What Psi should I run - Do a "Chalk Test" to determine

  1. FatBoy01

    FatBoy01 Banned

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    #1 Mar 3, 2018
    Last edited: Mar 3, 2018
    *CHALK TEST:

    Instructions:

    -In the morning, before sun beats down on your tires and before you drive the truck-

    1. Fill the tires to a good starting pressure. If you are unsure what pressure to start with then subtract 10 percent from the manufacturer's maximum inflation pressure on the side of the tire. If, for example, the maximum is 40 psi, then 10 percent of 40 is 4. Subtract the 10 percent value from the maximum psi value. So, 40 - 4 = 36. Use 36 psi in your tires. You could also use the following calculation for the starting pressure.
      • Weight of vehicle / (Manufacturers weight rating x 4)) x Manufacturers inflation pressure at weight rating
    2. Drive to a flat area. This can be your driveway or the street in front of your house. Just make sure there aren't a lot of cracks, bumps or pot holes in the ground.
    3. Using chalk, draw a thick, straight line across the width of the tire.
    4. Use Test Variance 1 or Test Variance 2 for the completion of the instructions.

    Test Variance 1
    1. Drive the truck forward at least one-full truck length.
    2. Inspect the chalk on the ground. A tire with the proper air pressure should press the chalk line evenly across the ground. This means you'll see the entire chalk line imprinted on the ground. If your tire is over-inflated, you'll only see a small portion of line in the center. If you're tire is underinflated, you'll see only the sides of the lines since the middle of the tire is not making contact with the ground.
    3. Adjust your tire's air pressure according to the chalk test results and try again until you get the chalk line to press evenly across the ground.

    Test Variance 2
    1. Drive the truck to the end of the street and back or around the block.
    2. Inspect the chalk on the tire. A tire with the proper air pressure will show the chalk evenly worn across the tire. If your tire is over-inflated, the center of the line will be worn more than the edges. If you're tire is underinflated, the outer edges of the line will be worn more than the center.
    3. Adjust your tire's air pressure according to the chalk test results and try again until you get the chalk line to evenly wear across the tire.

    Over-Inflated = More wear on the center of the tire = center of chalk line visible on ground = chalk line worn more in center

    Under-Inflated = More wear on the outer edges of the tire = outer edges of chalk line visible on ground = chalk line worn more on outer edges


    Chalk-Test.jpg

    *Gleaned from other internet websites...
     
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  2. $uicide$hift

    $uicide$hift Well-Known Member

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    I assume this should be done when the tire is cold same as when you check air pressure? If that is the case you may want to call that out in the write up.

    Solid write up by the way
     
  3. OP
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    FatBoy01

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    #3 Mar 3, 2018
    Last edited: Mar 3, 2018
    Yes, Jeff .... I edited that post regarding this..

    Indeed guys/gals should not be fooling with tire pressures / be doing a Chalk Test when tires are warm. Do the chalk test when tires are cold.

    Do NOT change/adjust tire pressures when tires are warm.
    Reality is, best time to check/adjust tires is in the morning before the sun starts beating down on the tires/before you drive the vehicle.

    Hint: If you are say driving down the road and decide for whatever reason you need to adjust tire pressure on a warm tire... and, you know that you adjusted all your tires to proper inflation very recently when they were all cold..... anyway... you have one tire that is down a bit. Say your TPMS display on your dashboard says one tire is down lets say 3-4 lbs psi. Well, stop and check tire pressure on the other 3 warm tires and inflate your problem 4th tire to the same exact psi as the other three warm tires. This is a way to deal with psi adjustment on a warm tire. Do not inflate or deflate / adjust that problem tire using the routine cold tire psi you use. Do this, and then next morning, when tires are cold, check/adjust psi on all tires. Oh, and do keep an eye on that problem tire over the next few days. Perhaps a tire stem leak, small puncture...

    -Best to always keep a decent/known to be accurate, tire pressure gauge in your vehicle-
     
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  4. Dynomite1371

    Dynomite1371 Well-Known Member

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    37 cold pressure is perfect for me. It's winter in Maryland. They heat up to around 40 lbs depending on the outside temperature. I'm thinking 35 when, and if nice weather ever arrives. (Door jam does say 37 cold for Rubicon.)
     
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    FatBoy01

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    Really, it is good to do a Chalk test with a vehicle like the Wrangler.

    Also, you do the Chalk Test to determine what psi to inflate tires to on a given vehicle and then that is the psi you use. Also, prudent to keep in mind manufacturer's psi rec..

    You use that psi, Winter, Summer, Fall. (Unless, you are aired down for the beach, etc.)

    I'm getting the vibe that you change psi dependent on outside temperature's "when nice weather arrives", "depending on the outside temperature" which is incorrect.

    Find the proper psi per the Chalk Test" and again use that psi, Winter, Summer, Fall. Do a seasonal Chalk Test. You don't keep willy nilly fooling with psi based on temps, etc. Also, prudent to keep in mind manufacturer's psi rec..
     
  6. Blood Type J+

    Blood Type J+ Well-Known Member

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    Yes, pressure should always be checked cold but shouldn't the chalk test be done on warm tires? The warm tire pressure is where most of the tire wear is going to happen unless the vehicle is only driven short distances.
     
  7. OP
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    FatBoy01

    FatBoy01 Banned

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    What I have been taught but Im not an expert...... You can do a Chalk Test when hot. Warm psi. Make note of psi for reference. As I explained in the original post here, you do the morning, chalk test and that is your cold PSI. Cold psi is what you set your psi when tires are cool. That is what you run your tires at.

    You never air down/bleed off air on hot days or add air on cold days. You find your cold psi with chalk test and you use that.
     
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  8. Dynomite1371

    Dynomite1371 Well-Known Member

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    I've done chalk test. And I monitor wear. I had almost 50k on my last KO2's and was told by dealer, "they look like new" I said "Yelp" lol. So honestly I'm particular about how the ride feels, finding that balance between road handling and tire wear is the trick for me. I will say that I have a real pressure gauge (not the plastic stick style) and the computer tire pressure readings in the JL have been spot on. And I'm assuming that in the summer months that what is running pressure now (@40 psi) could change. If not, I'll leave them alone at 37 cold. I love the KO2's btw, great everyday tire for all conditions.
     
  9. OP
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    FatBoy01

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    Are you doing front to rear rotations or what. Yes, decent mileage you got...
     
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  10. Dynomite1371

    Dynomite1371 Well-Known Member

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    On the JK I did 5 wheel rotations at about 7k (same time as oil) Now I don't know what order they were done in, because I had the Service Department do it. On this JL I'm doing all my own maintenance! (I had a couple bad experiences with them and I don't trust them with this vehicle) So I'll have to do some research as to the tire order on rotations. Any advice?
     
  11. OP
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    FatBoy01

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    I never put the spare in the picture.


    For 4 wheel drive vehicle
    ooo.png
     
  12. JL_MX

    JL_MX Well-Known Member

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    I did the chalk test and kept dropping my tire pressure to 28psi. The tire wear seemed almost the same as with 36psi. I think the tire has more rounded corners(see blue lines in stock picture) and dropping the air even more would be incorrect. My picture is taken at 36psi but it's almost the same at 28pis. Should I keep going lower until I get contact on those red square areas?? (See stock picture)

    I drove the jeep at 28psi and felt it unstable/soft, maybe the tires are weak at 28psi?

    One more thing... Now I get the warning from the TPMS for low pressure. Is there a fix for that?

    Thanks

    STT Pro.png
    IMG_2772.jpeg
     
  13. rizej

    rizej Well-Known Member

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    To change the TPMS alarm limit you'll need to use something like an AEV programmer* (https://secure.aev-conversions.com/shop/procal-module). These aren't out yet for the JL Wrangler but they will be so keep an eye out.

    *The AEV programmer I linked to is for a JK and NOT a JL
     
  14. jericbarg

    jericbarg Well-Known Member

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    Chalk test will get you in the ballpark.

    A tread depth gauge used in 3 locations across the tread pattern will allow actual wear to be followed.
    You need to measure when tires are first installed(baseline measurement) to get correct readings as some tires do have a rounded(edge) treat pattern.
    Then just remeasure after 100 miles and follow/adjust from there.
    I've never had an issue using this methodology since 1979 when I begun racing, matter of fact my gauge is a Goodyear from the 60's. On the track I use a infra-red temp gun and my gauge after every run to make precise adjustements as those tires cost $1100+ each.

    The gauge will cost less than $5 and last forever.

    BTW- I was the only member of my Viper club to wear the tires evenly until the others discovered my "method" back in 2000, after teaching them they all enjoyed proper wearing tires.
    Being the youngest member back then no one wanted to listen, they are believers now.
     
  15. JL_MX

    JL_MX Well-Known Member

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    Thanks!
     
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