Calculator
Stopping distance calculator
Two distances add up: the ground you cover before you react, and the ground you cover while the brakes work. Speed, the road surface and your tread depth set both.
Total stopping distance
β
Tread depth changes the braking distance on wet roads only, using the braking efficiencies measured in the Hunter Engineering wet test on our tire safety page. On dry pavement worn tread does not lengthen the stop; on snow and ice the tire type matters far more than the tread depth.
The same stop at other speeds
| Speed | Reaction | Braking | Total |
|---|---|---|---|
| 25 mph | 55 ft | 40 ft | 95 ft |
| 35 mph | 77 ft | 79 ft | 156 ft |
| 45 mph | 99 ft | 130 ft | 229 ft |
| 55 mph | 121 ft | 194 ft | 315 ft |
| 65 mph | 143 ft | 272 ft | 415 ft |
| 75 mph | 165 ft | 362 ft | 527 ft |
The math, shown
Reaction distance = speed Γ reaction time. Braking distance = speedΒ² Γ· (2 Γ friction Γ 9.81 m/sΒ²). Friction: dry 0.80; wet 0.52, calibrated to the 234 ft Hunter Engineering result at 60 mph on new tread; packed snow 0.30 with winter tires and 0.20 with all-season tires; ice 0.10. Wet braking is multiplied by 1.09, 1.20 and 1.52 for 6/32, 4/32 and 2/32 in of tread.
Questions people ask
What reaction time should I use?
One and a half seconds is the standard figure for an alert driver who is not expecting the hazard, and it is what road-design manuals use. A driver looking at a phone is at two seconds or more before the brake pedal moves. At 60 mph every half second is 44 feet.
Why does speed matter so much?
Reaction distance grows in step with speed, but braking distance grows with the square of speed. Going from 30 mph to 60 mph doubles the reaction distance and quadruples the braking distance. That is why a small speed increase turns a near miss into a crash.
Do worn tires stop worse on dry roads?
Barely. On dry pavement a worn tire has as much rubber on the road as a new one, sometimes more. The tread exists to move water, so the penalty shows up in the wet: at 60 mph a tire at the 2/32 in legal minimum needs 122 more feet than a new one in the Hunter test. That is the number this calculator uses.