What is the most effective method to adjust the pedal assist timing for braking on an ebike without compromising the motors efficiency or rider safety, and are there any specific tools or software required to fine-tune this setting. How do manufacturers like Bosch, Shimano, and Yamaha approach this issue in their respective systems, and are there any notable differences in their implementation. What are the potential risks or drawbacks of adjusting pedal assist timing for braking, and how can riders mitigate these risks to achieve a smoother and more responsive braking experience. Are there any industry standards or guidelines that dictate the optimal pedal assist timing for braking on ebikes, and how do these standards vary across different countries or regions.