Mimi, A simple back-of-the-envelope calculation would be to divide the current tire circumference by the previous tire circumference. This would give you an estimate of the fractional difference the new, larger tire would travel for each revolution of the tire. Using the numbers you supplied gives a value of approximately 1.071. If you are used to driving at 60 m.p.h., in theory the new tires would actually be taking you at 60 x 1.071 = 64.26 m.p.h.
Of course this is a pretty simplistic estimate. If you want to maximize your gas mileage, that's a more complicated experiment that would need you to fill your gas tank (be sure to always use the same type of gas--the higher the percentage of ethanol, the lower your mile per gallon), drive a set distance at different speeds and re-fill the tank to see how much you used. Oh, and be sure that the prevailing wind speed and direction is the same every time you repeat the drive at the different speeds. Diana ******************************************************** Diana R. Tomchick Professor Dept. of Biochemistry University of Texas Southwestern Medical Center 5323 Harry Hines Blvd. Dallas, TX 75390-8816 (214) 645-6383 (office) (214) 418-5827 (cell) diana.tomch...@utsouthwestern.edu On Jul 31, 2012, at 11:09 PM, "Mimi Jasek" <mjca...@gmail.com> wrote: > Ok, I need help. I have a Ford Escape that we use as our main caving vehicle > due to great gas mileage. Due to age, miles, and need for stronger sidewalls > and better traction, we traded our old tires for new. Love them, but because > bigger, noticed huge drop in gas mileage at same speeds used to traveling, > and I seem to be staying up with or passing everyone!! > > Old = P235/70R16 normal street tires > > New = LT245/75R16 E Toyo OPAT OWL 120Q > > Don't want a speeding ticket, and need my good mpg back, or close to it. Can > anyone tell me how much to decrease my speed, and if the reduction is the > same for all speeds? If not the same, how much decrease at what increments? > > I believe my old tires were 28" diameter (spare is that) with 7.33' > circumference, and new are 30" with 7.85' circumference. > > I have to believe there are more than enough math wiz/ tire savvy folks out > there to get me some answers, but if I am asking the impossible, tell me. I > do have a tachometer as well as a speedometer if that helps. > > For us, mpg means a lot due to cost of gas, and determines how many trips we > make. I would really appreciate any help anyone can give me. > > Thanks, > > Mimi Jasek > > > > Sent from my iPhone > --------------------------------------------------------------------- > Visit our website: http://texascavers.com > To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com > For additional commands, e-mail: texascavers-h...@texascavers.com > ________________________________ UT Southwestern Medical Center The future of medicine, today. --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
