🏁 Rock Racer / U4
High-speed rock racing inspired by full-size Ultra4 / King of the Hammers — machines that both crawl obstacles and race between them.
Rock racing blends rock-crawling with wheel-to-wheel or timed racing, mirroring full-size Ultra4 competition. Rigs need suspension and power to move fast over rough ground as well as the articulation to climb. Formats range from timed courses to head-to-head. Rules on power, tire size and suspension vary widely by series.
| Named for | Varies (large) |
|---|---|
| Focus | Speed + crawling combined |
| Typical drivetrain | IFS or solid axle, high power |
| Example rigs | Axial RR10 Bomber, Losi Rock Rey, Vanquish builds |
📋 The exact rules vary. Tire diameter, wheelbase, motor and body limits differ by sanctioning body and event. Check the current rulebook for your competition — e.g. SORRCA for scale scoring, or your local club / series for comp classes. Blank beats a wrong number, so we don't publish measurements that change year to year.
Building a rig for this class? Browse the model database or identify your RC.