IMHO The biggest problem with the XXX-4 is durability. I have improved my own car with the following mods:

Aluminum suspension supports. If you are buying a properly sorted racer it should have at least some of these. Get all of them. Rear get the -1,3 degree.

Cut down front shock towers. I lopped off the top of the shock tower altogether. My front shocks now mount about 1 inch above the front control ball joint. They lean in at about 45 degrees, which makes the spring and damper rates very progressive. It also required clearancing the front suspension arm for the spring perch, but the material removed is in the meat of the arm, and they haven’t broken yet. Also, be sure you get the updated arms. I believe there are 3 versions of arms, original (fragile), 1st revision (better, 1 or 2 molded into the arm), graphite revision (best, an X brace is built into the center of them).

Cut down PsychoTec / Art’s Hobbies rear shock tower. The PsychoTec rear tower does not have the large triangular holes that the Losi graphite one does. I cut the ears off of the tower, and mounted the rear shocks 5/8s” above the rear wing mount upper screw. To accomplish this I had to move the rear shocks back to the front of the suspension arm / shock tower like the original XXX-4. The control link gets flipped to the back side as well. This leans the rear shock as well, which matches the front.

Screws. Make sure that all screws are as long as the holes are deep. Someone markets a titanium kit with short screws. DO NOT USE THESE SCREWS, they are not long enough and may pull out in certain locations. Upper screws on rear diff / belt cover is very important!!!

Finally, the rear bumper must be attached to the chassis to support the rear belt cover / rear suspension pivot (or tagging something with a rear wheel may rip it all off). I removed the rear bumper and razed off the two leading tabs that keep it above the chassis plate. I then drilled two countersunk holes in the bumper (in the corners) and two in the chassis plate (below the front hinge point of the suspension arm). I cut plates from K&S brass stock, drilled it to fit, and screwed it together using low profile nuts. This lashes the rear bumper to the chassis and allows it to support the rear-most screws of the belt cover (which has a lot more plastic than the leading screws). The -1 degree rear suspension support must be used to allow the arm to clear the brass plate.

Finally, I run my suspension very loose, red pistons and 30 wt. Oil with XXX-4G+ Pink and 2" Green springs. I have fuel tubing limiters on the shock shafts that limit travel such that the limiters hit when the car is depressed to 5/8” of ground clearance. This allows the wheels to react quickly to the ground but the car is still ‘thrown’ into the air off of the jumps (and it lands well too).

Thank you Robert!

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