Deflating Tires for Unimproved Roads

[Blue~Go]

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.

Just a guess, but I bet they are presuming that you ran it "all out" on the freeway or whatever. In other words, the tire got low, the driver didn't realize it, and carried on as per normal. That would probably overheat the tire (and maybe put more stress on the companion tire that was still full, if the dually).

This is only conjecture, but it's what came to my mind.

I do think one would want to be extra careful when deflating duallies, at least at first. Just to be sure the inner sidewalls don't get too close to each other/make more heat. That may not happen, but by proceeding slowly and keeping an eye (and an IR thermometer) on things, you'd establish a baseline. And of course not running at regular speeds.

[Blue~Go]

Aren't the Viair units more for roadside emergencies and occasional topping up? I don't know their design intent.

Viair makes a whole bunch of different ones. The one the fellow I quoted in italicized text above chose (from my notes) is one that at the types of pressures we run basically has a 100% duty cycle. He regularly deflates/inflates a 3/4 ton Ford with a camper on the back.

Viair do also make little cigarette lighter "I'm on my way to the opera and just want to add a few pounds to this one tire without getting dirty" type; but they also make some that off roaders consider decent and others that will inflate the really big Class A type tires. Actually, they make so many different models that I've waffled vs. just buying one. I'm the type who has to read all the specs, and with a jillion models I keep putting it on the back burner

[Roger D]

I have the Viair 88P. One of the smaller models. Surprisingly effective. If I did it again I'd go up a model mainly to get the carry bag.

[pdemarest]

My reasons for wanting to air-down the tires are partially to get more traction on snow/ice but primarily to soften the ride and shock to the rig when operating on bad roads. (Okay, its more about the ride but protecting my Chinook sounds better!). The roads here in California are in pretty bad shape and there are even some highways where it would be nice to easily air down to smooth things out.

On the compressor type I've decided that a cheap 110 volt model would be sufficient for the number of times I'd use it and would also be useful around the house. I'm now reviewing what we have in the rig now to see what can come out to make some room for the compressor.

[Blue~Go]

That'd be my reason, too. Say a long washboarded road - those are rather unappealing with fully inflated tires. And of course it's nice to have for regular inflation duty too, when necessary. Kind of annoying to jockey the rig around to an air pump and then find out... it's broken (rinse and repeat).

Roger: Thanks for the comment on the 88P.

[ltg]

This a big if. But, if you have the room, I recommend the Porter Cable Model CMB15.

[Blue~Go]

This thread has reminded me that it's silly (for myself, just IMO) for me to continue to go without an air compressor, just because I can't figure out which one I want. In my defense, I had been doing quite a bit of traveling with a buddy who has the 450P-RV - but I should still have my own.

Time to get through the research!

Even though these usually drive me nuts, I clicked on the 'Need help choosing your compressor?" link on the Viair page. The following graphic (plus more) was at the link. Obviously we don't fit tidily into any one category, but it's something to start with. Figured I'd share it here. Click twice to make it legible.

There is other helpful info on the page, including an invitation to give them a call if you need more advice.

http://www.viaircorp.com/4x4-off-road/c ... portables/

Okay, back to it...

BG

PS: After reading over a few more of their pages, I think I am going to give them a call sometime this week. I don't think I need a specific RV one, because that means they include two 30' hoses vs. just one 30' hose. I think I can reach all of the Chinook tires with one 30' hose (and on my buddy's, the two hoses are a pain to stow because they get tangled, etc.).

I also don't think I need the 450P or even the 400P because those will fill to 150 psi. Our Chinooks may be RV's, but our tires can only go to 80psi, and actually for our weight ratings (E-350 Chinooks), we wouldn't really be going over 60psi.

They list tire sizes, but I think those must be outside diameter (will measure mine).

And then Automatic or not? I'll have to figure that out.

They also offer different chucks (such as one "backwards" one for duallies that don't have extended stems). I wouldn't need that though. I think there are also screw on or press on ones.

In summary, I think the 450P-RV is probably overkill for my Chinook, even for "off road" inflation/deflation (vs. topping up). Just storing that extra 30' hose would be a real pain. So.... let's see how helpful their help folks are. Maybe something like the 300P would be a good fit.

[caconcourse]

I guess I was lucky when we bought our 2001 Concourse that it came with a factory installed air compressor mounted inside the chassis behind the battery compartment. I know the Baja came with an on-board compressor, so maybe it was an available option at one time. It has a tank, looks to be about 1 or 2 gallons, and a valve mounted in the fiberglass next to the driver door step. The compressor runs off the 12V and the tank fills whenever the ignition is turned on, so it is always ready. It looks like it works up to about 90 psi. I bought a nice accessory kit with quick releases and inflators and a coiled hose, so we can reach all the tires.

It is very handy for topping off the tires, and was invaluable when we woke up with a flat inside dually one morning on a long trip. We have braided valve extensions which are bolted to the wheel simulators behind the simulator locknut. On our trip, one of the simulator lug nuts worked loose (fell off), and the braided extension bracket was hanging in mid air. I tied it up with a nylon cord to keep it from breaking, but the motion made the valve work itself loose inside the tire, and caused a slow leak a week or two later. We pumped the flat tire up with the compressor, and found a nice tire shop nearby that also served 18-wheelers, so they were able to re-seat the valve in the wheel and replaced the missing simulator locknut with an over-sized nut from their stock and we were good to go, for about $50. The villain was our local tire shop who failed to tighten the simulator locknut properly.

Clay

Factory installed compressor

Compressor valve

[Blue~Go]

I could see where that would be really slick. I'll have to consider it. On the other hand, maybe there are times I'd like to use it elsewhere (even on a nearby vehicle) and so portable would be nice. Hmmm, more to consider.

[Blue~Go]

I just spoke with the very helpful Jesse at Viair. I'll try to write down the details, although there were a lot (whew).

So, if you look at the chart I posted above, you see that the "RV" compressors don't necessarily fit for us (although of course they would work fine, I've used my buddy's 450P-RV and it's great). But, it will go up to 150psi and have a 100% duty cycle at 100 psi. It also has 60' of hose (plus 8' of electrical cord). So kind of overkill. I have thus temporarily ruled them out.

If you look in the next column to the left, it's for people who want to "air up or down" for going off-road. I might like to start trying this. Not sure if I will but I'd like the capability. You can see that those are all battery hookup ones (alligator clips), and even the smallest of those, the 300P, will work for a 33" tire (stock tires on the Chinook are just under 30" diameter).

The next choice is about Automatic or not. They are plusses and minuses to each. Basically, in order to check the air in the tire as you are filling, you have to cut off the flow of compressor air. On the non-automatic one like the 300P, that means you walk over to the compressor, shut it off, then back to the tire to look at the inline gauge. So right now you are thinking Automatic for sure, right? BUT, on the Automatic you have to hold it on all the time you are filling, like a gas pump where they have removed those little holder-onners. But when you let go of the trigger the compressor stays on (but kind of like in neutral so no air is flowing) and you can check the air pressure right there. With the non-Automatic you don't have to hold the trigger while it fills. The 300P is not Automatic. I think you have to go to the 400P or above to get that.

There are at least three different chuck types available (not all on all models). The 450P-RV and the 300P both have the one where you put it on and then flip a lever down. I know some of the smaller ones (77P vs. 78P for example) have either a screw on or the flip down. And there is a reverse chuck they mention (like to use on duallies that have short stems), but I'm not sure which model(s) that is on.

I then asked about someone who only wants to use it in the "normal" way to add air to a low tire. Then the 87P or 90P could be fine. They don't have thermal cutoff, and the gauge is on the compressor not on the hose at the tire.

So I'm still not sure which one I want! I'll have to compare prices, but I'm thinking maybe the 300P if I don't want the Automatic function (not sure I do). I'll have to look at my buddy's compressor again because I don't remember having to hold the compressor air flow on, so maybe that's no big deal (or maybe I even misunderstood).

If you narrow it down to two or three models you can look them up on Amazon or wherever and compare more details.

By the way, they said that the duty cycle is basically linear. So, for example, if a compressor had a 33% duty cycle at 100 psi, it would have a 66% duty cycle at 50 psi. Since many of them are rated at much higher psi than we would typically use with stockish tires, that may come into play in choosing. The 300P and up have a thermal cutoff.

Hopefully this doesn't muddy the waters even more. I'm still not out of the woods in terms of completely understanding the nine billion choices

BG