>Date: Mon, 17 May 2004 22:49:15 -0500
>From: Terrible Tom <SilverEightynine@aol.com>
>Subject: Re: DML: Speaking of gas prices and mileage...
>
>steve preston wrote:
> > I don`t really understand that,Bill! I always thought
> > that smaller diameter tires required more engine rpm
> > to cover the same ground. It seems that any reduction
> > in that diameter would have to speed up the engine at
> > least a little bit. I guess maybe a less aggressive
> > tread design could reduce drag,and that could be
> > enough to offset the difference. I don`t know. I went
> > a size UP (from 70 to 75R) on my tires (last
> > year?),just to make the truck sit a little higher and
> > take up some wheel well space. Also to save a little
> > money! But I neglected to measure mileage before and
> > after,which I wish I`d have done now. Steve
> > P.
>
>Guy at work said to me "oh you are going to lose fuel economy by going
>to those bigger tires" when I informed him I planned to stuff 35 inch
>shoes under the Ram.
>
>While it may be true that I would be rolling around with more weight and
>the engine would have to use more power to turn bigger wheels - they are
>not that much bigger - I have approx. 32's now - stock. Also the loss of
>aerodynamics isnt that much to worry about either. This truck already
>has the aerodynamics of a skyscraper.
>
>I may see a loss in city driving - but a larger tire will rotate less
>times than a smaller tire and will in turn lower the number of RPM's the
>engine runs at while at highway cruising speeds. (final drive ratio)
>This is where I am looking to make my primary gains. The way I drive -
>I know I have a snowballs chance in hell, to get good MPG figures in
>town. I'm in the process of getting a more economical means of
>transportation around town.
I have some slightly oversized tires on mine, I can't remember the aspect on
my 92 2WD stock, but I've got 235/75 Wilderness ATs on stock 01 wheels and
my city mileage isn't great, but i've pulled 22-23 mpg going by the trip on
long interstate runs consistently for the last 4 years. And that is going
by the trip odometer, and I know for a fact that the speedo (and therefore
the trip) is off by 5-7 mph at highway speeds or right around 10%. So if
you look at it that way, you are getting the advantage. I didn't think of
it when I got the tires but I figured it out as I went along. BTW truck is
a 92 3.9L with around 165K on it and I pulled 18 mpg last tank of mixed
driving.
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