Voodoo Hot Rods™ Front Radius Rods are of 'sprint car' rather than 'hairpin' design for good reasons rarely talked about.
Popular 'hairpin' radius rods feature a short tube welded to the trailing end of the upper and lower radius rod links that mounts the rod end that bolts the radius rod to the chassis.
The 'hairpin' design usually features near 90-degree bends just before the point where the upper and lower links weld to this short tube. Front radius rods carry loads along their length mainly in compression and any bend along the link represents an engineering compromise as load must be transmitted through this redirected path. The more acute the bend angle the greater the engineering compromise.
On 'hairpin' radius rods the welds securing upper and lower links to the short tube represent a further engineering compromise as weld length is short due to near 90-degree angle where the links meet the tube. Under severe braking, the substantial load of vehicle mass multiplied by velocity has to be carried by these short welds in shear.
If these welds fail the front axle will not be attached to the chassis except via the main leaf of the transverse front spring, spring shackles and spring perch bolts. As these components are not designed to locate the front axle longitudinally in the chassis, the axle could fold back under the frame taking steering and brake function with it.
Another relevant issue with radius rod design concerns the type of bushings used. When a car with a live axle corners, or one end of the axle encounters a bump in the road, this end of the axle moves up or down relative to the other end. When this occurs radius rods have to twist to accommodate axle movement.
This calls into question the suitability of commonly used rod ends featuring hard polyurethane bushes claimed by manufacturers to 'tighten up' suspension for more precise and responsive handling. Polyurethane bushes achieve this by reducing the total amount of deflection possible compared to OEM automotive rubber bushings.
When four bar front radius rods with hard polyurethane-bushed rod ends first came onto the market manufacturers claimed the twisting forces fed into the four bar links caused them to act as anti-roll bars. Perhaps not a great idea in retrospect as four bars are not made from the same type of spring steel that an anti-roll torsion bar is. And as most four bar designs feature a welded sleeve on one end of the link, twisting forces risk breaking the weld holding the bushing sleeve in place. Proof that twisting forces are fed into radius rods is evident, as rod end lock nuts constantly loosen.
Optimizing suspension design and ride quality, Voodoo Hot Rods™ Front Radius Rods offer bind-free operation.
Manufactured from 7/8-inch O.D. x .156" wall seamless steel tube, Voodoo Evolution™ 32R Front Radius Rods feature 5/8-inch polished stainless steel, polyurethane-bushed rod ends at the axle batwing with a spherical rod end at the chassis mount. Spherical rod ends eliminate bind but are poor at insulating chassis from road vibration, so the rod end mounting bolt passes through large rubber automotive bushings mounted in the Voodoo Evolution™ 32R chassis.
Voodoo Hot Rods™ use a 'sprint car' style radius rod design as these feature a straight, one-piece upper link that mounts the front and rear rod ends on the same section of seamless steel tube. This maximizes the ability of the upper link to carry compression loads under braking along a straight path between the rod ends, and eliminates the risk mounting the rear rod end to a welded tube.
The lower Front Radius Rod link features a significantly lower bend angle than typical 'hairpin' radius rods to better transmit load. This and the slightly upward angle of the lower link results in a shallower angle where it meets the base of the upper link and a significantly longer, stronger weld. The Voodoo Hot Rods™ Front Radius Rod Kit also comes with center and rear radius rod reinforcing gussets that owners can choose to install.
Just how much lower the front ride height of the Voodoo Evolution™ 32R is compared to reproduction Deuce street rod frames is evident from the position of the Front Radius Rods adjacent to the front chassis rail. Rather than hanging under the rails the straight upper link sits just below and parallel to the base of the hood side.
The Voodoo Evolution™ 32R Front Radius Rod Kit is only offered in seamless DOM steel tubing, as this is stronger than stainless steel and does not work harden with use.
Voodoo Hot Rods™ will be working with a leading hot rod suspension manufacturer to offer independent front suspension in 2013.....read more
TECH PROFILE: Suspension bushes - why there's no universal solution