Re: [a/s] 2WD vs. 4WD

[John Hilty <hilty@xxxxxxxxxxxxx>]

Al,

I am certainly not an expert here, but the few factors of difference that I know
about are these:

virtual@islands.vi wrote:
> 
>   I'd like to get opinions regarding the relative merits of 4 wheel drive tow
> vehicles as compared to a 2WD vehicles of similar size and horsepower. What are
> the trade offs? I figure that there have got to be situations when the extra
> traction would be desireable. Is there a downside to 4WD as it relates to fuel
> economy and maintenence expenses?

4WD vehicles are heavier because of the additional machinery, i.e. transfer
case, driveshaft, drive axles, etc. You will note when looking at tow ratings of
comparable 2WD and 4WD vehicles that the tow rating of the 4WD is slightly less
by the amount of that additional weight while the GCWR remains the same. Fuel
economy is less with 4WD also, presumably because you are pushing more weight
and you may be asking the motor to do additional work to turn additional
components in the drivetrain whether 4WD is engaged or not. 4WD obviously
provides better traction in slippery situations, but in my experience it also
provides a rougher ride. The longer wheelbase vehicles have a better ride so if
you go for a long bed crewcab it would not be as choppy as a Jeep CJ.

>   The same question can be rephrased to address another question. Namely, the
> relative merits of diesal vs. gas engines.

Deisel engines reach their peak horsepower and torque output at lower rpms than
gas engines. This suggests that the fuel consumption and engine wear is less at
any given power output. The maintenance on diesels is more critical however.
Fuel and oil filters and oil changes are more frequent must do tasks. The
crankcases are also typically larger and thus more expensive to maintain
properly. If you plan on traveling to or live in higher altitude, note that
normally aspirated gas engines typically lose approximately 3% of their
available power per 1,000 feet of elevation above sea level. Most diesels are
turbo charged nowadays and do not suffer from this problem. Diesel fuel prices
currently are less than gas, but sometimes have been more. The trucking industry
has done somewhat of a good job of keeping them down and should continue to
exert their influence. I remember buying diesel for my first Mercedes for 33.9
when gas had shot up to 50.9 and higher back in the early 70's and thinking what
a bargain I was getting.

John H.
-- 
hilty@airstream.net
http://www.skyboom.com/johnhilty/