Specs

From the dealer's page

Beta has added two new motocross models to join the big brother 450 in the RX range. All-new 250 and 350 RX 2 strokes are the new bosses in town! Beta’s 450 RX has been racing on the world MXGP tour for four years and the AMA USA Supercross series for two and has proven to be a serious contender. The Italian Beta engineers decided to “Go Big” for 2026 and add not only a 250 cc bike to race in the proper classes but also added a 350 RX smoker as well for everyone else! All Beta MX models are designed with the trademark RideAbility in mind. A motorcycle that is overall easier to ride. 250 RX: Another all-new model for 2026 is the smaller brother to the 350, the long-awaited 250 RX! Like the 350 version, this 2-stroke powered motocross model will appeal to all of those wanting a high-revving, lightweight 250 that can tear up berms with a distinctive sound that can only be heard from a Beta. The 250 RX also receives new engine cases along with the new cylinder, cylinder head, and exhaust. The 250 uses a single-spark head. Finally, a Beta Moto model that can run in many 250 classes. Engine: Both engine capacities received a completely new, purpose-built engine. The 350 RX was designed to obtain the greatest linear power delivery and give riders the option to exploit the great power available when needed, while the 250 RX can count on explosive performance, ready to compete in races under all conditions. » Head: The first noticeable difference when looking at the new engines is certainly the dual-spark-plug head on the RX 350 2Str, while the 250cc still relies on a classic single spark plug. This differentiates the two motorcycles’ character even further, with the 250cc providing riders with a high-revving engine that competes with the likes of 250 4Str bikes, while the 350cc manages to keep a greater torque and rounded delivery, enhancing its ease of recreational use, at lower speeds while still provides enough overall horsepower for race use. » Cylinder, piston, and power valve: to further differentiate the two bikes, apart from the obvious engine capacity, Betamotor engineers worked on new cylinders and pistons, designed specifically for each engine. The power valve, too, was calibrated accurately to manage the two deliveries by adopting different springs. » Crankshaft: the two motorcycles have a different stroke, with the 250cc reaching 72mm and the 350cc reaching 73.6mm. » Crankcase: new engine crankcases, with different internals between the two capacities, matched with each model’s crankshaft. » Gear box: gear boxes are shared between both models, with the only difference being the final ratios of the sprockets, 13/50 for the 250 and 13/47 for its big sister. Exhaust: also new for both models. Exhaust systems were designed to enhance the features of both engines, and differ in the internal silencer diameter, which is bigger on the 350.