Just as a little point about how nice the bicycles were, who among Retrogrouch Blog readers wouldn't start salivating like one of Pavlov's dogs over a mid-'80s mint condition red Specialized Allez SE with SunTour Superbe components, just like the bikes from the 1985 film American Flyers? . . . Exactly. Also, I have one of the early Stumpjumpers with the lugged frame and twin-plate fork crown, and the workmanship on that frame is fantastic.
Anyhow, as I'm gathering up components for a bike build, I thought I'd take a close look at one of my favorite triple cranksets - the Specialized ST, sometimes known as the "flag" crank because of the logo engraved on the arms. It's a really well-designed crank - simple, pretty, and strong. I've used them on a few bike builds over the years, whether built for myself or for others.
|It's the kind of design that looks good on a bike whether new or old.|
I was able to get some info about the cranks from Jim Merz, who had been one of the pioneering framebuilders in the Portland, Oregon bike scene until he went to work for Specialized as a product designer in 1982. He has also been a "Master Frame Builder" for the company. Jim was the designer of these cranks, and many other high-quality components. According to Jim, the cranks were cold forged, using the strongest alloys available, and with rings made from 7075 T6 aluminum - the same as was used by Campagnolo. As mentioned, the cranks were manufactured for Specialized by Sugino.
|As a contrast, the sharp transition between the arm and the spider on this old Campagnolo crank serves as a stress riser, where cracks could develop. Lots of old Campy cranks suffer this fate. With continued use, a crack like this could eventually break all the way through. (photo, minus added text, from fixed.org.au forum)|
Another detail about the crank that makes it very versatile is its 110/74 bolt circle diameter (BCD). Though that would quickly become the most common standard for triple cranks for the next couple of decades, it was still a pretty fresh development when this crank was designed.
|The crank used the 110/74 BCD which means that chainrings are easy to find, even today.|
In the 1970s, as long-distance touring bikes gained popularity (especially after the epic Bikecentennial ride of 1976), and then at the end of the decade when mountain bikes were in their infancy, finding a good wide-range triple crank with seriously low gearing wasn't so easy. There were numerous "standards" for bolt circle diameter, and very little compatibility between different brands. One of the more popular choices for tourists and early mountain bikers was the TA Cyclotourist -- not necessarily because they loved the crank so much (it had some idiosyncrasies) but because it could be had with a then-diminutive 26 tooth granny ring. The TA had a tiny 50.4 mm BCD onto which the biggest chainring bolted. Then the middle and inner rings bolted directly onto the outer ring with an 80 mm bolt circle. One downside of the crank was that the space between the rings and the crank arm was so narrow that it could create interference with some front derailleurs. And the whole thing bolted together with a confusing mess of different sized nuts and bolts. Also, larger chainrings on the TA crank could lack stiffness. The bigger the ring, the more it could flex. Still, for many people, and for quite a while, it was the best thing going.
Stronglight had certain models that were very similar to (or interchangeable with) the TA Cyclotourist, but they also had other, more modern triple cranks (their model 99 comes to mind, for example) that used a proprietary 86 mm BCD. Those were also copied by Sakae Ringyo (SR) and used on some of Trek's early touring bikes. They were decent triple cranks, but the smallest chainring one could install was 28 teeth. Low, but not low enough for some tourists and mountain bikers.
When Shimano released its original Deore group in 1981, which was intended to be a premium group for touring bikes, the first generation Deore crank copied the 50.4 BCD used by TA. But in typical Shimano fashion (does not play well with others), only the outer ring was interchangeable with the TA Cyclotourist. The middle and inner rings used a proprietary 85 BCD, making them compatible with nothing else. It also meant that the lowest gear was limited to 28 teeth.
In 1982, Sugino released the AT triple crank. "AT" stood for "Aero Tour" but it probably wasn't a coincidence that it was just like "TA" backwards. The AT had the outer and middle rings bolted to a 110 mm circle, which could accept rings as small as 34 teeth (They also offered rings as large as 53 teeth, but nowadays it's hard to find them larger than 50). A second set of threaded holes was set into the spider with a 74 mm bolt circle, which could accept a granny ring as small as 24 teeth. Altogether it was a good combination. The larger rings still got plenty of support, avoiding the flex that would come with a smaller bolt circle. Middle rings could be as small as 34, and the 24 tooth granny ring was about the lowest gear anybody was offering at the time. I remember a number of bikes in the '80s, especially sport-touring models, that came with 110/74 cranks that were set up as doubles. Turning them into triples if the owner wished was a simple operation. The cult-bike Bridgestone XO-1 came equipped like that, too.
As Jim Merz tells me, he designed the Specialized crank in 1983, using the same 110/74 BCD. Sakae got a version on the market very quickly. When Shimano redesigned their Deore crank, around '84, they made a rare choice to adopt 110/74 as well. Pretty soon many in the industry were embracing a common standard for triple cranks. Even TA started making cranks and rings to the standard. And there was much rejoicing.
As usual, the idea of common standards has gone out the window, and cranks today are all over the place. Innovations such as MicroDrive in the '90s made bolt circles and chainrings even smaller (more ground clearance for mountain bikes, I guess), and now more and more cranks have discontinued 5-bolt spiders in favor of 4-bolt versions - many with their own unique asymmetrical bolt patterns, and others with removable spiders. But luckily 110/74 rings were once very common and can still be found today without trouble.
The ST triple crank had a less expensive sibling, designated as the ST-4. Overall, the cranks looked very similar, with the most obvious difference being the logo. However, the real difference between the two was not in the logo, but in the manufacturing. The ST crank was cold-forged out of the strongest available aluminum alloy, whereas the ST-4 was made by the process known as gravity casting -- sometimes mistakenly called "melt forging" but there is a difference. Read on . . .
|That's the cold-forged ST on the left, and its similar-looking sibling (minus rings) on the right. The model designations are marked on the back, but the logo ("flag" vs. "S") is a quick identifier.|
Cold Forging vs. Hot Forging vs. Gravity Casting vs. Melt Forging
They're all fine ways to make a bicycle crank, but differences in methods and materials affect the strength - and differences in the manufacturing cost obviously affect the price. A really good description of all the methods can be found in the 1992 Bridgestone catalog, but here's a quick summary:
Cold forging starts with the strongest alloys, and requires several major wallops (not a technical term) with hardened forging dies with tons of weight and pressure -- as in, hundreds of tons. Cold forging imparts a grain structure that makes the component very strong, but the tooling and equipment mean more expense. Very few bicycle component makers can afford the massive forging "hammers," and therefore most actually have their cold forging outsourced to specialists. Because of the added strength, cold forged components, like cranks, can be made sleeker and lighter. By the way, Jan Heine's blog had an interesting article last year about forging hammers and the companies that do such work (HERE).
Hot forging involves alloys that are slightly lower in strength than cold forging (though still very strong), heating them to make them softer, then giving them typically one or two hard wallops in the forging dies. It still imparts a grain structure to the component so the parts are very strong, but it takes fewer wallops and less tooling so the cost is lower.
Gravity casting and melt forging both involve melting alloys that start out as somewhat lower strength from either of the previously described methods - but between the two, gravity casting uses a stronger alloy than melt forging. In gravity casting, the molten metal is poured into a mold, then allowed to cool slowly while any air bubbles that might be present gravitate upward and out. In melt forging, the molten metal is forced into a mold under pressure, then liquid-cooled quickly. It is the fastest method and probably requires the least expensive tooling, though the material is not necessarily as strong, nor do the parts develop the same kind of grain structure. For that reason, melt-forged components tend to be "chunkier" to make up for it. Melt forged components also don't take to anodizing, so the finished products are often painted or powder coated. It goes without saying that melt forging is the least expensive of the described methods.
By the way, the '92 Bridgestone catalog says that the Specialized ST-4 crank was gravity cast, but then got extra strength by being whacked in a forging die for good measure. How cool is that?
Cranks in the Vintage Market:
If you're looking at either of these Specialized cranks on the vintage marketplace, like eBay, keep in mind that the prices will vary more by condition than by the model of crank. Most buyers and sellers on eBay or elsewhere probably don't really know the difference between the two versions, nor do they know or care what the things sold for when new. A really clean ST-4 will probably sell for more than a badly scuffed ST, regardless of what the original prices might have been. It's good to know what you're getting, though. Sometimes I see these selling for $100 or more, but unless it's unused, mint-in-the-box, I'd say that's ridiculous. Clean used examples like the ones shown above can often be found for under $50.