tire pressure?

Hi...

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

Reply to
Ken Weitzel
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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.

Reply to
Richard

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

Reply to
Matt Whiting

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...

Reply to
treeline12345

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.
Reply to
MoPar Man

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')

Reply to
Bill Putney

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.

Ken

Reply to
KWS

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')

Reply to
Bill Putney

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

Reply to
Arthur

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.

Reply to
treeline12345

Hi...

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

Reply to
Ken Weitzel

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.

Reply to
treeline12345

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