Donald,
I'm pretty sure that unless you recalibrate the computer(for the new
tire size)so that your speedometer and odometer are correct, you MPG
readings should remain about the same as they were before you got the
new tires.
BUT,You MAY ACTUALLY BE GETTING BETTER GAS MILEAGE...(the numbers used
are for example only)
Your new tires are bigger and make fewer revolutions per mile(90) than
your old tires(100). Your truck still thinks it has the old tires and
is still going by the revolutions per mile of the old tires. So when you
reach 90 revs you have ACTUALLY gone a mile. The computer thinks you've
reached a mile at 100 revs. After 1000 revs you have actually gone 11
miles not 10. Let's say it takes a gallon of fuel to make 1000 revs.
The computer thinks it took a gallon of fuel to go ten miles when it
ACTUALLY took a gallon of fuel to go 11 miles.
Sounds like Jr High Algebra... :-) If a train travelling 60mph leave
chicago at 4:00pm and a train travelling at.... You get the picture.
BTW I went to the dealer the other day to ask about reprogramming the
computer because I want to get the same tires that you have. Nobody in
parts or at the service desk knew that you could do it. I was
persistant and asked to speak with one of the mechanics on the floor.
They sent me out there and the guy said it was a 15 min procedure max.
And they do it all the time! Go figure...
-----Original Message-----
From: Mallett, Donald B [mailto:Donald.Mallett@BNSF.com]
Sent: Tuesday, June 17, 2003 1:43 AM
To: 'DML'
Ok, Bear with me on this again. Last year I put on a set of 31x10.5R15
replacing the stock 255/65r15 badyears. I have gone to the DML
TireCalc.cgi and found the new tires to be 8.74% larger in
circumference. The question is, will this increase or decrease the
overhead computers MPG read out?
Please simple easy to read answers!
*-------------------------------Y2KOTA-------------------------------*
Don Mallett
Y2K QC 4.7L Auto SLT+
http://www.mallettservices.com/y2kota.html
http://www.dakota-truck.net/profiles/dakota/QwkvWz@DAJFf6/profile.htm
*-------------Straight home & no playing in the puddles!-------------*
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