Here's my report: On my '04 Duramax (4x4 GMC cab and a half, about 7700#)
I've run stock tires (LT245-75R16) and also
the next size bigger -- 265's. I was in the habit of recording all fuel put
into the tank, as accurately as the pumps measured
it (readouts are down to the hundredth of a gallon). I also recorded the
mileage on the odo as I put the fuel in. So - I had a
record of the first 100,000 miles or so of fuel economy/use. I also, by the
way, calibrated my odometer useing a GPS, so I'm
confident that the miles, as read off the odo times a small correction factor,
are correct. I got various mileage depending on
the load and so on, but -- when I went to the larger tires and corrected the
odo for the slightly larger circumference of the
tires (they were about 3/4" taller, which'd come out about 2 1/4" more
circumference) -- my fuel economy went down.
Down by about 5% on average (for load and those other factors). As soon as I
put the stock-size rubber on (new set of tires)
the economy went back to the original numbers.
The tires were of similar tread pattern, manufacturer, and so on, so I figure
that the difference was from the tire size. Which
tells me that themanufacturer geared the truck for those size tires -- and
only those.
TYhat's what I found -- putting bigger tires on my truck cost me fuel, not
SAVED me fuel. YRMV.
Jon
On Dom Jul 20 14:54 , BWANA343@aol.com sent:
>Being the car guy on my block, lately I've been getting involved in the "how
>do I get better gas mileage" discussion at neighborhood gatherings.
>Besides the usual advice, we also kicked around the merit of going to a
>larger, as in taller, tire to effectively raise the final drive ratio for the
>longer legs.
>I researched tire sizes and find that to get a perceptible mpg difference,as
>in ten percent, the tire size and corresponding weight goes up tremendously.
>Most of the taller tires are truck/SUV and E rated and heavy.
>I'm thinking the added sprung weight and cost of the tires might neutralize
>any mpg added. Plus,the Speedpo/odo would read off, too.
>Yeah, I know, Duh ?
>Bob W
>
>
>
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