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 experience from the Dmaxstore team.

2001-2005: Duramax trucks with 5 speed Allison, Stock Ratio is 3:73

33"-35" Tall tires we recommend running a 4:10 gear ratio. This will put you back to stock with 35" tires. With 33-34" tires you will be slightly lower than stock.

37"-38"-40" Tall tires we recommend running a 4:56 gear ratio. With 40" tires you will be exactly back to stock gearing. With 38"-37" tires you will be slightly lower than stock. However, we recommend being lower than stock to help correct the heavyweight of these large tires.

40"-42" Tall tires we recommend a 4:88 gear ratio. With a 40" tire you will be slightly lower than stock. The lower ratio is better if you are looking to improve towing performance.