Harley-Davidson Sportster S vs RKS RZ125

The Harley-Davidson Sportster S (2025) and the RKS RZ125 (2026) are compared with the same Moto Kıyas physics model under identical conditions: flat dry asphalt, no wind, a 75 kg rider and no passenger. The Harley-Davidson Sportster S is a cruiser with 1,252 cc, 120.7 hp and 228 kg; the RKS RZ125 is a sport bike with 125 cc, 14.5 hp and unlisted weight. Power-to-weight with the rider: 398.3 hp/ton versus 63.8 hp/ton. On this measure the Harley-Davidson Sportster S is 524% ahead.

In the simulation the Harley-Davidson Sportster S covers 0-100 km/h (speedometer) in 2.97 s and the RKS RZ125 in 13.42 s; the Harley-Davidson Sportster S is quicker by 10.45 s. In the 100-0 km/h brake test, braking distance without the 0.3 s reaction time is 44.7 m for the Harley-Davidson Sportster S (with ABS) and 36.4 m for the RKS RZ125 (with ABS). The RKS RZ125 stops 8.3 m shorter. Calculated top speed: 194 km/h (manufacturer claim) versus 125 km/h (estimated from power and drag).

All values are an estimated simulation, not road-test measurements. Technical data comes from the sources listed below; the model uses model-specific parameters calibrated against published road tests for the Harley-Davidson Sportster S and class-average calibration (no accepted model-specific road test) for the RKS RZ125. Open the interactive app (currently in Turkish) to watch the run side by side and change the load.