Several factors change the stopping distance of a vehicle, and each one affects either the thinking distance, the braking distance or both. The driver's reaction time only affects the thinking distance: a longer reaction time means the vehicle travels further before braking begins.
The speed of the vehicle affects both parts. At a higher speed the vehicle travels further in the same reaction time, so doubling the speed doubles the thinking distance. The braking distance increases by much more, roughly four times for double the speed. The mass of the vehicle affects the braking distance: a vehicle with a greater mass has more momentum, so for the same braking force it takes a greater distance to stop.
The state of the brakes, the state of the road and the amount of friction between the tyres and the road surface all affect the braking distance. Worn brakes give a smaller braking force. A wet or icy road, or worn tyres, reduce the friction between tyre and road, so the tyres grip less and the braking distance is longer.