tire pressure?

Discussion in 'General Motoring' started by Ken Weitzel, Oct 8, 2005.

  1. Ken Weitzel

    Ken Weitzel Guest


    Have one more question, if I may?

    Driver side front tire was leaking down; took it into Walmart and
    asked them to fix it up. (mistake?)

    They did, but both on the bill and verified with a pressure guage
    they've pumped up both tires to 35 psi.

    Tires say max 35 psi; the door panel says 30 psi.

    Ride now is harsh, so harsh that body noises are obvious. On the other
    hand fuel is expensive (but my lifestyle is such that it doesn't
    matter much) And it might feel harsh because of my lifetime of
    soft boatlike GM ride.

    Which do you folks recommend?

    Thanks, and take care.

    Ken Weitzel, Oct 8, 2005
  2. Ken Weitzel

    Richard Guest

    35 psi might be a bit high. Try 32 psi cold. But remember, as the temp drops
    over the next month or so a 35 psi tire will become a 32 psi tire .

    Richard, Oct 8, 2005
  3. Ken Weitzel

    Matt Whiting Guest

    Well, this topic was beat to death fairly recently, so you may want to
    search the ng. Basically, their are a range of opinions. I fun my
    tires at the max pressure that the tire maker allows. I don't find the
    ride all that harsh on my minivans at 35 PSI. I find it gives the best
    and most even tire wear and maximizes MPG. However, if ride is more
    important to you, then use the car maker's recommendation. It is meant
    to be a decent compromise of ride, mileage and tire wear.

    Matt Whiting, Oct 8, 2005
  4. Would not the tire size, make and vehicle gross weight have anything to
    do with all of this? It's all a bit strange. I thought I had
    over-inflated the Voyager's 14" 205x70 and was all set to let air out.
    But it was actually under-inflated. So there went my advanced
    perceptions of tire pressure.

    Pressure was around 30 psi. The placard has it officially at 32 psi. I
    try to keep the tires at 39 psi [cold pressure, tires rated to max 44
    psi cold]. Nice comfy ride. Still can't figure out why it felt
    over-inflated when under-inflated. Usually under-inflated is a mooshy,
    soft but quiet ride. But it explained the mpg loss until the oxygen
    sensor started to act up instead.

    Just when I thought I was getting ahead...
    treeline12345, Oct 9, 2005
  5. Ken Weitzel

    MoPar Man Guest

    For some reason, automakers feel compelled to post tire PSI numbers on
    the car (door jab) or in the operating booklet. Maybe it's the law
    (however quaint).

    Technically the only time these numbers are right are when they
    pertain to the oem tire.

    The PSI you should put into any given tire will depend on the size of
    the tire (the VOLUME of space inside the tire), the load you will put
    on the tire, the width of the tire (which plays a role in the first
    item), the construction of the tire (thickness of sidewall), etc.

    Tire makers are notorious for not providing PSI vs load charts for
    their tires. They only indicate the max load and max pressure.

    No doubt there are liability fears over making the correct information
    more available or correctly posted/printed in appropriate locations.
    Give as little information as possible, and make it as vague and
    un-specific as possible. In the case of tire makers - if you don't
    have to provide it, then don't provide it.

    Vehicle makers would like to see you ride with tires that are more
    under-inflated than over-inflated. Under-inflated tires will absorb
    more road bumps and reduce the work of the suspension system to handle
    pot-holes and such. Automakers can essentially let under-inflated
    tires "eat" road problems and don't have to put extra cost and
    engineering into the suspension system to do this (more "protection"
    for aluminum alloy wheels for example if the tires absorb punnishing
    city potholes).

    Under-inflated tires also make it harder to roll larger vehicles
    (SUV's) so again they'd rather see an under inflation rather than over
    inflated. They may even purposely post low PSI numnbers on the door
    jamb decal to insure this (Ford vs Firestone for example).

    If the tires fail or wear prematurely, the owners will blame the tire
    (brand and maker) so the auto maker has nothing to lose by posting low
    numbers (ie it doesn't reflect poorly on them or have negative
    consequences unless you really dig into the issue, which few do).

    Ideally, you want a PSI that prevents (as much as possible) the tire
    flattening out as it rolls. Shape change for the tire equals internal
    heating and wear - which you want to avoid. Then again, you can't
    inflate tires to 100 psi either. Unless the roads you drive on are
    really bad, you're better off with 35 PSI vs 30 PSI for a typical
    passenger car tire (215/60/16 or 225/55/17). If you consistently car
    pool or load your vehicle with more than just the driver, then you are
    definately better off with 35 psi.

    For summer highway driving, the fact that the PSI goes up because the
    air inside gets warm is a good thing because

    1) highways are generally smoother than city/urban roads, so there are
    likely to be fewer dammaging or irritating bumps or other
    irregularites (over-inflated tires _might_ result in reduced road
    noise vs under inflated tires).

    2) fewer stops and starts on a highway also puts reduced load on the
    tires, very little lateral or shear forces because you're usually
    going in a straight line (curves are banked, etc).

    3) higher speeds means more rotations per second or per minute for the
    tires. Each rotation equals tire distortion or flattening, which
    equals internal heat generation and wear. Increase the PSI and you
    reduce the extent of tire deformation pre rotation, which reduces
    internal wear and heat generation (not to mention reduced rolling
    friction, and better fuel economy). When you get off the highway,
    internal air temperature will go down, so will PSI, and you shift the
    operating point of the tire to city/urban roads, where road handling
    (road contact, bouncing, cornering, etc) become more important.
    MoPar Man, Oct 9, 2005
  6. Ken Weitzel

    Bill Putney Guest

    I'm surprised they aren't required to put microprocessors in the tires
    to adjust the air pressure for all operating conditions. I saw a
    commercial on TV this morning for a freakin' toothbrush with a
    microprocessor built into it! Idiots!

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    address with the letter 'x')
    Bill Putney, Oct 9, 2005
  7. Ken Weitzel

    KWS Guest

    The popular Sonicare toothbrush has a microcontroller of some sort in it.
    This is how they provide a less vigorous initial mode, time the cycle and
    provide the points to switch quadrants during the brushing process.

    Technology overtakes us all, Bill. Then there is the microprocessor
    controlled toilet in Japan.

    KWS, Oct 9, 2005
  8. Ken Weitzel

    Bill Putney Guest

    Heh heh! The one I saw was an Oral B product. So I guess there are at
    least two microprocessor controlled toothbrushes on the market now. :)

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    address with the letter 'x')
    Bill Putney, Oct 9, 2005
  9. Ken Weitzel

    Arthur Guest

    Suggest you over-inflate the tires before the snow flies. Once it does, the
    air pumps in gas stations freeze up and stop working. If your tires are
    low, it's tough to get them pumped up in the dead of winter, especially a
    Canadian one.

    Happy Thanksgiving to my Canadian neighbours.

    Arthur, Oct 9, 2005
  10. Eh?

    There's this $15 little 12 volt auto pump, eventually does the job.
    Need to get one now. They get sold out during the summers with all the
    air mattresses and beach balls that need filling. Might be handy when
    things get messy.
    treeline12345, Oct 9, 2005
  11. Ken Weitzel

    Ken Weitzel Guest


    Not too pretty much fun to use at 40 below, though, eh? :)

    If you're picking one up at Wallmart, look carefully. The
    gauges read up to 200 psi, so all of the "tire pressure" range
    is compressed into a tiny portion of the bottom of the scale.

    There are (or were) two that look identical side by side on the
    shelf. They look identical, but aren't; one of them has far, far
    easier to read gauge. (at least to my old eyes)

    Take care.

    Ken Weitzel, Oct 9, 2005
  12. I just looked at one. Even distribution of numbers from 0 to 300 I
    think. Not the biggest numbers in the world but could make out 20 40 60
    which would be enough to work with. Not worried about 200 psi at the
    moment. Now if I'm trying for 37 psi, that's a problem since a small
    mark between 35 and 40 but doable.

    You bring up a good point, although a cold one. What if the pump does
    not work well in 40 below? I don't know. It has a short air hose, very
    short, but a long electrical connector but that's not important. I
    guess one could try and connect a long air hose so the unit is inside
    the vehicle working with warmed air. Another hassle. Might work though.
    Need to ask those in your neighborhood.

    So another suggestion. Those cans of inflatable air, like Fix-A-Flat. I
    keep them under the seat. The cheap one-shot cans as well as the large
    reuseable cans. Since it's in the usually warmed vehicle, it's at a
    useable 70 F or whatever it needs to work. If not, I put them right
    under the heater to get them nice and toasty but not exploding. The new
    formulations may not be explosive as the old dangerous, nasty ones
    were. In any case, if it's used, it's nice to warn any tire worker that
    the stuff is inside the tire and can come flying out if one unmounts a
    tire. It turns into a liquid as I recall and sloshes around inside the
    tire. It does work and seals slow leaks well. One just drives a mile or
    two for the stuff to really expand and swell and seal a tire. Now does
    it expand and seal in 40 below? Don't know. If I mess up screwing it
    onto the valve, it's like filling a tire with shaving cream. Oh joy!

    At this point, I think I would just call up those in the business and
    ask what do you do at 40 below 0 F with an underinflated tire? Is this
    McMurdo Base? Ah, what do you guys do when your tires go pffft at 100
    below? Liquid nitrogen? Just kidding. Probably freeze the rubber into
    smithereens. On second thought.
    treeline12345, Oct 10, 2005
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