Contractor Job Estimator
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BuyStopping Distance by Speed and Surface
Bookmarkable physics-estimate grid — reaction plus braking from 20 to 70 mph across dry asphalt, gravel, wet asphalt, snow, and ice
Same formula and same published μ values as the braking / stopping distance calculator. Reaction time is fixed at 1.5 s so the grid is comparable. Change time or speed in the calculator if you need a different case.
Why braking distance squares: guide. 60 mph walkthrough: comparison. Hardware vs surface: troubleshooting. Automotive index: hub.
Need a speed the table skips?Same math, adjustable reaction time and surface.
Open Calculator →How to Read This Table
Braking-only cells ignore reaction. Total cells add 1.5 s of travel at that speed. Reaction is the same for every surface at a given speed — ice does not slow the clock. Double a speed and the braking column grows by about four, not two. That is v² / (2 μ g), not a DMV mnemonic.
Formula: db = v² / (2 μ g) with v in ft/s and g = 32.174 ft/s² (constant-deceleration kinematics; TxDOT / AASHTO SSD uses the same physics as 1.47 V t + 1.075 V²/a). μ: FHWA Speed Concepts Informational Guide Ch. 4 — dry typical emergency 0.70 g, wet 0.40 g, snow 0.22 g, ice 0.15 g. Gravel: Engineering Toolbox “Car — Traction Force,” dry rolled gravel 0.6–0.7 (table uses 0.60). Cells rounded to the nearest foot.
Braking Distance Only (ft)
No reaction time. Level road. Published typical μ. Not a skid-test certificate.
| Speed (mph) | Dry asphalt μ=0.70 | Gravel μ=0.60 | Wet asphalt μ=0.40 | Snow μ=0.22 | Ice μ=0.15 |
|---|---|---|---|---|---|
| 20 | 19 ft | 22 ft | 33 ft | 61 ft | 89 ft |
| 30 | 43 ft | 50 ft | 75 ft | 137 ft | 201 ft |
| 40 | 76 ft | 89 ft | 134 ft | 243 ft | 357 ft |
| 50 | 119 ft | 139 ft | 209 ft | 380 ft | 557 ft |
| 60 | 172 ft | 201 ft | 301 ft | 547 ft | 802 ft |
| 70 | 234 ft | 273 ft | 410 ft | 745 ft | 1,092 ft |
Any trade
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Brakes, Pads & Tread Gear
This calculator is a physics estimate. Pad thickness, fluid condition, and remaining tread are what actually change the friction you get in the real world. Measure those before you trust a number from a screen.
Lisle 81850 Brake Lining Thickness Gauge Set
Longer-than-expected stops are often thin pads, not a wet road. Measure lining thickness at the caliper instead of guessing from the warning squeal.
View on Amazon →
OMT One-Man Brake Bleeding Kit with Vacuum Pump
Spongy pedal and fade on a long descent are fluid and air, not friction coefficient. Bleed and refresh the fluid; the calculator cannot see a boiling caliper.
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AstroAI Digital Tire Tread Depth Gauge
Wet and snow μ assume a tire that can still evacuate water and bite packed snow. Bald tread on wet asphalt is not the 0.40 in this dropdown.
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8MILELAKE 24-Piece Brake Caliper Compressor Set
Pad jobs are how you restore the friction the physics model assumes. Compress the piston without destroying the boot, then torque the hardware.
View on Amazon →
Run the Stopping-Distance Numbers
Speed, reaction time, and a published μ for the surface. Reaction + braking = total. Estimate only.
Open Stopping Distance Calculator →
Need the Reference Table?
Bookmarkable physics estimates from 20–70 mph across dry, wet, gravel, snow, and ice. Same formula, same μ values.
Open Stopping Distance Table →As an Amazon Associate, TestTalkHQ earns from qualifying purchases.
Total Stopping Distance (ft) — 1.5 s reaction + braking
Reaction column is v × 1.5 s. Add it to braking, or read the surface total directly. Raise reaction to 2.5 s in the calculator if you want AASHTO design conservatism.
| Speed (mph) | Reaction (1.5 s) | Dry asphalt total | Gravel total | Wet asphalt total | Snow total | Ice total |
|---|---|---|---|---|---|---|
| 20 | 44 ft | 63 ft | 66 ft | 77 ft | 105 ft | 133 ft |
| 30 | 66 ft | 109 ft | 116 ft | 141 ft | 203 ft | 267 ft |
| 40 | 88 ft | 164 ft | 177 ft | 222 ft | 331 ft | 445 ft |
| 50 | 110 ft | 229 ft | 249 ft | 319 ft | 490 ft | 667 ft |
| 60 | 132 ft | 304 ft | 333 ft | 433 ft | 679 ft | 934 ft |
| 70 | 154 ft | 388 ft | 427 ft | 564 ft | 899 ft | 1,246 ft |
What This Grid Is For
Comparing surfaces at the same speed, and seeing how fast the v² term grows before you get on a highway in the rain. It is not a following-distance policy and not a reconstruction table. If yesterday’s dry stop grew and the pavement did not, that is hardware, not a missing row.
Ice at 70 mph is not a rounding error.Look at the ice total versus dry at the same row. Then leave more space than either number.