Anti Roll Bar Motion Ratio Convention

[browney]

Hi,
I was wondering what the convention is relating the motion of an anti roll bar to the linear motion of a wheel.

With a motion ratio for a strut, you are comparing two linear motions, so the convention is simple.

However with a roll bar you are comparing the rotational motion of a torsion spring to a vertical wheel motion. Is the convention that people normally use distance along the arc that the end of the blade (where a droplink would connect for example) travels?

[Rodak]

Anti-roll bars are typically the blade type, with the blade rotated to change stiffness as required.

[Tim.Wright]

Hi,
I was wondering what the convention is relating the motion of an anti roll bar to the linear motion of a wheel.

With a motion ratio for a strut, you are comparing two linear motions, so the convention is simple.

However with a roll bar you are comparing the rotational motion of a torsion spring to a vertical wheel motion. Is the convention that people normally use distance along the arc that the end of the blade (where a droplink would connect for example) travels?

Expressing the motion ratio in radians/m will mean you can use it in the same way as a spring's motion ratio (WheelStiffness = ArbStiffness x MotionRatio²). Energy unit's check out with Nxm at the wheel and Nm x (rad) at the bar.

This assumes all the compliance in the ARB is coming from the twist of the bar, but this is rarely the case.

[godlameroso]

Hi,
I was wondering what the convention is relating the motion of an anti roll bar to the linear motion of a wheel.

With a motion ratio for a strut, you are comparing two linear motions, so the convention is simple.

However with a roll bar you are comparing the rotational motion of a torsion spring to a vertical wheel motion. Is the convention that people normally use distance along the arc that the end of the blade (where a droplink would connect for example) travels?

Expressing the motion ratio in radians/m will mean you can use it in the same way as a spring's motion ratio (WheelStiffness = ArbStiffness x MotionRatio²). Energy unit's check out with Nxm at the wheel and Nm x (rad) at the bar.

This assumes all the compliance in the ARB is coming from the twist of the bar, but this is rarely the case.

The sway bar bushings have compliance, the end links shouldn't if they use spherical/rose joints, there are end links that use hardened rubber to good effect, not sure how much compliance that would add. Also since you're tying the control arms via the ARB and limiting their independence, the compliance is shared non-linearly by the entire axle.

[Greg Locock]

In a road car you also lose some torsion in the twist of the chassis, and the deflection of the inner arm bushes. Unless you are using fairly big lumps of cast iron it is rare to see a body mounting point with a stiffness in excess of 5000 N/mm referred back to the floorpan, which is about the radial rate of the D blocks and typical suspension bushes.