Automotive tire pressure

[hillrider]

So as the wife was driving out of the garage this morning, I noticed the edges of the tires weren't wet (it was raining). the jeep has been riding a little rough since they were were installed. The door sticker calls for 35 lbs and they read 38 lbs. I don't think 3 lbs would do it, and it's not hard to check, but I'm just wondering if the door sticker might be a guideline and correct pressure will vary from tire to tire depending on sidewall stiffness and seven other things.

Anyone got any thoughts on tire contact patch??

[jfoster]

The door sticker is for the oem's. If you changed to a different tire it may have a different psi rating (on the sidewall). Typically they say if the center is wearing more that it indicates over pressure and outer tread wear is from low air pressure. I have a Tahoe which the tires recommend 44 psi @ maximum weight rating. But at 40 psi its wearing the center of the rears and not the front so I run less, 35 psi rear and 40 psi front.

Edited January 14, 2013 by jfoster

[XV1100SE]

I know for my Mustang when I changed from OEM Pirelli's to Michelin Pilot Sport AS (GREAT tire by the way) I set pressure to 30psi (as per door sticker) but found them soft. The Michelin site says that for their tire on a Mustang to go to 32psi. Made a difference you could feel driving the car !

 

Check the tire mfr to see if they recommend a pressure for that tire on a Jeep.

[kevin-vic-b.c.]

Go by the tire,,,,, NOT the car door ! The car door has no idea what kind of tires you have under it.

 

By the way, how you checked the tires this time is the best way to test them if it is not raining then wet the driveway and drive car into garage and look at the print it leaves... it should look the same as the tire tread.

 

Way too many people adjusting after market tires by OEM rating tag.... that is wrong.

 

[BuddyRich]

ALWAYS read the side of the tire. That's what I do. I don't think they make them for 32psi anymore....

 

[Flyinfool]

The door sticker on my truck calls for 35psi. With the tires that I have on it I run 50 psi. I just changed out the tires after 50K miles and they were worn perfectly flat and even across the thread which means that my load, pressure and alignment was perfect.

As everyone else said, forget the door sticker, unless you still have the original factory tires. Even if you get a new set of the same make, model and size of tire. the pressure may need to change a little due to changes in method of manufacture or raw material sources over the years.

[MikeWa]

Tires need the pressure listed on the sidewall. Problem is some tire dealers are still intimidated by the Ford - Firestone fiasco. So they have orders from management to only follow the pressure on the door jamb. You'd think tire dealers would know better. But they want to pass all of the liability off to the car manufactures. So you might take your car in for an oil change with 45 lbs pressure in the tires and get it back with 35 psi. Just something to keep an eye out for.

 

Mike

[DarkLeftArm]

I read a good article a long time ago in a 4X4 truck publication of some sort. The guy said each tire should be treated separately, and brought up/let down to its correct pressure according to its footprint. He parked his rig on smooth concrete, and used a business card or matchbook to slide under the edge of the tire as he adjusted the air. When he could just no longer get it under the edge of the tire, he recorded and maintained that pressure. He reported great tire life, and good handling.

[hillrider]

I read a good article a long time ago in a 4X4 truck publication of some sort. The guy said each tire should be treated separately, and brought up/let down to its correct pressure according to its footprint. He parked his rig on smooth concrete, and used a business card or matchbook to slide under the edge of the tire as he adjusted the air. When he could just no longer get it under the edge of the tire, he recorded and maintained that pressure. He reported great tire life, and good handling.

 

thanks Arm. That fellow may have eaten too much baloney for lunch, but his system makes sense to me.

[Power Trippin]

The sidewall tire spec is the maximum allowed. You can run any psi you like. More press will wear out the center of the tread. Less pressure will wear out the edges of the tread. The manufacture puts the psi spec on the door placard because they have done extensive testing on the vehicle and the tire. Do what you like, but if your using tires that came with the vehicle from the manufacture, you should stick closely to the door placard spec.

[REDRIDER52]

thats fine to go by whats on the tire but a lot of new cars & trucks have sensors in them that are set at factory my truck is 60psi front 80psi back when they get under or over factory psi a message comes up to check pressure for that tire

[Squidley]

I ran a tire store back in the late '90's when the Ford/Firestone debacle was going on. I'll NEVER run a tire by what the vehicle mfgr says in the door jam. I have always ran the tires at what the max sidewall pressure states. The tires are designed to run at that pressure and the sidewalls are engineered to keep the tread in the optimum shape.

 

Something a lot of folks dont think about is an underinflated tire, will heat up and delaminate a lot faster in hotter climates. This is what happened with the Explorers with the Firestones on them. It happened in the deep south, Texas, Arizona and such. The tires blew out due to being under inflated and the vehicles crashed.

 

Pay attention to the sidewalls, my wifes SUV had a P rated tire on it and the pressure is 44lbs. If I ran them at 35lbs, which many tires are, I would be seriously underinflated. 1 more thing to keep in mind, the max load rating of the tire is calculated with the tires being at their max pressure. Lower the tire pressure, more diminished the load capacity...

[Flyinfool]

Max sidewall pressure is not always best.

Max sidewall pressure is for if the tire is to be loaded to its max weight carrying ability. If the tire can carry a lot more weight that it will ever see where it is mounted then a lower pressure may be more appropriate.

 

Perfect case in point. Do you run the max sidewall pressure in your MC trailer tires? Have you heard of anyone that thinks it is a good idea to run max pressure in a MC trailer tire?

[Squidley]

Max sidewall pressure is not always best.

Max sidewall pressure is for if the tire is to be loaded to its max weight carrying ability. If the tire can carry a lot more weight that it will ever see where it is mounted then a lower pressure may be more appropriate.

 

Perfect case in point. Do you run the max sidewall pressure in your MC trailer tires? Have you heard of anyone that thinks it is a good idea to run max pressure in a MC trailer tire?

 

 

I dont necessarily disagree with you Jeff, a healthy dose of common sense goes in with all this. Many folks aren't like us here with bikes and such. I can't tell you how many thousands of people I had to educate on tire pressures. It's somewhat easier to err on the side of caution and keep the tires damn near fully inflated than guess or not know squat about them and risk blowing out a tire....

[Flyinfool]

I dont necessarily disagree with you Jeff, a healthy dose of common sense goes in with all this. Many folks aren't like us here with bikes and such. I can't tell you how many thousands of people I had to educate on tire pressures. It's somewhat easier to err on the side of caution and keep the tires damn near fully inflated than guess or not know squat about them and risk blowing out a tire....

 

I can agree with that.

Under inflation can cause a tire to blow out, Max pressure will at worst cause a harsh ride and center tread wear.

[jfoster]

I ran a tire store back in the late '90's when the Ford/Firestone debacle was going on. I'll NEVER run a tire by what the vehicle mfgr says in the door jam. I have always ran the tires at what the max sidewall pressure states. The tires are designed to run at that pressure and the sidewalls are engineered to keep the tread in the optimum shape.

 

Something a lot of folks dont think about is an underinflated tire, will heat up and delaminate a lot faster in hotter climates. This is what happened with the Explorers with the Firestones on them. It happened in the deep south, Texas, Arizona and such. The tires blew out due to being under inflated and the vehicles crashed.

 

Pay attention to the sidewalls, my wifes SUV had a P rated tire on it and the pressure is 44lbs. If I ran them at 35lbs, which many tires are, I would be seriously underinflated. 1 more thing to keep in mind, the max load rating of the tire is calculated with the tires being at their max pressure. Lower the tire pressure, more diminished the load capacity...

 

Just curious how much weight your carrying? My Tahoe weighs approx. 5900 lbs (me plus my gear) and the V rated Goodyears are rated at 2200 lbs each (8800 lb) at 44 psi. I'm 2900 lbs below their rated capacity. I see what your saying, but to me unless your operating at a vehicles gvwr I wouldn't think running a tire at 35 psi being severely underinflated? Don't get me wrong, I've tried 40 psi on all four and had more premature wear on the rear.

[Squidley]

Just curious how much weight your carrying? My Tahoe weighs approx. 5900 lbs (me plus my gear) and the V rated Goodyears are rated at 2200 lbs each (8800 lb) at 44 psi. I'm 2900 lbs below their rated capacity. I see what your saying, but to me unless your operating at a vehicles gvwr I wouldn't think running a tire at 35 psi being severely underinflated? Don't get me wrong, I've tried 40 psi on all four and had more premature wear on the rear.

 

The sidewall is what really doing the majority of the work when your running full pressures. Underinflation will do the damage on the inside of the tire, where nobody see's it. I know where your going with the max pressure and that of the truck. Many people don't know how much weight they are carrying.

 

I tell folks this to keep a margin of error, besides people that understand how tires work, who religiously checks their tire pressures? A truck is a perfect example, guys think "it's a truck, it's meant to haul weight" thats true, but just about every 1/2 ton truck has P (passenger) rated tires and not LT (light truck) dump a load of stone or a bunch of lumber in the back and that tire is in trouble if it's not at max air pressure.

 

If you understand how tires work, you can figure out your perfect pressure, but I know I dont (read not going to) have the time to play with that. I rotate the tires at about 6K and keep them right up at max. I get reasonable wear and I'm not concerned with a tire being underinflated should I load the truck up with gear or folks or both and pull a trailer. It's just easier for me to do it like this and forget it. It's all about how you take care of your vehicle, some folks are good at checking their pressures....many aren't

[hillrider]

Settled on 32 lbs. They came from the factory at 38. They sticker said 35 and when I dropped to that, I picked up 1/2 inch of contact patch. Another 3 lb drop didn't improve the patch but improved stability. Think I'll stay at 32. thanks for the help