Z Scale Truck and Coupler Review
by David K. Smith, 2 March 2009
Z scale has at last reached the point where we now have competing brands of trucks and couplers. This is both good news and bad news: good because it means the scale is maturing, and bad because it inevitably gives rise to some confusion. In order to assist modelers trying to make sense of it all, I've assembled this guide to provide information on specifications, performance, compatibility and fidelity, as objectively as possible.
But first, a few disclaimers.
1. This article assumes the reader has a basic understanding of model railroading. It's not meant to be a "beginner's primer" on trucks and couplers.
2. Märklin trucks and couplers are not covered in detail, while Pro-Z and other Japanese products are not covered at all. The principal focus is on American-prototype freight trucks and knuckle-style couplers.
3. This review is not 100% comprehensive; Z scale has been around in America since the 80s, and I don't have samples of everything that's ever been made. There's quite a lot of information here, but there's still plenty more yet to present—for example, I've only just begun gathering information on passenger trucks. I'll be revising the review as time permits.
For additional information, including in-depth details on Märklin and Japanese products, plus conversion techniques and other tips, Do It Yourself in Z provides a truly outstanding resource.
Summary of Revisions
Subsequent to first publishing this article, four significant events have taken place:
1. Full Throttle (William Dean Wright) has officially released their "Bowser Buckler" trucks/couplers, now featured on their rolling stock and also available separately.
2. AZL has substantially redesigned their 36-inch wheelsets. (I am deeply honored to have learned that this very report was responsible for their decision to improve their wheelsets.)
3. Fox Valley Models has introduced metal replacement wheelsets for Micro-Trains trucks.
4. Full Throttle has released "Will's Wheels," metal replacement wheelsets for Micro-Trains trucks. (These were not available for review at this writing.)
In 1972 Märklin introduced Z scale to the world, and the era of the scale's birth imposed certain manufacturing limitations. Out of necessity, trucks and couplers were anything but realistic. Twelve years later, Kadee (now Micro-Trains) entered the market, and among other things they introduced Z scale automatic knuckle couplers based on their N scale Magne-Matics—a vast improvement, both functionally and aesthetically, over Märklin's claw. Micro-Trains' products soon became the industry standard, used—until recently—by every other manufacturer of rolling stock... except, of course, for Märklin.
In 2008, Micro-Trains ceased OEM sales of their trucks and couplers to other manufacturers, and have gone so far as to forbid the use of their trucks and couplers on any rolling stock not made by Micro-Trains. This of course forced other manufacturers to seek alternatives, and presently the market is in a bit of chaos. American Z Lines (AZL) was the first competition to appear, starting off with a 100-ton roller bearing truck with their own coupler. They followed this with their second truck, a Bettendorf-type with a revised version of their coupler called the "Auto-Latch."
Meanwhile, William Dean Wright (a.k.a. Full Throttle) has introduced a modified version of his own exclusive new trucks with metal wheels. They were originally supposed to feature fully-automatic magnetic couplers, but unfortunately the pre-production prototypes did not function as planned. In order to get them on the market sooner rather than later, the couplers were modified to be semi-functional: they couple easily, but have no means of uncoupling. Functional couplers may be introduced later, after the bugs are ironed out, but there's no official word when or if this might happen.
And now Fox Valley Models has tossed their hat into the ring—in a manner of speaking. Following the tremendous success with their N scale replacement metal wheelsets for Micro-Trains trucks, Fox Valley Models has introduced 33-inch replacements for Micro-Trains Z scale trucks. Their success in this new market might be gauged by the fact that the first production run sold out in a matter of weeks.
Understandably, as a consequence of this market fracture, the modeling community is standing like a herd of deer caught in the headlights. Which works with what? Which offer better performance? Which are more accurate? Follow along to find out.
Currently Available Products
The sheer breadth of the range of available products alone makes it patently clear that Micro-Trains solidly dominates the market. And, after having had something of a monopoly for a quarter-century, it's doubtful anyone could hope to catch up. This is not to say there's no room for competition, but it's a good bet that Micro-Trains will in all likelihood remain the industry leader. They also strengthened their position by providing Märklin-compatible products from the outset.
As of this writing (March 2009), the following Z scale trucks, couplers, and related items are available from Micro-Trains.
Trucks with couplers (1 pair):
Trucks without couplers (1 pair):
Bulk packs of trucks with couplers (10 pair):
Trucks with Märklin couplers (1 pair):
AMERICAN Z LINES
Undaunted by Micro-Trains' vice-grip on the Z scale truck and coupler market, AZL entered the fray in 2008 with their own truck, coupler and wheelset designs. As of this writing, the following items are available from AZL:
Full Throttle has introduced their own exclusive new trucks with metal wheels and semi-automatic couplers. They come fitted on their own rolling stock, and are available separately as replacements, along with Micro-Trains-compatible replacement wheelsets.
Note that Full Throttle has released a 70-ton roller bearing truck, but it's only available on rolling stock, and not available separately as of this writing.
FOX VALLEY MODELS
Fox Valley Models offers 33-inch replacement wheelsets for Micro-Trains trucks.
The single most critical part of any truck is the wheelset, and wheel geometry is key to reliable performance. The following table provides the vital statistics for all three competing brands of wheels.
NOTE: This table is in the process of being revised and expanded, with additional data to reflect variations in product lines as well as greater measurement accuracy.
Although AZL's earliest wheelsets evidently had problems with Micro-Track switches, all currently-available wheels perform adequately. Full Throttle and Fox Valley wheelsets are too new to have established a track record for performance, but based on their measurements—they are both a near dead-on match for Micro-Trains—and their flawless behavior on my test track, these metal wheels should perform very well indeed. In particular, Full Throttle wheels have a healthy fillet (the curved part where the flange meets the tread—see the section above on Flange Profiles), which enhances their ability to stay centered on the track. This is a feature that real wheels have, and for the same reason.
It's worth noting that quite a few modelers express a preference for metal wheels. According to the vast majority of reports I've read from experienced modelers, metal wheels tend to roll easier, track better, last longer, and require less cleaning than plastic wheels. And those who like the sound that metal wheels make appear to outnumber those who don't. Here's just one of many typical observations all echoing the same observations:
We have run our layout for literally hundreds of hours over the past few years, and found the plastic MT wheels gradually build up grunge on the tread and spread it around the layout, even with constantly cleaning the track. The metal wheels do not seem to have this propensity.
What gives metal wheels their performance edge? First, their extra mass improves their ability to follow and stay on the rails. Metal requires less cleaning because acetal plastics (such as Delrin) tend to be a "dirt magnet" due to the combination of a microscopic film on the surface (this film is why the plastic is slightly slippery—and nearly impossible to paint) and electrostatic charges that build up as the plastic rubs on the metal rails. And while acetal plastics seem indestructible, there have been reports of axle points wearing down after a significant amount of running, and worn or damaged axle points will lead to increased drag and wheel-dropping.
Do metal wheels really roll better? To answer this, I conducted a simple test. I fitted three identical cars with sets of trucks from the three manufacturers, placed each one on a 320-mm length of Micro-Trains flex track, elevated one end, and measured the point at which the car began to roll. I then repeated this with the other two cars. The results: Micro-Trains, 10-12 mm (~3.5% grade); AZL, 6-8 mm (~2% grade); Full Throttle, 4-5 mm (~1.5% grade). To be sure, it was not a definitive test; in order to be precise, I'd have to repeat the process many times with different sets of trucks to average out natural product variations. Plus, there are other variables at work; but even without exhaustive testing, it's pretty clear which wheels offer better rolling characteristics.
There is unfortunately no "industry standard" for axle length. When AZL introduced their trucks, the axle lengths were substantially longer than those from Micro-Trains. This disappointed many modelers who wanted functional couplers and metal wheels. Just to add to the confusion, when Full Throttle first introduced their own trucks, the axles were also slightly longer than Micro-Trains', even though they were intended to be the same.
Recently, Fox Valley Models has addressed this market need with replacement wheelsets that fit Micro-Trains trucks. (This follows their highly popular N scale replacement wheelsets.) Subsequently, Full Throttle has corrected the length of their axles, and they are now selling Micro-trains compatible replacement wheelsets.
Unfortunately, at the same time that Full Throttle corrected their axle length, they also changed the wheel profile, specifically the fillet, that which is responsible for their superior tracking. Evidently this was done in response to performance issues with small-radius curves and handlaid track, which is odd, since I have the tightest radius curves made on my layout (<6 inches) as well as handlaid track, and the wheels track on everything perfectly. But I'm only one modeler, and presumably this change was not done in a vacuum.
When comparing model wheels with real ones, the only meaningful dimension to consider is wheel diameter because, out of necessity, model flanges and treads are significantly larger than their real-life counterparts. Although the difference between 33-inch and 36-inch model wheels is difficult to perceive, it is noticeable when they're placed side-by-side. Some modelers have remarked that AZL 33-inch wheels appear larger than Micro-Trains 33-inch wheels, when in fact the difference is imperceptible; this is likely an illusion due to AZL's larger flanges.
For the record, Micro-Trains 33-inch wheels measure 33.2 scale inches, and their 36-inch wheels are scale 36 inches. AZL 33-inch wheels measure 33.4 scale inches, and their 36-inch wheels are scale 37.2 inches. Full Throttle and Fox Valley Models 33-inch wheels measure exactly 33 scale inches. And just for reference, Märklin wheels measure 38.25 inches (just about right for 125-ton trucks—if anyone ever made such trucks in Z scale, that is).
Why are model flanges and treads so large? If one was modeling a non-functional diorama, exact scale wheels would certainly be possible. But in order for them to function, flanges and treads must be oversized. Consider that the margin of error for model track gauge is about the width of a wheel tread that was exactly scaled down, which means exact scale wheels would not stay on the rails of model track. Scale flanges would only be effective if model trucks were equalized, allowing the wheels to track the rail perfectly, and the models weighed enough to make the tracking effective. There are other obstacles as well, due mostly to the fact that the physical forces at work in the real world do not scale down along with the model. Therefore we must live with discrepancies for the sake of functionality.
Numbers aside, there is one cosmetic aspect a wheel presents to the world that's not affected by physics or functionality: the shape of its face. And in this department, the Micro-Trains wheels come out on top, with slim tread edge and deep, smooth, sweeping curve toward the axle; AZL's newly-revised 36-inch wheels have a vastly-improved face design and take second place close behind Micro-Trains. Not to pick tiny nits, but if AZL is looking for top honors, they'll have to round out the scoop shape in the face—presently it's stepped, with a hard edge. But kudos to AZL for taking a giant step in the right direction!
Full Throttle and Fox Valley Models could both use some improvement in the cosmetics department; indeed, it's curious that these two wheels are cosmetically nearly identical—the only way I can distinguish them, actually, is by measuring their axles. While this is not an accusation that someone copied the others' design, it is nevertheless a curiosity, especially considering that they are both so different from AZL wheels—proof that the design options in Z scale are not the limiting factor, as has been claimed. The greater surprise, actually, was that Fox Valley wheels were so, well, ordinary-looking, considering that their N scale wheels are cosmetically the second-best in the business (close behind BLMA's newest offering, which features an N scale industry first: the backs of the wheels have the correct profile!).
The range of products from Micro-Trains is mind-boggling, including six truck styles: Andrews, Archbar, Bettendorf, 70-ton roller bearing, 100-ton roller bearing, and four-wheel passenger. After manufacturing Z scale trucks and couplers for twenty-five years, they've made some changes to their line, as one might expect. Evidently their very first trucks were tooled around 1982 by Nelson Gray, a model manufacturer from whom Micro-Trains (still Kadee at the time) obtained all of their original Z and Nn3 rolling stock.
Micro-Trains has since re-tooled the Nelson Gray trucks, and the new tooling quality is without question the best in the business. It's easy to differentiate the early Micro-Trains trucks from current ones: aside from the really crude tooling, the wheelsets tend to fit loosely, and are prone to drop out.
Some trucks will exhibit chronic wheel-dropping due to a weakness inherent in the design: one side of the bolster has a relief to clear the end of a body-mounted coupler pocket; this thin spot has a tendency to split, allowing the truck sides to spread and the wheels to drop out.
With the exception of their 100-ton roller bearing trucks and passenger trucks, which only come with truck-mounted couplers, all Micro-Trains trucks are available with or without couplers. Those without have the same weak spot in the bolster; trucks with couplers do not have this "Achilles heel."
Note that trucks with and without couplers use two different bolter pin types. Trucks with couplers take "round" pins, while those without take "flat" pins. The latter design prevents trucks from swiveling too far; they would otherwise be able to spin 360 degrees around the pin.
IMPORTANT: One thing modelers need to be aware of—and on the lookout for—is that old tooling trucks are still sitting around in some dealers' stock, and still being sold as new. This highlights one of the shortcomings of buying over the internet.
AMERICAN Z LINES
AZL currently provides us with two popular freight truck styles: a generic 100-ton roller bearing and a generic Bettendorf-style. The tooling on their first release, the roller bearing, is below par; ironically, this was done by Bowser, producer of Full Throttle's excellent new trucks. Tooled by Sanda Kan, AZL's Bettendorf represents an improvement.
William Dean Wright (a.k.a. Full Throttle) chose a Bettendorf type truck for his first release. As noted above, it was produced by Bowser, and currently stands as the second-best in the business as far as tooling quality and particularly fidelity.
Note that Full Throttle has released a 70-ton roller bearing truck, but it's only available on rolling stock, and not available separately as of this writing.
Can trucks be swapped? Yes and no. The bolster geometry of all three truck brands match, so in many cases it's a straight swap. However, because AZL and Full Throttle trucks are longer (read: correctly sized), their side frames may interfere with stirrups and other details on certain rolling stock, particularly Micro-Trains boxcars and cabooses.
Note that Full Throttle's trucks may prove to be less problematic than AZL's in this respect, as Full Throttle's trucks are around .030 inches (0.75 mm) narrower across the journal boxes. At any rate, truck-swapping will be a trial-and-error process for modelers for the foreseeable future.
While Micro-Trains still has no equal in terms of tooling quality, their accuracy deserves some scrutiny. It may come as a surprise that all of their trucks are substantially undersized, the wheelbase being up to a scale foot too short. This may sound trivial, but when something is only five feet long to begin with, it represents a 20% error, which is most definitely noticeable. In addition to being a foot too short, Micro-Trains' 100-ton roller bearing trucks have 33-inch wheels, when they should have 36-inch (swapping out M-T 36-inch wheelsets would only make the undersized-truck issue slightly worse).
What's curious is that some modelers remark that AZL and Full Throttle trucks look "too big," when in fact they have the correct wheelbase. The only explanation is that they've been conditioned by seeing Micro-Trains "dwarf" trucks for decades, and now correctly-sized trucks don't look right. I can only hope this changes over time.
While both of AZL's trucks have the correct wheelbase, they missed the mark on the height, particularly on their roller bearing truck—notice how "squashed" it looks. Also, the tooling on the roller bearing appears soft and indistinct—a "melted ice cream" look. This definitely compromises its appearance, and hopefully will be addressed now that the wheels have seen a radical improvement.
Then along comes Full Throttle, introducing a truck that hits the ball out of the park: it's got correctly-sized wheels at the correct wheelbase in a truck that's got the best overall proportions. In particular, notice how the side frames rise up above the bolster—this is how real trucks are, which explains why they're proportioned correctly. On top of this, the coupler pocket is shorter than that of either Micro-trains or AZL, resulting in more realistic spacing between cars—especially hoppers.
Having said all of this, many modelers could care less about any of these issues—to them, it's all just a lot of pointless rivet-counting. They just want trucks and couplers that work. Some modelers, however, do care about realism and accuracy, and those who would like to learn more should review Appendix A.
As stated previously, Micro-Trains' Z scale couplers are based on their N scale Magne-Matics, an enormous improvement over the only other available option at the time, the giant Märklin claw. The couplers consist of four parts: knuckle and shank, thumb and shank, spring, and trip pin. The spring is very delicate, allowing the couplers to couple with the slightest pressure. Magnets in or under the track pull the trip pin to one side, allowing the couplers to separate.
Curiously, as unbelievable as it may seem, it would appear that Micro-Trains has only one mold for their Z scale coupler. If by some chance they had more than one, then they all had precisely the same flaw in the knuckle face—a flaw that I've found on every coupler I own, and I own quite a darned few of them, from original-issue 80s vintage through to present-day. Considering the hundreds of thousands of injections they must have pulled from that mold, it must have paid for itself by now. Surely they could afford to re-tool it—preferably without the flaw?
AMERICAN Z LINES
Excluding various unique designs for products such as their locos, AZL is now on their third generation of truck-mounted knuckle coupler. Unlike Magne-Matics, AZL couplers were never meant to provide hands-free remote uncoupling. Thus they're not suited for "operators"—that is, modelers who wish to perform switching—or anyone who desires hands-free uncoupling. They're more appropriate for "runners" and, in particular, those who run long trains (50+ cars) at model train shows, where Micro-Trains couplers will sometimes fail.
Although they appear to be nearly identical, AZL's three coupler designs can be distinguished by their appearance and, in particular, their behavior. The first two versions, which come on their roller bearing trucks, have a tiny pin molded onto the side of the knuckle, and the coupler also moves side-to-side in the pocket with relative ease. However, the couplers do not couple easily—sometimes they will not even couple under considerable pressure, behaving more like dummy couplers than anything even partially functional. Also, the first generation had an internal design flaw that allowed the couplers to pull apart easily; this was corrected in the second generation.
Their third design, the "Auto-Latch" coupler, was originally exclusive to their Bettendorf trucks; going forward, they're replacing the older couplers on their roller bearing trucks. The Auto-Latch is new tooling; it has no pin on the side of the knuckle, and the shape is also improved. There's almost no side-to-side play in the pocket, but the couplers will couple with relatively gentle pressure (although not as easily as Micro-Trains).
The Full Throttle coupler represents an all-new design that's totally different from either Micro-Trains or AZL. In function, the coupler is closer to the McHenry in N scale: the knuckle (blue) pivots on the trip pin like a hinge. But instead of a metal spring on the side of the knuckle, as in the McHenry, the Bowser coupler has a "cat whisker" spring that presses against the side of the solid, one-piece coupler shank. The end of the shank (black) has a pair of cat whisker springs that press on the inside of the coupler pocket to center the coupler.
A this point in time, Micro-Trains remains the only source for fully-functional couplers with hands-free operation in Z scale, but this comes at a price: the dreaded "slinky effect." Micro-Trains couplers are sprung internally in such a way that permits movement along the coupler shaft axis, and when they are under tension, the couplers will extend out of the coupler pocket slightly. When a train is in motion on relatively level track, subtle changes in tension will cause the couplers to extend and contract; eventually the cars will oscillate, producing the characteristic (and, to many modelers, annoying) slinky effect, as the whole train expands and contracts rhythmically, like an accordion.
In spite of their inability to uncouple, AZL couplers do have some positive noteworthy performance attributes in contrast to Micro-Trains. First, no slinky effect. They have an entirely different internal design that does not allow the couplers to extend out of the pocket. Also, the Auto-Latch couplers will stay coupled more reliably than Micro-Trains, which is a benefit for fellows who run long trains at shows. In fact, they are claimed to withstand seven pounds of pull—that's right, not seven ounces, but seven pounds!
In theory, Full Throttle's design should work; unfortunately, the knuckle "spring" was too stiff, preventing the coupler from uncoupling magnetically. There was also an issue with the trip pin not remaining in alignment with the knuckle. Since re-tooling is presently not an option, Bowser elected to release the current design in a form that operates like AZLs, which can couple but cannot uncouple. The trip pins were clipped off at the knuckle.
In spite of these issues, they at least couple easily, with a gentle push (as compared with AZL, where it requires a firm shove). It's also worth emphasizing that Full Throttle couplers exhibit no slinky effect, and should remain reliably coupled under the stress of long trains.
All three coupler types will couple with one another in any combination. And, with the exception of early AZL couplers (which must be treated like totally non-functional dummy couplers), they will all couple with relative ease.
NOTE: The compatibility aspect cannot be overstated, because there is evidently some confusion among modelers as to which will work with what. If you must have magnetic uncoupling, right now you have only one choice—Micro-Trains. But if you simply need cars to couple together, it does not matter which coupler a car has—they will all play nicely together.
While vaguely following the general overall form of an AAR Type "E" coupler, model couplers are anything but realistic, simply because functionality will always compromise appearance, especially in smaller scales. Out of necessity, they will all be oversized and oddly shaped, and there's nothing that can be done about it. In general, all three couplers are for the most part fairly similar in terms of overall size and shape, and difficult to distinguish with a casual glance.
If you're picky about appearance, you'll note that Micro-Trains couplers have an unsightly plastic loop around the trip pin, which some modelers optimistically claim looks something like an air hose. This is definitely an "eye of the beholder" thing.
Since AZL couplers do not uncouple, their appearance suffers fewer compromises, although their shanks are longer than they need to be, exacerbating the problem of excess space between coupled cars. While oversized, the knuckle has a more realistic shape, with no odd holes or trip pins.
Cosmetically, Full Throttle's couplers could be described as a cross between Micro-Trains and AZL. However, their ability to achieve closer coupling is a truly remarkable achievement, compensating to some degree for their shortcomings.
At the end of the day, modelers must choose based on what they expect to do. Operators and anyone else looking to do hands-free uncoupling still have only one choice: Micro-trains. Runners can more or less mix and match; those who run long (50+ cars) trains may want to make the switch to AZL or Full Throttle to avoid accidental uncoupling, as well as eliminating the slinky effect. Modelers looking for cosmetic accuracy have Full Throttle's beautiful Bettendorfs and AZL' improved roller bearing trucks. Those few who care about achieving the greatest fidelity for their modeling should review Appendix A.
In My Opinion
Z scale has come a long way in nearly four decades, but it still has a ways yet to go. I was not alone in feeling dismayed, even betrayed, by Micro-Trains' draconian decision to cease OEM sales. But in the process of researching and preparing this report, I've come to the conclusion that it was perhaps one of the best things that could have happened to the scale.
Micro-Trains could have remained the industry standard, and held a virtual monopoly on trucks and couplers indefinitely. As an example of just how dependent the industry had become on Micro-Trains, their OEM policy change very nearly put Full Throttle out of business. If it wasn't for Will's tenacity, we might have lost his wonderful product line, and more particularly, he would have lost his livelihood. That's a scary thought, and had Will gone under, I don't think I could have lived with myself had I been the one responsible for the OEM policy change at Micro-Trains. But Will survived, thankfully, and now we've gained a growing range of truck and coupler options, further freeing the market of Micro-Trains' stranglehold.
Another surprise to emerge from all of this was the realization that Micro-Trains completely missed the mark in terms of accuracy—in particular, that all of their trucks averaged about a scale foot too short, which is not a trivial discrepancy. Then there's the slinky effect, which has plagued us throughout Z scale's history, something we've just had to live with because it was the only game in town.
The new kids on the trucks and couplers block will not find it an easy market to break into, though, and both of the newcomers are having some teething problems. We'll need to give AZL and Full Throttle more time to see if one of them emerges as the new champion, or if the market will remain fractured. Ultimately, the market will shape itself through economics. Our voices alone will not be enough to influence it significantly; it will require our wallets.
For what it's worth, even though the Full Throttle product fell short of its intended target, I personally think it's still a winner. Consider: metal wheels, correct wheelbase, and a unique new coupler that provides close-coupling and no slinky effect—two Holy Grails of Z scale trucks and couplers in one product. Even if Bowser never perfects their fully-automatic coupler operation, I still choose them over the others.
In closing, allow me to answer to those who might accuse me of bias against Micro-Trains. Believe me, I'm right up there waving their flag as the champions of Z scale; there is absolutely no doubt that they produce products of unmatched quality and reliability, and the vast majority of modelers are perfectly content with their products. It's just that some modelers appreciate what AZL and Full Throttle are attempting to do, and because of this we know that it's possible to improve on what Micro-trains has done. At the same time, we must also acknowledge the reality of the situation: through their own business actions, Micro-Trains is responsible for bringing about much of the competition they now face; only the most myopic Micro-Trains supporters could possibly turn a blind eye to their blunders.
I'd like to thank the following individuals for contributions, corrections and encouragement: Ed Kapuscinski, Gregg Mahlkov (RIP) and Tom Mann, with very special thanks to William Dean Wright for so generously allowing me to introduce and review his new products, and to Robert Kluz for his vast knowledge of all things AZL, as well as samples of the new AZL wheelsets. Also thanks to Darrell Sawyer, Freight Cars Illustrated, for kindly providing many of the prototype truck photos.
Copyright © 2007-2013 by David K. Smith. All Rights Reserved.