Tires are out-of-round

Why?

Yousuf Khan

Hi,

It's ~possible~ the sealant has coagulated into a mass at one location in the tire. If you weren't having problems with the rest of the tires, too, I'd suggest squirting a small amount of water into the tire with the valve stem removed, then reinflating and driving. Many, if not most, sealants are water-based and if they haven't dried completely may reconstitute themselves slightly and spread around removing the "lump."

Rick

No, it's not likely to have coagulated, the sealant was just put on recently

*after* the flatspotting took place. I figured that there might have been a leak in the tire because it had gone low, so I put the sealant in. So it's a recent application. Little did I realize that it would throw off the balancing scales as much as it did.

Anyways, I've pumped the air upto 40psi in the front and 36psi in the rear (heavier front end when not loaded in the back), up from 34 and 32 respectively. It seems to have made the vibration move up in speed range and lessened the severity; it's now happening after 90km/h rather than 80 km/h. I think if I pump it up another 2psi front and rear, it'll go away at my usual highway driving speeds.

Yousuf Khan

At 42 psi, you might be creating other problems, not the least of which involves really bad emergency handling. I wouldn't run the tires at that pressure, especially at highway speeds. But that's just me. :-)

-John O

Well, the snow is all gone now, so I don't think number of emergencies is going to be all that great in number right now. Besides this is just temporary until the vibration goes away. Once I start noticing no vibrations, I'll start bleeding the tire pressures down again.

Yousuf Khan

You don't need "great number" of emergencies. Just one is enough to kill you (or someone else).

Cheers,

If your Subie was able to hold the ground at 30 psi when you hit 1g on dry concrete, at 42 psi it might just break loose at .5g. Your stopping distance during a hard braking situation will be much longer. On wet pavement, you could end up with handling similar to a frozen road. If you hit a big pothole it could blow the tire. The strain on your suspension will be much greater with overinflated tires.

That's the way I see it, but it's your car. :-)

-John O

Okay, okay, everybody, I won't raise the pressure up any further than where I've already taken it to. :-)

Yousuf Khan

To Yousuf Khan-

I had a similar vibration as you described which turned out to be due to non uniform wear which was in turn due to misalignment. The OEM tires could not be saved and were replaced- after only about 13000 miles.

I will have to deal with similar vibration of my Nokian snow tires next fall- but first I'll check how my new all-season tires behave in snow.

I suspect the car (02 Forester S) was was supplied originally with the suspension misaligned but who is to know for sure? There was no obvious problem on the road, but the car does handle better after realigning and fitting new tires.

Hope this helps.. Doug.

whoh... what's all this about his tire pressures being "too high?"

stay under the tire mfg's rated sidewall max pressure and you will be FINE.

in fact, i'll bet a new set of falken azenis that his tires with doorsill sticker +10 psi pressure will outperform yours at doorsill sticker pressures.

will his car eventually develop more squeaks and rattles from a harder/harsher ride? pretty likely. will he lose 50% of his traction... ABSOLUTELY NOT!!! to even suggest that it is true speaks volumes about your experience with adjusting tire pressures.

imo, people should stick to things they KNOW about.

ken

IME, too high a tire pressure (above recommended pressures) gives:

1) rougher ride 2) better mileage 3) more "chatter" over bumps - ABS kicks in more often 4) more understeer 5) less traction

Yeah, increase the pressure if you're increasing the weight of the vehicle - that keeps the footprint the same. But a

25% change in PSI? That's going to give you nearly 25% less tire in contact with the road. That's going to impact your braking distances significantly.

Ain't this the truth.

May I ask you

- what do you *know* about traction of overinflated tires?

- whether you've ever ridden a "road" bicycle with tires at 100+PSI, and had to do an emergency stop?

Cheers,

Notice I used the word MIGHT.

The poor guy has rotten tires, and his gut tells him to blow them suckers up to solve the problem. he's asking for a spinout or worse...maybe he spins into you or me...but you 'holler' at me??? Whatever.

-John O

why don't any of you folks who think the doorsill pressure is gospel go to a local autocross, and ask those who are ACTUALLY COMPETING what tire pressures they run. after you gather that information, ask those folks who go to road racing tracks what tire pressures THEY run. hint: it's around 40psi.

the doorsill pressure is a SUGGESTION to those who cannot determine for themselves what a properly inflated tire wears like. for 99% of the time the doorsill pressure can be taken as a minimum, the sidewall pressure the maximum, and the optimal somewhere between the two. if you drive like granny and you like a cushy soft "american" ride, then sure, use the doorsill. if you find yourself cornering like a madman and the shoulders of your tires wearing the worse for it, up the pressure. your max lateral acceleration will increase as a result; it's that simple.

as for this thread, i'm done arguing with armchair engineers.

ken gilbert

The theory remains just that a theory, the reality has now been tested. We got some nice slick conditions here over the weekend, not snow, but cold rain and hail, and the high pressure tires performed exactly as well as they did at lower pressures. Could not tell a difference. Didn't take them any easier than I normally do under these circumstances either.

Yousuf Khan

Thanks for taking that bullet. :-)

-John O

Actually remembering back to the debates about the Ford Explorer/Firestone Wilderness tire blowout controversy, several years ago, I think the problems occurred because the recommended tire pressures on the door sticker was too low, and Firestone claimed that it wouldn't have happened if Ford had recommended a higher tire pressure. That's my recollection anyways.

Yousuf Khan

Which underscores the importance of proper tire pressure. Premature catastrophic tire failure can happen upon either under or over inflation. It is a dangerous logical fallacy to assume that just because the Ford Explorer's door 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.