got most of my information from them when i went to buy my new tires for my dodge... Went with 265/70/17 Bridgestone Dueler A/T revo's ... AWSOME TIRE.... mud snow ice you name it, it handles it, the best thing about them they are quiet on the highway...
then i got the Firestone Destination's M/T 31 x 10.5 on 15's on my wifes ford ranger..... very nice ride.. quiet as well
Now I have a question ,My newer tirer size says that my speedometer is running 2.1 miles per hour slower. How does this effect my gas mileage figuring. That 17 rpm less per mile. How does that change my miles per gallon and my odometer readings.
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We love cruisin in our PT and our boat.
The thing that I personally would do if I wasn't going to change it with a programmer, would be drive a few trips to places I knew the distance (Like 100+ miles) and calculate the mileage that way. Otherwise I don't know what the formula would be for calculating the exact mileage.
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2005 4x4 Quadcab Laramie, Hemi, Debaged,4.56 Detroit TrueTrac, 3" Lift, CAI, Dual SS 40 Delta Flowmaster's, Magnaflow X-pipe, QTP cutouts, Electric Fan, PML Trans & Diff Pans, MotoBlue UDP
You've got me thinking about this now... for a formula to figure out your actual miles per gallon if your speedo is off. The best I can come up with on the spot is that there is no formula. I could be totally wrong, and if there is an actual solution, I'd like to see it (just because). Just jotting a few things down, it seems that the formula is going to depend on your average speed. For example, if you're traveling with a reading of 60mph on the speedo, you are telling me that you're actually travelling at a speed of 62.1mph. If you were to drive for one hour exactly at this speed, you're going to go a distance of 1.035 times farther that what your odometer actually says. However, if you're speedo said 105mph and you were actually doing 107.1mph, the multiplier would be 1.02 times farther. So if there's a way you can travel for say an hour with the cruise control on and not varying speed, all the way from fill up to fill up, so you can get the exact gallons of fuel you've gone through, then divide: [(speedo# + 2.1) / speedo# * number of miles logged on odometer] / gallons that would theoretically give you your correct miles per gallon. I would think the turnpike during lite traffic would be the perfect place to figure this. Fill up at the first service center, and somewhere at say an hour away, start to look for another and fill up again to find how many gallons you've gone though.
probably not too helpful, but I'm not sure there's an exact way to do this.
***edit: thought about this a little bit more. and that 2.1 mph is only going to be true at a certain speed. so what i said earlier about 60=62.1 and 105=107.1 is not correct. this needs to be a ratio or a percentage. i think it could be calculated easier if you use revolutions. if i figured this out correctly, as your tire size increases by 1 inch, the circumference of the tire increases by .03% meaning your going that much farther. so no matter what you're odometer says, add .03% to it and divide by the amount of fuel. (remember that .03% is per inch that the tire size increases, so if you increase two inches, you'd use .06% to compensate for the two inches in increased diameter.
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