function calculateDragStats() {
// 1. Get input values
var weightInput = document.getElementById("vehicleWeight").value;
var hpInput = document.getElementById("engineHp").value;
// 2. Parse values
var weight = parseFloat(weightInput);
var hp = parseFloat(hpInput);
// 3. Validation
if (isNaN(weight) || weight <= 0 || isNaN(hp) || hp <= 0) {
alert("Please enter valid positive numbers for both Weight and Horsepower.");
return;
}
// 4. Calculations using standard drag racing physics formulas (Hale/Moroso derived constants)
// Formula for 1/8 Mile ET = 3.85 * (Weight / HP)^0.333
// Note: Constants vary slightly by source, 3.85 is a standard baseline for good traction.
var pwrFactor = Math.pow((weight / hp), 0.333333);
var etEstimated = 3.85 * pwrFactor;
// Formula for 1/8 Mile MPH = 175 * (HP / Weight)^0.333
var speedFactor = Math.pow((hp / weight), 0.333333);
var speedEstimated = 175 * speedFactor;
// Power to Weight Ratio
var ratio = weight / hp;
// 5. Display Results
var resultBox = document.getElementById("result");
var etDisplay = document.getElementById("resET");
var speedDisplay = document.getElementById("resSpeed");
var ratioDisplay = document.getElementById("resRatio");
etDisplay.innerHTML = etEstimated.toFixed(3) + " sec";
speedDisplay.innerHTML = speedEstimated.toFixed(2) + " mph";
ratioDisplay.innerHTML = ratio.toFixed(2) + " lbs/hp";
resultBox.style.display = "block";
}
function resetDragStats() {
document.getElementById("vehicleWeight").value = "";
document.getElementById("engineHp").value = "";
document.getElementById("result").style.display = "none";
}
Understanding 1/8 Mile Drag Racing Performance
Whether you are tuning a street car for the strip or building a dedicated dragster, knowing your theoretical performance numbers is essential. This 1/8 Mile Drag Racing Calculator uses physics-based formulas to estimate your Elapsed Time (ET) and Trap Speed based on your vehicle's weight and horsepower.
How the Calculator Works
This tool utilizes standard power-to-weight ratio formulas commonly used in motorsports engineering. The calculation assumes "good run" conditions, meaning optimal traction, shifting, and weather conditions. The core formulas are:
Elapsed Time (ET): The time it takes to travel from the starting beam to the finish line. It is heavily dependent on weight transfer and traction.
Trap Speed (MPH): The speed at which the vehicle crosses the finish line. This is a better indicator of raw horsepower than ET is.
The Physics of the 1/8 Mile
In drag racing, the 1/8 mile is becoming increasingly popular compared to the traditional 1/4 mile, as it places a higher premium on reaction times and the initial launch (the "60-foot" time). The math behind the run relies on two main variables:
1. Vehicle Weight
Weight is the enemy of speed. The heavier the car, the more force is required to accelerate it. When entering your weight into the calculator, ensure you include:
The curb weight of the vehicle.
The weight of the driver (with helmet/gear).
Fuel load and fluids.
Any modifications or cargo.
2. Horsepower
For the most accurate results, input your Flywheel (Crank) Horsepower. If you only know your Wheel Horsepower (WHP) from a chassis dyno, you should factor in drivetrain loss to estimate the crank HP:
FWD/RWD Manual: Add approx 15%.
RWD Automatic: Add approx 18-20%.
AWD: Add approx 20-25%.
Why Do My Real World Results Differ?
The calculator provides a theoretical baseline. Real-world drag racing results will vary due to several external factors:
Traction: Spinning tires at the launch will drastically increase your ET, though your Trap Speed might remain similar.
Density Altitude (DA): High altitude or hot, humid air reduces the oxygen available for combustion, lowering your actual horsepower.
Gearing: Improper gear ratios can cause the engine to fall out of its power band or force an extra shift right before the finish line.
Aerodynamics: While less critical in the 1/8 mile than the 1/4 mile, a high drag coefficient can still impact trap speeds.
Improving Your 1/8 Mile Time
To get closer to the estimated numbers provided by this calculator, focus on the first 60 feet of the track. Improvements in suspension setup, tire compound (slicks vs. radials), and launch technique yield the biggest reductions in ET. Remember the rule of thumb: for every 100 lbs of weight removed, you can expect to shave approximately 0.1 seconds off your time.