99 Rodeo Tire Pressure?
A. Ward Francis, Jr.
recommends 26psi, but I believe that is because it makes for a softer ride
for traditional car users. The mechanic at the dealership uses 35psi for
his SUV. I was wondering if something in the middle like 30-32 would be the
best compromise? Ride firmness and height would seem to be factors. Please
advise.
Sincerely,
Austin Francis
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rec)sounds high to me for 90% of users. Don't exceed the max printed on the
tire sidewall. As for ride height - this is pretty silly. You probably have
225s or 245s ? So ride height won't change much more than a few fractions of an
inch with any change in pressure short of grossly over or under inflating your
tire. This is sometimes done off road for traction purposes in stuff like fine
sand, but isn't of much benefit for pavement dwellers. Changes in pressure will
effect the following: Handling and steering response - minimally as the tire
contact patch changes area. Ride - albeit again minimally - more effect on ride
can be had by using different tires, tires with different aspect ratios
(sidewall height), and by altering shocks and springs. Wear patterns - not
insignificant over the long haul - it's a damn shame to replace a tire that has
center or side worn tread while the tread is OK elsewhere. I dare say that the
manufacturer's engineers know more about the proper tire pressure than the local
mechanic. You don't say what it is you are trying to achieve - or is ride
height and firmness your goal? You only say they are "factors".
George S.
the exact same tire that was shipped with the vehicle.
What does one do if/when one changes to a different tire model or brand?
Auto manufacturers not only set inflation recommendations, they often choose
specific tire models, to satisfy the soft ride requirements of the masses.
Consumer Reports (those evil Isuzu-hating bastards) have pointed this out in
past tire reports.
They state that very often OEM tires sacrifice performance for comfort.
To answer the original question in a nutshell:
Use the inflation number stamped on the side of the tire.
Your ride will be harder but gas mpg and tire tread life will both increase.
Irregardless of whose inflation recommendations one uses, there are specific
situations where "airing down" is desirable, such as on sand.
--
George
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George S.
<SNIP>
> Inflating to
> the max pressure, particularly in a vehicle that's lightly loaded (not
full of
> people, stuff, or carrying trailers) tends to reduce the contact patch to
a more
> central region of the tire, which reduces rolling resistance and increases
> (slightly) mpg as you've stated and likely will make for a somewhat harder
ride
> as well. It also can sharpen steering response, and some handling
> characteristics. It will also cause your tire to wear more toward the
middle,
> which depending on the tire design may result in premature wear (like
5k-10k
> miles, not too much).
My experience has been the opposite regarding tire wear.
On all my cars (front wheel drive, rear wheel drive, 4 wheel drive) my front
tires wear on the outside edge.
SOP tire rotation (front to back/back to front maintaining rotation
direction) results in four tires with worn outside edges.
Eventually, I have all four tires removed from the rims and swap tires to
the opposite side of the vehicle (still maintaining rotation direction).
This results in a "new" outside edge on all four tires and the entire wear
process repeats.
Premature tire wear in the middle of the tire has never occurred at max.
inflation.
If anything, tread wear has probably been slightly extended by reducing the
burden on the outside edges.
Note: The above mentioned outside edge wear is not associated with improper
wheel alignment.
--
George
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> specific tire models, to satisfy the soft ride requirements of the masses.
Yeah. I've also heard and believe that this is often used to eke out an
extra point in fuel economy.
> To answer the original question in a nutshell:
> Use the inflation number stamped on the side of the tire.
> Your ride will be harder but gas mpg and tire tread life will both increase.
Not necessarily. There is a certain weight distribution on a tire (not
necessarily 25% of vehicle weight BTW unless you happen to have a mid-engined
vehicle), and the inflation number stamped on the tire is almost always for
maximum rated load - which is often also stamped on the tire. Manufacturer
inflation pressures take into account many factors - many mentioned above, but
also to ensure that the cross-sectional geometry of the tire provides good
contact with the road for a tire of a given SIZE on a vehicle. While all tires
are different, the characteristics as far as inflation and tire geometry are
fairly consistent in a given tire size(width and aspect ratio). Inflating to
the max pressure, particularly in a vehicle that's lightly loaded (not full of
people, stuff, or carrying trailers) tends to reduce the contact patch to a more
central region of the tire, which reduces rolling resistance and increases
(slightly) mpg as you've stated and likely will make for a somewhat harder ride
as well. It also can sharpen steering response, and some handling
characteristics. It will also cause your tire to wear more toward the middle,
which depending on the tire design may result in premature wear (like 5k-10k
miles, not too much). Note that all of these effects are subtle within about 3
psi of each other(and the tire pressure changes as the tire warms up anyway),
but going from 26 psi to 35 (usually the max on a truck tire) is pretty
significant - a 35% increase in pressure - I'd think twice.
A. Ward Francis, Jr.
Sincerely,
A. Ward Francis, Jr.
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George S. <please use signature> wrote in message
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> <nom...@noplace.com> wrote in message
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>
> <SNIP>
>
> > Inflating to
> > the max pressure, particularly in a vehicle that's lightly loaded (not
> full of
> > people, stuff, or carrying trailers) tends to reduce the contact patch
to
> a more
> > central region of the tire, which reduces rolling resistance and
increases
> > (slightly) mpg as you've stated and likely will make for a somewhat
harder
> ride
> > as well. It also can sharpen steering response, and some handling
> > characteristics. It will also cause your tire to wear more toward the
> middle,
> > which depending on the tire design may result in premature wear (like
> 5k-10k
> > miles, not too much).
>