Deflating Tires for Unimproved Roads

[pdemarest]

I'm in the process of shopping for an air compressor so that I can inflate my tires after deflating them for off-road/unimproved road travel and wondered how low I can safely go with tire pressures. I usually run 55-60 in the rears and 65 lbs. in the front but on these back roads that can lead to a punishing ride that shakes everything in the rig. Any experience with running the tires at lower pressures? Recommendations for air compressors and deflators?

thanks,

Paul

[b6fischer]

Here's what I'd use:
https://www.amazon.com/Boulder-Tools-De ... B01M0L7JS2. We use these when access the OBX beach roads.

I highly recommend spending the money on a VIAIR product, about $150 - 250 and lots of models.These are what off-roaders use to inflate. (I have burnt out a $40 unit and the $80 one I currently run is so slow... Wish I had bought the VIAIR originally)

Bill

[pdemarest]

Hi Bill - saw that deflator on Amazon earlier today and liked the concept. With 6 tires and bad knees I can't spend a lot of time airing out the tires!

On the cheap compressors - I have one of those all-in-one air compressor/jump starter things but it takes forever to inflate, is super loud and starts heating up pretty quickly. I'm only considering the compressors that attach directly to the battery or are 110 volt; figure I could fire up the generator if I needed to air up the tires after some backroad travel.

[Blue~Go]

I've been eyeing up a Viair myself. I can't recall the model number off the top of my head but there is an "RV" model. Has hoses that will reach all the way around, decent duty cycle, etc. I think it was like $239. But you could probably make a lesser one work. I'm only shopping (although buddy has the one I mentioned and no complaints).

One thing to look at is duty cycle. Some with lower duty cycles, if you were going to re-inflate six tires you have to sit around giving the thing a rest (use ten minutes, rest it ten minutes, or etc.).

I think most of the better ones are going to have battery clips (vs. cigarette plug which can only then draw so much). (Oh, duh, I see you already mentioned that.)

[pdemarest]

I think the Viair's have a 33% duty cycle - but I have no idea what that means.

I'm also wondering how much I can deflate the tires before I'm creating a safey issue. What's the lowest psi. I can go to before it compromises the load capacity? I'd like to go down to 40 psi all around.

Paul

[Blue~Go]

Duty cycle is an expression of how long you can run vs. rest. Here is how Viair puts it:

Duty cycle refers to the amount of time a compressor can be operated in a given time period at 100 PSI, and a standard ambient temperature of 72° F. It is commonly expressed in percentage format: Compressor on time ÷ (on time + off time) = Duty Cycle %.

They do make some that have basically a 100% duty cycle. I think they are popular amongst the 4WD crowd who are doing this daily. For example, I think the Viair 450P-Auto has a 100% at 100 PSI. But I believe it will be slower than some other models (slow and steady).

I have been eyeing up one of the several "RV" models from Viair. The one my buddy has I believe came with two of the coiled hoses (so you can reach further from the battery). I don't know that it has the 100% duty cycle but perhaps it's faster. They (almost unfortunately) make a jillion models. Maybe I could get a lesser one --- I have to wade through them again one of these days!

Here are some notes I saved that were written by a conservative off road RV-er with a 3/4 ton truck+lightweight truck camper. No duallies so that is one difference, but otherwise similar to us.

The “how low to take them down”: Measure the distance from the ground to the wheel rim on your vehicle. If you reduce that by 25%, the new distance is your target. Whatever pressure it takes to get to that target is your lowest “safe” air-down pressure.


I might try a bit less than that and see how it goes. I'd probably measure a baseline temp of the tire with an IR thermometer and then keep an eye on it. That said, I have not tried it yet.

Additionally:
The most common recommendation among those more qualified seems to be 20 MPH for 20 PSI, reducing it 5 MPH for each 5 PSI lower. That’s for light SUV-level rides, so the best option for the Ford is to use 20 MPH as a maximum, and get out occasionally to feel the sidewall heat.

The second method I’ve come across as a guide for how low tire pressures can safely go is 25% of the maximum pressure shown on the tire sidewall. In my [his] case, 25% of 80 PSI means a 20 PSI minimum, which sleeves in pretty well with my conservative measuring of wheel rim height reduction at 25 PSI. This method is generalized, while the measurement method is specific to the vehicle.

BG

[dougm]

The compressor that feeds the air suspension on my Chinook is continuous duty even though it doesnt run very often. The preset pressure switch in the main reservoir shuts it off at like 120 pounds. You can buy the compressor by itself without purchasing the air suspension kit however it runs in the neighborhood of $1200 and up for the 12 volt version. A less expensive alternative is these ARB compressors, i have never used one but they are big with the offroad crowd and based on what i have read they are of good quality. https://www.extremeterrain.com/arb-high ... &gclsrc=ds

[pdemarest]

Blue - 20 psi is a lot lower than I was planning on going but its good to know that I could take them down that low if needed. Also good to note that running them low will make them run hotter, although I don't anticipate that being a problem on this upcoming trip as it will be pretty cold at that time of year.

Doug - I'm envious of your air suspension! I just had to replace my air suspension in my Navigator with coil-over struts as the system was flashing error codes and my compressor was running non stop. Given that there are leveling sensors at each wheel, a computer that controls the system, a relay known to go bad, and the possibility that one of the bags was leaking it was time to just ditch it and convert the car to springs. Just the cost of diagnosing the problem would have exceeded the cost of the conversion as most repair shops don't want to tackle it due to the complexity of the system. Still, I do miss the ride but at 176,000 miles I couldn't justify overhauling the air suspension.

[ltg]

I am unsure about all tires, but for rv tires, Michelin says that a tire that is run with less than 80% of the recommended tire pressure for the load it is carrying is considered a flat tire. That tire should be removed and inspected by a tire specialist before being placed back in service.

[Scott]

Doug, is your compressor dedicated to just the airbags? I guess a continuous duty spec would then make sense since it's not required to move much air.

Paul, I think you were smart to consider a 120v unit. Inflating six large tires from 20 to 60 psi is going to take a lot of compressor. Aren't the Viair units more for roadside emergencies and occasional topping up? I don't know their design intent. The ARBs are nice, but $500... Not sure how many offroaders are dragging along generators, and their rigs usually look packed to the gills, so they need the compact 12V ARB style. But if I had a generator aboard anyway, and I wanted to adjust the tires down/up as you're planning, then a 120V compressor wins for a few reasons. Higher flow, higher duty, lower cost, more diverse capabilities (home use), not sapping any batteries, comes with a reservoir (tank), etc. It'll be larger, but that's about the only downfall. Of course the noise of the generator is a factor, but that will be eclipsed by the painful noise of any compressor. Plus you'll be exercising your generator, which is healthy for it. And even if it does puke, "decent" compressors are under $100. I have a mini 120V compressor and it'll run all day long. It smells a little hot now and again, but it always moves air without complaint.

I like the scientific approach to determining a deflation threshold, as Blue posted. Less pressure certainly yields more traction (to a point obviously). Look at the tires on those Icelandic snow jeeps! But many offroaders (the ones I've seen on the Rubicon) are in an entirely different boat when it comes to tires. They beat the snot out of their tires, and it's very important to them to make those impressive ascents, at any cost, so they're less concerned about the state of their sidewalls. They're also (typically) much lighter than an RV, they have friends and spares galore, and often times they go home on a trailer.

If you need more traction on sand or whatever to prevent getting stranded, then sure air down, and bring a shovel and a recovery strap. If it's for a more cushy ride, meh I'd leave the tires where they are, and just tolerate the noise until I get there. Turn up the tunes! That's what I do anyway.