What factor makes quick stops more challenging while cornering?

When cornering on a motorcycle, the bike's weight is shifted, which reduces the amount of traction available for the tires. This is because the tires are not only required to maintain grip for steering but also to generate friction needed for braking. As you lean into a corner, the available grip is divided between turning and stopping. Therefore, when a quick stop is required during a corner, the reduced traction makes it more difficult to brake effectively.

The other factors, while they may contribute to motorcycle handling, do not specifically address the inherent challenges of cornering. Increased speed can influence braking distance but doesn't directly explain the traction issue. Increased brake sensitivity is more about the rider's control of the brakes rather than cornering dynamics. Finally, riding with a passenger can change the motorcycle's handling characteristics, but it is the reduced traction during cornering that plays the key role in challenging quick stops. This understanding is essential for riders to manage their speed and braking input while navigating turns safely.