Question about Tire Pressure

[Rob Binsky]

I purchased a 2019 Ranger XLT Sport off the lot a few weeks ago, with some extra bells and whistles that had already been installed at the dealer. Included were:
62180 Level Kit (ProComp 2.25”);
9007-1013373 tires (Hankook 275/55R20 113T, 20” rim); and
HC32-1A189-A tire pressure monitoring system.

I questioned them as to what my tire pressure should be, and my salesman said “what’s on the door.” I don’t think that’s right. What’s on the door seems to be for 17” tires, i.e., OEM tires, and I don’t think that’s what I’ve got.

Be gentle with me because this is all new to me.
1. I have 20” tires, right?
2. How do I find out what my pressures should be, and how do I get a door sticker that’s accurate?
3. Is my leveling kit 2.25”?
4. How do I read my TPMS? Is it accessed on the dashboard with the steering wheel controls?

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[jsphlynch]

For determining tire pressure, I believe you will find this document (pdf warning) useful. Your intuition is correct that the tire pressure on the door sticker no longer precisely applies, but the difference will be pretty minimal. Look us your specific tires in the table in the link I provided, but I'm guessing that optimally you will want to decrease pressure by a couple PSI relative to the door sticker recommendation.

 

[Rinn69]

Or use the simple chalk test. Flat road (side to side flat--little or no crown to it), some chalk (kids "sidewalk" chalk works great), tire pressure gauge. On a straight stretch of flat road, draw a line about an inch wide, across the tread, get in the truck and drive it straight ~100 ft. Stop, get out and look at the chalk line. If it is gone in the middle, but still on the outer edges, the pressure is too high. If it is gone on the outer edges, but still present in the middle, the pressure is too low. Once you get the pressure right, the chalk will wear evenly across the width of the tread. Click on the link below---there are a bunch of videos to choose from.
https://www.youtube.com/results?search_query=tire+pressure+chalk+method

 

[DHMag]

Or use the simple chalk test. Flat road (side to side flat--little or no crown to it), some chalk (kids "sidewalk" chalk works great), tire pressure gauge. On a straight stretch of flat road, draw a line about an inch wide, across the tread, get in the truck and drive it straight ~100 ft. Stop, get out and look at the chalk line. If it is gone in the middle, but still on the outer edges, the pressure is too high. If it is gone on the outer edges, but still present in the middle, the pressure is too low. Once you get the pressure right, the chalk will wear evenly across the width of the tread. Click on the link below---there are a bunch of videos to choose from.
https://www.youtube.com/results?search_query=tire+pressure+chalk+method

I prefer this method, but I also do it twice. Once with the tires cold, and again with the tires hot. Unless you have nitrogen filled tires, hot and cold don't apply.

 

[j0shm1lls]

Looking at the 'standard load inflation table' for the stock 110 load index tire at 30PSI, is 2028lbs. Going to the 113 load index tire, the closest weight higher than stock is 2039lbs at 28PSI.

Not a big diff, but set them to 28PSI when cold (early morning is best).

 

[VAMike]

Unless you have nitrogen filled tires, hot and cold don't apply.

that's not actually true...

 

[Rob Binsky]

Thanks, guys. The chart from jsphlynch gave me some guidelines, and I like the chalk test recommended by Rinn69 and DHMag. I guess when the snow stops and the temp gets above 50 here in Montana I’ll try it. So far BB3 is the only one I’ve found on here with 275/55/20 tires. I’m sure there are others. He’s running 35 psi, so I’ll use that as a starting point. I’m probably making this more difficult than it is.

ok, j0shm1lls, I don’t get what you said, but I have read many of your posts and respect your input. It confuses me tho, that you are recommending 28 psi, less than the OEM 17”. I guess what you’re saying is load index is a more important number than size?

 

[j0shm1lls]

ok, j0shm1lls, I don’t get what you said, but I have read many of your posts and respect your input. It confuses me tho, that you are recommending 28 psi, less than the OEM 17”. I guess what you’re saying is load index is a more important number than size?

Yeah it doesn't really make sense to me either, but if you look at the table in the PDF for ISO-Metric standard load tires, that is what it recommends.

The yellow highlighted numbers are for your stock tire, and the green highlight is for your current tire. It is the closest in load carrying capacity in lbs without going under.

HOWEVER, I just noticed that earlier in that PDF, it has a warning of not going under the factory recommended PSI. So in this case, the chalk method might be your best bet.

Edit: Sorry if I confused things more heh

 

[Rob Binsky]

Yeah it doesn't really make sense to me either, but if you look at the table in the PDF for ISO-Metric standard load tires, that is what it recommends.

The yellow highlighted numbers are for your stock tire, and the green highlight is for your current tire. It is the closest in load carrying capacity in lbs without going under.

HOWEVER, I just noticed that earlier in that PDF, it has a warning of not going under the factory recommended PSI. So in this case, the chalk method might be your best bet.

Edit: Sorry if I confused things more heh

The chart the way you highlighted it makes perfect sense. But I agree that 28 psi doesn’t make sense. How would you like to come to Montana and help me with the chalk test?

 

[j0shm1lls]

The chart the way you highlighted it makes perfect sense. But I agree that 28 psi doesn’t make sense. How would you like to come to Montana and help me with the chalk test?

Hah, I'd love to, buuuut its a bit of a drive.

 

[Rob Binsky]

Hah, I'd love to, buuuut its a bit of a drive.

However, you have a cool truck to do it in!

 

[t4thfavor]

that's not actually true...

Air is something like 79% nitrogen already, so the laws of air apply to the laws of nitrogen, and vice versa.

Check with Bernoulli, I don't think he made laws for each type of gas

 

[P. A. Schilke]

Air is something like 79% nitrogen already, so the laws of air apply to the laws of nitrogen, and vice versa.

Check with Bernoulli, I don't think he made laws for each type of gas

however the gas was not dry...moistrure abounds.

best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co Retired

 

[VAMike]

however the gas was not dry...moistrure abounds.

Bernoulli applies either way. Dry nitrogen is more stable under track conditions if you're running tires hot enough to boil any moisture in the tires. On the street you're either probably not running that hot or the couple extra psi doesn't matter.

 

[BHunted]

Moisture cannot boil out of a sealed container. It will covert to steam, cling on to surfaces and when cooled coverts back to water....
Nothing coming out of a typical compressor is perfect. You want perfect, or near it, you'd have to pipe pure nitrogen into the tire.

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