Issue link: https://read.dmtmag.com/i/703695
100 nAugust 2016n www.thunderpress.net THUNDER PRESS Wheels 'n' spokes Fully half of my collection of motorcycles has wire-spoke wheels. All street bikes, by the way… and mostly old enough to be leery of. When you're dealing with elderly spoke wheels, you tend to be mindful that they should not be ignored or taken for granted. Particularly when they are approaching "ancient" sta- tus, yet get ridden fairly frequently. Regular pre-ride checks, both visual and physical, are practically manda- tory. Funny how there's less of a sense of caution when it comes to alloy wheels, as fi tted to the other half of my bikes. (Although, in truth, there shouldn't be!) Over decades of riding machines thus equipped, I've never had a problem with a spoke wheel until now. Yup, in spite of all my caution, inspection and checks, one of the old bastards snuck up on me recently with a surprise attack of, not one, not two, but four… four broken spokes! All of them on the side of the rear wheel that has the most load, that being the side where both the drum brake and the drive chain reside. Much irritation, disgust, expense and effort were soon to be engaged before replacement and repair could be accomplished. Along with thoughts about dealing with this, I got to wondering; with all the techno- logical progress in solid alloy wheels over the last 40 years or so, how is that spoke wheels have survived? Re-inventing the wheel? Historically, wire-spoked wheels are responsible for killing off the old wooden wagon wheel. Rather conve- niently, the whole notion was more or less high-graded, and then adapted, from the bicycle, some 130 years ago. Mind you wooden wheels had and have advantages, just not many. They are also organic and therefore liable to rot and suffer from insuffi cient structural strength and integrity. Spoke wheels swept the board—lighter, stronger, more durable by far. Of course the four-wheeled world moved on to welded-steel wheels (noted for launching hub caps into the weeds under duress; don't ask how I know) and eventually to alloy wheels, almost universal today. Meanwhile, motor- cycles used spoke wheels—period! Right up until the 1970s that is. The wheel technology in the form of "cast" or "mag" wheels—that should have done to spoke wheels what spoke wheels did to wood ones—came along right about then. First used in racing with names like Morris, Kim-Tab and Shelby Dowd coming to mind, these pioneering wheels really were "mags," as in made of magnesium. Although, right up until the 1970s, steel wire spoke wheels were lighter and stron- ger than even cast magnesium wheels. Then a guy named Tom Lester came along with a patented idea for work- able, less exotic cast wheels for the masses (the "background of the inven- tion" for patent #4047764 makes for very informative reading). The concept of wheels that required no inner tubes and could be used with radial tires was irresistible! But tire technology at the time was struggling to keep pace with motorcycle technology; horsepower wars were escalating rapidly and even the newly emerging "superbikes" were running tubed cross-ply tires. So, when cast wheels emerged, "tubeless" was made possible almost right away… radial was in the future. OEMs from every nation piled onto the band- wagon. Very quickly cast wheels were seen on almost all brands of mass-pro- duced motorcycles. Perfect! Well, as it turned out, not really. A "cast" of thousands Filtering down to production road bikes, "cheaper" cast wheels were often hugely over engineered, and seven, nine (or more) "spokes" on alloys were quite common, usually heavier than equivalent wire spoke wheels and worse… early alloys could stress or fatigue fracture and they certainly cracked in high-impact situations. There were legitimate fears over their strength and lon- gevity. Porosity and sectional integrity was a concern too, largely because it was damn hard to cast a one-piece wheel that had equal (and appropri- ate) strength in hub, "spokes" and rim. Getting it right in one area often meant a weakness in another. That's because a solid wheel works differently than a laced wire-spoke wheel. Speaking "spoke" Cast wheels of the era (like wooden wheels with wooden spokes in a previous era) operate in compression, and for a heavy load, were adequately strong, straight up, but triangulating a wire-spoke wheel gave it a lot more strength in bending (torsion) than a cast wheel in compression. The key to the construction of a conventional spoke wheel is that spoke wire is very strong under ten- sion, much more so than it is under compression, and the wire-laced wheel basically hangs the rim in "tension" around the hub… from a spoke! A so-called "radial" spoke pattern (each spoke straight out from the hub to the rim) is plenty good enough to demonstrate this. The problem with radial-spoke wheels is you need a lot of spokes to have any real resistance to bending or breaking under rotating loads. On the other hand, spokes laced in a conventional "cross" pattern gain some really impressive rigidity from the "triangulation" (angling spokes from one point of the hub, to another on the rim… in a "crisscrossing" pattern)… putting strength pretty much where most effective, and not carrying much redundant weight. So, a properly laced wire-spoke wheel can be very light and very strong by any standard. Put another way, for cars, cast wheels were more practical, because car wheels tend to be smaller in diameter, wider in section and with careful internal ribbing, could be made as strong where needed, as needed, especially as loadings are less variable in the horizontal plane (cars don't tip or lean to go around corners… you hope!). But for bikes, with a larger, Rebuilding spoke wheels is not rocket science! Normal humans can manage. It requires patience, logic, simple tools and putting the fi rst spoke in exactly the right place, just like it shows in factory ser- vice manuals. That most of us are afraid of tackling a task like this is the reason "professional" wheel building is not a lost art… yet. The closest thing so far to a true substitute for a wire wheel was Honda's "Comstar," capable of using tubeless radial tires, yet because of its com- ponent-based "composite" design… rebuildable. It was never perfected and never handsome, so it never caught on. Pity.