Rear axle ratios and impact on towing
Suppose you have a choice between two axle ratios, say they are a 3.09 and a 3.45. And let's say the vehicle has an 8 speed transmission, so there's plenty of gear flexibility. Ok, so there's roughl...
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It will be a Jeep Grand Cherokee, actually. And I guess I don't truly get an axle choice per se. The diesel gets a 3.45 whereas the hemi (which I'm leaning toward) gets a 3.09. But I'm still interested in the theory behind rear ratio selection. If one had two different rear end/tranny gear combos that would both yield the same RPM at the same highway speed, am I correct in understanding that both combos will transmit the same HP and torque, and therefore produce the same towing experience?
I realize it isn't entirely that simple in prectice, because the ZF 8-speed's gear spreads are larger than 10 or 12 percent. 8th is 0.67, 7th is 0.84, 6th is 1.00, 5th is 1.29, etc. With the 3.09, what 1 gear lower will tend to do is bump the RPM up an extra 10%-20% (vs the 3.45 and the next higher gear), putting it a little higher in the power band for a given speed. Not a bad thing.
(edit): Fred, we were typing at the same time and I think you've answered my question pretty directly. Thanks. ;)
I realize it isn't entirely that simple in prectice, because the ZF 8-speed's gear spreads are larger than 10 or 12 percent. 8th is 0.67, 7th is 0.84, 6th is 1.00, 5th is 1.29, etc. With the 3.09, what 1 gear lower will tend to do is bump the RPM up an extra 10%-20% (vs the 3.45 and the next higher gear), putting it a little higher in the power band for a given speed. Not a bad thing.
(edit): Fred, we were typing at the same time and I think you've answered my question pretty directly. Thanks. ;)
