Wet Braking Test Comparator
Compare wet braking distances under matched test conditions. Calculate deceleration and impact speed at the shorter stopping point.
Compare published results under matched conditions.
Wet Braking Test Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wet Braking Test Comparator Works?
The Wet Braking Test Comparator works by converting each published wet stopping distance into an average deceleration and comparing tires tested under matched speed, surface and conditions. The tool uses 4 steps.
Check matched conditions
Confirm both results share the same start speed, end speed, surface and test series.
Enter both distances
Type the distances, for example 30.0 m and 36.0 m from 80 km/h (50 mph) to 0.
Compute deceleration
The comparator returns 0.84 g and 0.70 g.
Find residual speed
The comparator returns the speed of the longer-stopping car at the point where the shorter-stopping car has stopped: 33 km/h (20 mph).
Wet Braking Test Comparator Formula
The Wet Braking Test Comparator formula is a = v² ÷ (2 × d), and the residual speed is v_res = √(v² − 2 × a₂ × d₁).
a = v² ÷ (2d)a_g = a ÷ 9.81v_res = √(v² − 2 a₂ d₁)- v
- Start speed (m/s)
- d₁, d₂
- Shorter and longer stopping distance (m)
- a₂
- Deceleration of the longer-stopping tire
Worked example
From 80 km/h, a 28.0 m stop equals 0.90 g, and a 34.0 m stop equals 0.74 g. The second car is still moving at about 34 km/h (21 mph) at the point where the first car stops.
Wet Braking Test Comparator Conversion Table
The Wet Braking Test Comparator conversion table converts 6 wet stopping distances from 80 km/h (50 mph) into deceleration and residual speed.
| Stopping distance | Deceleration | Deceleration (g) | Extra distance | Speed at 28.0 m |
|---|---|---|---|---|
| 28.0 m (92 ft) | 8.82 m/s² | 0.90 g | +0.0 m | 0 km/h |
| 30.0 m (98 ft) | 8.23 m/s² | 0.84 g | +2.0 m | 21 km/h |
| 32.0 m (105 ft) | 7.72 m/s² | 0.79 g | +4.0 m | 28 km/h |
| 34.0 m (112 ft) | 7.26 m/s² | 0.74 g | +6.0 m | 34 km/h |
| 36.0 m (118 ft) | 6.86 m/s² | 0.70 g | +8.0 m | 38 km/h |
| 38.0 m (125 ft) | 6.50 m/s² | 0.66 g | +10.0 m | 41 km/h |
What is Wet Braking Test Comparator?
A Wet Braking Test Comparator is a tool that compares wet braking results published by tire testers under matched conditions. Magazines, automobile clubs and tire makers publish wet braking distances for tires in one size on one test day.
Results only compare inside one test. Surface, water depth, temperature and test vehicle change absolute distances from one test to another.
Residual speed shows the real-world meaning of a gap. A few meters of extra distance leaves a car still moving at 30 km/h or more.
What are the uses of Wet Braking Test Comparator?
There are 4 main uses of the Wet Braking Test Comparator, including tire test reading and safety-led choices.
Tire test reading
Turn test tables into deceleration and impact speed.
Safety-led choices
Rank tires by wet stopping in a region with frequent rain.
Budget trade-offs
Weigh price savings against extra stopping distance.
Driver education
Show the effect of tire choice on wet stops.
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