Quote:
Originally Posted by wcs531
I was assuming the ratio may have been targeted towards rated fuel economy for advertising (not real world fuel economy). It could be to reduce excess strain, but since when does BMW care about longevity past the warranty period? 10k+ mile oil change intervals, "lifetime" transmission fluid, etc. I would guess the e70's towing limits are more chassis related than engine/transmission related - they both seem pretty stout.
Also for non towing situations, shaving a few hundred RPM while cruising at 80mph for hours on end would have to reduce engine wear a reasonable amount in addition to better mpg.
|
We’re talking about a stock x5d right? It would be a mistake for a stock x5d to change to 3.15 final ratio. It’s already slow as is stock. And I should correct myself, the drivetrain wouldn’t be as affected but the powertrain would be very affected by this. You’d be bogging this engine everytime you shifted gears casually driving, even WOT. A deleted and tuned x5d would probably fair better but it would still put strain on the powertrain.
It has nothing to do with economy. An X5d gets worse economy on the highway if you drive above 75mph, which most people do. It has to do with performance and strain on the engine/transmission. And towing would only exacerbate it. It would of course still do it, it has diesel torque, but that doesn’t mean it’s good for the powertrain.
The n57 got the 3.15 gearing because the 8spd gives you two more gears down low to accelerate and a better gear ratio spread up top for highway speeds. If they had the 6speed for the v8 models and i6 models they would probably use the same 3.64 final ratio or something in between, maybe not though because they have much more rpm to work with.