Intro

[twomountainlions]

When in camping mode, I tend to leave them at 30 psi all the time. If it's a particularly long and rough trail, I'll reduce to 20 psi. If I get stuck in sand, then it's ~10 psi, but that has never happened with this truck. If it's a long highway stretch I'll bump it up to 38.

The tires are 35x13" and are rated for 4,000 lbs each at 65 psi. My actual weight is about 2,000 lbs per.

Viair has performance specs on their website. At 80 psi the fill rate to about half what it is at 20 psi, but it should still work well. I bought a clone of the 88p digital, so I'll let you know how that goes when I get it. If it works ok I plan to rig it so I can fill two tires at once. It comes with a silly-long hose, instead of a long cord... but I'll make my own long cord, and change the hose.

According to other sources fill rate for some of the 2 cfu pumps (normally rated at 0 psi) drops to be really slow, like 1 psi per min by the time tire gets over 65psi.
Vair has RV pumps that are output rated at 80 psi, not at 0 psi, and these are $300+ pumps they recommend for tire situation like mine.

For 30-ish psi tires anything like Vair 88 should work ok, especially if its 4 tires to inflate, main thing not to get amazon lemon.

Based on what many people with truck campers, I guess heavy ones, say they seem to have their tires at 65-80psi, even 110. I wonder how you arrive to 38 psi as optimal highway pressure for the weight, since your tire is weight rated at 65 psi, I understand you reduce psi based on actual weight but relationship must be non linear and its usually better to give things much extra room, I thought

 

[rruff]

I wonder how you arrive to 38 psi as optimal highway pressure for the weight, since your tire is weight rated at 65 psi, I understand you reduce psi based on actual weight but relationship must be non linear and its usually better to give things much extra room, I thought

If you want to be fancy you can do a chalk test, but I'm not that fancy. I looked at the Toyo inflation tables for my tire size and load rating, pressure vs weight. They aren't Toyo tires, but the ratings are standardized. It's not linear, but not that far from linear. I'm just guessing on the weight, I haven't actually weighed it... and 2,000 lbs/per is my future fully loaded guess. I also check the tread depth to make sure they are wearing evenly, and they are.

38 is probably higher than I need. I do plenty of highway driving at 30 (to get to town from camp spots), and it still handles fine and they don't get hot. I think radials are pretty tolerant of PSI.

My tires are 325/65r18, E rated for 3,860lbs at 65 psi, and S speed rated for sustained running at 112 mph with that load and pressure at high temp.

 

[bullfrog !]

The biggest problem I have had with low inflation and I mean really low pressures as in 10 to 20 psi off road is side wall cracking due to age and heating, still tires lasted over 5 years and 30,000 miles. The chalk test is easy and effective in keeping tires wearing even in my opinion. Some manufacturers void warranty even with as little as 1/32” variance in tread depth just so you know!

 

[twomountainlions]

If you want to be fancy you can do a chalk test, but I'm not that fancy. I looked at the Toyo inflation tables for my tire size and load rating, pressure vs weight. They aren't Toyo tires, but the ratings are standardized. It's not linear, but not that far from linear. I'm just guessing on the weight, I haven't actually weighed it... and 2,000 lbs/per is my future fully loaded guess. I also check the tread depth to make sure they are wearing evenly, and they are.

38 is probably higher than I need. I do plenty of highway driving at 30 (to get to town from camp spots), and it still handles fine and they don't get hot. I think radials are pretty tolerant of PSI.

My tires are 325/65r18, E rated for 3,860lbs at 65 psi, and S speed rated for sustained running at 112 mph with that load and pressure at high temp.

I see. I drove with somewhat underinflated tires on this heavy rig before and got a lot of tread wear. I had early tread wear issues with other vehicles in the past and tire shops had hammered it into my head to inflate to spec, they always wanted to overinflate to minimize wear, actually, so Im pretty diligent with inflating to what the door plate says now

 

[twomountainlions]

I'm thinking wrong advice might have been given to the OP and I want to take back what I said here earlier.
Yes, having a vehicle where you can go from living quarters straight to the driving seat is a big deal for safety if OP is female, which just occured yo me might be the case.
Yes, it feels a lot more secure to have a rig which you don't have to exit to escape the area if needs to be. Much more secure and peaceful feeling in such rig. Its generally quite safe out there in remote areas (versus cities) but never know, better safe than sorry. Its more peace of mind when you know you can just drive off, even though a chance of this happening is tiny

 

[twomountainlions]

Ordered 7cfu Vevor tire inflator for about 70 bucks on amazon, they got 15% coupon going, shall see how well it works. I only deflate to remove lodged rocks between duallies though, reinflating all 6 to 80 psi would still take too long. Like they say dont go anywhere where you cant afford to be towed out of.

 

[eDJ_]

There are modified rear axles for Pro Masters becoming more and more available now. I guess they realize that a growing share of the market for Pro Masters are wanting to go off road. Generally, when an aftermarket item becomes popular the manufacturer begins to make it and offer it as an option.

Note the road clearance now:

There can only be so much relief for road clearance as otherwise the new axle would bang against the floor when it deflects from bumps, ruts, and pot holes.
The exhaust system may have to be shortened to vent in front of a rear wheel.
I would also construct a large mud flap that runs across from one wheel to the other made perhaps from a piece of old conveyor belt.
That's the compromises in doing this.

 

[rruff]

If I buy another I think I'll get a Viair 85 or 88 with the auto shutoff... or better, this 88 clone for $65. It's good to have a spare. I need good pumps, as I use them pretty regularly.

https://www.amazon.com/dp/B0CJFCRKB...psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9ocXBfc2hhcmVk

I did buy the 88p clone and it inflates at ~3.3 psi/min at 25 psi (35x13" tires), and the shutoff and gauge are accurate.

 

[rruff]

There can only be so much relief for road clearance as otherwise the new axle would bang against the floor when it deflects from bumps, ruts, and pot holes.

I'd lift it a couple inches and install bigger tires.