Compare both changes on one scale
For this model, two setups with the same weight-to-power ratio have the same estimated 0–60 mph time. Increasing rated horsepower by 10% multiplies the power by 1.10. Dividing the original weight by 1.10 gives the same ratio at the original power. That works out to a 9.09% weight reduction. NHTSA’s weight-to-power equation
Start with a hypothetical 3,500 lb car rated at 300 hp. Adding 30 hp raises it to 330 hp. Keeping 300 hp and removing about 318 lb produces a matching power-to-weight ratio. The table uses the unrounded weight in its calculations.
| Setup | Curb weight | Rated power | hp per US ton | Est. 0–60 |
|---|---|---|---|---|
| Original setup | 3,500 lb | 300 hp | 171.4 | 6.10 s |
| Add 10% power | 3,500 lb | 330 hp | 188.6 | 5.72 s |
| Reduce weight by about 9.09% | 3,182 lb | 300 hp | 188.6 | 5.72 s |
Compare changes you could actually make
Start with the rated power you can substantiate and the weight the new setup actually saves. Avoid counting a manufacturer's engine rating and a wheel horsepower measurement as though they were the same. Use the same basis for the stock and modified setups.
Check both plans in the upgrade comparison and add the cost of each if you know it. Seconds saved shows the predicted gain. Cost per tenth lets you compare options that save different amounts of time. Compare two upgrades
Account for traction and gearing
The model compares rated power and curb weight. During a measured run, grip, shift points, power delivery, and launch conditions also matter. If the vehicle already struggles for grip at the start, equal model gains can produce different results on the course. Keep your timing method consistent and compare the new setup with a measured baseline.