Airring Down Commercial Bead Tires?

[tmckenna13]

My current "big rig" chassis has 10x285.75mm wheels on it. Currently planning on doing "floater" front wheels with a 385/65r22.5 tire. My question is, for soft sand what are the "rules" for airring down? I know in theory the profile of commercial truck tires is more likely to de-bead at lower pressures but I'm curious what kind of personal experience people have. (I have an SUV I drive on soft sand beaches and air down to 12psi and it drives amazing. I know commercial truck tires cant be airred down that low, thats why Im asking here)

 

[tbone1004]

I'd be concerned going lower than 80psi or so on them since there is no safety bead, I know some will go to 40psi if you're careful about sharp steering angles. A lot of it will depend on the actual front axle weight though.

 

[Peter_n_Margaret]

This is well below the yellow line to get over a particularly soft dune.

Cheers,
Peter
OKA196 motorhome

 

[tbone1004]

View attachment 875488
This is well below the yellow line to get over a particularly soft dune.
View attachment 875489
Cheers,
Peter
OKA196 motorhome

unfortunately the beads on 19.5 tires are very different than 22.5's which do not take airing down nearly as well

 

[Joe917]

I regularly dropped our 315 80 22.5s to 60 psi, never an issue. 9400kg.

 

[tmckenna13]

I regularly dropped our 315 80 22.5s to 60 psi, never an issue. 9400kg.

Do you start seeing the "pancaking" of the tire around that pressure? I have zero experience with commercial truck tires so Im just trying to get some real life info about best practices.

 

[tmckenna13]

I'd be concerned going lower than 80psi or so on them since there is no safety bead, I know some will go to 40psi if you're careful about sharp steering angles. A lot of it will depend on the actual front axle weight though.

I should be well below the total capacity of the tires. I have a friend with a 4x4 international 7400 that tows a huge fifth wheel on the same beaches I drive on. He says he airs his 22.5 tires down into the 20s and has never had an issue.

 

[Hotshotliving]

I should be well below the total capacity of the tires. I have a friend with a 4x4 international 7400 that tows a huge fifth wheel on the same beaches I drive on. He says he airs his 22.5 tires down into the 20s and has never had an issue.

Really? I have an international 7400 and I also run mine at 80psi all around all the time. I am concerned about airing them down though for that same fear. Is there a calculation for total weight vs total acceptable tire pressure. Obviously I wouldn’t be running anything less the 80psi while driving.

 

[tmckenna13]

Really? I have an international 7400 and I also run mine at 80psi all around all the time. I am concerned about airing them down though for that same fear. Is there a calculation for total weight vs total acceptable tire pressure. Obviously I wouldn’t be running anything less the 80psi while driving.

Yup. I mean I will admit hes a bit cavalier with some "rig related" stuff, but hes been using the International for years and said he never had a problem, and his fifth wheel is HEAVYYY. It's dually tandem axle, so 8 tires total. He also has a C5500 super C now, that he 4x4 converted and runs 22.5" floaters on, assuming he airs those down pretty low as well.

 

[charlieaarons]

Really? I have an international 7400 and I also run mine at 80psi all around all the time. I am concerned about airing them down though for that same fear. Is there a calculation for total weight vs total acceptable tire pressure. Obviously I wouldn’t be running anything less the 80psi while driving.

Note recommendation in Unimog manual for deflation/speed recommendations for 445/65R22.5. Note, above in the thread by Peter/Margaret, the completely (mathematically ) linear nature of relation of load & inflation.
There’s no such data that I’m aware of for 22.5 tires with numerically higher aspect ratios.
Do the arithmetic, don’t exceed speed limits for applicable deflation %. And cross your fingers or something else superstitious, since if internal beadlocks on Hutchinson type 22.5 wheels exist…I’ve never seen them.

 

[charlieaarons]

Also recommend: adjustment of road (high speed highway) pressure in linear proportion to load which should be measured accurately and/or increased by 10% over calculated value ESPECIALLY if ANY GUESSWORK is involved, for safety.
The %s in above chart applicable for 445/65R22.5 should be adjusted numerically UPWARDS for “shorter” tires. The mentioned 445s have about 11.5” sidewalls. A regular old 11R22.5 (aspect ratio = 90) has a 9.9” sidewall. At the other end of the spectrum, a 225/70R19.5 has only 6.2” sidewalls. Before squish. Think about potential for internal damage from edge of rim and lateral stress on the bead area, which already isn’t designed for highly deflated running on fractional (“xy.5”) wheels.