Why use front and rear ARBs

[colinmseries]

This is something I've not been able to resolve from reading. My understanding is that an ARB adds roll resistance to that already provided by the wheel springs/bars and so allows a better compromise of wheel spring/bar rate. I realise that it adds to the overall rate at a particular corner in bump but does not do so in pitch or dive.
Assuming most practical vehicles require more roll resistance at one end than the other, why do I see production cars using an ARB at both ends? Why not optimise the wheel spring/bar rates and add a single ARB to the end needing more help in roll?
I have Milliken and a couple of other books I have seen you recommend to others. Thankyou, Colin.

 

[patprimmer]

I have to say hard cars low cars feel better on a smooth surface.

Regards
Pat
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[Yawing]

yes the maximum grip for a non aero car without any geometry issues with lots of wheel travel usually means soft springs bars...BUT race tracks/roads quite often have chicanes or turns after each other in quick succession, where a quick change of direction is desired. hence why it is best to aim for a reasonable roll per G rate as it correlates to weight transfer rate (ignoring damping and dependant on inertia) so we are back at stiffer ARBs/springs

 

[evelrod]

McPherson struts, Goran. Front spring rate was 650# and the front bar was 600#/inch non adjustable. Rear was live axle, coil over @ 450# springs and 75#/inch nominal, but adjustable to higher rate. 1778 lbs. semi dry wt. (had 12 qts oil and some ballast. I don't recall how much as it varied from driver to driver. SCCA driver wt. is "180". At the time (early 80's) Dennis weighed 200+ and I weighed about 165.

Now, on our Lotus Cortina, I have 300 front/Koni/250 bar and ~150 rear leaf springs/ Panhard bar/ Koni/75+ bar. Car weighs ~1900 wet with 175hp Evelrod/Omnitech twincam. Decent race/show car with my 120 lb. son in it. Not a beater.

Greg, it's a lot easier to design it right in the first place, I guess. Making road cars into race cars requires many compromises not leading to the optimum setup. Certainly the Mini Cooper was, and still is, a challenge. Actually it is quite good and is probably the safest racing saloon I have ever driven. It has saved my ass several times where in a Cortina, Alfa or, BMW I would have been toast! It's not the fastest Mini but it's a loooong way from being a "back marker". Ck the stats on mylaps.com. Several forum members have stopped by at the track and I would be happy to chat with any member, time permitting.

The way I have the suspension (oxymoron?) set on the Mini, the front upper control arm only has one inch between the bump pad to the mounting pad for the bump stop which is removed. In a hard corner at speed things hit and the rate goes off the chart. I need the rear bar to rotate the rear properly. Without it the thing pushes like a plow. It sounds terrible, but it seems to work. Mostly, no one even notices. Vintage rules don't allow much and I already bend the rules to the breaking point.

Rod

 

[ubrben]

"New Postpatprimmer (Automotive)
5 Jan 09 17:46
I have to say hard cars low cars feel better on a smooth surface. "

We're dealing here with response as well as total grip. A softer car will have more grip, but be harder to drive, because of the movement.

Ben

 

[DDurusky]

Just to add some more counter intuitive swaybar stories, my blasted, yet beloved BMWs..

I've found that a big front sway bar on an E30 or E36 will actually combat understeer by limiting roll and compression and thus keeping out of the ugliest places of the camber curve.

Actually, same with VWs (particularly MK4s), you need to raise them above factory ride height to get into a reasonable part of the camber curve! wretched things...

 

[GregLocock]

Yup, as Chapman meant to say, even a bad suspension can be made to work if you don't let it move.

Cheers

Greg Locock

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[evelrod]

Works for me, Greg!

Rod

 

[patprimmer]

That is also provided you don't hit a bump.

Regards
Pat
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[thundair]

Just to add a surprise I found by accident.
I had taken the front sway bar off of my 66 Mustang and mounted it on the rear.
Although it was my second mustang build time got away from me and I was unable to put the bigger bar on the front.
I drove it a couple of weekends and was surprised how well the rear only kept it from rolling up on the outside front tire.
I forgot to mention that it had 600# springs in the front and 250# center eye in the rear.
I didn't leave it that way, but it was an interesting find.
Later I put a small ARB on the back of a Ford van and it really made a difference...

Cheers

I don't know anything but the people that do.

 

[Yawing]

Yup, as Chapman meant to say, even a bad suspension can be made to work if you don't let it move. CheersGreg Locock

This above means stiff springs, not stiff ARBs.

In real life no suspension setup is perfect, there are always compromises. ie camber will roll off on the ourside, or you will have roll steer on the rear axle,etc.

also if your car is as soft as physically possible to just about bottoming out you might have maximised contact patch load variation, but that doesnt help much when you cant get your tyres up to temp to generate any grip

 

[BillyShope]

Some comments from an old timer:

Fifty years ago, the goal was to simply not have any sway bars. The first test cars of a new design went to the proving ground "naked," where the trunks were overloaded and they were put through a series of handling tests. If "problems" were encountered, a front sway bar was added. And, of course, the bean counters would then complain about the extra cost.

I remember a '59 model from one of the big three was scheduled to begin the proving ground tests when a VP showed up, asked about the test, and declared that he would conduct the test himself. He drove it one lap around the high speed oval and declared that it did not need the sway bar. Bootlegged tests later indicated that it definitely should have had one.

One other thing: I know it will never happen, but it surely would be nice if we could all speak the same language. An anti-roll bar (ARB)...to a drag racer...means something entirely different from that which I was trained to call a "sway bar" or "anti-sway bar." To the drag racer, an ARB is a REAR sway bar with a ridiculously high rate and adjustable linkage. The adjustable linkage is used for static preloading and the high rate brings more of the driveshaft reaction torque back to the rear wheels as an aid in equalizing rear tire loads. (This is, of course, for a RWD car with beam rear axle, which is still so common at the drag strips.)

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[evelrod]

Thanks for that link. So often the young folks ask questions that I cannot give an appropriate 'non complicated' answer. The link should satisfy all general questions...especially 'drag racing' which is the most common form of automotive racing in my neck of the woods. I did a bit of drag racing in the mid 1950's and it was great fun (for me, not my parents)! ;o)

Rod

 

[Pcar928]

Lotus elise and exige as well as the Mclaren F1 have only a front sway bar. I know for a fact that the F1 has relativly soft springs and both cars use slightly wide tires in the front based solely on weight distribution, and especially considering the very high power to weight ratio of the F1. Maybe this is to take some of the extra load from only having the front bar without getting unbalanced... So I guess its possible to even things out with a Front sway bar only if you are willing to have wider front tires to balance understeer.