The Dirt (Episode 1): New Tires = New Tire Pressure

Discussion in 'Renegade Write-Ups' started by LimitlessEAD, Mar 29, 2017.

  1. LimitlessEAD

    LimitlessEAD Member

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    • The day has come and you have finally pulled the trigger. You are off to get new tires on the Renegade. Now what?

      Everyone wants their tires to last as long as they can, right? Well, the first step is to start off with the right tire pressure. Sounds pretty simple, but there is a bit of science to it. Read on and we will dive into the how to's....

      Tires used in the instructions:
      OEM Tire: Continential CrossContact LX Sport - 215/65r16 98H SL (Standard Load)
      New Tire: Falken Wildpeak AT3 - 235/70r16 109T XL (Extra Load)
      • Step 1: Figure out what your factory tires Load Index Rating is, and the recommend Tire Pressure (PSI).

        Locate the Load Index Number on your tire:
        [​IMG]

        Locate the Recommended Tire PSI in the drivers side door placard:
        [​IMG]

      • Step 2: Find the Load Carrying Capacity for your OEM Tires in the correct load chart (bottom of post) using the Load Index and PSI you have located.

        [​IMG]

      • Step 3: Take note of the Load Carrying Capacity you just found.

      • Step 4: On the correct load chart find the Load Index of your new tire and travel over to the closest Load Carrying Capacity (Round up), travel straight up the chart to find the PSI for your new tires!

        [​IMG]

      Tires Pressure Changes For the Example ONLY:
      OEM Tire: 35 PSI
      New Tire: 28PSI


      This should give you a great starting point to fine tune the tire pressure that works best for your driving needs.

      FAQs:

      Q: If I don't change my tire pressure what will happen?

      A: The tire wear will be uneven, performance/traction will suffer, and it will shorten the life of the tires you just paid for! Too High, and you will wear out the center of the tread faster, could reduce the contact patch and traction. Too Low, and you will wear out the sides of the tire faster and lose those precious MPGs.

      Q: If I lower the tire pressure will my tpms light go on?

      A: Yes, eventually. The options to change the default tire pressures in the car is limited. I was able to get the dealer to lower it from 35PSI to 32PSI. Those were the only two options at the time Fall of 2016.

      Q: What if I need to run lower then 32 PSI?

      A: There is a margin of error built in, so for example, 28 PSI will not trigger the warning when the default is set to 32. It will trigger the error light when lower then 26 PSI. For those set to a 35PSI default it would reason to believe the error will trigger at 28 PSI or lower.

      Q: Why can't I get the light to turn off, I'm higher then the margin of error? (EX: Currently at 30 PSI with Error)
      A: To reset the low tire pressure warning light without a scan tool you will need to fill all the tires at or above the recommended PSI that the cars computer is set to and go take a drive. In a few minutes it will clear. Once clear you can go back to the PSI you wanted as long as it does not drop below the margin of error level. This wasn't an issue at 28 PSI until the cold winter air rolled in and the tire pressures dropped. Just add some air and do the above.

      Q: I Just got new tires that are a different size do I need Alignment?
      A: No, you shouldn't need an alignment, unless it was bad beforehand. The suspension geometry has not changed, the whole car moved up from below the axle. Same as driving higher up a mountain, you are just higher then when you started!

      Q: Why do my tires tilt in, or why do they tilt in more now?

      A: They don't, the camber angle didn't change, remember no suspension geometry changes happened in the tire install, this include the camber angle of the hubs mounting surface. That is not to say the current camber angle is not "more exaggerated or noticeable" based on the tire, wheel and or spacers fitted at that time.

      Q: What is the Letter next to the Load Index rating number on my tire?
      A: This is the Speed Rating, and not related to this post, jeeps are not sports cars and this likely would not be a deciding factor for tire on a Renegade.

      Make sure to use the correct chart for Standard or Extra Load Tires. If you are unsure, check the manufacturers site, or online tire stores, they often have this listed

      [​IMG]

      [​IMG]

      There goes a few hours.... Look Forward to Episode 2......
     
    Last edited: Apr 14, 2017
    Webspells, ppholton, Rednewt and 4 others like this.
  2. robinsonmac

    robinsonmac Member

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    Awesome write up. This should definitely be a sticky in the tires and wheels sub forum. A must read for everyone getting tires larger than the oem. Thank you, looking forward to part 2.

    Sent from my SM-G930V using Tapatalk
     
  3. LimitlessEAD

    LimitlessEAD Member

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    Yeah, I was tossed up on where to put these as they will cover different topics. Do I spread them out into their perspective areas or keep them all in the Write-Ups????? I am open to suggestions...

    Maybe I can keep Episode 0 with all then links to each new episode Sticky In the Write-Ups,

    Then Post each in the correct forum sticky if requested?

    @ Mods, Should we move this to the Wheels & Tires?
     
    Last edited by a moderator: Apr 15, 2017
  4. robinsonmac

    robinsonmac Member

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    Just did the calcs, Holy cow! I should be running at 29 PSI w/ a 103SL load index. That just seems way too low, but I'll reduce it to 30 in the morning and give it a go for my 27 mile morning commute. Right now they are @ 38 w/ digital gauge & 35 on the TPMS. The tire shop had them at 40 cold, they went up to 42 at operating temp.
     
  5. LimitlessEAD

    LimitlessEAD Member

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    So I wonder if your car or your gauge is right? LOL. Someone is not telling the truth here. Yeah this should be a good starting point, you can obviously go up or down based on what works best for you. You can also do the chalk/paint test to see how the tires run at the pressure set. Maybe that will be the next write up....
     
    Last edited: Apr 14, 2017
  6. robinsonmac

    robinsonmac Member

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    I'll do the chalk test with them at 29 PSI & adjust from there. 103sl for these tires has an exact load index match @ 29 PSI. I'm going to buy a better guage as well. The one I have is a $6 Slime Wallyworld special. Great write up!
     
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  7. LimitlessEAD

    LimitlessEAD Member

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    My car and ARB gauge is only off 1 psi, or its how i read it. I would trust the car.
     
  8. robinsonmac

    robinsonmac Member

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    I wonder with the exaggerated camber if running them a little higher might help offset it & reduce the inside of the tire bias. I would think running them too low would exaggerate the inside bias & wear more or would it be the opposite?
     
  9. LimitlessEAD

    LimitlessEAD Member

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    My guess is the higher the pressure the more it would force the tire to wear the inside edge as it can not deform to the angle of the road as well. Think of it as a solid plastic wheel vs a foam wheel and what would touch.
     
    Last edited: Apr 14, 2017
  10. robinsonmac

    robinsonmac Member

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    Ahh, that makes sense.

    Sent from my SM-G930V using Tapatalk
     
  11. 17RLA4x4

    17RLA4x4 New Member

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    Cannot view any of the images in the first post, always get a error- do not have permission to view.

    Is there anyway you can repost or PM to me as I just ordered a set of Atturo XT Trailblade in 260/60r18 for my Renegade and would love to set them up correctly from the start.
     
  12. robinsonmac

    robinsonmac Member

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  13. red/green hawk

    red/green hawk Active Member

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    So original tires were Wrangler SR-A 215/65/17. Load index 98, SL, psi 35. I now have KO2s 225/65/17. Load index 107, D. According to the chart I should inflate the KO2s to 40-45 psi. Does this sound right?
     
  14. robinsonmac

    robinsonmac Member

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    No it should be the opposite, lower than stock. You need to find the weight for 98 @ 35 psi. Then find the psi for that weight or close to for 107. It's going to be low like 30.
     
    Last edited: Oct 31, 2017
  15. red/green hawk

    red/green hawk Active Member

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    Its low on standard low chart but when cross referenced with D chart it says 40-45, I'm confused.
     
  16. robinsonmac

    robinsonmac Member

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    Ah, forgot they are D. I would start with 40 psi & do a chalk test.
     
  17. ShinySideUpAZ

    ShinySideUpAZ New Member

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    I am running the same tire and I calculated 48 psi at maximum load. I started there, and did chalk tests up to 65. This is an 8ply tire It's got a lot of rubber to support it. Chalk test where still good at 65 PSI. The maximum HOT temp for this tire under load is 90 psi. I ended up setting mine at 55 psi with an ambient temp @ 60F. Right now in the afternoon after work when it's in the mid 90s. the drive starts with them at 57 psi and after 20 minutes highway driving I'm at 60 psi to 61 psi. Your tires should never heat up more than 4 degrees if the ambient is above 50F. I pulled my wheels off yesterday to do a break inspection and with 7,000 miles on the tires I can barely notice any wear.

    You find people who complain that the K02s have terrible tread life on the renegade I will guarantee they are running them at 30 to 35 PSI and are over temping the tire.
     
  18. robinsonmac

    robinsonmac Member

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    I called BFG when I got my LRC KO2's and they said I should run them @ no less than 40 psi & no more than 45 psi for the Renegade Trailhawk. I am currently running them at 41 psi, which gives me a perfect contact patch with even tread wear & only 2 degrees temp change on the highway even in 80 degree weather. The hard thing about Colorado is the temp swings from the high & low of the day. This morning it was 53 on my way to work, the high for today is going to be 77. Cold psi this morning was 38, when I leave work it will be 41. If I add air so the morning psi is 41, the afternoon the cold psi will be between 43-47 @ that psi I don't have an even contact patch and uneven wear.
     
  19. red/green hawk

    red/green hawk Active Member

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    Running at 42 and at 1st rotation I have even tread life all the way around. Tread depth still at factory specs. When its cold I was running 45. On some trails I ran them at about 30 in front and 25 in the back.
     

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