Bigger rocks, ruts, and ridges inevitably require bigger rubber. So in pursuit of ground clearance and more off-road performance than the factory configuration could offer, we stuffed a 34-inch 285/75/17 Toyo Open Country M/T tire under the fenders of our otherwise stock FJ Cruiser project. Surprise! They didn’t clear.
OK, it wasn’t much of a surprise. We knew that some massaging would be necessary to make the tire and Toyota play well together. Below is what is commonly referred to in the FJ community as a body mount chop, or BMC. It involves modifying the forward-most mount that links the frame to the body of the vehicle by trimming and rewelding.
Is this a job for the faint of heart? Definitely not. A body mount is a load-bearing unit, so welding proficiency is an absolute requirement. That said, the job is fairly simple and the reward is more rubber, without the cringe-inducing grinding of mud-terrains on metal in the middle of a turn.
This is the culprit body mount. Located at the rear of the front wheelwell, it is by far the first thing a larger-diameter tire will make contact with, severely limiting the turning radius of the FJ. The circular rubber disc is the body bushing, and the actual mount protrudes far beyond that.
Using a combination of a reciprocating saw and a cutoff wheel, a window was cut in the body mount.
Next, the portion of the body mount protruding past the rubber puck was cut away. Roughly 3/8 to 1/2 inch of material was left around the mount to ensure adequate support.
Using a flap disc, the hard 90-degree angle between the first and second cut was shaped with a flap wheel into a smooth radius. At this stage go slow, removing metal equally around the partial circumference of the body mount.
Here is the finish-cut body mount. Almost half of the mount has been removed, allowing for significantly more tire clearance. Now the mount needs reinforcement so it can continue to do its job supporting the vehicle’s body.
To reinforce the mount, a piece of steel will be bent. A quick trick to assess the length of metal plate that will be needed is to span the arc with masking tape. Mark the beginning and end of the tape.
Stick the masking tape onto a piece of steel plate, and transfer the length requirement with a Sharpie and a square.
A piece of 3/16-inch steel was deemed more than thick enough—it’s roughly twice as thick as the factory steel¬—and cut to length with a reciprocating saw.
Since we had a shop press handy, the flat plat was quickly and backyard boogey–style bent into an arc to match the contour of the chopped body mount. Similarly, the plate can be bent by hand with a hammer.
After some fine-tuning of the plate shape, it butted up snugly along the chopped body mount. We hit all the edges of both the mount and filler plate with a flap wheel in preparation for welding.
We unhooked the battery cables of the FJ—better safe than sorry—and tack-welded the plate onto the body mount. After verifying it had a tight fit all around, welding commenced in 1-inch increments, stopping periodically to cool the body mount with a damp rag. Overheating the mount will melt the rubber body mount, destroying it.
We wanted the modified mount to look factory, so the flap wheel was used again to knock down the welds and clean up a few sharp edges left over from cutting.
A quick blast of Rustoleum Performance Enamel coated the exposed metal of the new mount to prevent corrosion. The mount now displaces half the original square footage, adding valuable real estate to the fenderwell. With a slight amount of razor-blade work on the plastic inner fender, the mount completely clears the new Toyo meats from lock to lock.
The tires chosen for the FJ were a set of 285/75/17 Toyo Open Country M/Ts. These tires have a reputation for being extremely tough on the trail with pop-resistant three-ply sidewalls. They are a great blend of off-road capability and on-road manners.