Chalk test

[Stonetree]

I just purchased a set of Mickey Thompson Baja Boss A/T 35X12.50R17, load range D. Any idea what a good tire pressure is for these? I was doing the chalk test. I drove around to heat up the tires. Started at 41 lbs warm and kept going down 2-3 psi at a time. When I got to 30 psi all around, I stopped because that seems pretty low. The cold pressure is going to be about 28 psi. Even at that low a pressure, there is still a half inch on the sides of the front tires where the chalk doesn't come off and an inch on the sides of the back that doesn't come off. Seems like going lower would be dangerous on the highway. I'm concerned about them being at 28 psi cold now. Any suggestions?

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[ScLeCo]

D tires have a stiff sidewall. You're fine at 28-29 cold. Could probably go down to 26ish and be just fine.

 

[Copperhorse73]

I have load range E and run 31 front 28 rear to get a proper contact patch. last Oil change they inflated them to 39 psi on all 4 corners and I was gettin like 18 mpg running very heavy 37s, but the contact patch was hideous

 

[Silver-Bolt]

I am running the same tire on my F150 Raptor. I found the happy place at 33psi. Confirmed with a chalk test. The Bronco is about 500lbs lighter so 31-32psi sounds about right. How do they feel on the Bronco? They are heavy tires so I have held off putting a set on the Bronco. I have about 10k miles on the Raptor set and they are a great all around tire. Good in the wet, snow, and dry off road. Haven't had them in any real mud.

 

[Stonetree]

Thanks for the input. I just didn't want to go down too far and not be safe at highway speeds.

The tires feel great on the Bronco. Any performance hit from the weight isn't really noticeable.
From my research, these tires appear to be the best A/T tires for both snow and mud. Living near Pittsburgh, that's what I was looking for, so we'll see.

 

[Ozbronco]

I'm concerned about them being at 28 psi cold now.

Curious if your TPMS has kicked a warning for low pressure. I was running 33psi in k02s based on chalking but in colder weather they dropped to 31 and I got a low pressure warning that wouldn't go off till I aired them up a few pounds. Oddly enough, all 4 showed 31psi but only one kicked a warning.

 

[Stonetree]

Curious if your TPMS has kicked a warning for low pressure. I was running 33psi in k02s based on chalking but in colder weather they dropped to 31 and I got a low pressure warning that wouldn't go off till I aired them up a few pounds. Oddly enough, all 4 showed 31psi but only one kicked a warning.

Yeah, It's throwing the error. I just did the chalk test yesterday, so I haven't driven any distance yet. I was hoping the error would go away after driving a few miles. I'm guessing that's not the case.

What's the minimum psi to avoid that error?

 

[Silver-Bolt]

Thanks for the input. I just didn't want to go down too far and not be safe at highway speeds.

The tires feel great on the Bronco. Any performance hit from the weight isn't really noticeable.
From my research, these tires appear to be the best A/T tires for both snow and mud. Living near Pittsburgh, that's what I was looking for, so we'll see.

I ran 600 miles non-stop mostly at of about 75mph at 33psi. Very stable and handling was good. A week later I ran that same route again. Going from lighter "C" tires to these has cost me about 1 mpg. That is the only negative I have encountered.

 

[Aonarch]

Obviously a little overinflation will help with MPG, so I wouldn't worry about getting a perfect contact patch.

I'd run 29 psi cold if I were you.

 

[jzweedyk]

New tires are stiff. After about 1,000 miles do the chalk test again. 30 sounds about right, although around town you could go lower.

 

[Stonetree]

Obviously a little overinflation will help with MPG, so I wouldn't worry about getting a perfect contact patch.

I'd run 29 psi cold if I were you.

Sounds good. I'm thinking 29 in the back and 31 in the front.

 

[Stonetree]

New tires are stiff. After about 1,000 miles do the chalk test again. 30 sounds about right, although around town you could go lower.

I'll have to check again at 1000 miles. Thanks.

 

[Snacktime]

I run 25-30psi for around town, 35-40psi for one long trip. Still wearing out the center faster than the side lol.

 

[kodiakisland]

I start with a load inflation table, since PSI is size and weight (vehicle, not tire rating) specific.
Adjust from there.
https://www.toyotires.com/media/pxcjubjs/application_of_load_inflation_tables_20200723.pdf

25psi in that tire size supports around 4700lbs of vehicle weight. How heavy are you?

 

[sn1088]

I just purchased a set of Mickey Thompson Baja Boss A/T 35X12.50R17, load range D. Any idea what a good tire pressure is for these? I was doing the chalk test. I drove around to heat up the tires. Started at 41 lbs warm and kept going down 2-3 psi at a time. When I got to 30 psi all around, I stopped because that seems pretty low. The cold pressure is going to be about 28 psi. Even at that low a pressure, there is still a half inch on the sides of the front tires where the chalk doesn't come off and an inch on the sides of the back that doesn't come off. Seems like going lower would be dangerous on the highway. I'm concerned about them being at 28 psi cold now. Any suggestions?

My MT Baja Boss AT's (37x12.5x17) sweet spot is 32/33. You're not going too low. I called and spoke with MT (very helpful btw) and they did calculations based on old tire load rating/size, vehicle weight, new tire size (37's), etc and said for me to "start" at 33 psi. Haven't chalk tested and won't as they are just right for my comfort level. Good luck.

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