Tire Pressure

I'm sure there are some tire shop guys that are knowledgeable. I just have not found them yet. The guys in the shop change on a regular basis. Some just don't know and the others don't care.

The owner has other interest than learning about tire inflation pressure. Also they install all kinds of tires.

It's easier to just say tell the guys in the shop air the truck tires to 100# than it is to say air the steers to 105, air the drives to 80, air the spread axle trailers to 110, air the closed tandems to 80 and so on.

To be honest when I take my truck or trailer in if I can get my tire work done without them tearing up something I feel I have done pretty good.

The last three times in the tire shop I have had to replace lug bolts and nuts because of them stripping them out. I had to replace them myself while they were working on the tires.

Also I have to watch them to make sure they put the balancers on correctly and that they put the outside dual on where I can still get to the inside dual valve stem.

More than once I have arrived home and went to check the air pressure only to find they had put the wheels on wrong and I had to jack up the truck and change the wheel position to be able to get to the inside dual.

So you see I don't have a lot of confidence in the guys at the tire shop and they have earned it.

 

The thing is, normal use is susceptible to normal wear and tear (and trucking takes some of the tire components beyond normal use somewhat independently of weight).

My revised and more informed opinion, based on experience and questioning best practices, is that the point of inflating to max pressure is to have a margin of error (as I suspected). Where is the error though? Tire valves are quirky, they leak, because they get loose (or wear out), and do so while the tire is rolling, so having them at max pressure gives you the maximum margin for error in a leaking tire, which you don't know about yet, whether it's the valve core needing torqued or a nail you rolled over. The more air pressure it has, the more of a reserve is in there for the quirky situation that it is, in practice. Like the opposite of an air hose, where it has a working pressure and a burst pressure, for a margin of error, as a best practice. The truck tire's working pressure should be its max sidewall, because the burst pressure tends to be when it gets significantly lower, and can do so on the fly. Happens to me often enough to keep them inflated as a rule, and check the valve core tightness (or replace those) when they are underinflated, with no audible leak. The valves can leak intermittently, so it isn't always obvious on inspection, and I think they are more likely to leak the most while being vibrated over the road, where you wouldn't know it at the time. Just noticed that after fully inflating a tire the other day, which ended up being 30-40 psi lower at the next stop, so this isn't theoretical stuff I'm talking about. Having them inflated to a minumum, on the margin, gives you no margin of error.

You know, there's a reason for these ubiquitous cores and torque tools (ones at auto parts stores work for me). It is normal for valves to loosen by themselves or wear out (therefore it is equally normal for tires to leak, and this should be presumed typical at any time, to include a margin of error as the basis for preferring max inflation), especially with heavy use, as is the basis for trucking.

Still, I don't know how long it takes to blow out the average valve, Schrader may or may not make a higher pressure core, for the high pressure valve stems (yeah, it looks like they do for much higher pressure applications), but the one's I'm replacing look to be standard, so those may be typical on trucks, and I'm guessing the pressure is what wears them out, sooner or later (when they leak even if tight), well that's another gotcha (or something of an error in this margin of error? nah, standard air cores are said to range from 200-300 psi max, where up to 120 is probably okay, when the sidewall agrees, and the burst pressure is possibly much higher), mostly they get loose though.

 

For further reading, operator manuals say that underinflation, alone (apart from overloading), generates a lot more heat, which can cause a sudden tire fire or blowout. The heat also causes early tire damage (flex break, radial cracks, ply separation, irregular wear), because the tread contact with the road involves abnormal tire deflection when they're underinflated. So, truckers shouldn't be thinking that as long as the load isn't heavy, a low pressure tire won't matter. Low pressure by itself can be just as bad at lower weight as an overloaded tire (because it is essentially overloaded for being underinflated).

Going back to valves, what I've read in the operator manual confirms that most tire problems are caused as the result of slow leaks, and for as many underinflated tires as I find, it seems this is not well known or taken seriously. One thing I disagree with, that it says, is to check pressure with a gauge "weekly". I think for as serious a problem as this potentially is, they should be gauged each day when cold, which also clears out the valves and gives you a chance to listen for leaks there. Sometimes a valve core even fails on me from simply checking the pressure, so then I know it was on the verge of doing that while rolling, and it's better to replace it on a cold tire, so it can be properly inflated.

Perhaps I'm dealing with trailers that are run in relatively extreme conditions, as I encounter such issues more so than experts seem to expect them to happen (the ones I maintain regularly have ceased to have these problems nearly as often though). Such a trial by fire, for troubleshooting what was needed to keep them at proper pressure (and prevent tire fires for that matter), indicates to me that tires should be considered high maintenance equipment (because these issues can occur at any time), it doesn't take too long to check once you make it routine, however (and that's the way to do preventative maintenance with those). I think most tire problems can be solved by the driver, given the proper equipment and experience (trial & error, as it were). I kind of made it my hobby there for a while until it all made sense, and for how involved that got with developing best practices (without a shop at my disposal), I've found out how little training I had in the first place, not that it's complicated anymore, or a matter of superstition. I can't fix every tire, but more often than not it would be way more involved (at this point) to get a mechanic on the phone and go from there (or have it be between this and putting it off, not knowing what else could be done, which I think is mostly what happens in the real world).

Anyway, a couple of other tools I've tried are an extended valve cap remover + core tool, special order online (good for getting through the small holes on aluminum wheels), and another core torque tool on a small screw driver sized handle (which I found at a truck stop), that can give me easier access than the 4-way one pictured above at times (it's good to have different lengths depending on how the wheel is rotated too).

Even went as far as to seat a tire bead once, with a 5 gallon bead seater, which works without jacking up the wheel, and with an air hose plugged into the tire valve at the same time (the portable tank can be filled from the truck air system, as I configured a coupler for this from the parts dept.), but did so only to find it wasn't flat due to the valve leaking this time, the tire was actually punctured, I just couldn't hear where until I got some air in it. Still, I've seen this happen due to a leaking valve on a new tire (so it isn't necessarily a tire failure), and it could also happen when changing out a valve core, but for the couple I have changed, the bead stayed intact (I think the longer it sits flat, the more likely it will come unseated). Somehow this may seem extreme, although I've seen mobile tire technicians do the same, so it's common practice when the tire is okay otherwise (holding air afterward), and doable (DIY) depending on what you want to carry around, definitely need to have eye and ear protection for that too (at first I tried getting to an inner dual bead from under the trailer, and created an epic dust storm there, not enough of a gap on that side to seat the bead though, it's like everything else with truck wheels, hard to reach what we may have to work with from any angle).


Officially, it appears that the regs say a driver must "cause" various tire maintenance to be done, yet not by whom, so I figure that not having to drive the rig on a dilapidated set of wheels farther than absolutely necessary from where I started is safest in general (or it's unnecessary to wait around forever and a day until someone comes to me remotely), if I can cause it to be so simple. Well, 'if you want something done right', it's better to take your time than to find someone who's in a hurry... and I'm probably faster at that, for being there already.

 

Possibly a stupid question, but do you put it on the red or blue line?

 

Red. Unless you can inflate a tire with one foot on the brake pedal or have a hand brake that will stay down.

 

Thanks. The difference between the two lines were never adequately explained to me so I always get them confused.

 

Basically your air brakes have two chambers, one is the parking side and one is the service side. The parking side (Red line) requires air pressure to keep the brake released. The service side (Blue line) is just the opposite. It pushed the brakes down to engage the brake when air pressure is applied.
And something I learned the hard way and getting laughed at (I'm sure) by breakdown is all crossing the lines does and keep a valve open somewhere under the trailer.
A couple diagrams at http://www.totaltruckparts.net/brake/airschematics.html will show you how the system works.
-Steven

 

Thank you very much! So when I hook up the air line to fill tires to the red line I want to keep the trailer parking brake disengaged right?

 

Yes. Make sure the tractor brakes are applied, connect the air hose to the red glad hand and then push in the trailer valve. When finished airing up your tires pull out the trailer valve and connect it back to your trailer.

I went a different route and ran a 5/8" dot air line to a ball valve on the back of my tractor and have a female quick connect coupler screwed into the other side of the ball valve. I just connect my air hose to it and open the ball valve to inflate tires.

 

I keep meaning to do that same thing, Bdog. It's on my list. Also, I don't mean to complicate the issue with the brake line anti-freeze switchover. Not yet anyway.

One thing (besides all the other miscellaneous stuff in my toolbox) I never leave home without is a tire plug kit, the big truck sized kit. Bigger reaming tool and plugs than the automotive. It saved my delivery schedule once. Got a slow leak, couldn't find it, stopped at a Love's shop and it was right there on top of the RR drive tire, a nice machine screw. (I know, Love's found it, embarrassing. Not that I cared at that point) Love's refused to do a plug because the puncture was just on the sidewall, "company policy." I whipped out my go-go-gadget repair kit, got a plug in there, away I went. Smiling.

I totally agree with Camionneur (I have to, I'm afraid he'll post a new record length post if I disagree) about heat buildup and tire maintenance. The tire people and shop people I use and know tell me heat is the primary cause of blowouts. So then low air pressure can also cause crashes, excessive tire wear, reduced fuel economy, and contribute to a liberal voting profile. I definitely consider tire pressure and tire maintenance to be high maintenance equipment. I bought a killer digital tire pressure guage at the local NAPA store - accurate to 1/10th PSI. I was told that NASCAR teams use these guages on race day. Little point in checking tire pressures with a POS truckstop air pressure gauge, right?

I check my tire pressures frequently, and thump every morning in between. Some drivers say icky stuff about tire thumping, but it works. It may not provide an accurate pressure reading, but it'll sure tell you if a tire is flat, low, or off the rim. I check trailer tires every time. Almost every time the tandem tires are running on empty, and it's just a few minutes easy work to set them to the correct running pressure. (100psi) Safer, lower risk, better fuel economy, those minutes are time well spent, in my world. So, yeah, tires are a big deal.

I had a drive tire off the rim one morning at Coral City, IA rest area. It wouldn't grab the rim with the glad hand air chuck, so I figured to run it 20 or 30 miles, and warm it up, right? Well, I got to a mom and pop tire shop and it still wouldn't grab the rim, so after the kind, considerate people there said "maybe in a couple of hours," I ran the drive with air pressure up on a block, which took the flat tire off the ground,f which allowed that same flattire to grab the rim, ran it up to 100psi and away I went. Good trick, that.

My best tire trick so far was to purchase 8 new Michelin XLine EnergyD drive tires. They've been on there for 3 months so far, and the air pressure has not changed except for those differences caused by altitude and temperature. Great tires so far.