Gear Ratio Recommendation for Duramax Owners

[DmaxStoreJake]

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:

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

2006-2019 Duramax Trucks with 6 Speed Allison:

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