|In simplest terms the calculator uses Newton's second law (F = m.a) to calculate acceleration of a vehicle. Several physical phenomena come into play to determine the effective accelerative forces. This calculator accounts for many of them while ignoring some to be reasonably accurate yet simple. Specifically, effective accelerative force put down to the wheels (derived from drive-wheel torque), velocity-independent frictional forces, and air drag are considered.
The calculator takes the following parameters as inputs:
The following outputs are generated:
- Accelerative force: drive-wheel torque over the RPM band.
- Drivetrain ratios: gear ratios, differential ratio, and tire size.
- Parasitics: vehicle weight, drag coefficient, and frontal area.
- Driver attributes: driver weight and gear shift time.
The calculator provides some high-performance cars as presets to ease the task of entering inputs. Up to four vehicles can be compared for all the calculated metrics.
- Power: power (in HP) over the vehicle's RPM range.
- Accelerations: 0-120mph speed vs time charts, 30-60mph, 30-90mph, 30-120mph, 60-90mph, and 60-120mph times. Sheer acceleration (in g's) vs time is also plotted as a chart.
- Optimal shift points: best gear shift RPMs given starting and ending speeds.
- Others: peak power, peak torque, top speed, and cruising RPM.
|Frequently Asked Questions|
- What requirements should my computer meet to be able to run the calculator?
Macromedia flash 8.0+ is required. I have tested the calculator in Internet Explorer 7 and Firefox 1.5. Unfortunately, while most windows machines have Flash 8.0+, Linux machines are stuck with 7.0 (which is the latest version available on the Linux platform). Bottom line is that the program should work on most machines running Windows XP.
- Why is power/HP not taken as an input?
Power or HP is derived from torque. A dynamometer or dyno measures drive-wheel torque and converts it to power through some simple mathematical calculations. I can calculate power as well as a dyno so I don't need it as an input. If you're still not convinced, look at the power and torque plot generated in the outputs and it should match with the power plot in your dyno chart.
- Why aren't 0-XXX mph times and quarter-mile times calculated?
Too many variables such as tire slippage, clutch slippage, launch RPM, driver reaction time, suspension, etc. are involved.
- How is the top speed calculated?
There are two limits and the lesser of them rules. First, peak RPM and top gear ratio related. Second is related to the vehicle's ability to accelerate against the air drag forces which become very high at 100+ mph.
- How are the shift points determined?
Shift points are computed for a given start and end speed. The gear at the beginning, and the RPMs at which gears must be shifted are calculated for the fastest time.
- What physical phenomena are considered?
Air drag and velocity-independent friction.
- What factors contribute to the inaccuracy?
Several phenomena are not considered. Down force, clutch slippage, tire slippage, traction control and other smart things these marvels of modern science do.
- Which inputs are really important for accuracy?
The drag coefficient, frontal area, torque under say 3000RPM, tire size, driver weight, and shift time don't have to be very accurate. If they're not known, staying with the defaults will not induce large inaccuracy in the results.
- Can I submit my car to be added in the list of preset cars?
That'll be a help. You need to supply me with the data in a specific format. Download a sample file from here. Actually, it's in XML format but it is quite simple and you can open it in notepad to edit it. My email is .
- Should I hit the road and check if your calculations are correct?
No! There are several factors not considered in this calculator that limit the acceleration and top speed of a vehicle. Moreover, accelerations and top speeds that may be supported by the engine might cause other vehicle components to fail and can be dangerous. I strongly discourage overspeeding and street racing.
- Brian Beckman's Physics of Racing Series [link].
- Prof. Horowitz's webpage on propulsion and resistance [link].
- The Truth About Horsepower, Torque, and Acceleration [link].
- Horsepower and Torque [link].
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