wmoses wrote:
Rob,
You know I agree with you, right?
I am actually expecting a slight decrease in fuel economy not an increase.
As for the increased capability of the truck after the installation of a new gear set - I know that there is no linear relationship with rating, and said so. I merely was bringing up the rating of a factory 3.42 truck for comparative purposes for what can expect regarding tow ability (and power train longevity, perhaps) before vs after the mod. Of course changing to a lower gear as the need arises will still be there, rear end gearing notwithstanding.
Ratings are not simply due to gearing capability, but must also consider the entire capability of the power train as a whole over the period the manufacturer is prepared to warrant and (I would expect) the reasonable life of he truck to the owner, along with other less tangible aspects (again, I would expect) as towing ease and confidence, etc. lets not forget marketing influences as well.
BTW, all of this is my opinion as a practicing engineer since like most here, I have no direct insight into how manufacturers assign ratings.
Yes - market influences - dually diesel pickups have to jump through puddles on the construction site while hauling a backhoe...:)
A lot of "power" can be delivered through small components turning at high rpm (dragster). Slower rpm = increase size (ship's propeller shaft). Increasing your rear ratio (bigger number) will decrease strain on components ahead of the axle.
The old time rule of thumb is to gear a truck so at normal cruising speed in the normal cruising gear for the road speed the engine rpm is mid way between peak torque and peak hp (or governed speed). If you modify your engine with supercharging or turbocharging this usually moves the torque number up at lower rpm so the engine will "pull" taller gears.
All other factors the same the lower geared truck will outrun the higher geared truck uphill, against the wind, or in rolling land every time.
Possibly manufacturers can only "void" warranty if the warranty agreement states the modification you are planning will void the warranty. Changing your gearing should not impact a warranty claim for a malfunctioning passenger window ...
