoring the highest marks in an exam, lifting the heaveiest weight, running 100m in the fastest time, etc etc ? -> we humans, are nothing more than glorified animals who want to 'increase the chances of survival of oneself and propagate ones genes' more than anything. Proving 'i am better than you' is what we call 'ego boost' but in reality it is a way of re-assuring oneself that my chances of survival and/or getting a mate is better than others. This is the sole reason for 'competitiveness'.

But somehow, along the way in our evolution, the human has learnt to reduce the number of instances in daily life to supress this 'urge' to prove 'i am better than you' if the circumstances risk his/her life. => this I think is what we call 'common sense'.
Unfortunately, the urge to move fast is one such 'competitive need' that has not diluted easily. I mean, the same person who is ready to perform stunts on the highway to impress the co-passengers or to impress other vehicle drivers on the road, will very sensibly not risk crossing a slippery stream on foot to take a photograph even though he/she could have impressed others with his 'balance' and 'confidence'.
So, that is the nature of the beast we are discussing here - NEED FOR SPEED is less cerebral and more PSYCHE.
99% of the drivers in the world, right from F1/rally drivers to the teenager who just got his license yesterday, believe they are better at driving than what they really are.

[san_jayd]

Mates, the insults are immature-ish. This is a place to trade information, not jabs.

Originally Posted by Sutripta

Maybe you could point out what is relevant in that,

Certainly. This is from the article in wikipedia:

Drawbacks
Excessive roll stiffness, typically achieved by configuring an anti-roll bar too aggressively, will cause the inside wheels to lift off the ground during very hard cornering. This can be used to advantage: many front wheel drive production cars will lift a rear wheel when cornering hard, in order to overload the other wheel on the axle, limiting understeer.

This is from the article in turnfast.com

As with all good things, more is better only to a point. Because the anti-roll bar connects the left and right sides, this reduces the independence of independent suspension. Too stiff a bar, and you can cause too much loss in the ability of the left or the right wheel to independently respond to road surface imperfections. The purpose of suspension is to maintain maximum tire contact with the road. The purpose of independent suspension is to allow the left and right wheels to each seek that contact separately. The left wheel may need to be going down when the right needs to be going up. If they were tied together as with the old floating rear axles, one or both of the wheels is not achieving maximum contact. In fact, too stiff an anti-roll bar can actually cause an inside wheel to lift completely off the ground during hard cornering.
When cornering, the bar will twist with the outside end being pushed down, and the inside end being lifted (just like the body of the car). On the outside tire, this downward pressure helps increase tire traction. However, on the inside tire, the anti-roll bar is pushing up on the suspension reducing the downward force the spring is trying to place to keep the tire on road. If the anti-roll bar is too stiff, it will overpower the spring, prevent it from extending enough to keep the tire on the road, and the wheel will actually lift off the ground.

Originally Posted by Sutripta

In the meantime, can't understand
a) your original statement of 'at the same speed'.
b) relevance of sudden appearance of antiroll bars in current discussion.

a) Ignore it. I misunderstood you when you were inquiring about suspension travel.
b) Since their whole purpose is to prevent body roll, I thought they should be included.

Originally Posted by Sutripta

Lets return to the original premise that harder suspension -> 'more likely' to topple. ('more likely' is unquantified as of now)
Let us start with two cars, one with harder suspension than the other, but otherwise identical. (esp. identical with respect to ride height, suspension travel, suspension geometry, and weight distribution). And then apply mallumowgli's line of thought. Since his and yours conclusion are different, could you point out the fallacy in his reasoning.

I read the entire case study which mallumowgli has put up and there is no reason to disbelieve it. Points to be noted are that the study was done on independent suspension, non-linearities in stiffness were not considered, and actual testing was not done. And what that study didn't mention is by how much can a person go on increasing anti-roll bar stiffness, and what were the exact stiffness values in the vehicle used in the case study.

The conclusion which I would make overall is that too soft a suspension will give rise to excessive body roll, while too stiff a suspension will cause inside wheels to lose contact with the road, both increasing chances of rollover.

[Sutripta]

Originally Posted by SPIKE ARRESTOR

I know why you ask.

Spike

I'm sure you do! Equally sure others don't!

Originally Posted by san_jayd

Certainly. This is from the article in wikipedia:
....
and the wheel will actually lift off the ground.
.....
b) Since their whole purpose is to prevent body roll, I thought they should be included.

I would say a forced entry in our current discussion.
In any case, anti roll bars, because of their simplicity, are (mis)used sometimes, making it a controvertial subject. Maybe in another thread.

a) Ignore it. I misunderstood you when you were inquiring about suspension travel.

Not really enquiring. More a pointed question.

I read the entire case study which mallumowgli has put up and there is no reason to disbelieve it.

Was refering to his other previous post. http://www.team-bhp.com/forum/techni...ml#post3182160

Lets recast his line of thought:

Take two otherwise identical cars (as defined in http://www.team-bhp.com/forum/techni...ml#post3183692. To prevent nitpicking, ride height and weight distribution refers to static cases.) Also note that tweaking antiroll bars is not normally considered making the suspension harder/ softer.

Take the case when one inner wheel is just about to leave the ground. ie all suspension travel has been used up. This being a matter of geometry, the attitude of both cars is the same.

Now work out the forces (esp the horizontal component) necessary to get each of the cars in that attitude. Will the forces differ. What will be the cause of this difference, and what would it mean in the context of our current discussion.

Regards
Sutripta

[FlatOut]

I have enjoyed reading this thread. There is so much more to the whole debate than at first meets the eye, as plenty have touched on. I have included a video of five SUVs in a swerve test on a wet road – one of them appears to be compromised by its electronic safety system, only one makes it through without hitting obstacles.
One of the worst-ever vehicles for turning on its side through corners was the Suzuki SJ Jeep - it occurred regularly. This vehicle had stiff suspension. On the other hand, the vehicle which everybody expected to tipple over through a corner - the 2cv - never did and couldn’t be made to, no matter how hard you tried. It had perhaps the softest suspension of any car ever.

http://www.youtube.com/watch?v=P21lwEYY-D0

Originally Posted by DerAlte

If what you say were to be true ("the stiffer suspension makes it behave like a single unit(relatively)"), wouldn't rally cars - with stiff suspensions and virtually 0 body roll under normal circumstances - be spending more time on their sides or roofs instead of wheels

Successful rally cars I have observed have suspension (and wheels, tyres and geometries) tuned for a particular rally, aiming to keep the body as stable as possible while the suspension allows the wheels to articulate freely to maintain maximum grip on the track surface. Ideally there would be as little bottoming out as possible while having the suspension working well – restricted movement is transferred to the body which creates additional grip problems.

Originally Posted by shankar.balan

Common sense would presumably dictate that one cannot expect to drive a tall SUV the way one would, a low slung sedan or hatch, especially around corners and on twisty roads.
However, for those hell bent on proving their decidedly phenomenal capabilities, in blatant defiance of common sense and/ or the laws of physics, their appointments with the dark side will probably come sooner rather than later.
I guess they all are, in some sense, 'seeking close and rapid contact with the almighty' and given the above circumstances, are bound to meet with unprecedented success in their stated aim as outlined in this sentence!

How very true.

Originally Posted by chinkara

I don't see where this point of "Many Indian users buy SUVs for the wrong reasons" is coming from. Whatever their reasons, they are selecting a product, and if they are satisfied with the product then that should be it.

Like the mythical Punjab Dhaba owners using washing machines for lassi making, it is none of our business.

Disagree. Mass use of large 4x4s affects every other car driver. They form a visual barrier when overtaking, for example, are a lot nastier to hit/be hit by in an accident and are often driven as if they are as stable as a normal car with a false sense of security in the cabin.

[DerAlte]

Originally Posted by FlatOut

... On the other hand, the vehicle which everybody expected to tipple over through a corner - the 2cv - never did and couldn’t be made to, no matter how hard you tried. ...

Wonder why you used any other can than the Deux Chevaux at all? Or is it that each car has strong and weak points and we don't always hunt for the ideal car with no weak points? Can you compare the ground clearances of the Suzuki 'jeep' and the 2CV in the same breath? For the purposes of off-roading, they are obviously not comparable. This despite the fact that the 2CV and the venerable Suzuki Alto (in it's Indian avatar - the Maruti 800) perhaps have endured and conquered more bad roads and cross-country rides than the Suzuki off-roader.

Originally Posted by FlatOut

... Successful rally cars I have observed have suspension (and wheels, tyres and geometries) tuned for a particular rally ...

They still have extremely stiff suspensions, and vary only the damping - never the geometry (wheels and tyres are a different subject altogether, not suspension). The 2 successful ones I have sat in (Mitsubishi EVO and Subaru Impreza) were so bad for passengers no wonder they use special seats for the driver and navigator.

Originally Posted by FlatOut

... Disagree. Mass use of large 4x4s affects every other car driver. They form a visual barrier when overtaking, for example, are a lot nastier to hit/be hit by in an accident and are often driven as if they are as stable as a normal car with a false sense of security in the cabin.

That is honestly quite a weird logic against SUVs!

* Shouldn't you be complaining about buses and trucks on the roads too?

* Don't traffic accident statistics show a higher number of 'normal' cars causing / being involved in accidents than SUVs (percentage of each class of vehicle on the road)???

Isn't the issue that of bad drivers, bad driving habits and ignorance of limits of what they are using? How is it different from many individuals who get drunk and make a nuisance in public? Toppling in most cases is a direct result of bad driving and lack of vehicle control. Sure, a bad design doesn't help, but being a human (not an animal without intellect) why would one put oneself in a situation like that? That is a difficult question to answer.

[mallumowgli]

The question still remains, if you compare two 'equal' cars - same models, same manufacture, same everything, but with different suspension set-ups : one softer and the other stiffer, which will topple first?

[Guna]

Originally Posted by mallumowgli

The question still remains, if you compare two 'equal' cars - same models, same manufacture, same everything, but with different suspension set-ups : one softer and the other stiffer, which will topple first?

After this debate, I have been going through some articles on roll-over stability and surprisingly, most of them talk about parameters like CG, track width, but not about the suspension. But after all the debate I have come to conclusion that the car with softer suspension is prone to topple first because, when the car rolls the CG shits a bit towards the inner wheel making it more unstable.

[1100D]

Originally Posted by mallumowgli

The question still remains, if you compare two 'equal' cars - same models, same manufacture, same everything, but with different suspension set-ups : one softer and the other stiffer, which will topple first?

Very simple, the softer suspension vehicle will topple first. Although, on a less than perfect road condition, the stiffer suspension vehicle will probably slide out earlier (can still be controlled though). I have experience of same vehicle with 2 different anti-roll bar setup, reverted back to lighter Anti-Roll bar.

[mallumowgli]

Originally Posted by Guna

when the car rolls the CG shits a bit towards the inner wheel making it more unstable.

Though this seems logical, the debate has been that does this make the vehicle topple earlier than a stiffer one? san_jayd argument has been that the stiffer vehicle would reach the end of suspension travel earlier thus pulling up the inner wheels.

Originally Posted by 1100D

Very simple, the softer suspension vehicle will topple first. Although, on a less than perfect road condition, the stiffer suspension vehicle will probably slide out earlier (can still be controlled though). I have experience of same vehicle with 2 different anti-roll bar setup, reverted back to lighter Anti-Roll bar.

Please refer the above argument - it has not been so simple after all. No conclusive justification has been given as yet in this thread (let us leave out anti-roll bar out of this argument, since the effect of that on suspension is still a debate!!)

[Guna]

Originally Posted by mallumowgli

Though this seems logical, the debate has been that does this make the vehicle topple earlier than a stiffer one? san_jayd argument has been that the stiffer vehicle would reach the end of suspension travel earlier thus pulling up the inner wheels.

I am not sure if he was saying that. If the suspension travel is the same, on a given curve and at a fixed speed, the car with stiffer suspension rolls lesser, which means it still has a potential to flex/compress bit more before the outer wheel starts lifting. On the other hand the car with with a softer suspension has already leaned enough (and the springs can't flex anymore).

[FlatOut]

Originally Posted by Guna

I am not sure if he was saying that. If the suspension travel is the same, on a given curve and at a fixed speed, the car with stiffer suspension rolls lesser, which means it still has a potential to flex/compress bit more before the outer wheel starts lifting. On the other hand the car with with a softer suspension has already leaned enough (and the springs can't flex anymore).

In a certain type of situation this could be the case. Different situations will suit different setups - a suspension which is a little stiff is less able to turn the cornering forces into movement of the body on its suspension and so the whole car may be more prone to tipping. But, with suspension which is too soft a rapidly heeling body may hit the stops abruptly and this inertia may send the vehicle into a roll. Tyre behaviour plays a huge rôle in what happens in this sort of situation - it is possible that they can trip the car up. This is what happened to the Mercedes A class when it failed the Swedish elk test.

Originally Posted by DerAlte

Wonder why you used any other can than the Deux Chevaux at all? Or is it that each car has strong and weak points and we don't always hunt for the ideal car with no weak points? Can you compare the ground clearances of the Suzuki 'jeep' and the 2CV in the same breath? For the purposes of off-roading, they are obviously not comparable. This despite the fact that the 2CV and the venerable Suzuki Alto (in it's Indian avatar - the Maruti 800) perhaps have endured and conquered more bad roads and cross-country rides than the Suzuki off-roader.

I was challenging the idea that a car with soft suspension is more likely to tip over in a corner, not that a car with higher centre of mass will be more likely to tip. I've included the clip below just to make people laugh, not as any scientific comment. It rather backs up your comments about cars intended for the road having endured more poor roads and cross-country than off-road vehicles!

http://www.youtube.com/watch?v=88pfy3ibfGY

Complete nutters, the lot of them.

Originally Posted by DerAlte

They still have extremely stiff suspensions, and vary only the damping - never the geometry (wheels and tyres are a different subject altogether, not suspension). The 2 successful ones I have sat in (Mitsubishi EVO and Subaru Impreza) were so bad for passengers no wonder they use special seats for the driver and navigator.

Obviously this is your own experience. In mine, whatever motor competition I've been involved in, components like springs which have such a massive effect on car behaviour are changed according to the surface, foundations and even weather. Damping and hydraulic bumpstops are altered whilst driving in the case of rallying in the WRC (World Rally Championships). Here is a little excerpt from http://wrcbehindthestages.blogspot.c...prings-co.html

In the mid to late 90's, the works Toyotas were running very hard springs, in the range of 50-80N/mm on the front for gravel and as much as 90-100N/mm on tarmac, if I remember correctly. Things changed drastically with the involvement of top Nordic drivers and Toyota Team Sweden (TTS) who went, together with some evolutions of the Öhlins dampers, way down to values around 45N/mm on the front. In those days, this was a revolution.

Reading further into that page,

By the time I had joined Ford they were using 30N/mm on the front generally, for gravel, and around 50N/mm for tarmac (not so sure anymore on the tarmac rates, although I do remember we had a rain setup where the rates went down by 5N/mm all around). On gravel the standard setting was 30N/mm front and 25N/mm rear. I asked for a 30/21 ratio for my car. This gave my car a bit more grip on the rear and hence a bit more understeer, which suited my driving style better. I once tried a 30/27.5 ratio during Acropolis shakedown. It was slow and rubbish for me, way too much oversteer. All this to say that springs are super important for car balance and sometimes you don't know if you have the right setup until you tried them all and compare on the clock. In my case, I was significantly faster with the 30/21 balance even though the 30/25 felt better.

Originally Posted by DerAlte

That is honestly quite a weird logic against SUVs!

* Shouldn't you be complaining about buses and trucks on the roads too?

* Don't traffic accident statistics show a higher number of 'normal' cars causing / being involved in accidents than SUVs (percentage of each class of vehicle on the road)???

Isn't the issue that of bad drivers, bad driving habits and ignorance of limits of what they are using? How is it different from many individuals who get drunk and make a nuisance in public? Toppling in most cases is a direct result of bad driving and lack of vehicle control. Sure, a bad design doesn't help, but being a human (not an animal without intellect) why would one put oneself in a situation like that? That is a difficult question to answer.

It may be weird to your mind, but to me it makes sense - the more 4x4s on a given road, the restricted is one's line of sight. Which in itself is a major factor in road safety. I do complain about the number of trucks on the road - they are a major hazard in more ways than one. In the UK long-haul freight has steadily been removed from the railways onto roads, which I think is a poor decision given our existing traffic density. Government encouraged this since lorry drivers are mainly self-employed and do not go on strike, unlike railwaymen in the 1970s and early 1980s.

As for crash %s, there is a report here http://www.lscp.org.uk/lrsu/www/down...SUV_report.pdf which suggests that fewer SUVs are involved in accidents (London) but that is the headline for newspapers, reading the report reveals the facts. I would say fewer are involved in crashes because their drivers will be older, that they travel fewer miles than cars and they give a better view of the road and traffic ahead. I suggest that as SUVs become less agricultural and more car-like, their safety will improve for a variety of reasons. But for other road users SUVs are a greater hazard than a conventional motor car - they restrict vision and are significantly heavier than cars. At least in the UK we managed to ban bull bars, another SUV driver's 'safety addition', many years ago.

As usual, I agree wholeheartedly with the idea that the biggest nut in any vehicle is usually the one behind the wheel. Driver education is woefully lacking in most countries, I believe.

[Tejas@perioimpl]

For the technically oriented, here's a nice pdf:

Abstract:

In this paper, we present a methodology based on
multiple models and switching for real–time estimation of center
of gravity (CG) position and rollover prevention in automotive
vehicles. Based on a linear vehicle model in which the unknown
parameters appear nonlinearly, we propose a novel sequential
identification algorithm to determine the vehicle parameters
rapidly in real time. The CG height estimate is further coupled
with a switching controller to prevent un–tripped rollover in
automotive vehicles. The efficacy of the proposed switched multi
model/controller estimation and control scheme is demonstrated
via numerical simulations.

Full article here:

http://www.hamilton.ie/selim/SolmazA...ten_Yale08.pdf

[volkman10]

If you thought Midsize SUVs Were Safe, reports indicate it is a misconception.

The latest batch of crash test results from the Insurance Institute for Highway Safety IIHS reveals that a total of nine such vehicles that were recently tested to see how well they withstand the most brutal of frontal impacts, the small overlap test; only a handful earned laurels.



These are mid size SUV's, imagine how the new Gen Crossovers would fare?


http://www.carscoops.com/2014/04/tho...safe-iihs.html