Frequently Asked Questions
Learn how to get the most accurate predictions from DragCalc
How does DragCalc calculate quarter mile times?
DragCalc uses a physics-based simulation that accounts for weight transfer, tire grip, aerodynamic drag, and drivetrain losses. Unlike simple formulas, our calculator simulates the entire run step-by-step, modeling real-world factors like launch traction, gear shifts, and power delivery curves for different engine types.
What is density altitude and how does it affect my times?
Density altitude is a measure of air density that combines temperature, humidity, and barometric pressure into a single number. Lower density altitude (negative values or near sea level on cool days) means denser air, which helps both engine power and aerodynamics. Higher density altitude reduces engine power output, typically by about 3% per 1,000 feet.
Should I enter crank horsepower or wheel horsepower?
Enter whichever measurement you have. If you select "Crank," the calculator applies typical drivetrain losses (around 15% for RWD, 18% for AWD). If you have dyno numbers measured at the wheels, select "Wheel" and the calculator will use that power directly without additional losses.
How accurate are the predictions?
For properly set up cars with good traction, DragCalc predictions are typically within 0.1-0.3 seconds of actual quarter mile times. Accuracy depends on having correct input values and achieving good traction. The calculator assumes a skilled driver making consistent launches.
What is the difference between tire compounds?
Tire grip significantly affects launch performance. All-season tires have the lowest grip (coefficient ~0.88), while drag slicks offer maximum traction (~1.60). The tire grip slider lets you set any value between street tires and full slicks, accounting for different tire compounds and track prep levels.
How does the Reverse Calculator work?
The reverse calculator takes your rolling time (60-130 mph or 100-200 km/h) and estimates your wheel horsepower. Rolling times are less affected by traction and launch technique, making them a reliable way to estimate power. The calculator then predicts your quarter mile potential with that power level.
Why do AWD cars sometimes have slower times than RWD?
AWD systems have higher drivetrain losses (more gears, transfer cases, differentials), reducing power at the wheels. However, AWD cars typically launch harder due to better traction distribution. The calculator models both effects - you may see AWD cars with better 60-foot times but similar or slightly slower quarter mile times.
What transmission should I select?
Choose the transmission closest to your setup. Each preset includes realistic gear ratios, shift times, and efficiency. Modern DCTs shift fastest (~50ms), while older automatics like the TH400 have longer shift times (~300ms). You can also select "Custom" to enter your exact gear ratios and shift times.
How does surface grip affect my times?
Surface grip multiplies your tire's traction capability. Wet asphalt severely limits grip (0.50x), while a well-prepped drag strip can nearly double your traction (1.70x). Even with sticky tires, a poorly prepped surface will limit your launch performance.
What are 60-foot times and why do they matter?
The 60-foot time measures how quickly you cover the first 60 feet from launch. It's the most critical part of a drag race - a good 60-foot time sets up the entire run. For most street cars, 60-foot times range from 1.8-2.2 seconds, while well-prepared drag cars can achieve 1.3-1.5 seconds.