Common Tread

WTATWTA: Why do we still have spoked wheels on motorcycles?

Feb 13, 2018

When teaching tire class here at RevZilla, I often ask a question: Why do we have spoked wheels?

Often I get some blank stares. Usually one of our rookies knows the answer(s), but it does make for an interesting topic, because it seems like it’s pretty important. I mean, wheels are common to nearly every motorcycle, and the manufacturers must make them a specific way for a reason, right? So...

Why did one-piece wheels become common?

There’s lots of techno-jargon we can go into here, but let’s skip that. It’s not fun to read. Cast or forged wheels (which I am going to colloquially refer to as “one-piece” wheels from here on out) offer some pretty enticing perks: they never go “out of true.” They’re light and strong. (Weight can be a hard comparison. Often a spoked aluminum wheel is lighter than a cast aluminum one, but one-piece wheels can be made from magnesium or carbon fiber, which are wicked-light and often used in racing.) At really high speeds, small aerodynamic benefits matter and can be taken into account when designing one-piece wheels, which allow a bit more freedom than spoked setups.

Alloy wheel
The only hole that should be in a one-piece alloy or cast wheel is for the valve stem. RevZilla photo.

Because there are no holes in them, one-piece wheels also permit the use of tubeless tires. Tubeless tires allow for on-the-bike tire plugging. They also are a little less susceptible to blowouts, because there is only one hole leaking (the one at the puncture) rather than 41 holes leaking (the hole at the puncture, plus every single spoke hole.)

From a manufacturing standpoint, there’s less labor to cast a big batch of wheels then there is to build, lace, and true a spoked wheel. There are fewer parts to keep in inventory, and mounting tubeless tires is also less labor-intensive than mounting tube-types. All in all, one-piece wheels are pretty great.

So why are spokey-dokey wheels still being made?

Two reasons beat out all the others, and they’re different depending on the bikes upon which you find them.

In an off-road scenario, wheels are likely to sustain impact damage. Spoked wheels are excellent at transferring impact energy throughout the wheel relative to their one-piece brethren. They also have the desirable characteristic of bending, twisting, and flexing when exposed to too much lateral, axial, or radial force. Their failure mode tends to be a wheel that’s “taco’d,” which can often be whacked back into shape, ridden out, or at worst, fixed trailside with a few spokes. (The tube also helps reseat tire beads that slip off the rim more easily than a tubeless rig allows for.)

Repair
One of the downsides of tube-type tires, used with most spoked wheels, can be seen here: more difficult flat repairs. Photo by Brett Walling.

A one-piece wheel fails a bit differently. They’ll often absorb more energy and stay true for far longer, but when a failure does occur, the damage often presents itself as a cracked or bent wheel. If the wheel is either no longer structurally sound or unable to hold air, obviously, the prospect of getting home on time falls greatly.

Spoked wheels have a few other things going for them in the off-road world. They can be made light and cheap enough that they still have a place. Especially on small-displacement off-road bikes, where weight really matters (think about, say, a 110 cc kids' bike), the lightness of a spoked wheel comes far cheaper than an exotic one-piece.

Josh's 45
This bike probably wouldn't look right with alloy wheels on it. Mimicking the style of early bikes is the name of the cruiser and retro game. Photo by Panhead Jim.

Meanwhile, cruisers and retro machines have spoked wheels for one reason and one reason only: They look awesome. One-piece motorcycle wheels started showing up in the aftermarket around the mid-1960s, and the factories jumped on the bandwagon about 10 years later. If one’s trying to capture the look of American, British, or European bikes from that time period, spokes are a must-have.

And that’s it?

The orientation of the spokes is easy to see here. BMW image.

Well, there’s one more little piece to the story. In the quest to get the best of both types of wheel, new methods have been tried. Some have attempted (with only the most modest success) to seal the spoke holes in rims so inner tubes aren't needed. A better plan that is now in use by many OEMs, including Honda, BMW, and KTM, are cross-spoke or edge-spoke wheels. When viewed in profile, most standard spoked wheels appear to triangulate. The spokes run from the outside edge of the hub to the center of the wheel’s rim. (That’s the source of part of the spoked wheel’s lateral strength.) Edge-spoke wheels reverse that triangulation. The hypotenuse of the triangle, if you can follow along, now runs from the center of the hub to the edge of the wheel. Why do it this way? Well, it puts the holes for the spokes in the bead area of the wheel, so air won't leak out the holes.

Yam wheel
Yamaha's circumferential flange is easily seen in this shot. Photo by Nelson and Riles.

Yamaha uses a different method. Their hoops are built with a flange running circumferentially around the rim. That flange is then drilled to accept one end of the spokes.

The end result, in either case, are seamless wheels that offer the strength and flexibility of a spoked wheel with the on-bike puncture repair and easygoing maintenance that come with one-piece wheels.

At least for now, that’s why things are the way they are.