High-clearance Hybrid Radius Arms

[Peter Connan]

In the last few years a higher proportion of guys have been running larger tires.
There are a number of clearance issues when running tires of 35" and larger. Ideally the axle needs to be moved a bit further forward to clear the rear edges of the front arches. This is normally done by placing spacers between the radius arm and the bush at the chassis end, but this possibly places greater stresses on the pin section of the radius arm.

Furthermore the tires rub on the outside edge of the radius arms, reducing the car's turning circle.

Over and above this, the radius arm setup is already the limiting factor in flex of the front axle.

Some Australian companies manufacture and sell what they call "hybrid arms", which move away from the double top-hat style bushes at the chassis end and replace them with the same style bushes as are at the front end of the arm. This is probably significantly stronger, but require "drop boxes" to lower the pivot point below the chassis. This has a number of advantages on a lifted car as it reduces the angle of the arms, making them ride bumps much better as well as allowing the arms to be slightly longer which increases flex, but they do hang down from the chassis quite a lot.

[Peter Connan]

A forum member recently actually had an arm break, and while I believe this was an isolated incident, it did get me thinking. I think the current hybrid arms leave something on the table.

If we replace the dropboxes with a custom cross-member we can make the radius arms even longer and also bring the pivot points inwards, both of which will increase flex. Bringing the pivot points inwards also generates considerably more room for the tires to turn, thus restoring the turning circle, and at the same time it will be easy to move the front axle forward.

The result is an increase in length of the radius arms of about 24%, and the pivot points move about 25% closer together. The resulting improvement in flex would be about 50% assuming the shocks fitted have enough travel not to become the limiting factor.

Comparing this new system with standard radius arms and "ordinary" drop-boxes:

And zooming in:

[Peter Connan]

In summary, the advantages of this system over the Australian hybrid radius arm setup will be:
Improved flex.
Improved turning circle.

Over a setup consisting of Nissan arms and dropboxes both the above advantages are realized as well as:
Even more flex.
Improved robustness.

There are however two disadvantages:
1) I'm not sure I will be able to mount anti-sway bars to these arms.
2) It will unfortunately be a fairly expensive modification. I expect the kit to cost around R12k (as normal for my stuff, that is for raw, dirty un-painted steel but it will be professionally welded by somebody who unlike me can actually weld).

At that price, is there anyone here who is interested, or is this dead in the water? For reference, Superior charge $1510, which at the current exchange rate is R17 865 excluding duties and transport.

[Clem]

Peter's engineering skills always amaze me, even though I personally don't have a use for this particular kit.

[Anthony Forgey]

PC is a genius!