Current Analysis
New Vehicle Configuration
Available Differential Gear Ratios
Comprehensive Differential Database
Take note of your differential cover shape and bolt pattern and compare to identify your differential type. The list of available ratios is unique to each type, which is important to choose a ratio that can actually be installed.
RPM/MPH Across All Shift Points
Transmission Selected:
| Gear | Ratio | Shift | Shift RPM | RPM Drop | New RPM | Shift MPH | DS RPM |
|---|
Speed Categories for Final Gear MPH
Input desired RPM for each gear change in the Shift RPM column.
The calculator uses all available gears in the selected transmission. Enter each shift RPM, and it calculates MPH at shift, RPM drop, new RPM after shift, and driveshaft RPM.
Tire Size Calculator
Enter tire size (P225/60R16 format):
About Tire Growth: Tire growth occurs as speed increases. Standard estimate is ~3%, but it varies. Stiff sidewalls grow less; tall/soft sidewalls grow more.
Gear Tooth Ratio Calculator
Count teeth on both ring and pinion gears, then enter values:
Common Tire Sizes
| Tire Size | Diameter (in) | Action |
|---|---|---|
| P225/60R16 | 26.6 | |
| P235/75R15 | 28.9 | |
| P275/60R15 | 28.0 | |
| P315/75R16 | 34.6 | |
| 33x12.50R15 | 33.0 | |
| 35x12.50R17 | 35.0 |
Note: Truck tires in inch format (e.g. 35x12.50R17): the first number IS the diameter. Simply enter it directly.
Custom Gear Ratios (1-10 Speed)
Gears 1-5
Gears 6-10
Tips: Leave fields empty for unused gears. Ratios should generally decrease from 1st to highest gear.
Preset Transmissions
Select a preset or enter custom ratios manually. All calculations update automatically.
| Transmission | 1st | 2nd | 3rd | 4th | Action |
|---|---|---|---|---|---|
| PowerGlide | 1.82 | 1.00 | - | - | |
| TH350 | 2.52 | 1.52 | 1.00 | - | |
| TH400 | 2.48 | 1.48 | 1.00 | - | |
| C4 | 2.46 | 1.46 | 1.00 | - | |
| 700R4 | 3.06 | 1.63 | 1.00 | 0.70 | |
| 4L60E | 3.06 | 1.63 | 1.00 | 0.70 | |
| 10R80 | 4.70 | 2.99 | 2.15 | 1.77 |
Manual Ratio Entry
Instructions: Enter custom ratios above (min 2 required). These become available under "Manual Ring & Pinion Ratio Entry" in the Differential Type dropdown.
Quick Ratio Select
Ratio Guide
Lower (2.73-3.23): Better fuel economy, higher top speed
Mid (3.42-3.90): Balanced performance and economy
Higher (4.10-4.56): Better acceleration, lower top speed
Very High (5.00+): Maximum acceleration, specialized apps
Common Ratios Reference
| Ratio | Best For | RPM @ 60mph | Action |
|---|