zouch
Well-Known Member
- Joined
- Sep 17, 2020
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- XJ, JLUWD
hey, Phil,
bunch o' things here.
first, sorry; i thought i saw you say somewhere your tires were D rated.
next; variance from labelled sizes is a given that's well beaten to death, and not worth further discussion.
but if we're talking about products and specs, those labelled tire sizes are what we have to go by, since (as you're aware) the specs for a manufacturers 315/70s are not necessarily the same as the specs for their 35' tire; they're different tires.
starting with the basics.
Cold Tire Pressure means the pressure of the tire after it has been sitting unused out of the sun and at ambient air temps for at least 2-3 hours. setting your tire pressure under any other conditions is not going to give you relevant repeatable results.
there are allowances for when airing back up when tires are warm that allow ~4PSI above the target pressure. (there's even mention of this in your Users Manual).
i'm not familiar with any TPMS alert like what you describe; maybe it's a Willys vs Rubicon thing, but i don't see anything like that in the Users Manual outside of the Low Tire Pressure warning that's supposed to come on when you're significantly low on pressure.
i've never seen the Low Tire Pressure Alert come on except when aired down significantly and *not* in 4WD.
i've never seen a "Do Not Exceed" pressure listed on a tire. can we get a pic of that? (maybe it's a Toyo thing?)
TPMS alert ranges are adjustable beyond what the dealer may be willing/able to do for you. i see it mentioned as a feature in the Tazer manual; i'm not sure if there are other tools available that will do it. you might look into something like one of those if after verifying pressures your situation continues and you want to stop ignoring those warnings and make them actually helpful again.
for your case, i'd make damn sure i had an accurate gauge (or 3), check the tires in the morning before the sun hits them and they're the same temp as the air around them, and fill them to 35 (as that's your tire manufacturers max). after that i'd be honestly surprised to see the pressures rise much more than 10% in use unless there are changes in temperature or altitude unless your rig is loaded to a point past what those tires are rated for. (again, surprisingly, the Users Manual actually has some decent discussion on compensations for Temperature and Altitude.)
i would expect to find that 30-31 Cold is too low.
bunch o' things here.
first, sorry; i thought i saw you say somewhere your tires were D rated.
next; variance from labelled sizes is a given that's well beaten to death, and not worth further discussion.
but if we're talking about products and specs, those labelled tire sizes are what we have to go by, since (as you're aware) the specs for a manufacturers 315/70s are not necessarily the same as the specs for their 35' tire; they're different tires.
starting with the basics.
Cold Tire Pressure means the pressure of the tire after it has been sitting unused out of the sun and at ambient air temps for at least 2-3 hours. setting your tire pressure under any other conditions is not going to give you relevant repeatable results.
there are allowances for when airing back up when tires are warm that allow ~4PSI above the target pressure. (there's even mention of this in your Users Manual).
i'm not familiar with any TPMS alert like what you describe; maybe it's a Willys vs Rubicon thing, but i don't see anything like that in the Users Manual outside of the Low Tire Pressure warning that's supposed to come on when you're significantly low on pressure.
i've never seen the Low Tire Pressure Alert come on except when aired down significantly and *not* in 4WD.
i've never seen a "Do Not Exceed" pressure listed on a tire. can we get a pic of that? (maybe it's a Toyo thing?)
TPMS alert ranges are adjustable beyond what the dealer may be willing/able to do for you. i see it mentioned as a feature in the Tazer manual; i'm not sure if there are other tools available that will do it. you might look into something like one of those if after verifying pressures your situation continues and you want to stop ignoring those warnings and make them actually helpful again.
for your case, i'd make damn sure i had an accurate gauge (or 3), check the tires in the morning before the sun hits them and they're the same temp as the air around them, and fill them to 35 (as that's your tire manufacturers max). after that i'd be honestly surprised to see the pressures rise much more than 10% in use unless there are changes in temperature or altitude unless your rig is loaded to a point past what those tires are rated for. (again, surprisingly, the Users Manual actually has some decent discussion on compensations for Temperature and Altitude.)
i would expect to find that 30-31 Cold is too low.
I have C rated Toyo R/Ts. Yes, they are the 31570R17 not 35x12.50. Neither of those tires is 35" though. They are less than half an each apart from each other and the 305 is a tenth of an inch from 34" so I just feel like its easier to say 35" rather than 31570R17. If you look at a different tire from the same manufacturer, like the open country M/Ts, and the 31570R17 is a different diameter anyway.
The TPMS alert in the dash is what I am referring to that is "telling me". It is set to 37 PSI from the factory so it wants me to inflate over my max PSI. Dealer told me they cannot adjust it.
The PSI range on them is greater than 10% cold to hot. Even if I am not driving them, if I check them in the early morning and in the afternoon just sitting it will move about 10%. Even on the stock 33" tires inflated to 37 PSI cold it would move more than 10% when driving. Right now my "cold" PSI is around 30-31 depending on the temp in the morning and after a long drive at highway speeds will hit about 36 (which just so happens to be the threshold to turn off the TPMS alert). If I haven't driven it all day but check it in the afternoon, it might be 33-34 range. I have also in the past set them to 35 PSI cold and they will get up to 40 PSI after a long highway drive which I think is listed on the tire as the "never to exceed" pressure. My current approach is to air up to 35 PSI after wheeling and then they later cool down overnight to about that 30-31 range I mentioned before. I do even notice a difference in PSI based on which tires are in the sun vs the shade.
I've mostly just decided to not worry about it too much and enjoy the vehicle, but I was curious to see what the stock XR PSIs were.
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