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LH Lead-Foot · 02-21-2018, 01:43 PM

I chose to go with a 3.08 gear in the "GM" 12 bolt truck diff on my Eaton Posi. The 8.85" carrier has to be a type 3 for correct set up. There is a split in ratio's from type 3 to type 4 that many have with 4.11 gears. I was lucky as I have a diff spreader.
Here's my math with a 700r4 / 4L60 / 4L60e with an 0.70 over drive. With P235/75R16, that tire has a 29.88 diameter. At 60 MPH, in over drive, 3.08 final + tires=1454-1504 RPM with lockup. This should get the MPG up there in the mid teens or higher.

02-21-2018, 01:43 PM	#10
LH Lead-Foot Registered User Join Date: Jan 2018 Location: Omaha, NE. Posts: 214	Re: 3.08 Ratios in a K/10 Sub I chose to go with a 3.08 gear in the "GM" 12 bolt truck diff on my Eaton Posi. The 8.85" carrier has to be a type 3 for correct set up. There is a split in ratio's from type 3 to type 4 that many have with 4.11 gears. I was lucky as I have a diff spreader. Here's my math with a 700r4 / 4L60 / 4L60e with an 0.70 over drive. With P235/75R16, that tire has a 29.88 diameter. At 60 MPH, in over drive, 3.08 final + tires=1454-1504 RPM with lockup. This should get the MPG up there in the mid teens or higher.