Performance Line SX

Performance Line SX is Bosch's answer to the lightweight-eMTB boom: roughly 2 kg, magnesium-housed, and engineered to chase a 600 W peak from a modest torque figure. That torque is 55 Nm as the factory default on bikes built before October 2025, raisable to 60 Nm via a free eBike Flow app update (with the eMTB+ mode); bikes built from October 2025 ship at 60 Nm out of the box. Either way the trick is the same — a dynamic boost algorithm that rewards a fast, sustained spin rather than a heavy stamp on the pedals. Velomotion's PT Labs run lays it bare: at a normal 75 rpm with moderate input the SX delivers only around 320 W, but flick the cadence past 110 rpm and feed it real effort and it surges toward the headline figure, their dynamic-boost run measuring just under 560 W of pure motor output.

Don't confuse the EU 250 W rating with the ceiling. Bosch's nominal 250 W is the legal continuous figure; the SX is rated for up to 600 W peak and Velomotion measured ~560 W in short bursts at high cadence, with ~320 W on tap at a steady 75 rpm. The 250 W badge is a regulatory floor, not a wall.

That makes it a brilliant motor for riders who keep the cranks whirring on rolling, flowing terrain, and a frustrating one on a slow, steep, low-cadence grind, where the modest 55–60 Nm and a constant-load reading nearer 300 W means it 'runs out of steam pretty quickly.' Heat is the other limiter: housing temperatures climb toward 100°C and you'll see roughly 10–15% derating after 10–15 minutes of sustained climbing, sooner inside a carbon frame.

Treat it as a light-assist motor with a sporty top end rather than a CX rival, and it's superb — narrow Q-factor, gentle and easy-to-dose delivery, quiet at cruise. Just don't expect the dyno to confirm the 600 W marketing unless you can hold 110-plus rpm.