please help me with Tire Pressure - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > JK Jeep Wrangler Forum > JK General Discussion Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 09-09-2012, 05:27 PM   #1
Jeeper
 
Join Date: Apr 2011
Location: ny
Posts: 171
please help me with Tire Pressure

im not car techy or anything. and im confused. my 2012 2 door sport has these tires.

p255/75r17 owl on/off-road tires 17-inch aluminum wheels

is 35 psi correct for normal driving? my door pannel said 35 cold only it doesnt say anything about normal..

am i not reading it right. its strange because im 3,000 miles into driving and none of my tires need pressure.. i only drive on the road and light highway driving not much.

please help what the correct pressure should be at so i can get into a good habbit of checking it once a month or so.

michael305 is offline   Quote Quick Reply
Old 09-09-2012, 06:35 PM   #2
Jeeper
 
2five22's Avatar
 
Join Date: Jul 2012
Posts: 1,399
35 psi is dead on for stock tires and will give you the least rolling resistance for best mileage.

Are you expecting them to lose pressure over time? Natural rubber tires will do so, but natural rubber tires haven't been used for cars, trucks, SUVs, or vans in many decades.

2five22 is online now   Quote Quick Reply
Old 09-10-2012, 04:31 AM   #3
Newb
 
Join Date: Sep 2012
Posts: 4
Registerd to this forum to give you answer about tire-pressure.
Search with Google frequently for that because I once got hold of the formula , that the tire-makers use to determine the loadcapacity for lower pressure, and vice versa. Worked it out in spreadsheets and translated a few from Dutch to English to go worldwide with it.
Got much to know about tires when searching for information on the internet, but I am not a tire-specialist.
By reacting on several also American fora, I came to the conclusion, that the formula is not that holy as I declared it in the beginning, and found an article of an American J.C.Daws wich I also saved on my skydrive that belongs to my hotmail adres with the same username as here. Did not even totally agree with his way of calculating , and constructed my own univeral formula, from wich you can make both formulas by filling in other construction load( Lc ) and power to use (X).
Because I dont have a Wrangler, I will not introduce myself in a seperate topic.
Here the link to my skydrive, with several English maps and documents, between the Dutch ones.
https://skydrive.live.com/?cid=a526e...E092E6DC%21128
You can hover around it , the same as in a forum, and to use a spreadsheet, first download it by clicking right on it , and choose download. After download and eventual virus-check, open it in Excell or compatible program to use it ( Open Office Calc will do).

But now about your tires.
They are probably oversised for the vehicle weight .
35psi is what they call the reference-pressure( wich is not the maximum pressure as given on P and XL tires), and that is the pressure the tire-maker used to calculate the maximum loadcapacity up to the reference-speed of mostly 160km/99m/h( or if lower maximum speed of tire).
This is also calculated with a much more complicated formula.
So if you have only half the load on a tire then the maximum load, you can use a lower pressure, to get the same deflection of the tire, as for maximum load and reference-pressure. And that is the goal of all the calculations, that the deflection of the tire stays the same.
In the map of my link , you can find a spreadsheet "pressurecalculationwithtemp" wich is easy to use and good for up to that 99m/h, so enaugh speed I think for you.
It works with the reasonably save European calculation, to wich America swiched over in 2005. That is only for Standardload tires ( P-tires) and XL( reinforced/Extraload), for C-load/6ply and up the old power is still used in America, wich leads to more deflection of the tire at lower pressure and calculated loadcapacity for that.
Other thing is that you probably have about the same tires-profile as the tires that gave problems at the Ford-Explorer, so better is to highen up the reference-pressure to about 40 psi in the calculation, to get less deflection, and so saver. Taking all this into account , you will probably even come to a verry low pressure-advice, wich gives more gripp , also in sand, and is still save for the tires up to 99m/h.
I dont have the data of your car and tires, but if you give them , I can calculate it for you. I Estimate that you can even use as low as 21 psi wich is the lowest they go in Europe ( America 27 psi), and is no problem.
For fuell saving a higher pressure is better, but gripp and comfort are important to , I think.
jadatis is offline   Quote Quick Reply
Old 09-10-2012, 06:17 AM   #4
Jeeper
 
SeaComms's Avatar
 
Join Date: Jan 2011
Location: Noosa, QLD, Australia
Posts: 780
Umm.. interesting. but 35psi is not the reference pressure, its the recommended cold temp inflation pressure by the vehicle manufacturer, not the tyre manufacturer. For the OP's benefit, cold pressure refers to when the vehicle has been sitting for long enough for the tyres to cool back to the ambient air temperature.

I run about 34psi in mine, not for any other reason than thats the lowest I can go without tripping off the low pressure alarm. After 30,000 miles on the stock tyres mine are worn pretty much even across the tread face.

Dropping THESE tyres to 21 for road use at up to 99mph is not only stupid, its downright dangerous. The information given above is most likely based on road tyres on lightweight passenger vehicles, not a 4wd. I dont even go that low in the sand!
__________________
Cheers from Downunder, Dave.
2010 Dark Charcoal Pearl 'Renegade' pack (includes dual top options, 17in alloys, side steps etc).
2.5in Flexy springs, Bilstien 5100's, Teraflex rear trackbar bracket, Synergy front and rear sway bar links and front disco kit, Synergy steering damper relocation bracket, AEV front drop brackets, ARB front and rear bar, 10,000lb rope winch, Britax Xray Vision driving lights, GME 3440 UHF radio.
SeaComms is offline   Quote Quick Reply
Old 09-10-2012, 06:32 AM   #5
Jeeper

WF Supporting Member
 
kbwwolf's Avatar
 
Join Date: Sep 2011
Location: Wisconsin
Posts: 12,048
Quote:
Originally Posted by jadatis View Post
Taking all this into account , you will probably even come to a verry low pressure-advice, wich gives more gripp , also in sand, and is still save for the tires up to 99m/h.
I Estimate that you can even use as low as 21 psi wich is the lowest they go in Europe ( America 27 psi), and is no problem.


I'm w/Seacomms...that sounds downright dangerous to me.

OP, go with the door placard for your stock tires. Aftermarket is a different story, but no matter what tires you run, you can always find the optimum PSI by doing a chalk test:

How to Chalk Tires | eHow.com

Use the chalk that carpenters use in string lines, so it'll transfer well from your tires to the asphalt. Don't buy the permanent chalk...it'll say on the bottle.
__________________


"What we see depends mainly on what we look for."
—John Lubbock
kbwwolf is offline   Quote Quick Reply
Old 09-10-2012, 06:39 AM   #6
Jeeper
 
C.L.'s Avatar
 
Join Date: Mar 2011
Location: North NJ
Posts: 1,918
Quote:
Originally Posted by kbwwolf View Post


I'm w/Seacomms...that sounds downright dangerous to me.

OP, go with the door placard for your stock tires. Aftermarket is a different story, but no matter what tires you run, you can always find the optimum PSI by doing a chalk test:
Count me as a 4th for a "don't do that! with regards to 21psi in stock tires. They'll either blow out from the heat generated, or you'll dent a rim in the first pot hole you hit. I don't even run that low on the street on 35x12.50x15 MTs! I think the JK's tire sensors will start pinging at you if they go below 32psi anyway; that should tell you something...
C.L. is offline   Quote Quick Reply
Old 09-10-2012, 06:40 AM   #7
Newb
 
Join Date: Sep 2012
Posts: 4
The chalk test is verry inaccurate, and can do for diagonal tires, wich are not used that often. Radial tires stay with the total wide on the ground in a large range of pressure, so the chalk wears off evenly.

And the 35 psi is the reference-pressure of a P-Tire in America, and that is what the car-maker adviced for this car.
Those advices are kept verry high after 2000, also in Europe.
But before 2000 lower pressures where adviced, wich sometimes lead to tire-damage, because the calculation was not right in America, and the maximum load was calculated wrong for some tires, wich is still the case.
Its like , letting everyone walk on shoe-sise 13, so they will never be to small.
jadatis is offline   Quote Quick Reply
Old 09-10-2012, 06:43 AM   #8
The Bad Guy

WF Supporting Member
 
daggo66's Avatar
 
Join Date: May 2009
Location: NJ exile living in Baltimore
Posts: 21,496
Help with tire pressure on stock tires? Not "car techy?" What are you going to do when it needs gas?
__________________
Tom

"I've got two things in this world, my balls and my word and I don't break them for no one."
daggo66 is offline   Quote Quick Reply
Old 09-10-2012, 06:52 AM   #9
MallCrawler

WF Supporting Member
::WF Moderator::
 
kjeeper10's Avatar
 
Join Date: Feb 2011
Location: Connecticut
Posts: 31,521
Quote:
Originally Posted by daggo66
Help with tire pressure on stock tires? Not "car techy?" What are you going to do when it needs gas?
Full service
__________________
2007 Rubicon/Rock Krawler TR 2.5 coils/rear TB/Rancho 9000 31/32XL shocks/Teraflex monster TB/Synergy highsteer,tie rod, ball joints/Hankook MT 315-75-16 on Level 8 ZX's/MC front SB links/Rancho geo brackets & shocks/Fox ATS stabilizer/Adams front DS=Frankinlift from hell.

Lifting your JK? Read this!!



Click HERE to become a WranglerForum Supporting Member!
kjeeper10 is offline   Quote Quick Reply
Old 09-10-2012, 07:04 AM   #10
Jeeper

WF Supporting Member
 
kbwwolf's Avatar
 
Join Date: Sep 2011
Location: Wisconsin
Posts: 12,048
Quote:
Originally Posted by kjeeper10 View Post
Full service
Only in Oregon.
__________________


"What we see depends mainly on what we look for."
—John Lubbock
kbwwolf is offline   Quote Quick Reply
Old 09-10-2012, 07:13 AM   #11
Newb
 
Join Date: Sep 2012
Posts: 4
Low pressure alarm is set to the pressure the car manufacturer advices, but can be re-set. But give me some data of car and tires, and I will calculate as an example here, in wich I use reserve weight for savety, and you will still see that it can go lower without damaging the tires.
for carts also verry low pressures are used, for same reason, of over-sised tires and more gripp . Only thig is that they dont have problems damaging the tires a little.

What I need at least are from the car , the Gross Axle Weight Ratings (GAWR) front and behind. From the tires the maximum load, expressed in Kg/LBS or the loadindex, and the kind of tire for determining the reference-pressure (Pr).
Tire data are written on the side-wall, look if you see XL/Extraload/reinforced on the tire, then you need Pr=41psi , but probably not, because you already wrote that they where P-tyres ( standard load/A-load/2py) so you need Pr=35 psi.
Difference between Pr and Pmax is used for higher speed and camber-angle above 2 degrees, so probably not needed here.

So give the data and let me calculate and be amazed.

Once calculated it for a Westfield, a verry light car with also oversised tires,
Then still used the maximum pressure of 60 psi for those Toyo tires, and even came to 1,4 bar/20psi, wich was sayd to be commonly used .
So I wont say it will come that low, but it is possible.
jadatis is offline   Quote Quick Reply
Old 09-10-2012, 07:56 AM   #12
Jeeper
 
mgola27's Avatar
 
Join Date: Jul 2010
Posts: 516
Quote:
Originally Posted by daggo66 View Post
Help with tire pressure on stock tires? Not "car techy?" What are you going to do when it needs gas?
Don't be too hard on him, Tom. There are so many people who never think about tire pressure until the tire is actually flat (that's why we have our TPMSs) and this poster is trying to learn.

michael305, the sticker on the door jamb will tell you what the correct pressure should be set to when the tires are "cold." What "cold" means in this instance is a tire that has not been driven more than a mile in the past three hours. So, if you've been driving around and want to check your tires at the gas station, you are not checking a cold tire.

If you really wish to monitor your tire pressure/wear, buy yourself a pressure gauge and check your tires in your driveway before you drive and adjust as necessary with a small compressor.

As far as losing air, that doesn't generally happen, but changes in the ambient temperature will affect the relative pressure of the tires. So, when it gets colder out, you'll have less pressure than when it's warmer out.

I find that the change in seasons from summer to fall/winter to spring are the most difficult to manage, as the temperature variations can be more extreme during those times.

Happy Jeeping.

mgola27 is offline   Quote Quick Reply
Old 09-10-2012, 11:03 AM   #13
The Bad Guy

WF Supporting Member
 
daggo66's Avatar
 
Join Date: May 2009
Location: NJ exile living in Baltimore
Posts: 21,496
Quote:
Originally Posted by kbwwolf View Post
Only in Oregon.
New Jersey.
__________________
Tom

"I've got two things in this world, my balls and my word and I don't break them for no one."
daggo66 is offline   Quote Quick Reply
Old 09-10-2012, 11:05 AM   #14
MallCrawler

WF Supporting Member
::WF Moderator::
 
kjeeper10's Avatar
 
Join Date: Feb 2011
Location: Connecticut
Posts: 31,521
Quote:
Originally Posted by daggo66

New Jersey.
Still ?
__________________
2007 Rubicon/Rock Krawler TR 2.5 coils/rear TB/Rancho 9000 31/32XL shocks/Teraflex monster TB/Synergy highsteer,tie rod, ball joints/Hankook MT 315-75-16 on Level 8 ZX's/MC front SB links/Rancho geo brackets & shocks/Fox ATS stabilizer/Adams front DS=Frankinlift from hell.

Lifting your JK? Read this!!



Click HERE to become a WranglerForum Supporting Member!
kjeeper10 is offline   Quote Quick Reply
Old 09-10-2012, 11:09 AM   #15
The Bad Guy

WF Supporting Member
 
daggo66's Avatar
 
Join Date: May 2009
Location: NJ exile living in Baltimore
Posts: 21,496
Sorry, but owning/driving a vehicle and not knowing the basics, such as the correct tire pressure is flat out dangerous. Instead of testing new drivers on parallel parking, which some people while never do, they should be tested on the basics of vehicle safety.
__________________
Tom

"I've got two things in this world, my balls and my word and I don't break them for no one."
daggo66 is offline   Quote Quick Reply
Old 09-10-2012, 12:07 PM   #16
Jeeper
 
Join Date: Oct 2010
Posts: 95
There's nothing "magic" about tire pressure, IMHO. After a while you will be able to tell if the tire pressure is "OK" just by how the vehicle behaves... how it takes bumps... how it goes around a corner... how it rides... and, it's OK to experiment. For example, if the TP is too low... the vehicle will wallow more, ride will be really soft, turns will feel sloppy and sluggish... maybe more noise from the tires. If the TP is too high, the ride will be harsh, bumps will rattle the whole vehicle, turns will be crisp but not grippy... When the TP is just right, you'll notice a nice balance between all these factors. Then check the pressure with a gauge and use that number for a while. If you go off-road you need to air-down, as another example.
taoshum is offline   Quote Quick Reply
Old 09-10-2012, 12:22 PM   #17
Jeeper
 
mgola27's Avatar
 
Join Date: Jul 2010
Posts: 516
Quote:
Originally Posted by daggo66 View Post
Sorry, but owning/driving a vehicle and not knowing the basics, such as the correct tire pressure is flat out dangerous. Instead of testing new drivers on parallel parking, which some people while never do, they should be tested on the basics of vehicle safety.
Oh, I 100% agree. I just wanted to encourage this poster's behavior in finding out more about proper vehicle operation. What he learns here will hopefully transfer not only to other vehicles he'll own, but maybe he'll share with others that don't know.

mgola27 is offline   Quote Quick Reply
Old 09-10-2012, 12:24 PM   #18
Jeeper
 
mgola27's Avatar
 
Join Date: Jul 2010
Posts: 516
Quote:
Originally Posted by taoshum View Post
There's nothing "magic" about tire pressure, IMHO. After a while you will be able to tell if the tire pressure is "OK" just by how the vehicle behaves... how it takes bumps... how it goes around a corner... how it rides... and, it's OK to experiment. For example, if the TP is too low... the vehicle will wallow more, ride will be really soft, turns will feel sloppy and sluggish... maybe more noise from the tires. If the TP is too high, the ride will be harsh, bumps will rattle the whole vehicle, turns will be crisp but not grippy... When the TP is just right, you'll notice a nice balance between all these factors. Then check the pressure with a gauge and use that number for a while. If you go off-road you need to air-down, as another example.
This is only true for those that care... and even then, the rears would be hard to tell by "feel" alone since they provide far less feedback than the fronts. Maybe a 2-door would be more communicative, but not as much on a four door.

mgola27 is offline   Quote Quick Reply
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




» Network Links
»Jeep Parts
» Featured Product

All times are GMT -5. The time now is 02:23 AM.



Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC