How critical is axle ratio?

dodge guy wrote:

Huntindog wrote:

Groover wrote:
Bottom line is that drive shaft RPM is irrelevant. What really matters is whether the engine is in its power band when you need it to be. Back when truck transmissions only had a 2.5 to 1 spread between high and low axle rations where much more important than they are with the newer transmissions that have a 7 or 8 to 1 spread.

The op is correct, unless you find yourself in first gear wishing that you had a deeper gear or in 10th gear wishing that you had a higher gear you get the same effect by simply changing gears.

I do suspect though that axles built with higher ratios may also be built to handle higher torque to the wheels, at least in some cases.

We have a winner. Rather than write all of this again, here is the readers digest version.
GM was late to the party of increasing their HD lines tow ratings. Ford and Ram were first, and they required higher (numericially) ratios to do it. When GM tried this approach, the Pinion gears would not live behind the Dmax. For those that do not know: as the rear end gears increase numericially, the pinion gear engages less of the ring gear, and thus is weaker.
So though the Dmax was more than capable of a higher tow rating, the gear set to make the performance acceptable was out of reach.
Enter GMs new Allison 10 speed. With lower gears available in the tranny, the rear gearset could actually be changed in the direction that would make it stronger. So that is what they did, and for good measure they increased the size of the ring gear on the duallys as well.

What I get out of that is that GM’s axles are weak. No other manuf had that issue with lower gears.