D

d745

Guest
Hi

Will changing tire diameter to a larger diameter on my pickup truck help
improve gas mileage?


 
Probably not. Of controllable factors, driving habits affect mileage
most. The difference in driving hard and easy can be as much as 20%
change in mileage.

I teach people to drive conservatively by suggesting that they drive
with the mental image of a crock of $hit on the front seat beside
them, and they don't want to spill it. No sudden acceleration, no
excessive speed, no hard braking. It works.

I had a friend who was a professional trucker. He was not slow, got
places as fast, or faster than most others. He could set a cup of
coffee on the dash (not in the holder!) and drive without spilling a
drop--he was that smooth. Showed in his mileage...

On Fri, 25 Mar 2005 08:42:41 -0500, "d745" <davel745@yahoo.com> wrote:

>Hi
>
>Will changing tire diameter to a larger diameter on my pickup truck help
>improve gas mileage?
>

 
Yes, no, maybe.

Your 'perceived' mileage will go down because of the increase in
diameter, but the actual mileage might go up depending on your gearing.

I went up 2" and my mileage stayed almost exactly the same 'if' I forget
I have a 5th gear or overdrive. If I use overdrive, my rpm are too low
so the engine lugs and just drinks gas. If I stay in 4th, my mileage
stays virtually the same as before which is a respectable 23 US mpg in
my CJ7.

If my gearing had of been slightly different or if I re-geared, my 5th
might still be useful and my mileage might have gone up but... The
manufacturers seem to match tires and gearing to get the best mileage
and power.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

d745 wrote:
>
> Hi
>
> Will changing tire diameter to a larger diameter on my pickup truck help
> improve gas mileage?
 
Mike Romain wrote:
> Yes, no, maybe.
>
> Your 'perceived' mileage will go down because of the increase in
> diameter, but the actual mileage might go up depending on your gearing.
>
> I went up 2" and my mileage stayed almost exactly the same 'if' I forget
> I have a 5th gear or overdrive. If I use overdrive, my rpm are too low
> so the engine lugs and just drinks gas. If I stay in 4th, my mileage
> stays virtually the same as before which is a respectable 23 US mpg in
> my CJ7.
>
> If my gearing had of been slightly different or if I re-geared, my 5th
> might still be useful and my mileage might have gone up but... The
> manufacturers seem to match tires and gearing to get the best mileage
> and power.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> d745 wrote:
>
>>Hi
>>
>>Will changing tire diameter to a larger diameter on my pickup truck help
>>improve gas mileage?

Mike makes some good points about gearing. Another
factor to consider is the with bigger tires, comes
more height. You will catch more air and the
resistance will have some effect on fuel
consumption as well.

--
-- Jack --
=================================
Everything you see is temporary.
=================================
Clean Up Return Address To Reply
=================================
Poway, California (San Diego Co.)
N 32° 57' W 117° 04'
At 508' Elevation
=================================

 
No but ... "The U.S. Department of Transportation says that most drivers can
improve fuel mileage by at least two percent by keeping their vehicle tires
at the maximum recommended pressures. You can find the carmaker's
recommended tire pressures in your owner's manual and on a tire decal or
placard in the glove compartment or on the driver's door post, near a
hinge." Note that this is not the max printed on the tire itself.

"d745" <davel745@yahoo.com> wrote in message
news:3824820e96b6155ca3a79b772c36794e@localhost.talkaboutautos.com...
> Hi
>
> Will changing tire diameter to a larger diameter on my pickup truck help
> improve gas mileage?
>
>


 
And in looking that up, I also read that a difference of 1/4 diameter
between tires on a 4WD/AWD vehicle ... you know the ones I mean, the ones
with the old (leaky) alloy rims, with at least one tire almost running on
the rim ... can cause damage to the transfer case/drivetrain.

"bowgus" <bowgus@rogers.com> wrote in message
news:_pCdndk6Q7OO4dnfRVn-qQ@rogers.com...
> No but ... "The U.S. Department of Transportation says that most drivers
can
> improve fuel mileage by at least two percent by keeping their vehicle
tires
> at the maximum recommended pressures. You can find the carmaker's
> recommended tire pressures in your owner's manual and on a tire decal or
> placard in the glove compartment or on the driver's door post, near a
> hinge." Note that this is not the max printed on the tire itself.
>
> "d745" <davel745@yahoo.com> wrote in message
> news:3824820e96b6155ca3a79b772c36794e@localhost.talkaboutautos.com...
> > Hi
> >
> > Will changing tire diameter to a larger diameter on my pickup truck help
> > improve gas mileage?
> >
> >
>
>


 
On Fri, 25 Mar 2005 16:00:56 -0500, "bowgus" <bowgus@rogers.com>
wrote:

>Will changing tire diameter to a larger diameter on my pickup truck help
>> improve gas mileage?
>>

Maybe.

Going to a larger diameter will change your overall effective gear
ratio, causing your engine to spin at a slower RPM for a given speed.
But, the larger diameter tire will be heavier, might be wider, and
will change the airflow characteristics of the vehicle. This will
offset some or all of any increase. (Might take away more than it
gives, thus causing worse mileage.)

I went from 265/75R-16s to 285/75R-16s and thought I might pick up a
slight mileage increase since I'm running low 4.3 gears. Didn't work,
and mileage actually slipped a bit. (My reasoning was that my dad's
truck is same but with 3.73 gears and he always gets 1-3 mpg better.)

Matt
99 V-10 Super Duty, Super Cab 4x4

 
Inflated to maximum pressure does not affect tire diameter. Period.
What it does is reduce the contact patch, sidewall friction and
flexing which do affect mileage.

On Fri, 25 Mar 2005 16:00:56 -0500, "bowgus" <bowgus@rogers.com>
wrote:

>No but ... "The U.S. Department of Transportation says that most drivers can
>improve fuel mileage by at least two percent by keeping their vehicle tires
>at the maximum recommended pressures. You can find the carmaker's
>recommended tire pressures in your owner's manual and on a tire decal or
>placard in the glove compartment or on the driver's door post, near a
>hinge." Note that this is not the max printed on the tire itself.
>
>"d745" <davel745@yahoo.com> wrote in message
>news:3824820e96b6155ca3a79b772c36794e@localhost.talkaboutautos.com...
>> Hi
>>
>> Will changing tire diameter to a larger diameter on my pickup truck help
>> improve gas mileage?
>>
>>
>

 
Maybe you're thinking circumference ... the diameter of a flat tire for
example, would be close to the diameter of the rim :)

"Peter D. Hipson" <phipson@deletethisword.darkstar.mv.com> wrote in message
news:61a94151i423csegq7ind5nihpvvi9p5ju@4ax.com...

> Inflated to maximum pressure does not affect tire diameter.


 
Just joking around Peter :)

"bowgus" <bowgus@rogers.com> wrote in message
news:XeydnVC07quURtjfRVn-2w@rogers.com...
> Maybe you're thinking circumference ... the diameter of a flat tire for
> example, would be close to the diameter of the rim :)
>
> "Peter D. Hipson" <phipson@deletethisword.darkstar.mv.com> wrote in
message
> news:61a94151i423csegq7ind5nihpvvi9p5ju@4ax.com...
>
> > Inflated to maximum pressure does not affect tire diameter.
>
>



 
Even if the tire is flat, the circumference (points of contact with road
surface) stays the same unless the rim spins inside the tire.

"bowgus" <bowgus@rogers.com> wrote in message
news:XeydnVC07quURtjfRVn-2w@rogers.com...
> Maybe you're thinking circumference ... the diameter of a flat tire for
> example, would be close to the diameter of the rim :)
>
> "Peter D. Hipson" <phipson@deletethisword.darkstar.mv.com> wrote in
message
> news:61a94151i423csegq7ind5nihpvvi9p5ju@4ax.com...
>
> > Inflated to maximum pressure does not affect tire diameter.
>
>


 
Well, at best we are both right, but the term diameter requires a
circle which a tire is not... <g> I should have said cirumference, but
when I do that more people misunderstand than when I say diameter.

It is so easy to think of a tire as round--that makes life easy. But,
tires are never round, and the math of tire deformage is quite complex
when the tire is under load. The math and theory of sidewall flex is
very interesting, to say the least. (When I got my master's I interned
at a Goodyear tire factory--one heck of an eye opening experience: did
you know a typical radial tire has almost 100 seperate parts? Or that
there are about eight different rubber compounds used in tire
manufacturer? That the maximum safe temperature of a tire is just
below the temperature that the tire was vulcanized at? There's nothign
that says that tires have to be black? (in the beginning they thought
it looked good, natural rubber color is dirty looking...)

The main point is that letting air out of the tire won't change the
number of revolutions that the tire makes to go a mile (which I think
you and I agree on!) despite what one semi-popular 4x4 magazine said a
year or so ago. If you put on a smaller spare, letting air out of the
opposite tire on the axel won't balance things out--it just makes
things worse!

On Sat, 26 Mar 2005 16:58:22 -0500, "bowgus" <bowgus@rogers.com>
wrote:

>Maybe you're thinking circumference ... the diameter of a flat tire for
>example, would be close to the diameter of the rim :)
>
>"Peter D. Hipson" <phipson@deletethisword.darkstar.mv.com> wrote in message
>news:61a94151i423csegq7ind5nihpvvi9p5ju@4ax.com...
>
>> Inflated to maximum pressure does not affect tire diameter.
>

 
It depends:

putting too large tires on will not let you run the motor at an ideal
rpm for the speed you are driving. Then you will lose mileage.

Depending how your truck is geard to begin with you will gain highway
mileage as your rpm will drop a little on the highway. You may lose
mileage in the city and onhighways with hills.

But it all depends on your gearing, if you lose enough power so you
cant run highways in your highest gear then you are in for a good hit
at the gas pump.

Matt

 
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