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Anti Roll Bar Steel

Anti Roll Bar Steel

(OP)
I have D=15mm ARB with ~ 100 lb/in stiffness, made of 4130 steel.
I would like to make a new 20-25% stiffer bar.
I'd like to keep all the dimensions the same, if possible.
Would changing to a different steel grade with higher Modulus of Rigidity change the stiffness enough?
Going thicker on D would do it,I know, but I'm trying to avoid more changes (bushings, end plates,etc.)
Any thoughts?

Mater artium necessitas

RE: Anti Roll Bar Steel

Roughly speaking, all steels have the same elastic moduli, so your only option is to change the size or change the material all together. For metals, you can try beryllium or molybdenum. Or, try ceramics or composites.

RE: Anti Roll Bar Steel

If the vehicle has alternative bars sizes available (smaller perhaps ?), just put another bar on the same attachments along with the original bar.

RE: Anti Roll Bar Steel

I bought the biggest factory bar for my '66 Galaxie hardtop (390 ci, 325 claimed HP, 4 speed, air conditioning) when it was nearly new. I loved that car.

Anyway, it turned out that it already had the biggest factory bar, so now I had two identical bars.

I spent a couple hours with a soaped kitchen knife, slicing the rubber D-shaped factory pivot bushings so they would both fit inside the retaining straps, while also keeping the bars about 1cm apart. I cut up some old shock absorber bushings to space the bar ends apart, with both bars installed on the factory link struts.

I don't know if your ARB setup has enough extra rubber/space to allow something like that, but if so, it's effective and cheap.

The double bar was still working fine when I sold the car, five years and 160,000 miles later.

Mike Halloran
Pembroke Pines, FL, USA

RE: Anti Roll Bar Steel

(OP)
Thank you everybody.
Well, I could go with larger D and taper down the ends to fit inside the control arm sleeves.
4130 or perhaps 4340 would be better?

Mater artium necessitas

RE: Anti Roll Bar Steel

1.25^1/4 = 1.057

15 mm X 1.057 = 15.9 mm Φ.

I wonder if shortening the arms a bit would be easier.

RE: Anti Roll Bar Steel

Mike and Tmoose you are the best. I love simplicity, translates into mod terminolgy as as lateral thinking in old terms, basics.
Golfpin

RE: Anti Roll Bar Steel

(OP)
how about using BERYLLIUM COPPER ALLOY 173 ?

Mater artium necessitas

RE: Anti Roll Bar Steel

You can probably find pictures of Powroll's technique of shortening motorcycle connecting rods for use with stroker cranks by heating the midsection with a torch while applying compression with a hydraulic jack. With a little fixturing, you could do something like that to an ARB's arms to make them shorter and a little fatter. You'd still have to quench and temper the bar to get back its mechanical properties, which could be a significant difficulty for a part as large and awkward as an ARB.

Or maybe you could machine a small end fitting to bolt onto the end of the rod and move the link attachment point inboard a bit. ... at some expense in link angularity, and eventual cracking of the ARB arm at the proximal end of the fitting because of the abrupt section change.

Or you could move the attachment points of the links farther out on the control arms, again adding link angularity and maybe some clearance issues.

OTOH, if you have to heat treat it anyway, you might as well just buy a 5/8" bar, and bend and forge it to what you need.

Does the factory or aftermarket offer a fatter bar? Rolling your own is lot of work.

Mike Halloran
Pembroke Pines, FL, USA

RE: Anti Roll Bar Steel

OP said - "how about using BERYLLIUM COPPER ALLOY 173 ?"

I did not even look up what the E of beryium copper 173 is, or if has enough elongation to survive being twisted into an ARB, but it looks like an 8 foot length of 5/8" is about $300.
http://www.onlinemetals.com/merchant.cfm?pid=19809...

An 8 foot length of Condition N 4130 is twenty-five US bux. I don't know how that heat treatment compares to what you have, or need.
http://www.onlinemetals.com/merchant.cfm?pid=7364&...

RE: Anti Roll Bar Steel

BeCu 173 has an elastic modulus of 130 GPa, so that will not provide higher stiffness than steel.

RE: Anti Roll Bar Steel

(OP)
Thank you for your suggestions.
I'm going to make a new one following Economy 101 and lowest PITA Factor.
Thanks again.

Mater artium necessitas

RE: Anti Roll Bar Steel

Increasing the diameter of an anti roll bar sounds like a good idea as it will give a flatter ride without increasing harshness over bumps but there can be downsides to this approach.


When the ARB creates a lifting force on the outer control arm an equal amount of lifting force is generated on the inner arm; due to the ARB geometry. This force pulls on the unladen control arm and tries to lift the tyre off the ground. This force is resisted by the static spring and compression damping of the damper itself as the control arm tries to go upwards. This reduces the amount of damping travel available to the shock if the car switches back quickly, an effect called “jacking” where the suspension continuously shortens due to the shock not being able to properly react fast enough to force inputs. While this is not a guaranteed effect, a larger bar will increase the likelihood of this occurring.

Another issue is that while driving you will encounter uneven bumps in the road. Without an ARB the suspension acts independently of each side, which allows a single shock / damper to absorb and damp out osculations without imparting significant loads on the other static dampers. This is an ideal setting for allowing the suspension to do it’s job … damping oscillations and maintaining tyre interface with the road surface. When you install or stiffen an ARB you are creating a second, direct load path for the connected corners. When the right front hits a bump, that force is now transmitted to the left front. This creates an unsettling effect compared to the first scenario as the suspension on two corners now reacts sharply to forces. This effect increases as the ARB stiffness increases.

A third issue has more to do with the fact that many people do not corner weight their vehicles. When you involve a large ARB the uneven ride heights and static load on the individual dampers creates a static torque in the sway bar. This increases the differential that the right and left side have when it comes to handling. That is to say, turning right and turning left create different handling characteristics, amplified by the bar’s pre-load.

If you are trying to obtain a small increase in roll stiffness you may be better off with slightly uprated springs.

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