Another reason you're mileage will drop is that the increased tire diameter will raise you slightly higher relative to the ground, which will increase your wind resistance. Wind resistance is the main reason mileage drops so fast at higher speeds too. -Vivian Loftin
--- On Wed, 8/1/12, Mimi Jasek <mjca...@gmail.com> wrote: > From: Mimi Jasek <mjca...@gmail.com> > Subject: Re: [Texascavers] Help - speed, tire size change > To: "Diana Tomchick" <diana.tomch...@utsouthwestern.edu> > Cc: "TexasCavers" <texascavers@texascavers.com> > Date: Wednesday, August 1, 2012, 12:01 AM > Ok, Diana, Nico, and Karl, thanks so > much. A lot of what you all said was close to some of what I > thought, but you defined it for me. > > I will use your info to try to solve our problem, and for > now just slow down. > > Lost 5+ mpg, which to me is a lot, for the cookie jar has no > funds for stock. > > If others reply to help, it will be tomorrow before I get > back to mail. Last load of laundry calls to be put away, > then this tired lady must go to sleep before another work > day starts:) > > Mimi > > Sent from my iPhone > > On Jul 31, 2012, at 11:42 PM, Diana Tomchick > <diana.tomch...@utsouthwestern.edu> > wrote: > > > 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 > > --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
