Performance Calculations and Formulas

Vehicle Weight with driver (in pounds)

1/4 mile time (in seconds)

1/4 mile trap speed (in MPH)



Horsepower based on time

Horsepower based on MPH

Horsepower at the wheels

Click here for additional formulas

The Horse Power Calculator below will calculate your approximate horsepower based on the vehicles weight, 1/4 mile time, and the 1/4 mile speed.


The calculator will spit out four different HP numbers.
(Extremely averaged drivetrain losses)
5-speed front wheel drives (using a drivetrain loss of 13%)
Automatic front wheel drives (using a drivetrain loss of 15%.)
5-speed all wheel drives (using a drivetrain loss of 18%.)
Automatic all wheel drives (using a drivetrain loss of 23%.)


This program averages the HP results from your 1/4 time AND speed. There are sometimes inconsistencies in the numbers. This will minimize this errors from an incorrect value.


The results are only approximate calculations.

Altitude Adjustment

Multiply your 1/4 mile time or your Trap Speed by
these numbers to convert adjust your fun to sea level

Track Altitude (in feet) Time Factor MPH Factor
1200 .9874 1.0129
1300 .9861 1.0143
1400 .9848 1.0157
1500 .9835 1.0171
1600 .9822 1.0185
1700 .9809 1.0199
1800 .9796 1.0213
1900 .9783 1.0227
2000 .9770 1.0241
2100 .9757 1.0255
2200 .9744 1.0269
2300 .9731 1.0283
2400 .9718 1.0297
2500 .9705 1.0311
2600 .9692 1.0325
2700 .9679 1.0339
2800 .9666 1.0353
2900 .9653 1.0367
3000 .9640 1.0381
3100 .9627 1.0395
3200 .9614 1.0409
3300 .9601 1.0423
3400 .9588 1.0437
3500 .9575 1.0451
3600 .9562 1.0465
3700 .9549 1.0479
3800 .9536 1.0493
3900 .9523 1.0507
4000 .9510 1.0521
4100 .9497 1.0535
4200 .9484 1.0549
4300 .9471 1.0563
4400 .9458 1.0577
4500 .9445 1.0591
4600 .9432 1.0605
4700 .9419 1.0619
4800 .9406 1.0633
4900 .9393 1.0647
5000 .9380 1.0661
5100 .9367 1.0675
5200 .9354 1.0689
5300 .9341 1.0703
5400 .9328 1.0717
5500 .9315 1.0731



Calculating Tire Diameters

(Quoted from Michael Kaczmar and the DSM archives)

Here is the way to figure tire diameters: Section width x one tenth of the aspect ratio.

Think of the aspect ratio as a percentage. This will give you the wall thickness in milimeters. Change that number to inches, by dividing by 25.4 and then muntiply by 2 and add the rim diameter. This should give you the theoretical tire diameter.

For example: 195/50-15 - 195 x 50% (or 0.5) ... 195 x 0.5 = 97.5mm. Multiply x 2 (you have two wall thicknesses in the overall diamter = 195mm. Convert to inches: 195/25.4 = 7.677". Add this to your wheel diameter: 15 + 7.677 = 22.677 ...

For government accuracy you are looking at a 22 - 5/8" tire diameter.

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