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Motorhead Memo: Wheels ’n’ spokes

By Kip Woodring

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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” status, yet get ridden fairly frequently. Regular pre-ride checks, both visual and physical, are practically mandatory. Funny how there’s less of a sense of caution when it comes to alloy wheels, as fitted 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 technological progress in solid alloy wheels over the last 40 years or so, how is that spoke wheels have survived?

Rebuilding spoke wheels is not rocket science! Normal humans can manage. It requires patience, logic, simple tools and putting the first spoke in exactly the right place, just like it shows in factory service 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.

Re-inventing the wheel?

Historically, wire spoked wheels are responsible for killing off the old wooden wagon wheel. Rather conveniently, 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 insufficient 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, motorcycles 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 stronger than even cast magnesium wheels. Then a guy named Tom Lester came along with a patented idea for workable, less exotic cast wheels for the masses (the “background of the invention” 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 bandwagon. Very quickly cast wheels were seen on almost all brands of mass-produced motorcycles. Perfect! Well, as it turned out, not really.

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 component-based “composite” design... rebuildable. It was never perfected and never handsome, so it never caught on. Pity.

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 component-based “composite” design… rebuildable. It was never perfected and never handsome, so it never caught on. Pity.

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 longevity. Porosity and sectional integrity was a concern too, largely because it was damn hard to cast a one-piece wheel that had equal (and appropriate) 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 wrong idea for a spoked wheel! Huge diameter, cross-one pattern, too many spokes, weakened rim and hub, narrow, massively heavy and flex prone because of it. Proves you can take any good thing and ruin it with wretched excess. But it sure is purty, ain’t it?

The wrong idea for a spoked wheel! Huge diameter, cross-one pattern, too many spokes, weakened rim and hub, narrow, massively heavy and flex prone because of it. Proves you can take any good thing and ruin it with wretched excess. But it sure is purty, ain’t it?

The key to the construction of a conventional spoke wheel is that spoke wire is very strong under tension, 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, slimmer wheel, and with a vastly wider range of angular loadings, it was harder to make a solid wheel as strong as a laced wire spoke wheel. So hard, in fact, that as late as 1984, when Honda introduced the first motorcycle fitted with tubeless tires, the wheels that they were mounted on were not cast alloys! With an R&D budget like no other in the industry, Big Red had come up with a third type of wheel construction! Starting in the late 70’s, marketed as “Comstar,” these wheels were made in a similar manner to the wire-spoke wheel in having a separate rim, and hub, but instead of being laced together with triangulated wire spokes in tension, they were connected by riveted, buttressed alloy plates in compression. Lighter than a wire spoke wheel, and many cast alloy wheels, they were almost as strong, courtesy of triangulation and cross-sectioning, and were certainly strong enough for race applications. The high-tech computer design indicated (among other things) a big advantage in that the separate components, the hub, rim and spokes, could be manufactured by different methods, and in different grades of material. Using a cast hub, extruded rim, connecting plates from rolled sheet, or possibly even “spun” (basically the metal “spun” out from maybe a 4″ billet, and press-molded to shape) this composite construction was said to offer the compliance of a wire spoke wheel, minimal cyclic fatigue, massive shock-loading resistance, and no cracking or fracturing. Still, not completely superior to wire spoke wheels overall… and ugly. Honda gave up trying to perfect a wheel no one liked, and switched to more conventional (and by now tubeless) cast wheels, as well as continuing to offer wire-spoked wheels. Ultra-exotic carbon-fiber wheels came on the scene at roughly the same time as Comstars (it should be noted), but for obvious reasons I shouldn’t (and won’t) explore here, have never become a mainstream alternative to simpler, cheaper wheels.

 

Just one of a number of ways to make a spoked wheel compatible with a tubeless tire, not to mention extremely light, and strong with its “cross-four” lace pattern! BMW offers tubeless spokes using a reversed spokes… why doesn’t Harley?

 

Which brings us to the next innovation in “cast” competition for the (now) century-old wire spokes. Namely, the hollow-spoke cast wheel, which if memory serves was created by the Italian company Marchesini in the late 80’s and appeared on Buells in the 90’s.

Until hollow spokes came along, to make a cast wheel stronger meant thicker spokes or more spokes or both, and both made the wheel heavier. Dymag in the UK were renowned for making some of the strongest and lightest magnesium racing wheels, but they did it by having deep “girder” spokes, very carefully pressure die cast, demanding expensive tooling and very slow manufacturing cycle time, as the wheel had to be control-cooled in the mold before it could be ejected and another one made. The Marchesini hollow-spoke wheel, by contrast, achieved a very high stiffness from minimal metal by using massive spokes—but hollowing them out—and saving expensive manufacturing costs by using a “lost wax” process, via simple gravity sand casting. Great for keeping low volume costs down, but not so great for making large volumes of wheels cheaply. “Productionizing” the hollow-spoke cast wheel was a task left to Yamaha, which they did with a slick low-pressure die-cast system. Soon enough, they were all like that. Come the Millennium, and Buell (among others) figured out more ways to minimize mass and improve strength and flex characteristics through Cad/Cam technologies resulting in a switch to (mostly six) very thin (almost see-through) spokes, some looking surprisingly like wire wheels!

 

Morris “Mag” racing wheel—looks kinda familiar, doesn’t it? Harley wheels from the 80’s are close copies, but being aluminum are nowhere near as light or strong. Morris wheels were made of magnesium alloy and as such had a fairly short service life... oh, and they could burn very brightly as well!

Morris “Mag” racing wheel—looks kinda familiar, doesn’t it? Harley wheels from the 80’s are close copies, but being aluminum are nowhere near as light or strong. Morris wheels were made of magnesium alloy and as such had a fairly short service life… oh, and they could burn very brightly as well!

 

And that is where we are now. Materials technology and manufacturing technology basically being refined to minimize the problems (and costs) of the cast wheel; softer more malleable alloy compositions helping avoid cyclic fatigue fracture and structural engineering tackling the weight/strength issue.

Where there’s a wheel—there’s a way

For one thing, running over an uneven surface, the bigger in diameter the wheel, the better (the limit is really based more on the human inseam than much else). How easy it is for a wheel to “ramp” a bump is significantly affected by the bump height and angle in relation to the wheel radius. Same goes with dips! Bigger the wheel, the earlier it encounters a bump, and on a shallower portion of the curve from the leading edge to the contact patch, thus offering more leverage to lift the bike over the bump. This is important! When spoke wheels were invented all roads were uneven, full of bumps and dips. Even today, for an off-road machine, bigger wheels are better. So much better that having bigger wheels is more of an advantage than trick suspension. For street applications and so-called ADV machines, tubeless tire technology required new, sealed rim-forms, and that has lead to some novel variations on the wire spoke wheel. Just to name a couple; there’s the “straight” spoke, using a ball-ended spoke with no bent “neck” to loop through a hub flange, then hook into a slotted rim. Then there’s the upside-down spoke, that puts the hook end through a flange on the rim, and the nipple through a flange on the hub.

Lester Cast wheels set off the revolution to put cast wheels on every street bike. The battles were won, but the war isn’t over—spoke wheels still serve a useful purpose and offer advantages after nearly 150 years!

Lester Cast wheels set off the revolution to put cast wheels on every street bike. The battles were won, but the war isn’t over—spoke wheels still serve a useful purpose and offer advantages after nearly 150 years!

Probably one of the more useful and less acknowledged “advances” in wire spoke technology has been the “forged” spoke, where the hook end is formed from forging the spoke as a single component, rather than taking stock wire, bending to shape the neck/hook, peening the end to form the button, and then threading. Materials, notably stainless steel alloys, have been improved too. There are proprietary formulas for spoke metals, hub alloys and rims, the idea being a sort of compatibility among the three that, combined with (what I call) computerized machine assembly, minimizes or eliminates many of the old bugaboos associated with spoked wheels. The modern spoked wheel doesn’t suffer loose or broken spokes, cracked hubs or bent rims nearly as much as the wheels of decades past (like mine). And they remain incredibly strong for their weight!

 

Hollow spoke cast wheels, as pioneered by Marchesini (and used by Buell), were wheels of choice for sport bikes all through the 90’s. Thing is, not all the copies of this type wheel were as virtuous as the originals. Some (I swear) were alloyed with lead and heavy as hell, not to mention easier to damage (I speak from experience and from owning a scale!).

Hollow spoke cast wheels, as pioneered by Marchesini (and used by Buell), were wheels of choice for sport bikes all through the 90’s. Thing is, not all the copies of this type wheel were as virtuous as the originals. Some (I swear) were alloyed with lead and heavy as hell, not to mention easier to damage (I speak from experience and from owning a scale!).

 

As mentioned above, the stiffest, most rigid spoked wheel is one with a radial spoke pattern; i.e., since the spokes go straight out from the hub to the rim without crossing another spoke, the spokes are 100 percent in tension. Thing is, this is next to no good for a wheel that is expected to take bumps and dips as the spokes below the hub will be loosened every time the wheel takes a hit, so the wheel will quickly come out of true. Yet…and yet… the real problem isn’t spokes coming loose (there are thread-lockers to deal with that); it’s that they can’t cope with rotational forces! Nailing the brakes or gassing it hard, especially while tilting the horizon… can snap radial spokes like bread sticks.

State-of-the-art cast wheel, again as used by Buell, but of a type currently in vogue. Harley cast wheels these days come in plenty of variations in looks and styles, but that can be deceiving. Not many are a functional improvement over the OEM wheels. Honestly, when it comes to wheels, cast or spoked, these days the decision is esthetic. Too bad!

State-of-the-art cast wheel, again as used by Buell, but of a type currently in vogue. Harley cast wheels these days come in plenty of variations in looks and styles, but that can be deceiving. Not many are a functional improvement over the OEM wheels. Honestly, when it comes to wheels, cast or spoked, these days the decision is esthetic. Too bad!

The ideal compromise is a two- or three-cross pattern, where every spoke crosses another two or three spokes. In any cross pattern the spokes are longer than in a radial pattern so although they only stretch and contract the same percentage as a shorter radial spoke, actual stretched length is higher. Meaning… you have a wheel that can absorb a higher force yet retain its true. The tradeoff is the wheel isn’t quite as stiff or as rigid as a radial-patterned wheel. The point being—if you’re transferring any forces other than the weight of the vehicle between the hub and the rim, you need leading and trailing spokes! So, justifiably, the wire spoke wheel is still with us and its design sophistication hasn’t exactly stagnated either! It is a very elegant and incredibly efficient bit of engineering technology, and its day is far from done… I think.

As for my old bike with the busted spokes… there is no alternative to fixing it…except replacing it. So, thanks to Fleabay, I’m doing both! I have a set of brand-new spokes with which to replace my old rim and hub. I also have a used wheel with no issues (yet) on its way as this is written. Replacing a spoked wheel is one thing. Rebuilding one… is another (“one-on-one in the wash” so to speak). The way I figure it, I’ve got nothing to lose by wheel building myself. If I manage it, I’ll learn something and save money. If not… Buchanan’s is close by. I’ll let you know how it turns out!

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