My Dad's '58 Chevy had coil springs and a 3-link rear axle (that did not appear in the '59 model). If it had an ARB, it was small. In, er, impromptu testing, I found that the car would easily roll far enough to rest on the outer bump stops, at which point the effective roll stiffness went up far enough to allow more vigorous cornering.

I have read accounts of fleet vehicle buyers being cheated (their words) out of ARBs by suppliers who executed the required tests (e.g. slalom through a line of cones) using a skilled driver who had no apparent difficulty doing so, but then finding their fleet drivers were unhappy with the vehicles' handling in service.

I am not in the vehicle business, but I am not aware of a general specification that specifically requires ARBs. It is, here in The Colonies at least, up to the buyer to specify exactly what is desired, or to require performance tests as mentioned above, with acceptance criteria that indirectly force inclusion of ARBs, or whatever features are required.

Perhaps IVECO thought that roll stiffness was not a major requirement for a 6x6, or maybe they thought that too much roll stiffness would lift a wheel on difficult terrain, when the wheel's tractive effort was very much desired.

Mike Halloran
Pembroke Pines, FL, USA

The problem with ARBs is that they reduce wheel articulation in roll, so they hurt off road performance. There are no legislative rules that I know of about roll stiffness or roll gain, although ARBs do affect some of the legal events, for example NHTSA fishhooks will be affected by the ARB. Many light trucks have a great deal of FARB in order to encourage terminal understeer, and improve traction if they are RWD.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

On this side of the pond, very few heavy-duty vehicles have anti-roll bars ... but the design of the suspension may accomplish the same effect by other means.

Thanks dear @BrianPetersen
But I have read many catalogues of heavy trucks and the result is that almost all of them have anti-roll bar (front & rear).
what do you think of why only the 6X6 doesn't have ARB on rear axle???

dear @GregLocock
So if ARBs are useless in heavy vehicles, why are they used in almost all catalogues of trucks?
I will be thankful if you take a look at pktrucks.com Go to chassis cab or tractor vehicles...
You will see in catalogues that almost all have.
Thanks if you think about it and explain why?

thanks dear @MikeHalloran for a complete try for helping,
Actually I want a technical guide to when the supplementary rear axle ARB can be added?

Why don't you think of the ARB need from the standpoint of "what total roll stiffness is required to control roll angle and roll steer requirements" ? If the springs are the same as non-6x6 trucks, there already is extra roll stiffness. If the frame is the same as non-6x6 trucks, the frame strength may be insufficient to support the extra anti-roll forces. If the extra axle(s) are in the way of ARB mounting points, then the efficiency of a roll restraint package may make it not worthwhile adding. If they have air springs, it is possible to manage roll stiffness actively (so of). Roll bars can contribute to rollover, too. And limit wheel travel when it's a good idea to have it.

What have your calculations told you about total roll stiffness needed and distribution front and rear and frame strength? If this is not in your skills inventory, leave it up to the manufacturer.

I did not say useless.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

I would look at the particular truck the drivers are griping about, figure out who the suspension supplier is and ask them about using an ARB. Agreed with Brian's comment above, most medium and heavy duty trucks I've worked on here stateside haven't had ARBs.