GM Truck Sales Bulletin
Subject: Axle ratio Selection, Silverado / Sierra 1500 Series 4x4 Models
It is generally accepted that a higher numerical axle ratio, like 4.10:1, produces more torque multiplication for added trailer towing performance etc., but burns more fuel. However, engineering improvements made to GM's full size pickups now provide the best of both worlds - economy and performance.
The Vortec 5300 V8 engine has significantly improved air flow producing close to peak torque and good fuel efficiency over a very wide operation range from less than 2,000 rpm to over 4,000 rpm.
The electronically controlled 4 speed automatic transmission features a 0.70:1 overdrive gear and a torque converter clutch that locks up in both 3rd and 4th gears for improved fuel economy.
A 4.10 axle ratio provides more load moving torque and it takes some load off of the transmission as the truck accelerates, so it upshifts faster and the converter locks up sooner. Elimination of any torque converter action, with the clutch applied, reduces heat build-up in the transmission for improved efficiency and durability. With a 4.10 axle ratio, the transmission will shift into overdrive sooner and hold in overdrive better. In overdrive, the final drive ratio is only 2.87:1 (4.10 x .70), a very fuel-efficient gear ratio.
In overdrive, cruising at 60 miles per hour the engine speed, with standard P245/75R16 tires and a 3.73 axle ratio, will be approximately 1780 rpm.
In overdrive, at the same 60 miles per hour but with larger P265/75R16 tires and a 4.10 ratio, the engine speed will be about 1870 rpm - less than 100 rpm more.
Between 1700 and 1900 rpm, both the torque and horsepower development of the Vortec 5300 V8 is increasing so the slight engine speed increase with the 4.10 ratio produces the expected performance improvement without a noticable increase in fuel consumption. In fact, when operating close to the Gross Vehicle Weight Rating (GVWR), or trailer towing, you can expect the 4.10 ratio to actually provide a gain in fuel economy.