and have to ask this question.
Do the vehicle manufacturer's door-sticker(or trunk sticker) tire
pressure recommendations always, sometimes, or never result in the
condition of the tire on the right-hand side("PROPER INFLATION") of
If so, is there a method one could use with their own tires, and a
chalk line or other marking method, to determine if their treads are
meeting the road as in that example?
And, would the tire pressure that result in even wear of the chalk
line on the tire in all likelihood be higher or lower than the car
manufacturer pressure, or even equal to the maximum inflation pressure
on the tire itself?
And finally, if a chalk test is done on tires, should it be done cold
or after only enough driving to get to a source of air, or if the
tires are a little warmer?
Thanks for your input on this and any other method you may have to
determine equal tread contact.
The chalk test is probably a waste of time. I know some people swear
it is a great idea. If you always drove in a straight line at low
speed on flat roads I suppose it might even be valid. But what happens
at high speed, in a curve, on a cambered road?
Tire pressure recommendations are not an exact science. Vehicle
manufacturers are trying to balance safety, cost, ride comfort,
handling, noise, tire life, fuel economy (meeting CAFE rules is a
priority), changes in the tire as they age/wear, etc. And they have to
do this for a wide variety of drivers with vastly different driving
styles and preferences, driving in radically different climates,
driving with radically different loads, driving at radically different
average speeds, and driving on many different types/qualities of
roads. Anybody who thinks driving slowly over a chalk line is going to
provide the "right" answer for tire inflation probably has an
unrealistically simple view of the world. Fortunately modern radial
tires are amazingly forgiving when it comes to variations in tire
pressures. Significant variations in tire pressure have much less
effect on tread wear than was the case for bias ply tires. Radial
tire construction tends to keep the tread relatively flat over a broad
range of loads and pressures. You can still under inflate a tire
enough to wear the edges, over inflate it enough to wear the center,
but the change in pressure necessary to cause extreme variations in
wear is much greater than used to be the case. The vehicle
manufacturer's pressure recommendations cannot be ideal for all people
under all conditions, but they are acceptable for most people under
most conditions. If you are driving at higher speeds for long
distances, or with the vehicle heavily loaded, then it would be
reasonable to go with a slightly higher pressures than recommended
(but never in excess of the maximum pressure listed on the tire).
If you want to do the chalk test, I can't see how it would hurt
anything. Most likely you will decide to add more air to the tires if
you use it. I'd run the test with the tire "warm" but you need to
adjust the pressure when they are cold....
Personally my tires last so long these days that I haven't replaced
them because of tread wear in years. It seems that after 50,000 or so
miles the tires become "bumpy," or I've had to have a couple repaired
and I decide I need new tires. At least for me tread depth is not the
limiting factor on tire life.
My advice is to start out with the manufacturer's recommended
pressure. If you want a stiffer ride add a few pounds of pressure to
the tires. Keep your eye on the tire's wear pattern (maybe even check
the tread depth across the face of the tire occasionally) and adjust
the pressure downward if it appears the center is wearing out faster
than the edges. If only one outside edge is wearing, then you should
have your alignment checked (or modify your driving style). If the
tires are uniformly wearing faster on both outside edges, then maybe a
little higher pressure is in order (but never exceed the tire's
maximum rated pressure). I would not recommend going lower than the
pressure recommended by the vehicle manufacturers. However, the truth
is almost all vehicle manufacturer's pressure recommendations are far
in excess of the "safe" pressures specified by the load inflation
table for a particular tire size and load. Vehicle manufacturer's tend
to go with the highest practical pressure recommendation in order to
maximize fuel economy. Raising the pressure by 4 or 5 psi over the
ideal pressure for ride , handling, and safety may only increase fuel
economy by a few tenths of a mile per gallon, but given the pressure
to meet CAFE targets, must manufacturers are willing to make the trade
off in ride, handling, and safety in order to get that marginal
increase in fuel economy.
Whew! Ed you have proved with that tome both my esoteric off the wall
questions and a cerebral conversation can exist here in the usenet/
google/whatever newsreader you use - world!
Actually Ed, one site recommending the chalkline test instructs you to
roll slowly forward, about the length of your own car. Then, get out
and see where the most wear is after a few rotations of the tires.
If I chalkline my tires I'm gonna find a level paved surface and get
up to at least 20mph for 100feet or more! Are you kidding? ROLL the
tires slowly over a couple a revolutions? That would be fine if we
all drove like that.
Keeping my car's tires(mind you, these are after-market but original
size Yokohama H-rated Avids) at 30 or 31psi has resulted in noticeable
shoulder wear - even wear to both shoulders of all four tires, meaning
my alignment is good - but noticeable just the same. That is what GM
recommends for the 2005 - 2007 Malibu with size P-205/65-R15 tires.
I think I'll try 32 or 33psi and see what happens.
Again, thanks for your well thought out reply - THERE IS HOPE AFTER
Really? I don't know about that. Like I said, the sticker on the
Malibu's doorjamb recommends 30psi for the size of tire in my other
reply. Both the factory originals and these Yokohamas I put on August
2007 have 35psi listed as their maximum inflation pressure. Doesn't
sound like GM is over specing the tire pressure to me.
The 35 psi maximum pressure for the tire has nothing to do with the
right pressure for a particular application. There are industry
standard tire pressure versus load tables for most tire sizes. Take a
look at http://marktg.toyotires.com/file/loadinflationtable.pdf .
A P205/65R15 is rated to carry the following loads at the following
Pressure Rated Load
26 psi 1213 lb
29 psi 1279 lb
32 psi 1334 lb
35 psi 1400 lb
(these rating are for passenger car use, if the tires are mounted on a
light truck, load ratings should be reduced by 10%).
A 2005 Malibu has a maximum loaded weight of somewhere around 4100 lb.
Assuming a 60% front / 40% rear load division, the maximum weight on
one front tire is around 1,230 lb. This corresponds to pressure of
around 28 psi. At the recommended inflation pressure of 30 psi, the
tires are able to safety support around 1,300 lb each. This is around
5% greater than required for a Malibu loaded to the max. For a Malibu
normally loaded (say 3,600 lb), the margin is even greater (more than
15% - at least 5 psi). The load inflation tables for the tire already
includes a safety factor. But they do not necessarily reflect high
speed driving. For the US, the speed limits are so low that as long as
you are at least close to the limit, you don't have to worry. But, if
you are going to do a lot of 100 mph driving, higher pressure would be
I have noticed that among US manufacturers that GM tend to run closer
to the recommend pressure for the max load than Ford or Chrysler. GM
tends to provide smaller tires as standard and run them at higher
pressures than the others. Not sure why.
As someone else pointed out, the diagram is pretty much irrelevant for
As it was once explained to me by a tire guy: A tire is designed to run
with a certain contact patch, which you get when it's carrying max. rated
load at max. rated pressure. If it's carrying, say, 80% of max. rated
load, then the ideal pressure is 80% of the max. rating, which gives you
the same contact patch.
On cars with standard size tires, I generally stay with the recommended
pressure, or maybe a bit over for one reason or another. On trucks,
especially with larger than standard tires, I use the above as a
guideline, and it's worked well for many years.
On Sep 12, 2:44 pm, firstname.lastname@example.org wrote:
Which in my case, is what I'm doing. I'm keeping 32lbs because
30psi(General Motors) results in rapid, but even, shoulder wear on all
four tires, but mostly in the fronts. Car rolls longer, fuel economy
is ^, and handling is a little tighter.
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