Need some help deciding if you should change the gear ratio in your Duramax diesel?
Changing the ratio to compensate for your larger tires will help improve fuel economy, lower EGT temps, restore towing performance, and put less stress on your transmission and drivetrain.
Here is some first hand Knowledge from the Dmaxstore team.
2001-2005 Duramax Trucks with 5 Speed Allison:
2006-2019 Duramax Trucks with 6 Speed Allison:
Changing the ratio to compensate for your larger tires will help improve fuel economy, lower EGT temps, restore towing performance, and put less stress on your transmission and drivetrain.
Here is some first hand Knowledge from the Dmaxstore team.
2001-2005 Duramax Trucks with 5 Speed Allison:
| Tire Size | Ring and Pinion Ratio | Estimated RPM at 65 MPH |
| Stock | 3.73 | 1872 |
| 33"+ | 4.10 | 1902 |
| 35"+ | 4.30 | 1881 |
| 37"+ | 4.56 | 1887 |
| 40"+ | 4.88 | 1868 |
| 42"+ | 5.13 | 1870 |
| Tire Size | Ring and Pinion Ratio | Estimated RPM at 65 MPH |
| Stock | 3.73 | 1652-1607 |
| 33"+ | 4.10 | 1739 |
| 35"+ | 4.30 | 1720 |
| 37"+ | 4.56 | 1725 |
| 40"+ | 4.88 | 1708 |
| 42"+ | 5.13 | 1710 |