Suspension question - anti roll bars

[AMC Rebel]

Having just replaced all 4 drop links on the Mondeo got me thinking. Don't anti-roll bars tend to inhibit suspension travel and work against the otherwise independent operation (of independent suspension)?

[spartacus]

You need to Google this, or read Alan Staniforths book, the title of which I can't remember right now. To some extent you're correct but there are many issues involved.

[M'coli]

The Race & Rally Car Source Book is bloody excellent! (https://www.amazon.co.uk/Race-Rally-Car-Source-Book/dp/1859608469)

 

In many ways your observation is correct, but the effect is marginal in bump and rebound in a way that a soldi axle isn't - the "independent" part of independent suspension is that if one wheel of an axle hits a pot hole or bump, the other wheel of the axle is generally unaffected by the bump, whereas on a non-independent system, the other wheel is and always stays parallel(ish) to the one hitting the bump, because they're linked solidly to each other by a bar or tube or suchlike.

[spartacus]

Yep, that's the book.

[Asimo]

Whenever I have done drop links, I've wondered what the car concerned would be like to drive with no anti roll, ie just leave the links off.  I have never bothered with that experiment but I would expect a much calmer ride and better traction. (And more roll of course)

 

Suspension design is a fascinating topic and is a good example of how, in engineering design, much of the work is balancing opposing requirements to achieve an acceptable compromise. One of my engineering heroes is Alex Moulton and he was very against the negative effects that anti roll bars have on ride

[forddeliveryboy]

Having just replaced all 4 drop links on the Mondeo got me thinking. Don't anti-roll bars tend to inhibit suspension travel and work against the otherwise independent operation (of independent suspension)?

 

tl;dr - they're effective, cheap, badly flawed but with careful application work well enough.

 

 

Yup. They mess with everything, but they cost pennies and resist roll so well that manufacturers love 'em. To be fair, they work very well on smoother roads and when they're not too stiff compared with the wheel springs and shocks. Done right and a car can have softer springing but better controlled roll without the side-effects being too obvious.

 

All but the very fastest T16 Saab 900s (pre-GM) did without arbs as did loads of BL cars. Setright labelled them 'an admission of failure', but for the cheapo MacPherson strut they're pretty much a necessity cos they can't cope with much roll.

 

For every action, there is an equal and opposite reaction, said Mr Newton. So what's the reaction to a car heeling less through a corner? Load is transferred from the inside wheel to the outside one, reducing grip, which is minimized by widening the tyre contact patches (so smaller front to back) - which creates more drag, problems with standing water, poorer grip on less than perfect surfaces and a bigger gap between wet and dry grip.

 

Add in the loads the nearside wheel feeds to the offside suspension and the offside to the nearside, the reliance on the suspension to try and damp the arb oscillations on poorer surfaces and lumpy roads and the loss of wheel articulation when no roll resistance is needed and it's clear why Toyota/Lexus, McLaren, Daimler-Benz and others are using alternative controls for roll.

 

McLaren uses the neatest system which is a more developed form of that used by the Toyota 4x4s, conceived by an art lecturer in Western Oz who was inspired by his old Citroën DS and designed a clever self-energising anti roll system which allowed adjustable roll stiffness. And his Toyota pickup was able to clamber over a tree trunk, as well as handle a slalom course with less heel and more quickly.

 

Slightly* ironically, Citroen hired the technology for its WRC cars until the WRC realised its effectiveness gave the cars an unfair advantage and banned it.

 

http://www.nauti-craft.com/chris_heyring.html

[M'coli]

Anti-roll bars also affect the behaviour of the axle at the other end of the car...

[forddeliveryboy]

Whenever I have done drop links, I've wondered what the car concerned would be like to drive with no anti roll, ie just leave the links off. I have never bothered with that experiment but I would expect a much calmer ride and better traction. (And more roll of course)

 

Suspension design is a fascinating topic and is a good example of how, in engineering design, much of the work is balancing opposing requirements to achieve an acceptable compromise. One of my engineering heroes is Alex Moulton and he was very against the negative effects that anti roll bars have on ride

It's possible to remove arbs but you're left with a car which can be bloody dangerous.

 

Moulton was right, but motoring is now mostly at medium and low speeds with lots of roundabouts. When people do go quickly, it's usually on smooth surfaces and straightish roads.

 

So well integrated arbs are perhaps more of a good thing than bad - only rarely today do you follow a car along a B-road where the occupants' heads are snapped left and right in the typical rock-roll motion of a vehicle where the bar rules the suspension. The wheel springing has been made sufficiently stiff that shock vertical movements hide the sideways neck-snaps.

 

But nothing comes close to supple springing, a low centre of mass and good geometries. Since this allows minimial arb stiffness or even none at all, it's a virtuous circle. To drive along an average English road at a decent lick, when the nearside wheels can move up and down without affecting the body or offside suspension is a bloody revelation.

[Stanky]

My only contribution is having replaced both front drop-links on a peugeot 206, then driven 60 miles, turned the steering onto hard lock to get into a parking space and had both of them twist clean off, I found no seriously untoward handling on the return journey, sans droplinks (and I assume therefore turning the ARB into a dead weight of no handling benefit?)

 

I suspect that spirited driving on back roads may have highlighted some more body roll, but careful driving on dual carriageway A-roads did not show any major shortcomings.

 

shit quality drop links are shit though and a false economy.

[RayMK]

It used to be common, particularly in the front engine, rear drive era, for an anti-roll bar to also provide the fore and aft location of front wheels suspended by MacPherson struts, enabling the arm for lateral location to be lighter and thus reducing unsprung weight.

 

Suspension design is indeed a fascinating subject.  Unfortunately, most modern cars have gone for wide, squat section tyres which give excellent grip on good surfaces but, to keep them flat on the road, suspension travel is limited so as to minimise geometric effects on wheel camber and roll is usually controlled by a stiff ARB.  The combined effect is often a jiggly low speed ride and a car which is bloody uncomfortable on B roads.

 

When I had a Citroen CX GTi Turbo 2, I considered its suspension to be perfect.  Roll was controlled adequately and good suspension travel, self levelling and low rate hydropneumatic springs (spheres) gave the car an extremely comfortable ride on motorways, A, B roads and country lanes while giving beautifully responsive, predictable handling.  Sadly, the accountants and the Nurburg Ring fanatics have taken the ride/handling compromise too far in the wrong direction.

[forddeliveryboy]

The squat tyres are dictated by strong anti roll bars (transfer of load to the outside tyre) which in turn are made necessary by strut suspension. Compared with supple wishbone suspension and taller tyres, the result is often a slower car unless you drive mostly on smooth ring roads littered with roundabouts.

Too right about the CX, they're utterly magic - but most people don't drive so quickly that such amazing grip and road holding is ever appreciated. Even many Citroenistes (especially outside of France) believed the marque was all about comfort, when in reality the comfort was simply the by-product of making a car grip real roads as well as possible.

As everyone today knows*, the stiffer the ride, wider the tyre, lower the profile and stiffer the arbs are the better your steed holds the road. Too little understanding that what works on a track doesn't on real roads - and t'other way round

[AMC Rebel]

My AMCs don't have ARBs (or sway bars as the Americans tend to call them). neither does my Chevy, but the body roll does take some getting used to  

[M'coli]

Neither of the Pug 106s had any ARBs, this may have contributed to me being tugged on the way to work one night because "It was on its door handles, you were driving it as if you'd stolen it..." according to the rozzer that spoke to me.  Good job he'd not seen me driving it the night before...

The Imp didn't have any as standard, but they didn't really suffer from too much roll anyway.

[forddeliveryboy]

It used to be common, particularly in the front engine, rear drive era, for an anti-roll bar to also provide the fore and aft location of front wheels suspended by MacPherson struts, enabling the arm for lateral location to be lighter and thus reducing unsprung weight.

 

 

Audi 100s formed the forward link for the front strut with the arb and I'm always surprised that such a simple, relatively crude suspension layout can be so comfortable and poised (it wasn't on Polos, which used a similar layout). I think they used high quality damping on the A6-named ones, which together with more progressive rate springs and decent travel made for a suspension which worked truly well.

[AMC Rebel]

Old Fords did that too - my 1600E, Mk1 Essy Van etc.

[Snipes]

Yeah the rally developed Cup subframe introduced a dedicated link called a "tension rod" that took wheel positioning away from the ARB.

[tommytwo]

Talking about Fords and Drop Links, I just replaced one on my Mondeo 3 which failed the MoT. Turns out when I show up for a  retest, the tester tells me I have replaced the wrong side. It was the other side that I should have done. And only one day left tomorrow to get the job done and the car retested.. I despair sometimes!

[4wheeledstool]

The subframe fitted to my grey Polo does away with the ARB.

 

 

With stiffer springs, the roll isn't too bad - but the bonus is now the wheel stays in the right place when hurling it round corners. When the ARB is locating the bottom of the strut as standard, the wheel moves forwards and backwards a fair amount when spanking it. Driven back to back with the subframe car, a standard one feels a bit vague and woolly when pushed, but much more pleasant when pootling.

[lisbon_road]

I have found one of the links on a Mk3 Astra broken.  Didn't seem to make much difference when I replaced it.  They're a weak point, but can be changed without taking the wheel off or lifting the car and cost nothing so not something to be worried about.

 

The way they work with a simple thread at the bottom would make fitting them to another car easy.  Many years ago I planned to fit an anti roll bar to the Viva but it would not cross my mind now.