Firestone tires and suv roll overs, what did we learn?

IsaacHayes

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heh, speed bumps in my car = feels like you're bottoming out. I hate the V shaped ones that not only bounce you up and down, but make your car roll side to side and cause your middle of your car to scrape on it. I want to take a jack hammer to those bumps, and the idiots that devised them. I honestly don't notice much of a rougher ride with higher inflation. If anything there is less bounce/recoil on speed bumps.
 

John N

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You should not run your tires at the max pressure stated on the tire! You are changing the handling dyanmics of your vehicle and making your vehicle less safe!

You decrease the contact patch reducing traction, handling, braking and and it can increase the likelyhood of uneven wear and blowouts, esp. when hitting potholes.

You should run them at (or at least near) the amount suggested for the vehicle, which should be printed inside of the door frame or in your vehicle's user manual.

Get good tires, keep them and the rest of your vehicle in good and safe working order, drive safe and be happy.

-john


Tire Safety Information, Final Rule

" 2. Misunderstanding and dangers associated with inflation pressure

As discussed in the NPRM, surveys indicate that consumers often do not realize that the recommended inflation pressure, which provides the cold tire inflation pressure for the maximum loaded vehicle weight based upon vehicle specification and operation as determined by the vehicle manufacturer, is labeled on the vehicle on a placard or the vehicle certification label by the vehicle manufacturer."

Tires Last Longer With Proper Care

"Overinflation, or putting too much air in the tire, is another common mistake. Putting too much air in a tire is almost as bad as not enough, resulting in premature tread wear in the center of the tire and increased operating temperatures that can, again, lead to a blowout. Also, don't make the mistake of thinking that if an underinflated tire costs you in fuel economy, an overinflated one will help your gas mileage. While it is true that an overinflated tire rolls more easily and can improve fuel economy a little, the costs of excessive tread wear and danger of blowout more than offset the small increase in fuel economy.

So, how do you tell if you've got the right amount of air in your tires? Well, you can't tell by looking at them. On today's low profile radial tires, it is almost impossible to tell when a tire is over or underinflated. In fact, most of the time a properly inflated tire will appear to be underinflated.

The Tire Industry Safety Council says that the only way to guarantee proper inflation is to check the tire placard located on the driver's doorpost, the fuel filler door, or inside the glove box and note the correct tire pressure for your vehicle. Then use an accurate tire pressure gauge to check the air pressure. "
 

IsaacHayes

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"Over inflation... resulting in premature tread wear in the center of the tire.." Even at max psi, my center of my tires does not wear more. I didn't state everyone should do what I do, but for my car, running them at max does not cause problems. I very frequently take my car to the twisties and know how it handles very well. It does not handle well with 30psi when my tires say max 44psi. 30psi the side walls geat scratched up just driving normally. My car is the heaviest combination of engine/trans for my body style. But the 4cly/5spd version has the same psi rating. All of the wheel size/tire combos for both the 6cyl and 4cyl are at the same psi. With a couple hundred more pounds on the front I want to run a higher psi. I do have skinnier wheels that I can mount a narrower tire for winter, and I don't air those up that high even though they have a taller softer sidewall. Of course the max PSI for those is only 5 over what the car says to run.

I do keep the rear with less PSI than the front. The rear is really light and you will wear the center more if you run them at the max. It is fun when the rear slides, but not recommended. The front being a little higher helps with understeer, as the tires aren't rolling over themselves. Keep in mind I have a very short sidewall performance size tires on my factory rims.

At least with my ride I know what I'm doing and know what handles and what wears. Also like I said before, my tires aren't the original ones the factory put on there, which may have had stiff sidewalls and been rated 35psi max like my previous ones.

Also, I usualy check/air up my tires while hot after noticing that the handling isn't 100% on. I can notice when just one tire is about 4-5psi different than the others. So when they cool down, they aren't at max PSI anymore.

Another thing I just thought of, is my wheels are very wide, and stretches every mm of tread to the ground. You will curb the wheels before the tires touch the curb. They are stretched that tight. So it makes sense that even over inflated, it would be hard for the centers of my tires to wear when they are stretched so flat. Looks like steam rollers. :D Now the skinny 6" wide wheels I run for winter use, even with a skinny tire it bows and the center sits out higher than the sides. The side tread looks like it comes over the sidewalls. Totally different look and way it contacts the pavement.

Lots of factors involved, but like I said, it works well for my car. Not recommending anyone do as I do. Just sharing my experiences. :)
 

Brighteyez

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I've never noticed any uneven treadwear from running tires at their maximum rated pressure either. Insofar as excessive tread wear, I'm not entirely convinced that is an issue as least in my case, as I mentioned I generally get about 70,000 miles on a set of tires (I believe they're usually rated for 40-50K?). And I usually don't run the tires all the way down to the tread bars; I almost always replace them when they get close (or if the sidewalls start to show signs of deterioration from age.) Of course as in all such examples YMMV.
 

wquiles

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I agree with John that max pressure stated on the sidewall is "generally" a no-no. I used to compete on auto-x events and we did used higher PS on the tires to compensate for the much higher g-forces - like from 36-38 going to 44-48 PSI, depending on the track that day.

We use colored chalk and marked going from near the edge of the thread, going up to half of the sidewall, and we did this every 90 degress (so 4 marks per tire). We then go on a practice run, at speed, and look at the marks. Depending how much chalk was "eaten" we would lower/increase the PSI on that particular tire until we had maximum tire contact patch, plus a little bit of the very edge of the side wall. This gives you max. grip for that tire, for that track, for that day.

For everyday driving, you would never reach that "high" on the side of the tire, so for proper thread usage, we always lowered the PSI on all tires after the event.

I should also note that some cars are more suceptible to PSI change than others. My '96 Miata was so awesome and so light, that I can tell differences in grip/performance if my tires were off 2 PSI from normal. The Miata was also so freaking balanced from front to rear, that for minor adjustments to create or compensate for oversteer I only had to add/take 2 PSI to the front tires - man I miss that car!

My point is that the values listed on the door/manual are not randomly picked. They are tipically designed to give you a safe and balanced ride, always leaning towards understeer - which is what 99.99% of all new cars and trucks are setup for from the factory. Every time you mock around with those values, you change the balance/feel of the car - please be carefull what you change ;)

Will
 

IsaacHayes

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I guess my driving can't really be considered normal though. I don't slow down in turns where most cars do. Only cars side by side me on sharp high speed turns are usualy corvettes. Most cars back off scared, while I go through it with no drama. Heh, when I first got my car, it understeered so bad and bottomed out going 30mph over small dips in the road. I was slamming the brakes constantly going down a straight road to not bottom out. Lift off the brakes right before the bump so the front sprang back up lol. I hate understeer with a passion, almost wrecked following a friend at normal speeds when my car didn't respond to turning the wheel. That's when I decided to fix my suspension and did a little upgrades.

I will never drive a car again that felt like a boat in a storm on the highway. I will change the tires/wheels/suspension so it handles like it's on rails. I guess that means I wont be driving any SUV's either! :crackup:

IMHO I still think a little extra air over the manuf door sticker works better. But other car companies may have a better working figure than my car does. YMMV!
 

wquiles

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IsaacHayes said:
IMHO I still think a little extra air over the manuf door sticker works better.
This is exactly my experience so far. Anywhere from 2 to 4 PSI higher than "normal" seems to work well to increase grip, with minimal negative impact to daily driving. I also tend to try to negate a little bit of the understeer built into today's cars, so I typically have about 2 PSI higher in the front tires, so my new "normal" values are like 2 more PSI on the rear and 4 more on the front. That seems to work for me in most cars. Like you said, YMMV!

Will
 
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cobb

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Rather its a wheelchair or car, I stick by max psi rating or more. My tires are rated at 65psi. They had about that in them, yet the sides were worn, but center fine. I pumped them to 65, but they still looked flat. I then went to 80 and man. They look fully inflated and handle great, like on rails
 

John N

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Seriously man, if you are running MORE than the MAX rated for the tires... you are asking for trouble. Basically not only are you using more than the vehicle mfg recommeds for your vehicle, but you are using more than the tire mfg indicates is safe. More than safe is unsafe, no?

-john
 

bfg9000

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The conventional wisdom is that too high tire pressures increase the likelihood of tire blowout if you run over something at high speed. Conversely, too low pressures increase the likelihood of bending a wheel.

To answer the original question, what we have learned is that most Americans simply do not understand the concept of risk. For the roughly 3 million Firestone tires equipped on about a half-million Explorers that traveled over 25 billion miles, there have been 1,183 claims of tread separation, 7% of which resulted in rollover. So the odds of rollover were about 3.3 per billion miles traveled. For most industries, three catastrophic failures in a billion would be pretty darned good (think batteries) and maybe even deserving of an award. But since this was 600 times the failure rate of Goodyear tires, there was a huge public outcry over those murderers at Firestone.

But 600 times virtually zero... is still virtually zero. The same members of the public that condemned Firestone seemingly have no problem with other actions that actually greatly increase the risk of rollover like: talking on the phone, fussing with the radio, or eating while driving. And those are listed on accident reports far more frequently than tire blowouts.

Actually just choosing an SUV greatly increases the odds of rollover more than anything else, so much so that the statistical rollover difference between Goodyear and Firestone tires just vanishes. The insurance industry knows that minivans that are just as tall and tippy as SUVs do not roll over nearly as frequently because the drivers that choose them drive more conservatively.
 

Shovelrider

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The problem from the begining was that Ford called for 26psi when the atx was on the Explorer.They used the same tire on the Ranger pu with more psi and never had a problem. Gm had the same tire on s10 with no problem, after the media outcry of a few non driving people BFS and Ford agreed to recall the tires and replace them but they also increased the psi, the new tires had a higher psi from Ford they also said that until your tires come in put your explorer at 35 and all will be okay. 26 in heavy veh with a full load high speed and the fact that most people don't check the pressure means that if the the tires had 20 psi they were lucky. So what we learned is that SUV's are not cars and need to be treated as such. We have the big vans at the precinct for going to details and they are not as tippy as most tend to think.
 

bfg9000

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Thing is, the recommendation still stands at 26psi today for all the replacement tires when mounted on Ford Explorers, and for good reason. As far back as 1988 it was known by Ford that the UN46 Explorer would lift two wheels during violent maneuvers at 55mph when the tires were inflated to 35psi, which would earn a "not recommended" from Consumer Reports. That would have been far less acceptable than the fuel economy penalty at 26psi.

26/26psi was recommended specifically to reduce cornering traction to prevent rollovers. Kind of makes you wonder about the people with "bling" ultra-low profile high performance tires on SUVs, doesn't it?

Bottom line is the tires fell apart from overheating at the low pressures but the vehicle was not stable enough to handle a blowout from any reason, or even to use properly inflated tires. So the moral is: tall vehicles should not have luxury car suspensions.
 

cobb

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I think thats why I like my tires fully inflated and then some. Of course my van is unloaded, so I can likely get away with that, but see good reason to lower it if I start to haul stuff or people.
 

IsaacHayes

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unloaded and high psi can cause your vehicle to slide when braking/cornering though... Or in the case of a vehicle with high center of mass, possibly tip.
 
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