To promote the deployment of small wind turbines (SWTs), thorough understanding of design parameter implications is essential. In-depth research is required to comprehend the influence of design TSR on off-design wind speed performance of multi-blade SWTs. In-house built blade element momentum algorithm was employed, which considered Reynolds number dependence of aerodynamic coefficients and correlated well with experimental results. Peak power coefficients were produced for 0.9, 1.5, 2 and 3 m diameter S826 rotors with blade numbers from 2 to 12 and design TSR of 2–10. Remarkably, regardless of diameter, greatest CP,max values were achieved around design TSR of 4. For peak efficiency, smaller the diameter, narrower the blade number and design TSR range. High-speed rotors have wider TSR range for high power coefficient. Yet, it was shown that operating TSR of low-speed rotors deviates less from design TSR as wind speed varies. It was revealed that low-speed (with a threshold design TSR of 3), low-induction multi-blade rotors provide high CP,max, better efficiency at off-design, shorter starting time and lower wind speed than three-bladed high-speed rotor. A small boost in operational TSR was found to effectively mitigate loss in off-design performance. These are key features to maximize energy harvesting.