Thursday, July 28, 2016

chalk test


Now that I have bigger tires I am just not sure what PSI to run. Over inflation or under inflation will cause your tires to wear unevenly. How does one tell if their tires are properly inflated?

My friend, and fellow Jeeper CPO, suggested the chalk test. However I am not sure I did it right?



Here's what I used.



Chalk
Tire Gauge
My Jeep 







First, I checked the tire pressure of all 4 of my tires. Three of them read 31 PSI and the rear driver was 29 PSI. 









Next, I chalked up a thick line across the width of my tires.






After all four tires were chalked I drove back and forth on my driveway. It is very flat since we just got it repaved. There were no cracks, bumps or pot holes. 

Then I inspected the chalk on the ground and on the tire. Check out my before and after shots of all four tires.


BEFORE

AFTER


I read an over-inflated tire will bulge, and only the center of the line will touch the ground.  If you're tire is under-inflated, you'll see only the sides of the lines since the middle of the tire is not making contact with the ground.

The chalk tire imprints on my driveway looked pretty even to me. However the chalk left on my tires puzzles me. Should I air down a little? Am I too high of a PSI? There seems to be too much chalk left on the edges of the tires. 



But where is the end of my tread. Check out this picture. Some of the treads are longer than the others. Where is the true end of my tire?



Another puzzle is what is my true PSI. My Jeep's internal reader which shows on my dash is 2 to 3 PSI higher than my digital reader.

I understand there is some debate on whether this is an accurate way to gauge proper PSI. There are a lot of variables to consider and it depends on the width of your wheels. 

My tires are 35 in Duratracs LT 315/70R/121/1180.
Did I do the chalk test right? What PSI do you run when you are daily driving? What size tires do you have?