Guides & explainers
The SpeedReflex Blog
Clear, sourced answers about speed and reaction time: how speedometers work and fail, how far vehicles need to stop, and how to read the numbers our tools give you.
Speedometers
Speedometer Guides
How speedometers work, why they read wrong or stop working, and how to check and fix them.
- 8 min read
Speedometer Not Working? Common Causes and How to Fix Them
A dead, stuck or bouncing speedometer usually comes down to one of a handful of faults. Here is how to narrow it down, test the speed sensor and decide what to fix first.
Read article - 7 min read
How to Calibrate a Speedometer — and Check It With GPS
Bigger tires, new gears or a swapped instrument cluster can all leave your speedometer reading wrong. Here is how to measure the error and the ways to correct it.
Read article - 6 min read
How to Read a Speedometer (mph, km/h and Metric Dials)
The needle, the two rings of numbers, the odometer and the tachometer — a plain-English guide to every number on the dashboard, including metric speedometers.
Read article - 5 min read
Why Do Speedometers Go So High?
Your hatchback’s dial runs to 140 mph but it will never get there. The reasons are part engineering, part readability, part marketing — and a bit of history.
Read article
Stopping distance
Stopping Distance Guides
How far cars, motorcycles and trucks need to stop — and what that means when they can’t.
- 6 min read
Semi Truck Stopping Distance: Chart, Formula and Why Trucks Need More Room
A fully loaded 18-wheeler needs about 450 feet to stop from 55 mph — roughly a hundred feet more than a car. Here is where that distance comes from.
Read article - 5 min read
Stopping Distances and the Severity of Crashes: Why 5 mph Matters
Drive 5 mph faster and you don’t just stop a little later — at the point where you would have stopped, you are still doing about 20 mph. Here is the maths.
Read article
Reaction time
Reaction Time Guides
Benchmarks and background for the reflex tests.
Average Reaction Time
What’s normal, good and fast — by age, stimulus and device, with sources.
Read GuideRuler Drop Test
How to test reaction time with a ruler, with the formula, a conversion chart and norms.
Open CalculatorAverage F1 Reaction Time
How fast Formula 1 drivers react at the start — and how you compare.
See Benchmarks
Tools
Put the Numbers to Work
Stopping Distance Calculator
Thinking plus braking distance at any speed, reaction time and road condition.
Open TestSpeedometer Calculator
How new tire sizes or gears change your speedometer — true speed, error and the driven gear you need.
Open TestReaction Time Test
Five frame-accurate attempts, your average, best, consistency and percentile.
Open Test