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http://www.autocar.co.uk/blogs/anyt...oll-and-why-peugeots-new-108-has-got-it-right



Autocar said:
Lean, tilt, lurch, sway - usually, we can reckon on body roll being the enemy of good handling. It allows the car’s bodywork too much unsettling inertia of its own, it shift’s the car’s weight in an unhelpful direction and for those sitting inside, shifts theirs about in much the same way.

It’s why racing cars barely roll at all, and why road car suspension engineers are locked in perpetual battle with the compromise between supple ride and teeter-free handling.

But, body-roll doesn’t always kill your enjoyment of a car, as I was reminded while punting a Peugeot 108 through a sequence of switchbacking bends yesterday.

Get your speed and positioning right, and you easily cajole this Peugeot into a gently rhythmic sway, the flattening tilt of its exit from one bend flowing smoothly into the tilt of the next if it’s heading the other way. And this can be quite a pleasant sensation if there isn’t too much of it, and aboard the 108, whose dampers make a decent job of controlling this city car’s body, it proves to be exactly that.

Body roll is at least as much a messaging system as steering feel and the sensation of sideways forces on your torso, the gentle tilt of windscreen against horizon a measure of how ambitious - or foolish - you’re being. Remembering drives in a couple of cars with no roll - or close to it - suspension is a reminder of the importance of body roll as a signal, too.

Years back, Citroën sold a version of its Xantia hatchback with no-roll hydropneumatic suspension. Badged the Xantia Activa, it was the realisation of a no-roll dream nursed by Citroën engineers (and others) since the 1950s.

And the Activa was startling and disconcerting in equal measure. You couldn’t help waiting for the roll that never came, because it’s what you’re used to, and mildly bewildered by the fact that it was very hard to work out where this Citroën’s grip limits were.

The same applied to the Land Rover Discovery II with its ingenious tilt-resisting suspension, whose limit I chillingly uncovered when the Land Rover sledged into straight-line understeer during a fling through a wet Highland bend. Circumspection swiftly followed.

Body roll makes it easier to judge where you sit within the car’s dynamic capabilities. The need to control its tilting build-up with a bit of steering, braking and accelerative subtlety can be a big part of the entertainment. Especially in road cars that haven’t been built to set a smouldering laptime at the Nürburgring.

Which is most of them, particularly at the 108 end of the market. I’d happily trade a bit of roll-resistance for the improved ride and subtle pleasures of body-sway across a whole heap of today’s cars. Although I’m not expecting that alteration to occur anytime soon.
 

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I always thought of a stiff suspension as being more for performance while a looser suspension with more body roll was more for comfort and casual cars. I'd be interested to see what this body roll really feels like. He seems to make a big deal out of it which makes me think that it is pretty pronounced.
 

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well unfortunately with all our modern intelligence we've decided that sporty means rattle your fillings out. No brains, no headache ;)
 

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I would sooner call it a looser suspension instead of body roll. Body roll sounds bad to me, like you feel like the car is about to roll over. Anybody else feel the same way?
 

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Loose suspension is something entirely different. Body roll and roll over are two different things too. The car body can pitch, roll and yaw on its suspension, though modern cars from Europe and Japan don't yaw so much. Roll, pitch and yaw are standard terms from aerospace.
 

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Anyone feel like explaining the difference between the three? Pretty sure I get what roll is. Never heard of the term "yaw" before though.
 

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yaw is rotation, yet distinct from roll. Roll is an effect that yaw COULD cause, but not exclusive.

Ships and boats do it. The trawlers I used to fish round Iceland on years ago did it spectacularly with pitching and some things you would not believe too :eek:
 

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Pitch is rotation where the nose goes up or down
Yaw is rotation where the nose moves to one side and the tail to the other
Roll is rotation where one side goes up and the other goes down
 

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Fishtailing in when the rear tyres lose grip and the rear of the car slides, then grip again, sending the car into a silde the other way, and so on. The car is out of control when this happens.

Yaw can be the car moving on its suspension. Softly sprung cars do this more. It can be a steady state slip angle of the tyres, which is normal. This gets progressively worse the faster you drive and can lead to a slide or a skid if you go too far. It can lead to fishtailing in the wrong circumstances.
 
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