Hope This Helps: Chalk Test for Tire Pressure

[cervelo15]

Let me start by saying in my confusion about which is the best tire pressure to run, I have this forum to thank for clueing me into the chalk test. I branched out and did some research, watched some YouTube videos and it seemed like the simplest test with such a big impact.

So I wanted to share my experience with doing the test this past weekend. I did this after warming the tires up after driving for a bit. Our house is on a hill and a curvy road to get out, so doing it right out side my front door wasn’t a great test because i couldn’t drive in a level, straight line. Colored each of the tires with chalk on a 6” cross section. Drove 100’ forward, then backed up on the same line making sure not to turn the wheel.

Front tires measured 40.6psi cold, went to 43 after driving
Rear tires measured 39.5psi cold, went to 42 after driving

Heres the results:
Front Tire - notice, the chalk was all worn away evenly; the red lines outline where the chalk was on the cross section


Rear tire - there was some chalk still left on the outside edge, but not much, I may still reduce the pressure even more in the rear. But overall, not bad.


But I’m gonna say, this was nowhere near the 36 psi that it called for on the door jamb sticker. When I had my previous Laramie, I ran 40 psi all around without any issues and the tires wore perfect.

Im hoping this helps someone out who’s looking for the right air pressure.

 

[ferraiolo1]

Thats because you're running a different type tire than what the door jam sticker was meant for. IDK why that was so hard to understand in the other thread.

Low 40s is a good pressure for those BFGs.

Nice work

 

[cervelo15]

Thats because you're running a different type tire than what the door jam sticker was meant for. IDK why that was so hard to understand in the other thread.

Low 40s is a good pressure for those BFGs.

Nice work

Thanks! I figured id give back some knowledge for the stuff I gleaned from this forum. Like Ron Burgundy says “it’s science”.

That other thread got out of hand and that guy wouldnt let up. But I can say experience is the best indicator and I’ve run 40 psi on multiple trucks and hadn’t one issue.

 

[HSKR R/T]

I usually run at least 5 psi lower in rear tires on a truck, when unloaded. Less weight in rear means you don't need as much air pressure.

I never did chalk test the factory Wildpeaks, but the door jam 36psi was too low for front tires. Way too much sidewalk bulge. I ran them around 40psu cold.

 

[Scram1500]

I have my Defenders (E rated) at 32 psi in the rear unloaded, 36 up front. 36 in the rear wasn't safe unless loaded. Tiny contact patch, zero tire buldge, lots of spin. They were also wearing in the center. Chalk test is a good tool, but also keep an eye on tire wear patterns

 

[dale661]

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

Use this to get the correct tire pressure.

 

[cervelo15]

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

Use this to get the correct tire pressure.

I did look at that link before and if I input my stock to aftermarket tire it lists the new PSI at 36, which is the same as the stock tire. Although this looks like a great tool, I’d only believe it’s a starting point. I believe in the look and feel and tangible elements with visible results instead of typing data into a computer.

So far, since I’ve kept this pressure, it rides comfortable and plush. It also rained yesterday, so I paid attention to the tread tracks when backing into the garage and it left a nice even pattern on the floor.

Don’t want to incite a battle, but I think this is a case by case basis to determine tire pressure.

 

[c3k]

Great stuff...and I agree.

Some off-roader streamers (brite life? The jeep guy and his wife), did a chalk test on a tire and didn't like it...and then the manufacturer contacted them and explained some stuff about the construction and purpose of that tire, and then the streamers loved it. Made some statement about the chalk test not always being right. FWIW. (Obviously, I've forgotten a lot of important details. )

 

[SurfRebel20]

My door jam reads 55 front and 45 rear. I usually run 45-50 front and 40 rear because I find the 35s to ride too stiff at factory psi recommendations

 

[cervelo15]

So a small update….had the day off today and figured, let’s re-do the test. This time, I pumped the tires up to about 46psi because there was some thought in the back of my head, am I running too low a psi? This could have just been my mind playing tricks on me, but I felt like the front tires were cupping a bit. I think there is a natural curvature to tires, theyre not entirely flat. I did this on a cold tire.

I ended up running 43.5 up front and 37.5 in the rear. At any given time, there’s ~6psi difference between the front and back. After driving around with the new pressures, I gotta say, it feels better. Not that it wasn’t comfortable before, but this feels much firmer and the truck seems to effortlessly float over bumps. It also seems peppier for some reason. I couldn’t quite figure out that last part, but if I dig back to my bike tire rolling resistance knowledge, the higher the PSI, the lower the rolling resistance. So maybe that has something to do with it. Plus, the tire bulge isn’t as concerning in the front anymore.

 

[HSKR R/T]

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

Use this to get the correct tire pressure.

That doesn't really work for all tires. The factory Wildpeaks can't be used as they don't have the correct load rating in the menus for rhem

 

[crazydive]

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

Use this to get the correct tire pressure.

@dale661, I just changed wheels & tires and used this tool to check what it will suggest. My old tires supposed to be 32 front and back cold, and this tool doesn't have 32. The lowest is 35. Anyway, with this settings It suggested the same pressure, however it gave me a warning.

OEM Size (LT275/55R20 E) Load Capacity: 1750 lbs. @ 35 psi.

New Size (LT275/70R18 E) Load Capacity: 2070 lbs. @ 35 psi.
**The capacity is much higher, however this size is not recommended to be used below 35 psi.

Chalk test on 38 warm is nice and even. It takes me to 32 cold. BFG KO2's A/T. Not sure if this is good pressure, and I don't have enough experience to judge correctly if this is too much bulging


Additionally, I found this...

Ok BFG emailed me back, ON A SUNDAY. Unreal. Great service. Here is the official answer.

"Assuming your OEM tire size was 275/65R18, with recommended tire pressure at 35psi; our new recommended tire pressure for LT275/70R18 would be 50psi for both front and rear tires."

275/70/18 BFG KO2 pressure? - Ford F150 Forum - Community of Ford Truck Fans

2015 - 2020 Ford F150 - 275/70/18 BFG KO2 pressure? - Hey guys. What pressure have you found best for these or any E rated 10 ply tire of this size? Thanks.

www.f150forum.com

it's from Ford forum, different tire change, however very similar settings so I'm extremely confused now

 

[HSKR R/T]

Havent chalk tested, but just watching dirt/dust on tire pulling into my garage(similar to chalk test I guess) I have settled on 40psi front, 37psi rear cold. Goes to 43/40 when warm. That's with 275/65/20 Kenda Klever M/Ts. When I tried using that calculator, it didn't have an option for the stock Fallen Wildpeaks load rating or pressure.

 

[cervelo15]

@dale661, I just changed wheels & tires and used this tool to check what it will suggest. My old tires supposed to be 32 front and back cold, and this tool doesn't have 32. The lowest is 35. Anyway, with this settings It suggested the same pressure, however it gave me a warning.


Chalk test on 38 warm is nice and even. It takes me to 32 cold. BFG KO2's A/T. Not sure if this is good pressure, and I don't have enough experience to judge correctly if this is too much bulging View attachment 126245


Additionally, I found this...


it's from Ford forum, different tire change, however very similar settings so I'm extremely confused now

I thought the same when I first was going thru this, I had a little more bulge in the front. Yours looks similar to what I had before I bumped up the pressure. But remember, our trucks are on the heavy side and most of that weight is up front. So you should run a higher pressure up front and a lower pressure in rear (unless you’re hauling or towing). I’ve run 43.5 up front and 38.5 in the rear for maybe almost 4k miles. Even wear, no cupping or uneven edges. It’s pillow soft ride too.

I can take a side shot pic tomorrow of what the front tires look like.

 

[crazydive]

Is there any difference with the air suspension? I understand simple logic of front heavier (engine, cabin) and lighter back (empty), however I'm asking because my sticker for OEM shows 32 front and back cold.

 

[cervelo15]

Is there any difference with the air suspension? I understand simple logic of front heavier (engine, cabin) and lighter back (empty), however I'm asking because my sticker for OEM shows 32 front and back cold.

Not sure about air suspension, since I don’t have that. Heres a pic of the bulge from my front tire. This is at 43.5psi and it’s a little more taut than your original picture.

 

[HSKR R/T]

Not sure about air suspension, since I don’t have that. Heres a pic of the bulge from my front tire. This is at 43.5psi and it’s a little more taut than your original picture.

View attachment 126308

Never judge a tires proper inflation by the sidewall bulge. Different tires have different thickness sidewalls. Some will bulge more than others, even at proper air pressure.

 

[Bt10]

That F150 guy was happy that BFG got back to him on a Sunday? This advice is so wrong, even the auto return email receptionist wouldn't say this!

50 psi on a halfton?
50 front and rear on an unloaded halfton?
35 psi on the OEM "P" tire equates to a needed 50 on an "LT" tire?

 

[LaxDfns15]

View attachment 126311

That F150 guy was happy that BFG got back to him on a Sunday? This advice is so wrong, even the auto return email receptionist wouldn't say this!

50 psi on a halfton?
50 front and rear on an unloaded halfton?
35 psi on the OEM "P" tire equates to a needed 50 on an "LT" tire?

OEM pressures on a Rebel are 55/45. I run 52/42 with 5k rotations, and there is still plenty of tread on my Duratracs after 30k miles. As multiple people have said repeatedly, not every tire is the same. Not every truck is the same. What works for an F-150 won't work quite the same for a Ram.

 

[Rlaf75]

I've run 40 psi in every vehicle I have ever owned and I've never had a problem. The tires always wore great with proper rotation and alignment