BuffaloBill
Well-Known Member
I agree about this powertrain. I too really like the 3.0. The engine, transmission, and rear axle ratio make it a pleasure to drive. Like you said, it seems perfectly matched for the stock tire size. It’s fun to drive!My JLURD powertrain is stock. My tire diameter is 32.8". Under normal highway driving conditions at ~65 mph, in 8th gear, I am usually around 1,800 rpm. The ZF-sourced 8HP75 TorqueFlite 8-speed, does a good job keeping the diesel at 1,800 - 2,200 rpm, which seems to be the sweet spot. The Jeep powertrain engineers picked the right final drive ratio (3.73:1) for this vehicle. It's the best powertrain I have had in my Wranglers.
Try running through the math once, assuming the rolling radius is half of the 32.8”. That works out to 615 rev/mile at the wheel. My dealer tells me the trans ratio on 8th is 0.64. Is that correct?
The stock K02 specs on tirerack shows that tire to be 635 rev/mile. That must be at rated load and pressure I imagine.
Anyway, using those two rev/mile figures, I come up with between 1590 and 1642 engine rpm @65. My tach indicates somewhere around 1600 at that speed (with stock K02), so I had concluded the 0.64 8th ratio may be correct. But I don’t know how accurate my tach reads of course.
Maybe our tachs read a couple hundred rpm different.
In the non-Winter months, I run 315/70/17 K02, which runs a bit less than the 35” I stated. With those, my tach shows 1500 @60.
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