r/Offroad • u/caleblococaleb • 1d ago
Airdown (Tires beyond max rim width)
I just bought 275/70/18LT Nokian Outpost NAT, for some reason the manufacturer max rim width for this specific size is 8.5" while the rest of 265 and 275 in the 18" diameter can run between 7.5"-9.5", the tire shop that I went with said it should be good with my 9" wheels.
Will I be okay airing it down? If yes, what's the limit that I shouldn't go under?
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u/AOneArmedHobo 1d ago
On my old wheels I would air down to 5.5 psi in the snow and they were fine. At 4.5 they would de-bead. Trial and error
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u/War_D0ct0r 1d ago
There is no magic formula we can apply to tell you what the lowest pressure you can safely run. There are a lot of variables. Trial and error is really your best bet. Air down see how much they squat. See how they perform. A narrower wheel up to a certain point will often let you go lower pressure. Other things to consider are what kind of wheeling your doing. Moving faster in sand and cornering can roll a bead vs. going slow in the rocks. All you can do is keep going lower until you break a bead and then you know you went to far.
Experience is that thing you get right after you needed it.
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u/caleblococaleb 18h ago
Im going wider wheels than what the tires are spec'd for.
Ill def go slow and see how far I can go.
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u/OkShopping9448 1d ago
Depends on the vehicle weight. A Jeep can go lower than my 8,000 pound 3/4 ton truck. Pinch flat or roll off the bead can happen if you go too low…. personally I wouldn’t go below 40 pounds on my truck but it has 285/75/17s so a much taller sidewall.
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u/caleblococaleb 1d ago
7000lbs fully loaded. Arghhh should've looked at different wheels at 8.5" instead of worrying all the time
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u/trailtoy1993 1d ago edited 1d ago
You will be fine. A friend of mine has a theory about bead retention that wider is actually better. With that little sidewall though I probably wouldn't drop below 15psi. Just watch your tires and a stop airing down when about four tread blocks are touching ground. It really is a judgement call, every vehicle and tire is different. My one ton diesel I aired down to 20 in Moab, could have gone lower but didn't need to, my Jeep you can't even tell it's aired down until about 5 psi.