Some derailleurs have interesting mechanisms but which are subtle or hidden and are easy to overlook. In contrast, the SunTour Superbe Tech uses a conventional parallelogram, but it looks highly unusual.
There are no gears in the design, but it might seem that way — from the outside, the operation is a mystery. Also, disassembling it is risky: you might never get it together again! Indeed, the first one I saw was damaged and disassembled; it was unclear if it was damaged before or after disassembly, but by the time I saw it, it was permanently damaged, and several mechanics opined reassembly was not possible, or at best difficult and not worth-while.
Many photos follow, but the key observation is that the mechanism is an parallelogram, The parallelogram is odd because it is assembled inside a box: the box is one "long side" of the parallogram. A bent wire is the other "long side" of the parallelogram. Finally, two triangular segments are the two short sides. It looks odd, but the operation is entirely conventional.
Overview: the derailleur in pieces:
Picture below: the upper and lower sub-assemblies. The upper sub-assembly is bolted to the frame. The lower sub-assembly holds the cage with the jockey pullies. Both pivots have springs. The upper assembly has a spring under the rounded dark gray plate; it is not visible in the picture. The lower assembly has a spring that sits above the rounded dark gray plate, it is shown sitting off to one side. For both springs, one end of the spring goes in a hole in the dark plate; the other end presses against the upper case. The dark wire on the righ to fhte lower plate is the "long side" of the parallelogram which sits inside the case:
Below: lower plate and linkage holds the cage spring and cage with jockey pulleys. The first photo shows the parts as they would be with the chain on the smallest/outboard sprocket; the second photo shows the parts as they would be with the chain on the largest/inboard sprocket:
The upper plate/case. The first photo shows the parts as they would be with the chain on the smallest/outboard sprocket; the second photo shows the parts as with the chain on the largest/inboard sprocket:
Below: more perspectives on the linkage. The wire that makes the "long side" is a very wide and not-tall "U", where each end fits in one of the dark-gray plates. Each dark gray plate has a "nub" that sticks up from the plate and contacts the limit adjustment screw:
Many modern derailleurs use a parallelogram with a spring on the bolt which attaches the derailleur on the frame. That upper spring allows the whole derailleur to "float" vertically and so the upper jockey pulley can closely follow the sprockets — and thus give good shifting.
In this derailleur, there is no such spring, so the derailleur has a fixed location relative to the frame. A fixed location allows a cable to run without housing from the frame to the derailleur, except for a short (approx 1 cm) and smooth bent tube mounted on the chainstay. This "housing-free" approach nearly eliminates cable friction and problems with the housing getting clogged.
The Superbe Tech was made briefly but withdrawn. [Disraeli Gears as of 2016/11] shows it as having been made in only 1983, with a GranTech variant offered in maybe 1985.
Several retrospectives say the derailleur design had problems and SunTour was having financial problems which kept them from investing more in improving the design.
The Superbe Tech was offered in mid-cage (Superbe Tech L 4800) and long-cage (Superbe Tech GTL 5400). They use use a conventional spring attached the lower parallelogram assembly, plus another spring inside the upper jockey pulley. The paired springs allow the upper jockey pulley to closely track the sprockets. However, to fit the spring inside the pulley, it uses a design which has high friction and wears quickly. (The spring-in pulley design was introduced in 1982 on MounTech derailleurs; presumably it took a bit over a year for SunTour to realize the extent of the problem.)
There is also short-cage version which uses normal pulleys. The short cage uses a conventional design where the upper pulley is offset from the cage pivot. The upper pulley thus follows a pre-determined path, rather than tracking the sprockets. If you have the right mix of rear sprockets and the front chainrings are close in size, then shifting can be good; but many common gearing combinations cause the upper pulley to move far away from the sprockets in some gears, leading to poor shifting.
Another reportedproblem is the parallelogram breaks. As shown above, the parallelogram's "long side" which is inside the box is made of a bent piece of where, which is about 1 mm diameter. It has been reported that this sometimes would break or the U would straighten. [Disraeli Gears as of 2016/11] shows an example where this has happened. It may be that the wire failed only under duress -- e.g., in a crash that would also have broken other derailleurs -- but the unusual design means the design gets blamed rather than the crash.
It is (perhaps) interesting to speculate about the durability of the "sealed" design. In principle, the pivots are protected from the elements, but the two main parallelogram pivots pierce the top of the "case" and so gravity may tend to carry in debris which can cause wear.
Also, it appears the bearing surfaces are thin (the thickness of the case) and made of aluminum, both of which probably contribute to faster wear.
Finally, there is no obvious lubrication port to flush out debris which does get inside; and as noted above, reassembly is challenging.
These are probably all solvable problems — a slightly more complex casting might allow construction where the lower main parallelogram pivot only exits the bottom of the case. A slightly more complex casting would allow the upper main parallelogram pivot has a "skirt" over the place it enters the top of the case. A lubrication port of some sort is clearly feasible.
It also seems likely that the fast-wearing upper pulley could be replaced with a conventional pulley plus an "external" spring placed next to the pulley.
Indeed, SunTour had such a design in the MounTech II GTL (1985). An example at [Disraeli Gears as of 2016/11] shows the secondary pivot also wore quickly, but likely that problem can be solved farm more easily than solving the spring-in-pivot problems. But again the design was scrapped, rather than continue to invest in improving it.
As an aside: the "spring in pulley" design is fundamentally flawed because it uses a large-diameter bearing and large-diameter seal to the outside world. Both are problems:
The pulley rolling over a large-diameter bearing has less leverage against the friction of the bearing compared to a small-diameter bearing. This can win if the large bearing has much less friction than the small one, but if the big bearing is merely the same friction as the small one, the small one wins.
Although bearing friction may seem so small as to ignore, studies have suggested that in many scenarios 1-2% of the rider's total power output goes to just pulley friction! The key observation is the drag force is low, but the chain goes fast, and power is force times distance, so a small force over a large distance is still significat. In turn, there is a trend towards both improved bearings and larger pulleys in order to reduce this drag. The SunTour "spring-in-pulley" design had more drag, so was going the wrong direction.
The pulley also has a large-diameter gap between the moving pulley and the stationary parts of the derailleur. This large diameter is a problem for several reasons: The gap is closer to the crud on the chain; the gap is longer meaning there is more length to let in crud; the gap is turning faster than with a small-diameter gap, so any wear happens faster (same observation as force vs. power above).
As an aside, these problems also occur with "center-less" wheels. Every year, one or more "designers" attempt to "revolutionize" bicycles by flogging bicycle wheels with no hubs and no centers; instead, the bearings are around the edge of the wheel. It looks cool, but it is very hard to make a centerless wheel which is durable, has low friction, and is strong. There are many reasons it is hard; one group of reasons is the bearings don't last as well.
You can imagine SunTour could have built a large bearing with "sides" that reach towards the center so the gap is a small diameter. You can imagine that, but that's not what SunTour did.
The Superbe Tech addressed at least two problems; the design did not work out, but the problems did not simply go away:
How have we progressed?
Vivo made a "grunge guard" rubber boot that went over a conventional derailleur. It helped both wear and clogging problems, but added friction to the derailleur motion and thus interfered with shifting. The effect was most pronounced with convention indexed shifting, which is already easily thrown off by friction.
An added problem is that rubber boots are prone to tear and start letting in crud that in turn causes wear or clogging . Although boots can be replaced, this is a maintenance effort and cost, so a system that offers less service, like the Superbe Tech, still offers a possible advantage.
Vivo then made a whole derailleur with a rubber boot. The boot was built-in rather than retrofit, so the friction problems were eliminated.
The Vivo worked well and was slated to be replaced by a revised version. However, Shimano bought the company and patent rights and the revised derailleur was never released. (It appears the company was bought for patents on the shift cable path, in order to compete with other big makers, and not because Vivo's derailleurs were seen as an obvious and immediate threat to Shimano.)
Derailleur pivots are today often made of more wear-resistant materials and the pivots are spaced more widely, so the wear that does occur has less effect on the derailleur's performance.
Mud and snow cloggling is still a problem with an open parallelogram. However, many more riders were suffering from wear than from frequent clogging, so reduced wear is still a significan advantage.
Derailleurs today often use a cable path that approximates the SunTour Superbe Tech, by having a short and nearly-straight section of housing between the derailleur and the frame. The short housing segment allows use of a sprung upper pivot (which the Superbe Tech did not have, hence the need for the sprung pulley). At the same time, a short nearly-straight section of housing has relatively little friction, even when mud/etc. gets in.
To summarize: derailleurs today are more resistant to wear, and somewhat less likely to clog. However, the pivots are still exposed to wear debris and not easy to clean/relubricate. Also, open parallelograms are still subject to mud/snow clogging.
So we have made progress in the (2016 - 1983) = 33 years since the Superbe Tech, but there is still an obvious improvement ... and we're not using it!