Chalk test
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JK Enthusiast
Joined: Jan 2013
Posts: 257
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From: Carmel
Chalk test
I searched the forum and can tell that this has been beat to death for finding the right PSI to run your tires at. How exactly do you do a chalk test or what is the exact name of the write up that shows you this. This forum is huge and seems like I can't find just a simple answer on how to do the "Chalk Test". Thanks.
JK Super Freak
Joined: Nov 2011
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From: morgantown wv
JK Newbie
Joined: Nov 2011
Posts: 39
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From: Charlottetown, PE
I don't agree with starting your tires off at max PSI.
Use the math trick and then verify with the chalk test.
I'm picking up a set of 35x12.5R17 mud grapplers for my 2012 JKU so I've just gone through this method myself.
Example:
- Maximum load for 35x12.5R17 Mud Grapplers is 3640 lbs @ 65 PSI
- Add up the max load for all 4 tires: 3640 x 4 = 14560
- Find the curb weight of your Jeep (curb weight includes fuel, all liquids). Mine is a 2012 Sahara Unlimited = 4269 lbs.
- Add the typical passenger weight plus any modifications that would change the vehicle weight (bumpers, winch, etc...) For me typical passenger weight total would be 300 lbs.
- Add this to your curb weight. 4269 + 300 = 4569 lbs.
- Math: (loaded vehicle weight / max load for all 4 tires x max PSI of tires) 4569 lbs / 14,560 lbs x 65 PSI = 20 PSI.
I'll probably bump up the 20 PSI a bit for a little more responsiveness/gas mileage for daily driving so I'll probably run them at around 22 PSI
It's possible that you just cannot get the wear on the chalk test to be perfect. If you can't get it perfect it's better to be slightly over inflated than any under inflated.
Use the math trick and then verify with the chalk test.
I'm picking up a set of 35x12.5R17 mud grapplers for my 2012 JKU so I've just gone through this method myself.
Example:
- Maximum load for 35x12.5R17 Mud Grapplers is 3640 lbs @ 65 PSI
- Add up the max load for all 4 tires: 3640 x 4 = 14560
- Find the curb weight of your Jeep (curb weight includes fuel, all liquids). Mine is a 2012 Sahara Unlimited = 4269 lbs.
- Add the typical passenger weight plus any modifications that would change the vehicle weight (bumpers, winch, etc...) For me typical passenger weight total would be 300 lbs.
- Add this to your curb weight. 4269 + 300 = 4569 lbs.
- Math: (loaded vehicle weight / max load for all 4 tires x max PSI of tires) 4569 lbs / 14,560 lbs x 65 PSI = 20 PSI.
I'll probably bump up the 20 PSI a bit for a little more responsiveness/gas mileage for daily driving so I'll probably run them at around 22 PSI
It's possible that you just cannot get the wear on the chalk test to be perfect. If you can't get it perfect it's better to be slightly over inflated than any under inflated.
Last edited by darkscion0; Feb 27, 2013 at 03:21 PM.