Proper Pressure

[808inthe949]

Hey all, recently got new tires. Pirelli Scorpion AT Plus 245/70 on stock 17's. My KJ is close to stock weight (no skids or armor yet) and I weigh less than 200lbs. Using the tire pressure equation (the one where you take you weight and the tires max crating load yadda yadda) and I got 19lbs pressure. This seems low for everyday driving. Most of my miles are highway/city. What do you guys think?

 

[Johnny O]

Hey all, recently got new tires. Pirelli Scorpion AT Plus 245/70 on stock 17's. My KJ is close to stock weight (no skids or armor yet) and I weigh less than 200lbs. Using the tire pressure equation (the one where you take you weight and the tires max crating load yadda yadda) and I got 19lbs pressure. This seems low for everyday driving. Most of my miles are highway/city. What do you guys think?

What is the pressure rating on the tires themselves?

 

[tommudd]

32 or so, do not go by pressure on tires unless you are running a F250 fully loaded

 

[808inthe949]

2337@44psi. When installed they set pressure to 40! Crazyness. Currently sitting at 31psi warm. Did the equation 2337*4= 9348
Est jeep weight 4200 (one passenger, no armor or skids, no extra cargo)
4200/9348=~ 44%. 44psi(max press) * .44 (vehicle is currently 44% of the max weight limit of all four tires combined)
Estimated psi for best tire tread wear is 19-20psi. This just seems low for mpg and tread wear

 

[David13]

Many tires fit on many different vehicles.

Usually the pressure on the tire is the MAXIMUM.

The appropriate pressure for your vehicle is usually on a sticker or decal on the door (driver's) jamb.

You can lower your pressure for driving and traction on sand or other surfaces. But then air back up for the highway.

So what do I think? Read the door jamb decal. Or sometimes it's in the glove box or idiot book.

19 pounds is way too low. At highway speed they will heat way up and **** out.
dc

 

[David13]

Oh, and check the air on a regular basis. Don't just assume the air goes in there on it's own. It don't. And no, you don't need to go to a "professional" to have the air checked.

 

[808inthe949]

Come on guys if I'm going through the process of using an equation to get my most ideal tire pressure, it's probably safe to assume that I know to check my tires often. The door jab psi is a recommendation for the stock tire size. Im not running stock size, and my tires have a different weight rating than the stock ones. So am I wrong to assume that the sticker in the door jab applies to stock and not every tire you put on? What if I put a large D rated tire? Wouldn't it need different pressure than the stock?

 

[Aceofspades]

I’ve been having issues finding the correct pressure for my tires load range E 10ply ... I’ve heard someone recommending I run 45...

Ended up trying the chalk test described here. Still not sure

 

[Johnny O]

Come on guys if I'm going through the process of using an equation to get my most ideal tire pressure, it's probably safe to assume that I know to check my tires often. The door jab psi is a recommendation for the stock tire size. Im not running stock size, and my tires have a different weight rating than the stock ones. So am I wrong to assume that the sticker in the door jab applies to stock and not every tire you put on? What if I put a large D rated tire? Wouldn't it need different pressure than the stock?

Don’t be offended. On the internet it is had to tell who knows what. My ISP doesn’t have the bandwidth to support my mind reading skills!

 

[John P.]

I have Firestone destination 245/65/17. I run them at 38 psi on highway and when I go off-road like in Arkansas this week I run them at 25.

 

[Motocomiot]

I fitted Scorpions exactly same size as yours on my ‘06 Liberty 3.7l. I run them on 35 for highway & 30 on snow or mud (I’m in the UK) They wear evenly and they stick like sh## to a blanket.
The equation looks a lot like one I used to use when towing cattle in a big trailer so I think it’s a bit simplistic. With an unbraked trailer it’s all about static weight but on a car/truck when your foot is ******* the brake the two front tyres will be carrying most of the curb weight plus the stress of slowing down two metric tons of metal…..
Using a common sense approach an extra 10mm tyre width isn’t going to make a heap of difference - they’ll hold more weight but there are too many other factors to consider.
Good luck and remember a lot of people don’t actually read the posts ….. let alone understand them

 

[808inthe949]

Still new here and not sure how to compose properly clearly lol. I do understand how you can't read minds and expect everyone to know certain things.
I'm currently at 31 so I'll go up a bit to 34-35 and see how a few hundred miles looks on the tires.
I'm glad someone has used these scorpions before as I don't see many mentions online.
Which is surprising because on tire rack their chart breaking down the most popular tires and how they compare to each other shows these tires as number 4 or 5. Way better than the wranglers with kevlar, KO2's, and wildpeaks everyone seems to love. They were cheaper too so I figured I'd give them a try.
How are they wearing? I'm glad they grip!

 

[XWrench3]

I run 35 PSI on all of my vehicles. the tires wear evenly, and i get good fuel economy. the only bad thing about that pressure, is i feel every bump and surface irregularity on the road. if you want a SMOOOOOOTH ride, I would run something like 27 PSI + or - a few. but you will wear the outer edges of the tire more than the middle. and of course, off road air them down to 15 psi.

 

[808inthe949]

Im more inclined to be concerned with tire wear vs. ride comfort. It is a lifted jeep after all I can't expect it to ride like an old crown Vic .
I have the stock 17's. Running 15 psi offroad won't break the bead? Obviously It will be more likely with aggressive driving

 

[turblediesel]

34 I started at 32 and the middle of the tire didn't seem to be wearing as much. Anything over 34 makes me feel every tiny pebble on the road. Goodrich all terrain KO light truck tires. More psi when towing especially in the back.

 

[XWrench3]

I have the stock 17's. Running 15 psi offroad won't break the bead? Obviously It will be more likely with aggressive driving

Certainly if your driving very aggressively you run that risk. I personally have never had an issue at 15 psi. One place you have to give tire pressure a lot of attention is in very rocky terrain. to much pressure can result in a bent (or broken if its aluminum) wheel, but to much, and you will not get enough contact patch on the rocks to get anywhere. also, sharp rocks can and will cut a tire sidewall more easily if your running higher pressures. i had that happen years ago, running 35 psi on a rocky trail, rescuing a stranded motorcycle after my buddy broke his wrist in a fall.

 

[tommudd]

Just do a chalk test and be done
Lots of variables , what I run say in the 04 would be way different than someone else with same size tires but not all the weight I carry always

 

[XWrench3]

Just do a chalk test and be done

what, is the chalk test?

 

[808inthe949]

Line of chalk across tread of tire. Roll 4-5 revolutions. Look at chalk on tire. If center is work but sides are still chalky, too much air. Sides worn but center still chalky, too low psi. Keep doing the test until the chalk is evenly worn across the tread.
Gotta be sure your jeep is in alignment tho cause that can throw the test off

 

[nbas]

I have been through this before, and chalk works well, but being an engineer myself, I wanted to find something from a tyre company explaining how to calculate correct pressure when you change tyre type and size. This is what I found:
https://www.jeepkj.com/threads/tire-pressure-calculation.62606/