Proper tire air pressures

[Stocker]

Now in the picture this is a prime example of an over inflated tire. The edge of the tread is not in contact with the road. The center of the tire will wear faster. There is no way an over inflated tire will wear the edges faster since the edges aren't even in contact with the ground. Do I need to know how much air is in the tire..NO. I just know whatever is in the tire is too much. Depending on the type of tire, how the person distributes the load, or maybe doesn't put anything in it, will change the amount of air needed to properly fill the tire so the full tread foot print will be in contact with the road. What you need to do, is check your pattern on your car and see if your tires are fully contacting the road. Once the dirt starts coming in contact past the edge of the tread to the side wall then you don't have enough air....Whatever that might be. A specification in your manual or what the factory recomends may not be right for your vehicle and your driving habits. As you lower the air pressure the foot print will get wider, making more contact. Too low of air pressure will wear the out side edges faster than the center. If this picture doesn't clarify it for you I will use my car and vary the air pressure with pictures and air pressure settings.

[FordNut]

Just don't get it do ya...

We've been driving these cars for over 2 years and we know about inflation pressure vs wear. Been there, done that. Someday you may understand. Then again...

[427435]

Now in the picture this is a prime example of an over inflated tire. The edge of the tread is not in contact with the road. The center of the tire will wear faster. There is no way an over inflated tire will wear the edges faster since the edges aren't even in contact with the ground. Do I need to know how much air is in the tire..NO. I just know whatever is in the tire is too much. Depending on the type of tire, how the person distributes the load, or maybe doesn't put anything in it, will change the amount of air needed to properly fill the tire so the full tread foot print will be in contact with the road. What you need to do, is check your pattern on your car and see if your tires are fully contacting the road. Once the dirt starts coming in contact past the edge of the tread to the side wall then you don't have enough air....Whatever that might be. A specification in your manual or what the factory recomends may not be right for your vehicle and your driving habits. As you lower the air pressure the foot print will get wider, making more contact. Too low of air pressure will wear the out side edges faster than the center. If this picture doesn't clarify it for you I will use my car and vary the air pressure with pictures and air pressure settings.


Stocker, you're probably wasting your time. There are some people on this board who believe the laws of physics don't apply to the rear tires on MM's. I've been running my rears as low as 22 psi and I'm getting more even wear than at 34 psi----but I don't like running that low. So, I've settled at 24 psi and will probably get 30,000 to 35,000 miles on the rears.

I did note that my right rear is wearing faster than the left---so I've rotated them side to side. Probably something to do with pinion or engine torque. Yes, I know that some say you shouldn't rotate side to side but the MM's owner's manual says you should.

[FordNut]

Stocker, you're probably wasting your time. There are some people on this board who believe the laws of physics don't apply to the rear tires on MM's. I've been running my rears as low as 22 psi and I'm getting more even wear than at 34 psi----but I don't like running that low. So, I've settled at 24 psi and will probably get 30,000 to 35,000 miles on the rears.

I did note that my right rear is wearing faster than the left---so I've rotated them side to side. Probably something to do with pinion or engine torque. Yes, I know that some say you shouldn't rotate side to side but the MM's owner's manual says you should.
For me, it has nothing to do with physics. A argued this same point for a long time. I ran my first set at 32 and they wore in the center. I ran the second set at 28 and they wore in the center. The third set is running at 38 and they are wearing evenly. Defies all I have learned through the years, but that is what my experience has been. Several other members have experienced the exact same wear pattern. Still doesn't make sense to me, but since I want to get as much use out of them as I can I'll run them at 38.

[Stocker]

Just don't get it do ya...

We've been driving these cars for over 2 years and we know about inflation pressure vs wear. Been there, done that. Someday you may understand. Then again...
Doesn't just apply to MM's. Applies to "ALL" vehicles!

[FordNut]

Doesn't just apply to MM's. Applies to "ALL" vehicles!
What kind of OIL do you use? What weight is the best choice?

[MENINBLK]

What kind of OIL do you use? What weight is the best choice?

OH NO! Not another thread hijacked by an OIL question !!! :hijack: :seesaw:

[looking97233]

Here's a link. Everyone go there and read it.

http://www.bfgoodrichtires.com/bfgapp/experts/index.jsp?style=0

On the right side of the screen there is a box "tire tips" at the bottom of this box is "tire pattern baldness" click on play.

That should answer it for everyone.

[cruzer]

I have 39,245 miles on my MM--first set of rears--32 #----16,500 miles---5/32nds on outer tread---0 /32nds on inner tread
second set---28 #----17,100 miles---outer tread 6/32nds---inner treasd---0/32nds
third set---5, 600 miles---outer---8/32nds---inner-----7 1/2 32nds--pressure 40 PSI !!!!!!!--works for me !!!

Don't ask me why---I just buy the tires :confused: :confused: :confused:

[LVMarauder]

Stock- Normally yes, I would agree 100% with you. But what cruzer and fordnut is absolutely right. I couldnt beleive it myself , my centers were GONE at 15k yes 15K!!! that was at 32 psi, I run 35-38 now and drop it to 20 in the backs whenever i really need to hookup at the track. Its weird but thats what alot of us are seeing.

[Marauderjack]

40+ PSI and I'll get 40K out of the rears!!! :beer:

My first set lasted 11K with 22-24 PSI....GO FIGURE!!! :o

Right now....at rest the center of the tread is concave with 44 PSI.....If I let it down to 30 or less it is flat and center will wear faster again at highway speeds!!!! :cool:

Do what you think is right for you but higher pressures has helped mine both front and back!! :bows:

BTW.....My fronts will probably go 60K miles or more!! :D

Marauderjack :)

[Bluerauder]

Still doesn't make sense to me, but since I want to get as much use out of them as I can I'll run them at 38.
I am running at 38 psi in the rears also and getting even wear across the tread. Currently over 18,000 miles. It works !!! :D

[bryanknie]

Same here been there done that. Finally on my 3rd set of rears, I ran 40 lbs, no issues. Defies everything I know and have learned, but works. Running 40 all the way around as it helps the edge wear on the fronts.

[MENINBLK]

Please remember that we are discussing the BFGoodrich KDWS on the rear axle of our Marauders (245/55ZR18 103W) ONLY...

What normal proper tire pressure dictates will work in 99.9% of all the vehicles we drive otherwise.
I've put in a question to BF Goodrich, to see if I can stir up some curiosity on their side,
and to also see if they can come up with a reasonable explanation of what we are experiencing.
I am holding my breath on this one, but since it is localized to ONLY our vehicle,
it is a small group, using just a single tire and size, and they may be interested.

For my winter tires, I am using Pirelli Scorpion Ice & Snow and I've got them inflated to 34psi.
I've got close to 4500 miles on them now and so far the wear looks normal.
I'll take a measurement and get back to you with my results...

[Heavy351]

Somebody on the BF Goodrich board posted a reply, link:

http://www.bfgoodrichtires.com/bfgapp/servlet/Controller/site.forums.LoadMessages?discu ssion_id=.1dcec03a&topic_id=.1dce8370


*RE: RE: ???Center wear on rear KDWS's
by TireNerd2
February 23, 2005 8:28PM


Nope. The KDWS does not have a softer compound in the middle of the tread. The KDWS uses a single tread compound accross the entire face of the tread. Center rib tread wear can be caused by many things. However, take it from me as a Tire Designer (6 years) and Ex-Test Driver for BFG (6 years), rear wheel drive, high horsepower, and high torque applications that exhibit accelerated center rib wear usually benefit from INCREASING cold inflation pressures. Now I know absolutely everyone in the public domain will tell you accelerated center rib wear is caused by over inflation, but believe me it's also caused by under inflation on the 'driven axle'. So in a sense both situations lead to center rib wear depending on whether the axle is being driven or not i.e. whether the tire experiences an engine driving torque or not. Adding some air to the rear axle of the Marauder in this example will stabilize the contact patch and help it maintain its shape better by keeping more rubber on the road under a driving torque. Essentially, if a driven axle tire is under inflated when it experiences a high driving torque, the leading edge of the contact patch is forced into the road and the trailing edge of the contact pathch is 'pealed' up (you can watch dragster tires do this when they stage at the line). When this happens the unit contact pressures increase at the leading edge of the contact patch, which increases contact stresses and accelerates wear. The centerline of the contact pacth just happens to be the location of highest contact pressures and so exhibits the highest wear rate. I know this may sound odd - and I know maybe counter to what you've heard BUT adding air reduces center rib wear in higher horsepower applications by stabilizing the contact patch shape. Keep in mind O.E. inflation pressures are a comprise by the manufacturer for ride and handling and not optimized for tire wear life. So add at least 5 to 7 psi cold to the rear axle tires and the KDWS wear life should increase.




Kinda confirms what we already know ......

[Bluerauder]

Kinda confirms what we already know ......
But now we know why .... thanks for posting and thanks also to TireNerd2. :2thumbs:

[Stocker]

I like that..."I drop it to 20 when I need to hook up at the track"......sounds like you probably drive like your at the track all the time....I tend to drive my cars and not abuse them.

In my Z28, I have been running 18psi in the rear since new. I have about 5000 on the 3rd set of Z rated tires and have been getting excellent treadwear across the whole time. Go figure. I guess I got to just go with what works.

I have been able to educate customers on tire pressures by showing them the pattern on their tires. When they acutually see with their own eyes in helps them to understand a tire pressure will vary with different tires, cars, and driving habits. And I have them document the pressure that best suits their car for the next mechanic to service it....so it doesn't get the "pump it up to what they put in all the cars."

[Warpath]

...A specification in your manual or what the factory recomends may not be right for your vehicle and your driving habits...

The specification is based on load capacity, handling, and tread wear. Under-inflated tires cannot hold as much load as properly inflated tires. Under-inflated tires lose cornering stiffness and affect handling. You should not advise changing the tire pressure - especially lowering it - without understanding the affects to handling and safety. The Explorer/Firestone fiasco was partially due to under-inflated tires. That is why the government is requiring OEs install tire pressure monitoring sensors in vehicles (slowly over time) because it is that important. I recommend you keep the tire pressure no lower than what Ford recommends.

[King Fubar]

I have 15,000 on mine and my rears a balding a bit too. I don't think it has anything to do with the pressure though :burn: :burnout:

[Romo53]

The specification is based on load capacity, handling, and tread wear. Under-inflated tires cannot hold as much load as properly inflated tires. Under-inflated tires lose cornering stiffness and affect handling. You should not advise changing the tire pressure - especially lowering it - without understanding the affects to handling and safety. The Explorer/Firestone fiasco was partially due to under-inflated tires. That is why the government is requiring OEs install tire pressure monitoring sensors in vehicles (slowly over time) because it is that important. I recommend you keep the tire pressure no lower than what Ford recommends.

HERE HERE!!!!!!

[Heavy351]

Are you seriously driving around on Z-rated tires at 18 psi? You need your head examined.

whats the cornering like? probably pretty plush otherwise.

Loosing control on a corner is less likely to get you killed than your rear tires simply self-destructing someday out on the interstate from all the heat they are now generating. I have done some work in this area: http://www.algor.com/news_pub/cust_app/goodyear/default.asp

We have consulted on tire design specifically to prevent the above from happening at low tire pressures.



I find it hard to believe any mechanic is going to ignore the factory pressure sticker when handling a customers factory spec tires,

I find it impossible to believe a mechanic is going to intentionally put in less.

After the Firestone incident noted above, such a mechanic probably wont be one for much longer :rolleyes:

[wsmylie]

Hey Heavy...the wheel strees experiment info presented on that Algor site is pretty interesting, Thanks.

[LordVader]

:bows: Heavy, that information has truly cleared up the murky waters regarding this age old issue of tire pressure. Good looking out!

[Heavy351]

Here' s an animation:
http://www.algor.com/products/analysis_replays/goodyear/default.asp

If you really want to geek out:
http://www.algor.com/news_pub/cust_app/goodyear/default.asp

We found that wheels see HIGHER stresses at LOWER pressures. The force applied from a properly inflated tire helps keep the wheel round. Not mentioned in the article were the analytical work done on the thermal properties of the tires. Pretty much they get hot, they get "gooey" the bead loosens up and BLAMMO!

Actually, BillyGman has personal experience in this area during his wonderful burnout. In his case the heat was coming only from the tread surface and the tire started to come apart inside of a few min. If he had kept going the tire would have stayed on the rim even at failure (bead would have been much cooler) When underinflated the heat is EVERWHERE and can be concentrated on the bead where the heat is dissapated more slowly and friction on the rim from the massive sidewall twisting on every rpm just makes it worse... All is bad.. very bad. :mad2:

[Romo53]

:mad2: I'm not going to re-hash our tire pressure experiment that was done. I went into detail on an earlier thread reference tire pressures and tire design. The only high performance vehicle where it is absolutely critical to run low (very low i.e. 8psi), are top fuel dragsters. If you run lower than recommended tire pressures, you risk your life and those around you. :depress:

[Vortex]

100% right!

[carfixer]

This has been a very educational thread. Thanks to all that participated, especially Heavy, great info for all of us. :up:

[69marquis conv]

Well, now at barely under 19K I see that my rears are also getting pretty darn light in the centers. Thanks for an excellent thread! I will keep all this in mind when I take the two TireRack rears out of the garage to have them mounted. After reading this I might not have to mount them quite as soon as I would have otherwise...