Why 4.1 axle?

valhalla360 wrote:

twodownzero wrote:
It is a myth that more RPM = lower fuel economy. You can "overshoot" the ideal cruise rpm by several hundred rpm without any realistic difference in fuel economy.

My older truck used to cruise in the 2,400 rpm range at 65 mph and now cruises over 3,000 RPM. There has been zero change in fuel mileage, city or highway. If it had overdrive, it would have probably seen a significant increase in mpg by going from the 4.10s it had to the 4.88s it has now.

If the myth that rpm=lower mpg would die, more people would be driving vehicles geared more appropriately. No gas 3/4 ton or bigger should have anything less than 4.10s these days. 30+ years ago, even without overdrive, 4.10 and 4.56 would have been much more common than 3.73s. With the .6x:1 overdrives that are common now, 4.88s or deeper would make for a better towing truck even with the 32-33" tires that come on these trucks from the factory. with the overdrive ratios they have, they would probably still get better mileage than the old 4 speed autos with .7x:1 overdrive ratios and 3.73/4.10 gears. With 6, 8, or 10 gears, there's simply no reason to undergear.

Somehow we've ended up in a situation where we have better control over air fuel ratio and higher ratio overdrives, and we decided to gear the trucks the same. That makes no sense to me. I imagine that it's because they're trying to squeeze every imaginable bit of empty fuel mileage out of these trucks but they're doing a disservice to those of us who work our trucks every day. Trucks have way more power than they had 30 years ago, so we can get away with it, but we'd be in a much better position to use that power with lower gears.

You should go tell the manufactures about this because they've spent a ton of money putting in overdrive gears to improve MPG over the last 30-40yrs. Obviously, they haven't got a clue and I'm sure they will be happy they can cut costs by going back to simple 3 speed transmissions.

Agree, lower rpm almost always = better rpm. You have lower pumping losses period. Modern semi tractors are designed to lug down to 1000 rpm under full throttle, full torque.

The only time this is not true, is if you're using so much throttle in a taller gear that the engine enter open loop (rich mixture).