New bigger tires, how do I figure
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Professional
Joined: Sep 2007
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New bigger tires, how do I figure
out my gas mileage? I went from 265/70r/17's to 285/75/17's, these tires are a lot bigger! I figured if I drive 60mph that is truely about 65mph, but my rpm's are a lot lower, can that be? Can I get better gas mileage now?
Is there a formula to help figure this out?
Thanks!!
Is there a formula to help figure this out?
Thanks!!
Administrator
Joined: Jul 2007
Posts: 24,686
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From: South Georgia/East Florida
RE: New bigger tires, how do I figure
It's called buy a tuner and re-calibrate or go to the dealer and have them do it. I've seen some dealers do it for free, but most charge a small fee...
Joined: Mar 2007
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RE: New bigger tires, how do I figure
They Will Charge You 1/2 An Hour - Mine Was $58. Dave Will Be Able To Tell You For Sure But, They Used The DRB III Scanner. They Calibrated Mine By The RPM of The Tire. You Can Find This Information On Your Tire Manufactors Spec or Measure Your Tires Road Contact Diameter and Divide That By How Many Inches In A Mile.
Administrator
Joined: Jul 2007
Posts: 24,686
Likes: 21
From: South Georgia/East Florida
RE: New bigger tires, how do I figure
Oh yea, and to answer your other question, the bigger the diameter of your tires, the lower your rpm's at a given speed. But don't think for a second that going to bigger tires won't decrease fuel economy...
Champion
Joined: Mar 2004
Posts: 2,703
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From: Bremen, GA.
RE: New bigger tires, how do I figure
On a 2004, it is best to re-calibrate your speedo by revolutions per mile. Here is a formule to figure out revs per mile..Take a piece of string and wrap it around your tire(follow the tread). We are trying to figure out how many inches around the tire is. Tie a knot or make a mark on the string so you will know where one end touches the other. Now measure the legnth of string in inches. Since we know that there are 5280 feet in a mile, we can multiply that by 12 and get how many inches are in a mile. Next divide the inches in a mile by how many inches you had when you measured the string. I am going to use 315 tires in the following example...
feet in mile 5280
times 12 = 63360 inches in a mile
a 315 inch tire is 109 inches around
63360 divided by 109 equals 581.285 revs per mile.
A dealer can put this in using the DRB III. Some programmers will also do this but I am not sure which ones.
Hope this is clear as mud. If you have questions on how to do this, PM or call me...DAVID
feet in mile 5280
times 12 = 63360 inches in a mile
a 315 inch tire is 109 inches around
63360 divided by 109 equals 581.285 revs per mile.
A dealer can put this in using the DRB III. Some programmers will also do this but I am not sure which ones.
Hope this is clear as mud. If you have questions on how to do this, PM or call me...DAVID
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Joined: Feb 2008
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From: Calgary, AB
RE: New bigger tires, how do I figure