Open tire = more grip.
| 1/4 mile | 5.67-6.13 |
| 3/8 mile | 5.43-5.83 |
| 1/2 mile | 5.00-5.43 |
Cross weight target: 50-54%. Left side: 54-57%. These are starting points — your track, your driver, and your tires will shift the window. If you're outside these ranges, fix weight distribution before touching anything else.
The Black Book scale sheet calculates cross, left, rear, bite, and wedge automatically for UMP Modified. Enter your four corners — it color-codes against these targets and tells you what to move.
Standard tire diameter for UMP Modified: 28 inches. The gear ratios above assume this diameter. If you're running a different size, the Black Book gear calculator adjusts MPH at RPM automatically.