Chalk method for tire pressure?

[mjmarinara]

Hi y’all
Got new BFGs and don’t want them wearing out quick, I’ve heard and read some conflicting views on whether or not the chalk method is actually a viable way to find what you need to run. Thoughts opinions?

I’m running 33x12.5 15 ATs k10 about 30 psi so far. Mostly Road unless mud or snow permits but ain’t looking for trouble.

Haven’t actually done chalk yet but I live on a dirt road and when I hit the pavement the fronts clean off evenly but the backs clearly are just hitting the center, 40 miles later the first 2 inches from the inside and outside are still covered in dirt.

[yuccales]

How about find a nice dry garage floor or ?, get a spray bottle and wet the tires then roll forward and check your "fingerprint".

[chevmn]

What pressure are you running? I often run a lower pressure on the rear than front due to less weight on rear. Especially if you are running a higher load rated tire, and larger tire (I run "P" or passenger rated tires for the most part since I rarely carry much if any load. My guess is you are running a load C or D tire, with more pressure than you need. Many years ago I always had a discussion with my dad.....he insisted on running the "maximum" inflation pressures on his tires, and very often he ran a load range d tire with pressures up toward 60 or 80 psi! You can imagine how an empty pickup rode. I know some disagree with running P rated tires on pickups, but I have never had an issue, and watch pressures, and adjust accordingly if I plan on carrying much load. And the larger the tire, I have found they need less pressure to carry that same load due to larger footprint. I always like some flex to ride better.

[geezer#99]

Do the chalk test but apply it when you get on dry pavement.

[jimijam00]

and when up to operating temp. setting pressure on cold tires is no good.

[Stocker]

Chalk test gives you a good starting point but doesn't take into account variables such as cornering or even the type of surface you drive on. Tread depth gauges are cheap and while it takes quite a few miles to start to notice a wear pattern, over time you can tell if your tires are over-inflated, under-inflated, or just about right. Takes only a moment to check a few areas across the face of the tread. At a minimum, check every time you rotate the tires.

[mjmarinara]

C load all terrains 30 psi.

I've run real high pressure in sedans, thats what state troopers around here typically do, 40+ for cornering on a 16" wheel not comfort, dont know if theyre concerned with tire wear but I am! Definitely never set initial pressure hot, only adjusted dropping pressure on a hot day on an autocross circuit.

I'll do a chalk test in a few days, for now heres pic of front and rear when i got home yesterday on the dirt, even here its the opposite, the centers of the rear have more dirt than the outside! probably drop it in the rear and keep the front, thread gauge when rotate is a good idea. the back looks a bit ballooned

[geezer#99]

Rims don’t look wide enough.
How wide are they?

[chevmn]

I have to agree with geezer, those look to be around 7-8 inch wide rim, and with a 12.5 tire you should have a 10 wide rim. The narrow rim pulls the outer portion of the tire in, which is explains why only the center is making contact with road. I'd go with a 10 inch rim, and drop the pressure (just my preference and I have ran down as low as 10 psi on the rear with larger tires).

[Myself]

Originally Posted by geezer#99

Rims don’t look wide enough.
How wide are they?

Rims definately are too narrow. I do the chalk test on ALL my vehicles, so does my son. We are seeing 10k miles more out of a set of tires. SUVs and trucks typically need to run less rear pressure than front because of the weight bias of the vehicle. My wife's F150 crew cab FX4 has 34x12.50x17 AT4 (rugged terrain) tires. We run 30psi in the front and 26psi in the rear. My Nissan Xterra has 245/75-16 Falken Wildpeak AT3 tires on it. Running 31 in the front and 27 in the rear. Here are those tires with 49k on them right now, rotated about every 7500 miles.

[Stocker]

I agree with the above, that size tire really should be mounted on 10" wide wheels. I know that people have run them on 8" wheels and are perfectly satisfied..... but that doesn't make it right.
8" wheels might be worth considering if you ran mostly off-road at very low pressures.

[mjmarinara]

12.5 on 8" is better for off road when airing down and the wheels and tires are already on so theyre not coming off for a good while.

But yes I do agree for on road stability and best tread life 10" wheel could be better. going to be going good bit lower psi in the rear will post pics when I do chalk test. thanks all good feedback

[geezer#99]

Are they 8 inches wide?
Look more like 7’s.
How did you measure them?

[geezer#99]

And instead of chalk, try this stuff.
Works better for long time testing.


https://www.walmart.ca/en/ip/bic-wit.../6000016943967

[special-K]

Chalk, dust, wetted are all ways to read tire contact on pavement. All give the same result. I never knew about using chalk but water or dust have always been available.

Unless hauling a significant load, I run less pressure in the rear than front due to the rear being much lighter, at least 5# less. A 12.50 mounted on an 8" wheel is an acceptable combination, minimal width. That isn't an 8" wheel in the picture you showed, narrower by an inch or more. Too narrow makes the tire tread "crown" no matter how low pressure you use. The beads are "pinched" resulting in the crowned tread surface. just run the lowest pressure you can or get wider wheels, if you want to get full mileage out of your tires.

[mjmarinara]

did the test, at 30 30 it was no good, front was halfway alright rears terrible i imagine. this is 28 27ish rear, maybe 500 yards straight line, went around town little bit chalk disappeared but roll was too gushy

thoughts?

[jimijam00]

overinflated. this will blow your mind....

...put enough weight in the rear, and the chalk on the edges will also disappear. and as you've figured out, tire pressure to ensure full contact patch on the ground and even wear (assuming alignment is dead nuts on) is not the same as ride quality. cruddy tires with taller and/or softer sidewall ride softer at proper inflation than they do overinflated.

[Stocker]

At least part of the problem has more to do with rims that are too narrow for those tires, as noted in posts above. You can't fix that with air pressure adjustments.

[mjmarinara]

yes, i am going to get wider wheels.

i love the look of original white steelie and the correct hubcaps, but since they seem to be made of unobtainium i think im going to settle for grey rallys, no rings maybe the "disc brake" style center caps, maybe not

i know its been asked to death on the internet but opinions of pros and cons of 15x8 vs 15x10 for pavement?

[Stocker]

For pros & cons, I pay attention to experts.

Tire Rack says 8.5"-11" and uses a 10" rim for their tire measurements on a 33/12.50-15 tire. That tire has a 10.3" tread width and 12.5" section width.

I would absolutely use a 10" wide wheel (measured inside bead-to-bead). You will likely get other opinions, but that's mine.

https://www.tirerack.com/tires/tires...omCompare1=yes

Click that link, then click on Specs

[hjewell2]

Originally Posted by chevmn

what pressure are you running? I often run a lower pressure on the rear than front due to less weight on rear. Especially if you are running a higher load rated tire, and larger tire (i run "p" or passenger rated tires for the most part since i rarely carry much if any load. My guess is you are running a load c or d tire, with more pressure than you need. Many years ago i always had a discussion with my dad.....he insisted on running the "maximum" inflation pressures on his tires, and very often he ran a load range d tire with pressures up toward 60 or 80 psi! You can imagine how an empty pickup rode. I know some disagree with running p rated tires on pickups, but i have never had an issue, and watch pressures, and adjust accordingly if i plan on carrying much load. And the larger the tire, i have found they need less pressure to carry that same load due to larger footprint. I always like some flex to ride better.

exactly

[mjmarinara]

Hello all,
I purchased Jegs vette style rally wheels, 15x10 4.25 bs, Not into what I think is going to look like a remote control car! pretty cool but not for me!

As much as I would enjoy better road turning characteristics, I do not what the tires sticking so far out of the fender well. Will 15x8s even provide a noticeable befit of both sidewall flex AND more even tread wear over the 15x7s compared to the 15x10s? Or is this just the nature of the beast with the 33x12.5 tires I got?

Thank you all very much for your experience!

pictured below, my truck currently with the 15x7s, i like this look but the tires are badly ballooned.

next looking at the 15x10s with 4.25 bs bolted up from the front.

then the yellow truck a picture of what I believe are 15x10s with similar back spacing and i do not want that look.

next the blue truck is a look i like, 15x8 truck rallys i believe bs to be 4.25, the same as the ones i bought.



We agree the blue truck has 15x8s? that will provide better turning with thread ware than the 15x7s?
I guess with extra 2in is clearly straight out of the fender!!

all tires pictures are bf at 33x12.5

any input is appreciated, I plan to return these wheels soon and get something more appropriate

[chevmn]

My bet is that the blue truck has 10.5 inch tires or close, and the wheels are 15x8. A 12.5 tire needs a 10 inch wide rim. Yes, they will fit a 8 inch rim, but not well. Many years ago I had 8 inch wide wheels, and purchased a set of 12 inch wide tires. I ended up buying different tires, and never went back to a wider tire. Of course my truck was not lifted, so I had fitment issues in front as well.

[mjmarinara]

Does anybody have pictures of stock height truck with 15x10s around 4" backspacing? thanks

[tdangle]

After reading this thread, I adjusted the tire pressure on my C20. I have 265/75/16 load range E tires on it and per the tire shop empty they recommended 40 front and 45 back. I lowered the rear to 40 and am amazed at the difference in the ride. For example tar strips in the road I feel with the front but not the back now. If I haul anything with any weight or tow it's a simple thing to air the rears up.