New feet for the ol' Prius

At some point during 2009 I began vaguely thinking about replacing the hardworking Hydroedges on the Prius. They had already served a solid 70,000 or more miles -- and that despite the feathering effects of a minor misalignment in a rear wheel, and a very slow recovery across the right-side pair had been ongoing once that was corrected. Then one of them suffered a fatal puncture on one of that summer's roadtrips, pronounced too close to the sidewall to reliably patch -- leading to having one oddball cheap-ass Korean tire on the car and the three remaining Hydroedges. Despite the odd tire still being fairly new, maybe at this point it was just time to employ the bigger hammer and get a whole new set. Among other advantages, it would fix the serious mismatch in the wheel speed delta indicator caused by the one odd tire being a slightly different size.

This was helped along by the parental collective wanting to supply a nice holiday-time present, so the decision was made to forgo the remaining service life in the old tires and swap to something newer and hopefully better. Not that the Hydroedges weren't fine tires in their own right, but there seemed to be some interesting new options emerging on the market.

In fortuitous synchrony with this idea being hatched, a fellow participant in one of the forums I'm on had read about my scary experiences with prematurely degenerating valve stems and a brief mention of having tire trouble on the recent road trip, and offered to send me gratis a set of four of the type of metal bolt-in valve stems I had favorably mentioned in the safety writeup. Said it wasn't any particular trouble or expense, he had 'em laying around. A while later, a package containing four Milton 409 type valve assemblies showed up in the mail. "Top shelf stuff", he said in a followup.

This was fascinating, but having never actually used such things yet it was unclear to me where to install the two rubber gaskets. [Well, if I had actually looked up the catalog page earlier in the game, I could have probably figured it out.] My forum buddy quickly set me straight -- only *one* is used at installation, and which one depends on the size of the rim hole. Okay, now it was bleedin' obvious -- I'd only need the one with the .453" diameter flange, as rims with the larger holes are fairly rare.

At the same time, having a collection of new stems recalled a tiny bit of concern about how firmly the little valve cores had been installed. At one point in the past I had discovered [by observing a minor straight-line anomaly developing in the aforementioned "green diamond", in fact] that at least one of my present rubber valve stems had been leaking just a little -- because the valve body itself wasn't tightened into the stem properly and a tiny bleed of air was getting out past that and the cap. Easy enough to fix with a valve tool at the time, but I thought it prudent to check that on these too. That led to total disassembly and inspection of all four.

Well, one of these things was not like the others. Its core body seal came out black instead of red, and somewhere I seem to recall a mention that red core seals indicate higher pressure tolerance than other colors. I cannot substantiate that but there are hints about different colors matched to different applications and conditions in some of the material on Schrader's web site -- either way, it was already clear that there was something odd about this third stem.

The difference didn't stop there -- one of this stem's mounting gaskets seemed to have a little problem: the lip was clearly distorted and wouldn't stand up straight. [It's the one on the left here.] That would be anything but straightforward to insert into a close-fitting rim hole. I figured that maybe the nut had been threaded down a little too far when the stem was put together and boxed and it squeezed the gasket, so I tried just leaving the gasket to sit for a while hoping it would straighten itself out.

It didn't.

Closer examination also revealed a defect of some sort in the gasket itself, which would very likely fail to seal properly even if installed right. I notified my forum benefactor and included the preceding three pictures, and he was kind enough to send along two *more* stems. Now I had a good set of four, red core seals and all, and with perfect timing to take along on my impending southern trip.
Working through all this also provided an excuse for me to construct a better Schrader valve core tool, semi-visible in green and silver here, that has a small hole all the way through and *doesn't* press down on the center pin when applied. I've already got one of those typical four-way tools with the thread reconditioners, as shown on page 15 of the abovementioned Milton catalog, but the little forky-stick it uses to remove the valve isn't cut deep enough to avoid pressing on the pin. That made checking all the old valves interesting since trying to just use the tool let quite a lot of air *out* of the tires which I then had to top back up. [Yes, I unweighted each wheel on a jack before going at that to avoid bead separation, but a proper tool could have made it much easier.] The tubular end of an old bicycle pump hose fitting happened to be the right diameter, and a simple slot dremeled across the end made the correct notch to grab the valve core bridge. Here, pre-installation, I figured I could just get all the cores out and make sure their little seals were in solid shape and torque them back in properly.

Fast forward to December, which found me temporarily in much warmer climates. After talking with the guys at the local Pit Stop Auto, we agreed that they'd have no problem using my supplied metal stems and letting me go into the shop areas and work with the tech to exchange some Prius-related hints for a little more info about the tire-mounting process. I never really documented the first time when the Hydroedges were installed, but wanted to collect a little more info on this go-round. Once I demonstrated that I pretty much knew what I was talking about, they were fine with it. More shops need to operate like this -- most of them have fallen victim to "too many lawyers" disease and are terrified of letting customers anywhere near work in progress. We scheduled a day after the tires would be ordered and delivered when I'd come back and have it done.

For the second time in its life, the car went up on a lift for getting all four wheels off at once. This is a multi-purpose rack, mostly designed for wheel alignment but can also be used for various other work that needs the vehicle lifted.

Ian was the technician assigned to me that morning, and was perfectly okay with me hanging around with him and snagging some pictures of the process. He had also undergone some nominal amount of hybrid training at some point and understood the quirks of the Prius control system.

Lifting was done much more carefully than the previous time at Hogan Tire back home, where they have those low-profile flat-plate lifts which just ram up under the pinch welds in a somewhat haphazard way. Here, Ian carefully placed the right type of rubber pads under the correct points at the rear axle beam and the front wishbones and made sure nothing would receive undue stresses. Not much extra lift above rack level was needed, of course, and this placement made for very little unweighting of the suspension.

The little steel rollers that the lifting scissors ride on, however, seem to have gotten a bit sketchy-looking over their lifetime on this rack.

Ian was rather amazed at the condition of my brakes at 120,000+ miles -- quite free of crud, and still on the *original* pads and shoes. I somewhat proudly pulled off one of the rear drums, saying "see? none of the typical old rust freezing it onto the hub" to show him the nice clean interior parts.

[This also shows, albeit badly washed out, my custom rework of the canonical "Mt. Washington" sticker which I could not in good conscience apply to my car with the as-given stock phrasing. The pix from that trip are still in process, and will hopefully hit the net someday.]

We rolled the wheels into the back, and Ian wrangled off the first Hydroedge and handed me the rim to go examine outside where there was more light. Here's the old stem still in the hole. There's quite a bit of old rubber gunk stuck to the bead area but that doesn't seem to affect the mounting of new tires at all. I'm still astounded that tubeless tires work as well as they do in the first place.

In many of these shots, the scarlet highlights are from sunlight bouncing off the brightly-painted red wall of the building.

The valve core of the old stem had already been removed, of course, to facilitate quick deflation. I didn't bother bringing down the 55 - 60 PSI in these before going to the shop, so that initial hiss was pretty loud as Ian removed the cores -- but the people at this place seem to understand the value of high pressure and didn't bat an eye when I told them the Hydroedges had spent most of their life well above sidewall.

What I wanted to do was get one of the old stems out without just cutting the ball off, to possibly do a bit of postmortem on where it bore against the rim hole. But really, these weren't dead at all, especially with not having been from the Chinese lot of defective Dills. I did accomplish the goal with minimal mangling, carefully prodding the flange back through the hole with a small screwdriver and working it out. Nothing seemed out of the ordinary, and I could see no notable effects from withstanding air pressure at or sometimes above to their on-paper limits all that time.

The new stem and its .453" collar fit *perfectly*, almost like it was designed for that rim, with plenty of room for the inner stem plate to seat.

The washer and nut on the other side fit with equivalent dimensional elegance ...

... and the whole thing gave a much lower height profile than standard rubber stems.

Meanwhile, Ian was already mounting up the new tires -- here letting the machine squidge the bead over the rim lip ...

... and then seating the bead with a bit of air pressure. As the final gap closed, the bead snapped up into the seating area with a quite energetic pop.

The new feet are Michelin Energy Saver A/S, made from the new "Green-X" silica-based tread materials and claimed to have very low rolling resistance. It's nice to see the "M+S" mud and snow rating right there too. Ian kept going on about how nice a tire these are -- not cheap by any means, but he was confident I'd be really pleased with them.

Sidewall is 44 PSI on these, and Ian said he'd pump them up right to there instead of believing any manufacturer BS from the car door placard. Yup, he knows his stuff. [Although a close look here shows that he installed the mounting nut backwards on this stem with the rounded side inward, but that's pretty insignificant.]

They are also a nondirectional tread, meaning I can go back to a cross-side rotation pattern if I want.

Next step was to spin-balance them all, and of course we'd first want the valves fully assembled with their fairly heavy metal caps installed. While this balancer isn't the much more fancy "road load" type of unit with an outboard roller, this one does its sensing magic quite well including determining whether to attach the calculated weight to the inside or outside of the rim.

The balancer's test spin doesn't take very long; if you blink you'd miss it.

After banging on the weights, a final spin check was done and all wheels came up dead-zero with no further correction needed. Cool. Not surprisingly, every wheel wound up with a largish weight mostly opposite the valve stem. With standard stems it's sort of a toss-up whether the valve will be at the lightest or heaviest part of the assembled wheel, as the valve may compensate more or less for the removed metal of the hole; but these metal stems are somewhat heavier than their rubber counterparts. Otherwise, Michelin's molding jobs generally produce a very uniform product; they don't even bother marking the "heavy spot" on their tires because for the most part there isn't one that would significantly affect mounting.

This is the last I saw of the Hydroedges and their bastard cousin, now sitting empty and unloved but nonetheless fondly remembered over several years of roadtrips, freight-hauling, energy festivals, car shows, and MPG competitions. Hopefully they would all find their way into some useful recycled function, such as being part of a macadam mixture for new road surfaces which is frequently done with ground-up tire rubber.

Take a close look at the big picture here. See any "center wear"? These spent their 70K+ miles of life above 50 PSI for the most part, and the wear shows dead-flat across the entire tread. That should lay to rest anything the ignorant naysayers claim about "overinflation" forever. What we *can* see, much more subtly on the top tire of the stack, is the slight cupping/feathering that had developed from the rear toe-in -- which was also well on its way to recovery after the rear hub was shimmed, but would now never have a chance to flatten out the rest of the way. I really did have mixed feelings about not being able to run that long-term test to its completion.

I finally understand how a torque stick works. It *looks* like a simple extended socket, which we'd expect to act as a rigid object that wouldn't limit anything unless it physically broke, but the way it works depends on the fact that a typical air impact wrench is driving it intermittently. The thin shaft twists elastically under each impulse, yielding just enough to *not* transmit any additional torque into the lug nut, and rebounds before the next hit. As Ian pointed out you can get up to the rated torque and then stand there letting it hammer away forever and just not be able to tighten down any further. Obviously if the wrench's output was steady, this trick wouldn't work as desired.
Ian also didn't bat an eye when I told him there was a little anti-seize on my lug threads, and he likely appreciated how easily the nuts went back on. Apparently there are a lot of sadly misguided people who actually believe that you should leave them dead-dry, and then they wonder why they can never easily spin them off and on by hand. They'll be the ones stomping on the wrench handle and breaking their own studs off two years from now, preferably at night in a cold rain, as they're wrestling with threads jammed up by surface corrosion and inevitable spalling.
On a prius in particular, and probably any other car that has lugnuts of this same sort, what really helps is to get a tiny bit of anti-seize in here between the outer nut body and the washer. This is the mating surface that makes that "crack!" as it breaks loose after being on the car for a while and accumulating a little bit of corrosion. On these the washer can tilt just enough to allow a thin tool to deposit a little wisp of anti-seize in there and then you can spin the parts and work it around to distribute. With these surfaces better able to slide over each other, lugnuts that have been undisturbed for a year-plus come off "like buttah" -- and that does *not* mean there's any compromise to holding torque or a tendency to self-loosen as the "dry parts" delusionists would have you believe.

With the car finally back on tarmac-firma, I settled our paperwork [including handing the guys at the desk a printout of my valvestem rant and a couple of flyers], and headed off. I could tell the difference within a hundred yards after pulling out of the shop driveway. These things really *roll*. My glides immediately seemed to be going longer, using momentum much more effectively. The car now felt like a 3,000 pound object sitting on an air table -- once the effort was applied to get it moving, it just wanted to keep going forever. And the *lack* of tread noise was a welcome relief from the rumbling of the Hydroedges I'd gotten so used to, not to mention the fact that the green diamond was once again usefully functional with the top and bottom LEDs almost invariant on a straight road.

With around-town average MPG reaching into the 70s on those warm flatland local roads over the next few days, I figured I'd made a good choice.

_H*   091225