Mechanics

98 PLYMTH TIRE PRESSURE

1998 Plymouth Breeze • 4 cylinder 2WD Automatic • 143,000 miles

I bought it used it had been painted (poorly) and there is no info in book or on body regarding tire pressure. Ive got lots of steering/front end noise but I would like to properly inflate tires! Cannot find this info online. Also - my brother recommended replacing timing belt. He said better to do it now than have it go on me. Is this a good idea?
Thank you for your time!
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Differentoctave
April 6, 2011.




Yes, replace the timing belt as preventive maintenance. This is an "interference" engine which means the open valves and the pistons occupy the same space, just not at the same time. If the belt breaks, the open valves will be hit by the coasting pistons and will be bent.

As an alignment specialist at a very nice Chrysler dealership for nine years, I never looked at the sticker on the door for tire pressures. For liability reasons that recommended pressure had to take into account any replacement tire you could buy. I went by the maximum pressure listed in tiny numbers on the sidewall. You'll have to look closely to find them but they are there close to the wheel. If it said "35 psi max." I made them 35 psi. If it said "44 psi max." I made them 40 psi. Never had a complaint of a rough ride and solved one person's complaint of "hard steering" by raising the pressure.

44 psi tires run very nicely at 40 psi. They would be under-inflated by over 20 percent at 35 psi but if the manufacturer put "40 psi" on the door sticker, some people would follow that after buying tires rated at 35 psi max. That means the sticker would have them over-inflating their tires.

Caradiodoc
Apr 6, 2011.
There should be a label on your car door with the correct tire pressures applicable to your vehicle. They vary quite a bit with different tire packages.

Wrenchtech
Apr 6, 2011.
I don't recommend using the maximum allowed pressure from the tire. You should always use the manufacturers recommended pressure. Adding a couple pounds equally to their spec will sometimes improve the wear but maintain the recommended stagger in pressure. Manufacturers assign specific pressures to specific vehicles and wheel positions. They factory in specific oversteer and understeer conditions that vehicle may be prone to.

Wrenchtech
Apr 6, 2011.
Thank you all so much! To: 'wrenchtech' - the label on the door was painted over before I bought it and Ive been searching ever since. Also, you said "maintain the recommended stagger in pressure" - Does that mean the front tires are at a different psi than the rear? The tire pressure seems low to me but they are at 35 I think. I recently put new tires on and they are marked 45 max. So perhaps I will raise pressure a bit. One more thing re the timing belt. Should I let my brother change it for me - is it a fairly straightforward job or should this only be done by a mechanic (I don't have a regular mech. So I would be choosing one cold. Thanks to you guys - technology is amazing, isn't it?

Tiny
Differentoctave
Apr 6, 2011.
No, no, no. 35 is likely too high already and yes many use different pressures front and rear for the reasons I gave you. If you go to a tire shop, they have a book with all the pressures. I have one but it doesn't go back that old.

Wrenchtech
Apr 6, 2011.
Thank you Wrenchtech - I went out and checked them and the are at about 30 psi. It's time for the oil change/tire rotation anyway so I will make a note of what the service center sets it. So, how about that timing belt? Can a fairly handy non-mechanic handle the job or am I asking for trouble?
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Tiny
Differentoctave
Apr 6, 2011.
It's not a real high difficulty job but it is high risk. If it's timed improperly or if the belt jumps off while driving, you can bend all the valves and that gets real expensive. The recommended interval for replacement is 105K

Wrenchtech
Apr 6, 2011.
I would be rather nervous about waiting until 150,000 miles to replace the timing belt just because of the potential for the severe and expensive problems just mentioned. The comment about "high risk" stated it very nicely and accurately. Be sure to point out the engine is running fine now in case a valve or two gets bent during less than careful service. It should be running just as smoothly when you get it back. In the 1980s, Honda recommended their timing belts be replaced every 75,000 miles, and they commonly broke at 65,000 miles. Lots of unhappy owners. Those were also interference engines.

We're going to have to agree to disagree on the tire pressures. My information comes right from the former head of Chrysler training for all of Wisconsin and the U.P. Goodyear tires, which are somewhat standard equipment on Chrysler products, are rated at 44 psi max. That doesn't mean they can hold up a pickup truck. These are standard small car tires with very soft sidewalls. That's why they need the higher pressures to maintain rigidity. 40 psi is where I never had a complaint of harsh ride or steering wander, and other Chrysler alignment techs were using the same pressure, but that pressure can not be listed on any door sticker because there are still other brands of tires out there with a maximum rating of 35 psi. People could read that "40" on the door sticker and over-inflate other brands of tires. That sticker has to cover any tire the customer could purchase in the U.S.

There is talk now of going to tires with even higher pressures for less rolling resistance and better fuel mileage. If those were run at 30 psi they would be severely under-inflated by about 40 percent. That would lead to excessive sidewall flexing and heat buildup. That's what happened with the huge problem Ford just had with their Explorer tires. They were using tires rated at 44 psi max. But running them at the sticker listing of 28 and 32 psi. Again, they couldn't put "40" on the sticker in case the customer bought replacement tires only rated at 35 psi max. The tires were failing from heat buildup and blowouts. There was nothing defective in the manufacture of the tires. They were just being run too low. The solution was to raise the tire pressures up to what the tire called for, not what the car might have installed in the future.

To add another dimension to the story, we sold a '96 Caravan to a former Chrysler mechanic who complained non-stop about "hard steering". Since it was a new model design that we weren't familiar with, we assumed it was "the nature of the beast" and after driving more of them, we realized they all felt the same as his. In an attempt to satisfy him, over numerous visits, we replaced the rack and pinion assembly, power steering pump, variable assist module, and we aligned it more than once. To all of us it felt normal but he still wasn't happy.

Finally, to clear up a whole lot of miscommunication, it turned out that what he was complaining about was it was "too hard to turn, ... When changing from one lane to another lane", not when turning corners! THAT can be an issue with "caster", which is the alignment angle that affects how hard it is to turn the wheels, but that is not adjustable on most front-wheel-drive vehicles.

Finally it didn't even pay for us to test drive it; we just let him drive it after each thing we tried. After my final "repair", he came back with a huge grin on his face and said whatever I just did, that fixed it. My "fix" was to raise the tire pressures from 32, (on the sticker), to 40 psi. The tires were very soft and that higher pressure reduced the rolling resistance. He said I couldn't do that because "it would ride like a lumber wagon", but he quieted down when I pointed out he just drove it and was happy. He had left the dealership long before 44 psi tires were around and wasn't even aware they existed.

That's the vehicle I brought up at one of the Chrysler schools, and the instructor said raising the tire pressures was the first thing I should have done, not the last ditch effort.

The final word on pressures will have to be left up to a well-informed car owner. Low pressure can lead to a blow out from excessive flexing and heat buildup but that isn't going to happen "right now". That will degrade the tire over many miles and lead to a sidewall blowout or tread separation. Fortunately that doesn't happen often. Many drivers don't recognize the loss of high-speed steering response from low pressures on the front or steering wander from low pressures on the rear. Ask a NASCAR driver if they can tell the handling difference between 5 pounds of pressure change and they will laugh. They can tell the difference in handling from a half a pound change, ... But that's their job. Us normal people aren't expected to be that in tune with our cars but you have to wonder how many people lose control and crash because their car didn't respond as expected. Tire pressure is just one characteristic that can affect handling.

Tires will not blow out from pressures that are near their maximum rating as long as they are driven below the speed and temperature ratings of the tires. There are still a few people who don't understand "cold" tire pressures. They will lower the pressure in the middle of a long trip. In fact, the manufacturer knows how much heat the tire will generate and how much that will cause the pressure to go up. As long as the pressure is below the maximum rating when the tire is cold, it is normal and acceptable for it to go higher during prolonged highway driving. Every tire has to have that safety margin built in. The manufacturer can not specify a "maximum hot" pressure because how many people are going to drive for a hundred miles just so they can check their tire pressures? Everyone has the same chance to check them when they're cold.

Related to that is the speed rating. Few people have heard that in many states it is illegal to drive faster than the speed rating of the tires. The rationale is that higher speeds generate more heat which can again, lead to tire failure. Look at the tires on a Viper or Corvette and you will see they have a very high speed rating even though there is no where you can legally drive that fast on the road. The point is the manufacturer KNOWS the car can go that fast so they put tires on it that can handle those speeds.

As far as lower pressures on the rear, that is done strictly for comfort. A tire that is too soft will allow the rear to sway back and forth sideways. A rear tire with pressure that is too high will have a harsh ride, and since front-wheel-drive cars are so light on the back, could lead to it dancing around on bumpy roads. That CAN also lead to easy loss of control on high-speed corners.

Ford pulled a trick on unsuspecting customers with their Tempos and Ford-built Escorts in the 1980s. They tipped their tires out so far on the top that they rode on just the outer edge. That made them ride real smooth compared to all other manufacturers' cars, so they sold a pile of them, but they didn't tell you that you had to really push it to get 15,000 miles out of the front tires. Nothing could be done to fix that because that angle could not be adjusted. What you got was what you get, and Ford didn't care what happened after the sale. That was not considered a liability issue on their part because owners were expected to check their tire wear periodically. That wasn't Ford's responsibility. Sure that was a huge loophole but they can't avoid the liability when tire pressures are in writing.

My recommendation is to visit any salvage yard or used car lot and look at the sticker on one like yours. Be sure it had the same size tires. If you keep your tires at those pressures, that is one less thing the other guy's lawyer can bring up when he tries to shift the blame for the crash from his client to you. Even when the other guy ran the red light, a good lawyer can convince a jury that you are partially at fault by being unable to avoid the crash due to less than ideal conditions that are your fault. That includes tire pressures, do-it-yourself brake jobs, even obvious tire wear because you didn't have the car aligned when it was needed. If I were ever called to court to explain what I did to a customer's car, I knew I was safe if the tire pressures were higher than what was on the sticker. I would not be able to justify a lower pressure than what was listed. You also have to consider that tire pressures go up just from sitting when outdoor temperatures go up. What was 32 psi last week could easily be 36 psi today. You don't see people rechecking their tires pressures every day even though the temperature changes.

What's worse is when people forget to check pressures in the fall when it gets colder in one or two days. Another problem is when that conscientious mechanic at the quicky lube place adjusts the tire pressures right after you skidded in off the highway. He won't know to make allowances for the heat buildup and leave the pressures higher than for a cold tire.

As I started to say twice, start with what is recommended for your car, then see how it handles. If it feels like you're driving in deep sand, raise the pressures up until the car feels stable. Remember, your tires' sidewalls are softer than those of other tire manufacturers. If the ride feels too harsh and "busy", like you feel every little bug in the road, it's okay to lower the pressures back down but I would never go lower than what's published for that car.

If you want to get really technical, you will see the maximum weight the tire can support right next to the maximum pressure on the sidewall. Your car weighs somewhere around 3200 pounds and about 35 percent of that is on each front tire. That higher weight is why higher pressures are called for on the front but that doesn't mean you can't raise the rear pressures up too. Again, it's more of a comfort thing.

Caradiodoc
Apr 7, 2011.
I have to emphasize the fact that the maximum tire pressure on the tire label and the proper recommended pressure for your vehicle are 2 entirely different things. I spent many years in the retail tire business and have had extensive factory training on the subject and I won't believe for a second that anyone in a manufacturer position would recommend anything but the factory recommended tire pressures that were determined by the engineer for that specific vehicle. If the maximum rating on the tire is lower than the recommended pressure, then you quite simply have the wrong tire on the car. Yes, lawyers will look at the tire pressures in case of an accident because it is a very important factor in the cause of the accident. Yes, temperature has a major effect on tire pressure and therefore they should always be checked under the proper conditions and pressures sometimes have to be adjusted for increased load.
Here is a site that will give you some accurate instructions on tire pressures.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=147&

Wrenchtech
Apr 7, 2011.
I count four times in four paragraphs where it says to run higher pressures than on the sticker. There is a real simple solution to cover your but t. You do what the guy signing your paycheck tells you to do and I'll do what the guy signing my paycheck tells me to do. You can be certain no tire manufacturer wants to risk a lawsuit and they are going to tell you whatever they think is most likely to meet that goal. The same can be said of car manufacturers.

By your logic if a tire manufacturer starts mass producing the new 60 psi tires for replacement use on the Prius, they should be run at the pressure on the door sticker which would have them only half inflated. That worked real well for Ford and Firestone.

Caradiodoc
Apr 7, 2011.

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