Differential Gear Ratio Question

Gentlemen, I was looking at the spec sheet and noticed that the gear ration for a manual transmission is 4.3 and for an automatic it is 3.9 while both are six speed transmissions. Why didn't they just use the same gearing ratio in both transmission variants? Is this why the manual gets worst gas mileage than the automatic? Whats the benefits of different ratios?

 

You neglected to factor in the fact that the MT's top gears are NOT direct but rather overdrives. You do the math and you will see.

Clay/Auburn, Wa.

 

They should have put the 4.3 in the auto and the 3.9 in the m/t.

 

Why is this? Would it have provided better gas mileage or performance?

 

in my experience, MT's have always had a higher gear ratio. Helps with off the line starts and torque

 

Personally, I'd like the gear ratios reversed because of the transmission's 6th. gear ratios. The .58 in the auto would be helped by a deeper axle ratio, yet the rpm's would still be under 2000 at most average freeway speeds. The m/t's .71 6th would benefit at highway speeds with the 3.91 with a bit lower rpm. Yet still have a decent crawl ratio in 4L.

"My opinion of course"

 

So which one revs lower say at 75mph?

 

The auto, that's part of the issue others are talking about...it takes very little additional load on the engine for it to down shift. I've only taken a very short test drive, so I haven't got any real world hands on, but the numbers tell most of the story. And I felt this might be a problem when they released the numbers. Like others, I would like to see the hp./trq. curve on this engine, and layer over the 4.0.

Many say "why get so hung up on this" I don't have a good answer, other then I've always been interested in it all...hp,trq, axle ratio, trans. gearing, transfer case gearing, hp/lb. trq/lb...