Edited and recalculated to show the correct .71 final drive ratio for the E4OD Trans
My 92 E350 Clubwagon with the 5.8 and E4OD came stock with 245/75/16 tires and the 3.54 gears. I changed the tires to 265/75/16. I tow a fairly light trailer. Total weight of the trailer and load is usually less than 1500lbs. I also have one of the biggest aerodynamically challenged toppers on the road slowing me down. The difference in tire height between the stock 245 and the taller 265's is 1.3 inches. The 265 tire is 31.65" tall.
With the 3.54's I wasn't real happy with the way the trans hunted in overdrive pulling the trailer. At 60mph with the cruise on it couldn't really make up it's mind which gear to be in. The slightest incline and the thing would start to hunt.
The van is in the shop right now getting the gears changed to 4.10's. I'm also having Detroit Truetracs installed in both the front and rear diffs.
I was curious about what kind of rpm increase the gear changes would give me at 60mph and 70mph. I found a website that does a rpm calculation if you give it final drive ratio of transmission (.71 for the E4OD in overdrive), tire size, diff gear ratio and vehicle speed.
This is the information I got from the website.
Final drive ratio of E4OD in overdrive .71
Tire size 265/75/16
An increase of 267rpm for the lower gears
An increase of 293rpm for the lower gears.
I have no idea what increasing my rpm between 267 and 293 at cruising speed will do the fuel economy. I'm hoping the increase in rpm will convince the trans to stop hunting and find it's happy place in overdrive.
After I get the gears changed I will need to get the speedometer re-calibrated so the brains that control the transmission shift pattern has the correct information coming in.