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
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