Had to drop air pressure

[dwtaylorpdx]

Ford had the spec in the manual right at the pressure rating of the tires, then you add the heat buildup and the pressure went over the line. And they were only a 4 ply rated tire with two real plys. I got to look at a set once, you could wad the tire up with your bare hands....

Dave

[Frank Lee]

That's not how it went down...

(Firestone exec) Lampe said the automaker's decision to set its air-pressure recommendation at a level lower than Firestone officials advised left little safety margin to guard against overloading the vehicle.

An underinflated and/or overloaded tire gets hot, not an overinflated one. The heat then caused the separations and other issues.

Ford had the spec in the manual right at the pressure rating of the tires, then you add the heat buildup and the pressure went over the line.

As a practical matter there is no over the line. Tires can take well over 100 psi, maybe approaching 200 psi before you need to worry about them bursting. A hot tire isn't going to build that much pressure.

[Christ]

To second what Frank has said - Look into Autocross. Those guys race with overinflated tires because they understand that the tire will provide better grip and cornering ability with less tire roll while over inflated.

Hence the reason I take their advice (as in my first post in this thread) when they say things like "run them on the street normally for 1,000 - 2,000 miles before you pump them up".

[dwtaylorpdx]

I checked my old e-mail and your right the FOrd deal was primarily under inflation but the number they were using was from the factory manual (I screwed up the direction sorry about that...

I have tuned enough winning road race cars to understand tire pressure....
Dirt track as well...

There have been many many tire jockey's injured or killed when inflating tires, and they got nowhere near 200 lbs doing it. The rim can fail before the tire.... I've personally launched the outer bead of a tire through the ceiling boards.

I would mention though that a overinflated tire run longer than the 45 seconds for an Autocross is a WAYY different thing than running a tire 20 lbs over inflated on the freeway under a 4000 to 6000 lb truck...

I run higher pressure at the track for time trials cause you only get 3 laps or
so and the tires don't get up to pressure that fast. But for a full half hour race I
start at 26 and they come off track at 42. (Hoosiers and Toyos both) If you start too high once the tires heat up they over cook the center and blister, then if you run them harder they shred. Each brand does have different characteristics as well, so nothing is 100%. Goodyears and Hoosiers are like 180 degrees different in tuning and how they heat up.

Cheers!

Dave

[Frank Lee]

These dead tire guys- were they just overinflating for fun, or were they trying to seat beads? Seating beads can be quite a strong transient load... different from overinflating seated tires...

When you start high on the racer the centers cook because the loads are concentrated there now and rubber doesn't reject heat all that well.

[CapriRacer]

Originally Posted by Frank Lee

I thought the separations were partly due to underinflated tires?

Who besides us has overinflated tires?

Frank brings up a good point.

The best information I have says that the failure rate of the Firestone tire was about ½%. Other tires on the same vehicle had much lower failure rates – as did other tires in other applications.

So if we are comparing failure rates of tires, remember that you have to have a fairly large sample size.

And the bursting pressure of tires? Most of the figures reported are for NEW tires. I have seen very old tires burst with as little as 35 psi in them. Obviously older tires are going to have lower bursting pressures, the question is where on the curve are your tires.

I urge caution when overinflating tires as the consequences of a tire burst can be quite severe.

[CoastRider]

I used to power into corners exceeding the SL by at least 5mph, I dont brake for turns, I never did unless I was going Really fast lol Like yesterday in my friends Reno it didn't like that so much 30 mph turn at 45 it spun right around.

[bikeracer]

Is it true that police, as somewhat standard practice, run their tires @ around 45psi? And for that reason, some of the HE tires didn't pass their safety/cornering/stopping tests because the combination of the different compound and higher pressure made them not so good for a robust chase scenario? Do they deal with uneven wear issues or just replace tires more often? It would seem a hassle for them to 'break in' all their tires.

[Christ]

I would imagine that police cars, which always have high performance tires on them, are run at the sidewall max.