First off, you will technically gain speed potential with 3.07s going from 31s to 32s if the engine can make enough power. However torque does suffer.
AX-15 and 3.07s are what you get when government bureaucrats, engineers, lawyers and sales get together and figure out a bait a switch scenario. All examples of doing the stuff you want is done with a different gear ratio and tires and the MPG sales point doesn't sound that bad due to unrealistic driving scenarios of running 3.07s. 3.07s are only somewhat practical with street tires 29" or smaller. Now, like most Americans I'm used to big HP and no shifting from OD 45+MPH ie pre-2000s. On a flat road and a mostly empty Jeep 29s are not horrible with the 4.0L. With most diesel engine torque curves 29s and 3.07s are fantastic for on the road activities, but we're only allowed and sold big HP not the torque some are describing. If the 4.0 had had the HP of our typical V8s we wouldn't all be asking about the tires and gear ratios.
On paper 3.07s can be more efficient on the highway, but the torque curve and the drag of the vehicle isn't even close above about 29" tires and when you get into more off-road oriented tires, you get a BUNCH more losses on the road compared to lightweight on-road tires. I have been able to use OD on a few rare occasions with 33s and 3.07s, but almost only on downhill slopes, oh and add a winch or some lights and the scenario gets more rare. Drop from 33s and it's better but almost imperceptible unless you're really paying attention. And the issue I have with that ratio and the 4.0L is that you'd need to run ~25" tire to even be close to the peak torque where you wouldn't have to shift from OD regularly on the highway. And if you tow anything, that's just another head scratcher on 3.07s. And personally I won't buy almost anything under 3.73:1 when I get a vehicle just due to most of the torque curves and transmissions that are on the current market.
Now will you be able to tell the difference in a 31 vs 32, probably not and in fact the 32" might be a 31" tire and if it's not from the factory it will be in a couple of years. Will it be a big deal in general..no. There will be a little be of additional shifting and since the vehicle is technically undergeared, performance, MPG, and wear are all going to be ever so slightly worsened. Now for a vehicle snob and engineer like me with an idea of how a vehicle, especially a 4x4 should be properly utilized and made, it annoys me quite a lot, because it's wrong on paper for the most part and slightly inconvenient in the real world. I think it's asinine for the RPMs to be so far away from peak torque on the highway with your OD and the most common tire sizes. IMO you should either be solidly in that range or just slightly under for an AUTO. Especially when the peak torque and torque from the combined gear ratios aren't enough to maintain highway speed when in OD.
I did run 3.07s for 6 or 7 years, so again it's more of a pet peeve, but the highway was a struggle and 5th gear almost had no use and I'm not sure why it was there. And when I went to mud tires, some lights and a winch, I dropped down to 29" tires and it made more sense to just trailer the Jeep at that point.
AX-15 and 3.07s are what you get when government bureaucrats, engineers, lawyers and sales get together and figure out a bait a switch scenario. All examples of doing the stuff you want is done with a different gear ratio and tires and the MPG sales point doesn't sound that bad due to unrealistic driving scenarios of running 3.07s. 3.07s are only somewhat practical with street tires 29" or smaller. Now, like most Americans I'm used to big HP and no shifting from OD 45+MPH ie pre-2000s. On a flat road and a mostly empty Jeep 29s are not horrible with the 4.0L. With most diesel engine torque curves 29s and 3.07s are fantastic for on the road activities, but we're only allowed and sold big HP not the torque some are describing. If the 4.0 had had the HP of our typical V8s we wouldn't all be asking about the tires and gear ratios.
On paper 3.07s can be more efficient on the highway, but the torque curve and the drag of the vehicle isn't even close above about 29" tires and when you get into more off-road oriented tires, you get a BUNCH more losses on the road compared to lightweight on-road tires. I have been able to use OD on a few rare occasions with 33s and 3.07s, but almost only on downhill slopes, oh and add a winch or some lights and the scenario gets more rare. Drop from 33s and it's better but almost imperceptible unless you're really paying attention. And the issue I have with that ratio and the 4.0L is that you'd need to run ~25" tire to even be close to the peak torque where you wouldn't have to shift from OD regularly on the highway. And if you tow anything, that's just another head scratcher on 3.07s. And personally I won't buy almost anything under 3.73:1 when I get a vehicle just due to most of the torque curves and transmissions that are on the current market.
Now will you be able to tell the difference in a 31 vs 32, probably not and in fact the 32" might be a 31" tire and if it's not from the factory it will be in a couple of years. Will it be a big deal in general..no. There will be a little be of additional shifting and since the vehicle is technically undergeared, performance, MPG, and wear are all going to be ever so slightly worsened. Now for a vehicle snob and engineer like me with an idea of how a vehicle, especially a 4x4 should be properly utilized and made, it annoys me quite a lot, because it's wrong on paper for the most part and slightly inconvenient in the real world. I think it's asinine for the RPMs to be so far away from peak torque on the highway with your OD and the most common tire sizes. IMO you should either be solidly in that range or just slightly under for an AUTO. Especially when the peak torque and torque from the combined gear ratios aren't enough to maintain highway speed when in OD.
I did run 3.07s for 6 or 7 years, so again it's more of a pet peeve, but the highway was a struggle and 5th gear almost had no use and I'm not sure why it was there. And when I went to mud tires, some lights and a winch, I dropped down to 29" tires and it made more sense to just trailer the Jeep at that point.
