Air pressure with 37s?

[zouch]

37" KM3s here, on a mildly built/armored diesel.

i find that if i don't want to see my Hot pressure climbing more than ~10% (indicating undue sidewall flex generating heat) they need to be in the 33-35PSI range cold, and that's been working well for me. not seeing any significant wear in the center vs the edges (but it's really hard to tell when we factor in the wear from off-pavement use with pressures in the sub-teens).

granted, the KM3s have an unusually narrow tread face making for a narrower contact patch which means they're already further over on the casing in a turn, but i hate the mushiness of an underinflated tire, especially in anything like an Emergency braking/avoidance maneuver.

i find talk of the "Chalk Test" interesting; unless people are going out and throwing their J**ps around at speed to simulate actual driving conditions, chalking tires isn't going to tell you anything especially useful; i think it's leading to a lot of underinflated tires.
for perspective; in Autocrossing, we would do a similar test (using white shoe polish, usually) to see how far *above* rated pressures we needed to inflate to keep tires off of the sidewalls.

Just curious what others are running for air pressure on road with 37s.


I did the chalk method and I'm down to 26 pounds front and rear. This is my first time doing the pressure this way, so curious what others are running.
My tires are
General Grabber X3 37/12.50R17 on method 105 beadlocks.

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[WannFly]

I have been running 26 cold, sometimes it climbs to 30-31 after extended driving on highway. May be I need more air, anything more than 26 cold, I find the ride not that great. I will start rotating at every oil change (4k miles) or 6 months whichever is earlier.

 

[BDinTX]

@zouch interesting... I've wondered the same about the chalk test. Are your KM3 C rated and do you think that make much difference?

 

[Terrymo]

37" KM3s here, on a mildly built/armored diesel.

i find that if i don't want to see my Hot pressure climbing more than ~10% (indicating undue sidewall flex generating heat) they need to be in the 33-35PSI range cold, and that's been working well for me. not seeing any significant wear in the center vs the edges (but it's really hard to tell when we factor in the wear from off-pavement use with pressures in the sub-teens).

granted, the KM3s have an unusually narrow tread face making for a narrower contact patch which means they're already further over on the casing in a turn, but i hate the mushiness of an underinflated tire, especially in anything like an Emergency braking/avoidance maneuver.

i find talk of the "Chalk Test" interesting; unless people are going out and throwing their J**ps around at speed to simulate actual driving conditions, chalking tires isn't going to tell you anything especially useful; i think it's leading to a lot of underinflated tires.
for perspective; in Autocrossing, we would do a similar test (using white shoe polish, usually) to see how far *above* rated pressures we needed to inflate to keep tires off of the sidewalls.

If you start out at a high pressure and test repeatedly as you slowly work your way down in air pressure you can get to a point that shows even contact. That’s a good enough starting point for me since I don’t throw my Jeep around.

White shoes went out of style with Pat Boone if I’m not mistaken.

 

[roaniecowpony]

I find that whatever "tests" I do at the measured pressure, to get those results, I need to run the tires at that pressure when warmed up to operating temperature. So, the cold pressure is just a reference point so you can air up when they are cold. Nothing more. Operating temperature and pressure are what matter to me.

I like the handling at 30 psi on my 37s. So, my cold pressure is a few psi below that. If I'm in the mountains when I air up after a trail, I know I'm traveling home to sea level where the air pressure is a few psi higher and therefore I need to inflate a few psi higher before leaving the mountains. Rough numbers I use are 0.5 psi/1000ft.

 

[zouch]

not really looking for "even contact"; tires are crowned for a reason.
what i might be looking for is even wear. what i don't want is. pressures so low that there's so much sidewall flex generating heat that it damages the tires in regular use. i might need those sidewalls for something more fun/interesting.

and whether or not i do it for fun (i don't), i absolutely do want to be able to throw it around in case the need arises. people are stupid on the roads we share; odds are i haven't seen my last opportunity to dodge someone doing something stupid, or suffering the consequences of doing the same.

If you start out at a high pressure and test repeatedly as you slowly work your way down in air pressure you can get to a point that shows even contact. That’s a good enough starting point for me since I don’t throw my Jeep around.

White shoes went out of style with Pat Boone if I’m not mistaken.

 

[roaniecowpony]

not really looking for "even contact"; tires are crowned for a reason.
what i might be looking for is even wear. what i don't want is. pressures so low that there's so much sidewall flex generating heat that it damages the tires in regular use. i might need those sidewalls for something more fun/interesting.

and whether or not i do it for fun (i don't), i absolutely do want to be able to throw it around in case the need arises. people are stupid on the roads we share; odds are i haven't seen my last opportunity to dodge someone doing something stupid, or suffering the consequences of doing the same.

Emergency maneuvering is more important than tire wear or whatever the chalk test is trying to do. I've actually made an evasive maneuver at 70 mph with my lifted 4 door on 37x12.5R17 tires on 8.5" wide wheels, at 30 psi. It works.

 

[Camaroboi13]

38psi cold, 41-42psi hot. It works for me, it doesn’t work for you.

 

[Terrymo]

Emergency maneuvering is more important than tire wear or whatever the chalk test is trying to do. I've actually made an evasive maneuver at 70 mph with my lifted 4 door on 37x12.5R17 tires on 8.5" wide wheels, at 30 psi. It works.

Things things go 70?

 

[roaniecowpony]

Things things go 70?

Downhill with a 50 mph tailwind.

 

[zouch]

no idea what that particular maneuver was like; no doubt sometimes we get lucky.

i like to try to keep odds stacked more in my favor.

Emergency maneuvering is more important than tire wear or whatever the chalk test is trying to do. I've actually made an evasive maneuver at 70 mph with my lifted 4 door on 37x12.5R17 tires on 8.5" wide wheels, at 30 psi. It works.

 

[roaniecowpony]

no idea what that particular maneuver was like; no doubt sometimes we get lucky.

i like to try to keep odds stacked more in my favor.

No doubt 40 or 50 psi will have a more stable tread. It's all a compromise.

 

[Jtphoto]

not really looking for "even contact"; tires are crowned for a reason.
what i might be looking for is even wear. what i don't want is. pressures so low that there's so much sidewall flex generating heat that it damages the tires in regular use. i might need those sidewalls for something more fun/interesting.

Not all tires are crowned. Haida tires are crowned as well as Patagonia, which is indicated on the tread by orange and blue inflation (contact patch) stripes on the tread. So the chalk test should be done to pattern to those stripes rather than full tread.
All my tires other than Haida 869 have been full contact patch tires, hence chalk test has been done to that.
My full tread chalk tests provide me a warm tire pressure of 27psi at most. I rotate every 5000klm and measure tread for wear every rotation.
If you were to follow tire inflation formulas that take into account vehicle weight and tire max weight capacity etc. you would see inflation numbers for 37s in the neighborhood of 22psi cold.
Following photo of Haida 869 with blue and orange contact stripes.

 

[Jtphoto]

It is to be noted that the bigger the tire, the greater the air volume, the lower the tire pressure.

 

[roaniecowpony]

Not all tires are crowned. Haida tires are crowned as well as Patagonia, which is indicated on the tread by orange and blue inflation (contact patch) stripes on the tread. So the chalk test should be done to pattern to those stripes rather than full tread.
All my tires other than Haida 869 have been full contact patch tires, hence chalk test has been done to that.
My full tread chalk tests provide me a warm tire pressure of 27psi at most. I rotate every 5000klm and measure tread for wear every rotation.
If you were to follow tire inflation formulas that take into account vehicle weight and tire max weight capacity etc. you would see inflation numbers for 37s in the neighborhood of 22psi cold.
Following photo of Haida 869 with blue and orange contact stripes.

22 psi would be fine if you never had to steer abruptly or corner hard. Tread stability already sucks on a 37" tire on a 17" wheel. But low pressures make it worse. Compromises, lots of compromises.

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