Searched but did not find... tire pressure Q

I changed tire size and want to know if I need to adjust the tire pressure any to accommodate the change?

Went from stock 245/75/16 Firestone LE2 to 265/70/17 General AT-X.

Thanks for answering my stupid question.

 

Best thing to do is the chalk test. If no chalk then stay around 30-32 when cold and it’ll be good balance between rolling resistance and ride quality.

edit: when I say cold I mean like 65-75F ambient.

 

If the Firestone's had a P in front of the 245 and yer new shoes say LT in front of 265 you'll prolly want to raise pressure a little.

There is plenty of wiggle room either way, experiment with it a bit and see what pressure feels best if you're really trying to make it a science experiment.

 

No LT here... didn't want the weight penalty of 10-ply when I don't do anything extreme. My Braid beadlock wheels look (and are) way more aggressive than my actual wheeling. I may occasionally see old mining roads at worst.

 

You'll need to adjust anytime you stray from stock. When the new tires go on , the door sticker is void. A lot of info here with a search.

G.

 

You're not stuck with an E rated, 10ply with all light truck (LT) tires - I run the LT265/75/16 Goodyear Duratrac with a C load rating, their sweet spot seems to be about 36psi.

Tire pressure is a lot like oil brand, everyone has an opinion!

 

Your stock tire should be a P245/75/16/109 @ 32 psi for a 2,172 lb inflated load rating(ILR).
If your new tire is a;
P265/70/17/113 @ 26 psi is a 2,194 lb ILR
265/70/17/115 @ 28 psi is a 2,149 lb ILR
LT265/70/17/121 @ 37 psi is a 1,964 lb ILR(LTs are not de-rated like P and euro metric; so 2,172/1.1=1,974)

It's not so much about the size, as it is the load rating, as you can see.
A distinction also exists between P and euro metric tires(this is the 265/70/17/115 from above; notice, no P prefix). P tires consider load rating and size, whereas euro metric only considers load rating.
From what I was able to find online, your tire comes in either a 265/70/17/115 or LT265/70/17/121.

 

No! No! No!!!! Please for the love of god will everyone please stop suggesting this gimmick (apologies Rock, I'm not bashing you). Chalk test is pointless and does nothing but makes you look silly stealing a kids chalk then spending hours trying to gain any useful knowledge, which you can't.

Short of getting out a temperature gauge, there is no way to determine proper pressure. Just don't go below what is on the placard and don't go above what is on the side wall of the tire. Anything in between is a personal preference.

 

I’m not taking offense.

This is for sure not right though. You cannot run our trucks at near max rated pressure and expect to have even tread wear. It highly depends on vehicle weight and our trucks may not require the exact same psi as we all have different tires and accessories. But this range in the low 30s is good for an overwhelming majority of our trucks.

 

They are all at 35 cold right now. We'll see how that goes.

 

This " pigheaded Dutch selfdeclared tirepressure-specialist" is able to calculate it for you.

Need from old and new tires next, can be read from sidewall
1 maximum load or loadindex
2 kind of tire to determine the reference-pressure, fi loadrange or plyrating can do.
Or if standard load or XL/ reinforced/extraload for P-tires.
3. Not super-important , but speedcode, fi S for 112mph maxspeed.

4 the original pressure advices.

Can also use only the new tires, but then need from car, GAWR's, GVWR, empty weight, and the way you load it with persons and load and dog fi .

 

at 35 cold, the tires will heat up when driving and the tire pressure will expand so in reality once the tires heat up you'll be close to 40 PSI which is way over the manufacturers rec.

 

I upsized, but still keep it 30 psi. 32 psi in the winter due to the fluctuation and temperature.

 

The heating up by driving is included in the cold pressure advice, and maximum allowed cold pressure given on sidewall.
Cold is when inside and outside tire temp is the same, and if you want to do it completely right, calculate back to 18degrC/65degrF.

So when fi advice is 35 psi, and on a hot day of 90degrF you will measure a cold pressure of 37.5 psi ( calculated it for you) , then dont blead air to bring it to 35 psi. The tire needs the lesser deflection it gives, to produce lesser heat, because the cooling diwn is also worse then, because lof lesser temp-differences, between rubber and in and outside air.

Cold pressure advice is to give the tire a warm pressure so deflection, that wont give a to high temp of rubber, when driving the speed ,for wich it is calculated.

Only measuring warm pressure is unreliable, because you dont know what temp the inside tire air is at that moment.
Only inside tire TMPS sensors give inside tire temp acurate, and some tmps systems calculate the pressure back to 65 degrF ( some say 68degrF) .

 

I got a little driving in but they only read 1 degree higher afterward. It is/was full on winter here as far as temps outside. I'm actually going to air down to 32 when I get a more accurate gauge instead of one of these pen things. And likewise will adjust when it gets warm. Good excuse to get that ARB deflator I've been wanting.

 

if you air down to 30psi the tires will heat up to 32-33psi this is what ive found with the stock size tires P245. my door jam says 30psi cold

 

Will do