Tires are out-of-round

[Ken Gilbert]

sticker was wrong that all door stickers are wrong. If you

are in doubt as to what may happen - contact two people.
One of them being the manufacturer of the car, and the
other being the manufacturer of the tire. They are the
ones best equipped to know. Almost everyone else is
speculating.

there is no speculation when one reads the sidewall of the tire to
determine max permissible inflation pressure.

that's the manufacturer's word--what else do you want?

end of story!

 

[Cam Penner]

there is no speculation when one reads the sidewall of the tire to
determine max permissible inflation pressure.

that's the manufacturer's word--what else do you want?

end of story!

The sidewall does not take into account the current load of
the car on it. It is the absolute max pressure of the
tire. Obviously, the pressure you want to inflate your
tire to depends largely on the weight you have on it.

 

[Yousuf Khan]

The sidewall does not take into account the current load of
the car on it. It is the absolute max pressure of the
tire. Obviously, the pressure you want to inflate your
tire to depends largely on the weight you have on it.

The more load that the vehicle is expected to carry, the more pressure that
the tire is expected to be inflated to. At the maximum loading limit, you
will also find the maximum tire pressure limit. But if you take the tire to
its maximum pressure limit without taking it to its maximum load limit, it's
not like as if the tire is going to explode due to not being put under
enough load.

It will just have its outside tread edges a little off of the ground at
worst, resulting in overinflation wearing patterns on the tread. But that's
actually what we're after here. We want the tire to pop out a little bit,
before we return it to its normal pressures.

Yousuf Khan

 

[Edward Hayes]

Several years ago Consumers Reports did a real-life-test of bursting
pressure of passenger car tires. As best as I can remember the lowest burst
pressure was over 200 psig. I think that says it all as far as worrying
about 10 or 15 psig over the manufactures recommendation as is no problem.
Ed Hayes

 

[CompUser]

news.ops.worldnet.att.net>,
(e-mail address removed) says...

Several years ago Consumers Reports did a real-life-test of bursting
pressure of passenger car tires. As best as I can remember the lowest burst
pressure was over 200 psig. I think that says it all as far as worrying
about 10 or 15 psig over the manufactures recommendation as is no problem.

Underinflation is considered "pound for pound"
more hazardous than overinflation. A bit too low
is much more likely to result in catastrophic
tire failure, than a bit too high.

"Too low" pressure results in excessive flex,
which generates increased temps, that delaminate
plies/belts and tire poppage.

 

[Ken Gilbert]

The sidewall does not take into account the current load of

the car on it. It is the absolute max pressure of the
tire. Obviously, the pressure you want to inflate your
tire to depends largely on the weight you have on it.

do you work on your own car?

have you checked the tire pressure while the wheel is jacked up off
the ground vs. when the car's weight is on it?

if not, go do so and come back and tell us if the pressure reading is
different.

i'm going to say this one more time: the doorsill pressures can be
realistically taken as the minimum recommended pressures for the
tires. below these pressures you can dangerously overheat your tires
and cause a subsequent catastrophic failure. however, for very short
term use (on soft surfaces, on a drag strip, etc) dipping below these
pressures may be tolerated.

the sidewall pressures may be taken as the maximum recommended
pressures.

it is _extraordinarily_ likely when using the doorsill pressures that
during hard cornering manouvers the shoulder of the front tires (which
see the most extreme sideloads and weight transfer) will be rolled
over and the contact patch of the tire distorted. this is immediately
identified by wear on the shoulder past the tread. without **any
question whatsoever,** increasing the tire pressure, up to the max
sidewall pressure, will decrease this effect and net an increase in
lateral accleration performance. the tires will hold their shape
better and much more vehicular control will be available to the
driver.

though this condition will generally result in greater center tread
wear, it will also result in less shoulder wear. these two wear
conditions must be balanced on a case-by-case basis. as i said
before, if you don't push the car through corners, then you won't be
rolling on the shoulders and you won't need to increase tire
pressures.

americans drive lincoln town cars and like a cushy, mushy ride. tire
pressures are ALWAYS a tradeoff between ride quality, tread life,
economy (rolling resistance), and traction.

contrary to what some armchair drivers would have you believe,
increasing the pressure of the tire up to the sidewall pressure does
not result in miserable braking and accelerative performance. this is
readily verified by GOING OUT AND TRYING IT YOURSELF.

for more information, see page 10 of
http://www.tirerack.com/images/tr_ownersmanual.pdf

l8r
ken

 

[John O]

Several years ago Consumers Reports did a real-life-test of bursting

pressure of passenger car tires. As best as I can remember the lowest burst
pressure was over 200 psig. I think that says it all as far as worrying
about 10 or 15 psig over the manufactures recommendation as is no problem.

Wow, that is high. I wonder what the peak pressure in a tire is when I hit a
pothole while braking on a hot day. No doubt it's less than 200, but tires
do blow from this sort of thing, don't they? Is that because of rim
deformation, or getting cut, or something in addition to the excessive
pressure?

-John O

 

[Cam Penner]

do you work on your own car?

have you checked the tire pressure while the wheel is jacked up off
the ground vs. when the car's weight is on it?

if not, go do so and come back and tell us if the pressure reading is
different.

of course it will be the same. You've got the same amount
of air in the same amount of space.

That tirerack document isn't a bad one. If I may quote it:

(wrt overinflation)
"If your tires are overinflated by 6 psi, they could be
damaged more easily when running over potholes or debris in
the road."

(wrt to raising pressure for competition)
"Tires should be reset to normal inflation pressures when
returned to the street."

Autocross and most other competitions with increased tire
pressure are usually held on surfaces free of debris and
potholes. American streets certainly don't generally fall
into this category.

 

[Rick Courtright]

actually what we're after here. We want the tire to pop out a little bit,
before we return it to its normal pressures.

Yousuf,

Setting aside all the barstool engineering that's been going on here,
how many miles have you put on the tires since you posted your initial
question, and what noticeably positive change have you experienced?

Rick

 

[Yousuf Khan]

Wow, that is high. I wonder what the peak pressure in a tire is when I hit a
pothole while braking on a hot day. No doubt it's less than 200, but tires
do blow from this sort of thing, don't they? Is that because of rim
deformation, or getting cut, or something in addition to the excessive
pressure?

I've never seen a tire blow from hitting a pothole, under any pressure.
They'll blow if the pothole contains nails or metal spikes of some kind, but
not just a simple pothole.

Yousuf Khan

 

[Yousuf Khan]

Yousuf,

Setting aside all the barstool engineering that's been going on here,
how many miles have you put on the tires since you posted your initial
question, and what noticeably positive change have you experienced?

So far, I've probably only gotten 500km additional driving (no need to get
on the highway for too long yet). And so far, the additional pressure has
delayed the initial onset of the vibrations from 80 km/h to 95 km/h and the
onset of really severe vibrations from 90 km/h to 105 km/h. I do believe the
onset of vibrations are starting to creep up the speed scale very slowly
(just a gut feeling at this point really, it's hard to tell the difference
day to day). I haven't yet inflated the tire all of the way upto the
sidewall maximum, I'm still a four psi below the maximum on the fronts; I've
hesitated due to the debate in here which made me chicken out initially.

Yousuf Khan

 

[John O]

not just a simple pothole.

Who said simple pothole? A relative lost a pair of tires--both right side
tires--when she ran over a hole on I-275. Broke the wheels too.

I have personally see potholes deeper than eight inches, and many years ago
I was in a car where we hit one with the right-rear wheel and the driveshaft
was pulled out of the transmission. Didn't lose a tire though, now that I
think about it. We get big ones up here...

Anyway.

-John O

 

[Ken Gilbert]

Autocross and most other competitions with increased tire

pressure are usually held on surfaces free of debris and
potholes. American streets certainly don't generally fall
into this category.

i drive like an autocross a good percentage of the time i'm in the
car... enough to warrant a quick response over a soft ass.

when i have a blow out i'll tell you. it ain't gonna happen.

ken

 

[Yousuf Khan]

Who said simple pothole? A relative lost a pair of tires--both right
side tires--when she ran over a hole on I-275. Broke the wheels too.

I have personally see potholes deeper than eight inches, and many
years ago I was in a car where we hit one with the right-rear wheel
and the driveshaft was pulled out of the transmission. Didn't lose a
tire though, now that I think about it. We get big ones up here...

Well, in any of those circumstances I don't think anything you do with the
tire pressures will help all that much.

Yousuf Khan

 

[Greg Reed]

Who said simple pothole? A relative lost a pair of tires--both right
side tires--when she ran over a hole on I-275. Broke the wheels too.

I have personally see potholes deeper than eight inches, and many
years ago I was in a car where we hit one with the right-rear wheel
and the driveshaft was pulled out of the transmission. Didn't lose a
tire though, now that I think about it. We get big ones up here...

Last fall and about 3 months after installing new $170-a-tire Dunlop SP
Sport 5000's on my Oldsmobile, I was run off the road by a teenager driving
his mom's minivan. I swerved to the right to avoid hitting him, and hit a
curb at about 50 mph. The curb was about 6 inches high and had masonry
bricks stacked on top of it (retaining a little flower bed) for a total
height of about 10 inches. It was at a business entrace, so that curb was
basically perpendicular to my direction of travel. The right side of the
car came far enough off the ground that the flowers in the aforementioned
flower bed were intact for several feet from the impact site. When I
inspected the damage, both right side tires had big bulges in the sidewall
(the front worse than the rear), but neither had burst. I was able to drive
about 2 miles to the tire shop, where they fixed me up with temporary
replacements and ordered new Dunlops for me.

Neither (stock aluminum) wheel was damaged, though the the wheel alignment
did need to be brought back into spec. I would imagine that much more
damage would have occurred at the highway speeds that your relative was
likely traveling on I-275, or with lower-profile tires. (The Olds wore
225/60-16's.)

- Greg

 

[Guest]

So far, I've probably only gotten 500km additional driving (no need to get
on the highway for too long yet). And so far, the additional pressure has
delayed the initial onset of the vibrations from 80 km/h to 95 km/h and the
onset of really severe vibrations from 90 km/h to 105 km/h. I do believe the
onset of vibrations are starting to creep up the speed scale very slowly
(just a gut feeling at this point really, it's hard to tell the difference
day to day). I haven't yet inflated the tire all of the way upto the
sidewall maximum, I'm still a four psi below the maximum on the fronts; I've
hesitated due to the debate in here which made me chicken out initially.

Yousuf Khan

Your description about vibration starting at about 80kmh (50 mph) sounds
like the problem I've had with two different tires that hit potholes. Once
examined by a competent tire shop, both tires (different time frame for
each) were found to have broken cords in the tread belt. The tires needed to
be replaced, but not before I got suckered into buying a new wheel.

Since the beginning of the thread has long since disappeared. my comments
may or may not be germane to the discussion.

 

[Yousuf Khan]

Your description about vibration starting at about 80kmh (50 mph)
sounds like the problem I've had with two different tires that hit
potholes. Once examined by a competent tire shop, both tires
(different time frame for each) were found to have broken cords in
the tread belt. The tires needed to be replaced, but not before I got
suckered into buying a new wheel.

Yes, it's possible that's what the issue is here too. But I'm going to try
to see if the solutions I'm trying now will fix it up. If it doesn't go away
in a few weeks, then I'll look into replacing the tire(s).

Yousuf Khan

 

[harv]

Don't screw around, get the tires checked out pronto! Don't wait a few
weeks! Think about the consequences of blowing one or more tires at speed.

 

[Yousuf Khan]

Don't screw around, get the tires checked out pronto! Don't wait a few
weeks! Think about the consequences of blowing one or more tires at
speed.

Well, of course I've already had it checked out! What do you think prompted
me to ask this question in this newsgroup in the first place? The Subaru
dealer (the guys who checked it out) suggested that I buy new tires,
preferrably *four* new tires! But my feeling is that that's just their
default suggestion. They never said that any belts were broken or anything,
just that the tires were flatspotted (i.e. "out of round"). But flatspotting
is very vague, and not all of them are permanent. I doubt that the dealer
did much of a thorough job of inspecting the tires, otherwise they'd have
more information for me. Right now it just looks like a cash grab.

Anyways, as for your worry about the thing blowing up at speed, it's already
been three weeks since the inspection and they haven't blown up at speed
yet. Nor have they blown up when I filled them to their maximum rated
pressure either.

Yousuf Khan