Radius Arm Mounts

One of my goals for our FZJ80 is to keep a relatively low frame height while maintaining as much up-travel as I can. I’m pursuing this in stages; first a 50mm lift to get the travel benefit of longer shocks and springs, then a 1″ body lift to increase the overhead room in the fender wells for larger tires, and eventually 37 or 38s.

Since I’m only lifting 50mm, I decided to pursue caster correction by lowering the frame side radius arm mount by the same 50mm to return both the caster and the anti-dive to factory specs. I looked around and found a bolt-on option to do just this; but that product is larger than I’d like, and I’m a big proponent of weld-on solutions. The other aspect that I was interested in was relocating the axle forward to create more firewall clearance for larger tire sizes.

(When the radius arm rear pivot is returned to its original height relative to the axle, the wheel returns to the middle of its arc at ride height – versus the more typical lifted arrangement in which the radius arm rear pivot remains in its location relative to the frame, and the axle centerline is lower than the radius arm rear pivot at rest. Because the wheel is returned to the factory arc path with my setup, the tire is again closer to the firewall at full compression. Moving the axle forward for increased clearance is beneficial in this scenario.)

So, I’ve made some Radius Arm Mounts to relocate the frame end of the 80-series radius arms down 50 mm for a 2″ or so lift and 25mm forward for that big tire/firewall clearance (and to improve approach angle.)

On paper, this down & forward relocation is good for 3.45 degrees of caster correction.

By making them weld-on, I’m able to run a reinforcing plane/rib up into the rear of the factory mount, increasing the weld area and tying everything together as a single structure. This also allows me to keep these mounts as svelte as possible so that any obstacle that the arm might slide over will not get hung up on the mount extension.

And even though they are weld-on, they do not obscure the stock hole, so if you change directions (not everyone is as concerned about not increasing anti-dive as I am) you can trim off the lower part and still have a reinforced factory mount for your trouble. 🙂

(but I don’t think you’ll end up doing that)

GW nugget on IH8MUD on 38s – running 2″ suspension lift, 1′ body lift, prototype 30mm RAMs

*the front axle is relocated 25mm forward, which is great for firewall clearance for increased tire sizes but expect some fender trimming in the front with very large sizes.

*I recommend using an old/spare radius arm bushing as a spacer along with the factory nut and bolt to hold the factory mount solid while tacking the RAM in place; then moving the bushing/bolt/nut down to the RAM to hold the ears parallel and coplanar with the inner walls of the factory mount for welding. – great excuse to finally get around to replacing those factory bushings!

*these are tricky to bend, and as such, often have one side (typically the outer, which has multiple bends) that may be bent slightly over 90 degrees – if this is the case, tack & secure the side that is bent to a perfect right angle to the factory mount first to hold it firm before opening up the other side for appropriate bushing clearance. feel free to contact me with any questions when you get to this step

Send my Radius Arm Mounts to me in