Wood rims downtown?

I recently got a note from a rider who's uncertain about riding wood in downtown Seattle. First, take a look at this "downtown," wood creation:

2500lbs and 600hp ?

Back to cycling, here's his question and, after it, my reply:

I'd love to buy some, but have a few concerns:

I ride a fixed-gear track bike with front brake. After reading some of the notes on your blog am a bit scared to ride the wooden rims in Seattle, on our streets, with the rain and friction of braking down our many hills... thus ruining your beautiful creations. I don't want these to only be on a "Sunday show bike", rather on my "everyday rad bike".

Tell me otherwise, convince me that I will love them and that they will last!


My reply to him:

(1) In specialty retail, when someone indicates fear ("scared") over a particular sport, route, component, etc., the wise purveyor does not push. Instead he/she says, "if you ever change your mind, we can discuss it again." Statistically, trying to change a mind that currently harbors uncertainty is a job for teachers and reformers, not retailers. So I have this reflex response to recommend you stick to aluminum.

(2) If you consider that millions of riders raced all over the world's mountains and valleys in all weather, then you have to believe it can be done. Like going skiing only wearing leather, oiled cotton, and wool. Part of the process is going where our forefathers went because we want to experience the sport the way they did.

(3) Recently, disk brakes have been perfected for bicycles and embraced by artisans, sculptors, and retro-minded creatives. A disk brake (like a mechanical Avid) is a 100% solution to all wood rim braking issues. There aren't many 100% solutions out there. It's so effective, visually benign, forward yet classical looking, and cheap that you should set your sights on it. Yeah, you need a disk brake fork, the mechanism, and so forth. But, if not today, someday soon your city bike should look this way.

When wood was inexpensive, rim makers plentiful, and labor cheap, preserving rims was a lower priority. Still, most riders in the '30's would have used disk brakes on their bikes if they'd been available. No hesitation.

Lastly, wood's coefficient of friction with rim brakes, especially in the wet, is truly superior. Except for the threat of grit (CX racing) caught up in the brake pads, wood is a better rim for Seattle than aluminum.

San Francisco's cable cars use wood brakes. Blocks of wood are pressed against the rails and you sure can smell the mild burning when descending.

While we're talking wood, I suggest checking this guy:
www.joeharmondesign.com

Now we're back to this blog. It is worth spending some time at Joe Harmon's site. The novelty is his prodigious creativity, independent thinking, the material sensation of wood, and Joe's interest in sharing every detail about this story. He's not about saving forests, cooling the planet, or going vegetarian. This is a materials based artistic project that challenges many preconceptions about wood as a structural element.

Take a look at this leaf spring assembly for the front suspension. It's made of Osage Orange, a rare and super tough wood he sources from Kentucky.



The materials scientists I've discussed this with have little doubt the car will work. The only uncertainty would be Joe's patience and money running out. For the rest of us, his is a wonderful lesson in the unexpected potential of natural materials combined with modern design.

Are wood rims or wood cars for you? Well, I guess I haven't yet answered the question. Oh well, got to go!

How Wood makes a Rim

To understand how a wood rim functions, we need to talk about density and the stiffness of shapes and materials. A bicycle rim resists bending according to the stiffness of the given material and shape. However, material near the rim's exterior does most of the work. Why? When the rim bends, this exterior undergoes the greatest deformation. For example, with a bend to the left, compression is felt on the left and tension on the right. These forces are greatest on the surface, furthest from the rim centerline. As it bends, the magnitudes of compression and stretching are greatest on the surface and this area puts up the greatest resistance. If the rim were solid, material in the center would barely detect the bending. For every degree of bend, internal deformation is smaller than that on the surface.

This principle favors tubes, whose mass is concentrated in their perimeter, far from the centerline. Therefore, hollow shapes are efficient and we certainly get our money's worth from the metals. Composites, likewise, end up imitating metals to produce efficient structures. How does a wood rim resist bending forces? After all, it's a solid that, according to the previous evidence, makes an arguably inefficient structure. Wood is much lighter than metals or composites, and this low density is what it leverages as a wheel rim.

Density (g/cm3)

• carbon fiber = 1.7
• aluminum = 2.7
• wood (beech) = .7

This is a huge difference, so wood is going to make a very different rim.

Because wood is so light, its resistance to bending is necessarily less than metals. Compared to the other materials, wood needs more frequent spoke support. So, we use traditional spoke numbers like 32 and 36 per wheel. In fact, wood's long reign as premier high performance rim is a major reason for these particular spoke counts. Even three decades after switching to aluminum alloys wheel makers retained these numbers. In the face of aerodynamic evidence, spoke numbers have come down dramatically. However, research shows that the wind resistance of larger spoke numbers only becomes a liability at high speeds rare outside of competition.

So, given more spoke support, what kind of wheel does this solid but very light material make? First, the lower spoke tensions that wood prefers allow it to move around more. This additional degree of motion allows it to absorb shock, to attenuate the vibrations of the road; the same as a lower pressure tire. But the actual deflection of a wood rim during riding is tiny, so the bicycle's quickness is not impaired. What seems to disappear are the higher frequency vibrations of pavement that can tire the body over time and make joints ache. An aluminum rim, built to lower tension, would also move around. Unfortunately, aluminum does not absorb energy to the degree of other materials like steel, wood or composites. So the comfort benefit would be small.

In addition to shock absorption, wood is harder to dent. Its low density means that a pot hole will create only local damage: a nick rather than a generalized dent that might interfere with braking. So, wood rims are legendary for resisting dents; a valuable asset in a world of poorly paved roads. One further advantage is the heat resistance of wood. Rim braking dumps large amounts of heat into the brake caliper and rim, in order to slow the vehicle. Aluminum rims eagerly accept this heat which, when excessive, can melt the tire or tire cement, causing failures. Wood rims refuse to accept this heat preferring, instead, to burn superficially at their surface. A wood rim pushed to braking extremes will create a barely detectable burning odor, but its tires remain cool. The flip side of this tendency is higher heat that brake pads see. Unable to hand off the heat to the wood rim, traditional brake pads will melt on wood. This characteristic can be managed.

On first glance, the thermal characteristics of wood seem similar to carbon fiber: neither readily accepting heat. However, the similarity is superficial. A carbon rim accepts heat slowly, a wood rim nearly not at all. During a demanding descent, brake pads can feel overheated with either material, but slowly and relentlessly the carbon rim becomes hotter and hotter. It dissipates the heat too slowly, so can reach melting temperatures. Wood, on the other hand, might burn a bit on the surface but as a bicycle rim will not reach elevated temperatures. Bottom line, no rim material is ideal for braking. Aluminum or carbon, wood or magnesium, dealing with thousands of watts and trying to protect an inflated tire is a tough and hazardous job.

Nature's Composite

I wrote this piece for the February 1985 issue of BICYCLE GUIDE magazine, pg 16-17, 106. So please forgive a few details that are owed to its vintage. Also note, all the wood rim makers listed have ceased production except for Ghisallo.

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In our never-ending search for better materials, the current rage is the space-age group of substances known as composites. Composites consist of microscopic filaments, which are bonded by glue into dense layers sandwiched around lighter materials. Perhaps the best-known composite system is the surfboard, in which styrofoam is covered with a thin layer of fiberglass and polyester resin to create an immensely strong but light structure. Composites using carbon fibers are currently revolutionizing aeronautics, as well as sports equipment such as tennis racquets, skis, golf clubs, and fishing rods. And the wheels that contributed to our Olympic track team's success were also constructed with composite materials.

But as we consider these materials, it helps to remember nature's own composite - wood. Structurally, wood is a system of fibers bonded by resin and arranged in sandwich layers around a light pulp center. Nowhere has this natural composite make such a valuable and enduring contribution to the bicycle as in wood wheel rims. The age of wood rims began at the dawn of cycling and, despite major advances in steel rim design and manufacture, continued until shortly after World War II. Whether for Madison-style track racing or for the destructive cobbles of Paris-Roubaix, wood had an unchallenged 130-year reign as a rim material that combined lightness with strength. Famous names of rim manufacturers such as Fairbanks-Boston (Michigan), Sieber (Milan), Mirass (Spain), and American (Michigan), bring back the scenes of great cycling battles staged on the polished wooden surfaces of dimly lit velodromes. Nothing could match the liveliness of wood rims on these tracks. "The tires just sang on wood rims,” observes former six-day rider Vince Gatto of San Jose. Their popularity faded only with the arrival of high strength aluminum alloys. When the first aluminum rims appeared, they seemed "dead" or "flat" compared to wood, but what they lacked in feel they gained in reliability and safety: they stayed true longer and they didn't shatter upon impact.

Wood's unique ride is partly due to its flexibility. Although aluminum may be stronger, wood can usually bend farther without sustaining a permanent deformation. This is a boon when striking a pothole. Also, small bumps and high frequency road vibrations are better absorbed by wood. A quieter, smoother ride results.

Wood's flexibility is a virtue in a world of poorly paved roads, but a liability in terms of strength. The wheels of today require high tension to accomplish feats like six-speed spacing. But wood rims can't withstand the highest spoke tensions, so they are better suited for track, five-speed, or symmetrical wheels that have less dish. Low spoke tensions can be noisier as the spoke shafts rub against each other, especially at the outer cross. This clicking sound can be silenced by tying and soldering, which helps explain the popularity of this practice in the past.

Wood rims also account for the early popularity of butted spokes. Butted spokes are more elastic than straight gauge spokes; they give more and accommodate the wide tension variations inherent in wooden rims. Butted spokes provide more continuous support at low tension and ought to last longer because they don't snap from full slackness to full tension as often as straight gauge spokes.

Wood makes a great braking surface that provides especially good performance in the rain. Wood's heat insulating abilities places the burden of heat dissipation on the brake pad so it dries quickly in the wet. But the pad is also inclined to melt more readily; with heavy use, the rear brake can spit tiny bits of melted brake pad at the back of the rider's leg. Rapid stops will also cause a very faint burning of the wood's surface, a pleasant perfume for the following rider.

Hardwoods such as hickory, elm, ash, and maple are favorite rim materials that are easily shaped once softened by steam or other moisture. A single piece of wood can be bent into a hoop and connected to itself with an elaborate finger joint, or several laminations can be layered and glued. Waterproof glue is used to bond the laminations while the rim is held round under pressure. Once dry, the hoop is shaped with cutting tools and drilled for spokes. The laminated construction generally produces a stronger and more rigid rim because care is taken to offset the direction of the grain and joint of each successive layer.

To get the most from wood rims it is important to store them in dry conditions; if they become wet, allow them to dry slowly. Each year the rims can be lightly sanded and coated with a waterproofing lacquer.

At least five companies still manufacture wood tubular rims. Three Italian firms - Ghisallo and Berlazzi of Milan, and Sieber, now located in Switzerland - offer rims in many sizes and weights. However these rims require an extra-long, 3/4-inch nipple that is hard to find.

Wolber distributes a French rim made by Darrigade that features full sockets like modern aluminum rims, allowing the use of conventional nipples. This rim weighs just under 400 grams and is bonded with waterproof synthetic adhesives.

Finally, one of Japan's oldest parts distributors, Sanno Sports of Tokyo, can lead you to the Japanese manufacturers that, up until 25 years ago, made wood rims for the Keirin circuit. The rims are hard to find now, so inquire for availability.

Will wood rims stage a comeback? I think not, but their novelty and pleasant ride guarantees that they ought to be available for many years to come. Rims of the future, if not made of metal, will most likely be made of synthetics. But as in the design evolution of other vehicles such as boats and planes, it took a long time to discover materials superior to wood. And it is fitting indeed that the futuristic disc wheels of the Olympics are closer in construction to wood than the tensioned wire and metal hoops to which we have become accustomed.

How Wood Rims are Made

Every few years, the Cermenati's travel to a favored grove of old beech trees in Slovenia. One is felled, milled, and the planks are taken back to Italy for aging.


When the time is right, the lumber is planed into smaller strips.


Traditionally, the long strips were soaked prior to shaping. Today, however, the laminations are thinner (just a few millimeters) and they can be bent without wetting.


The thin strips are coated with modern, 2-part epoxy and bent into a spiral wound, hoop shape. Between each strip is a layer of cotton cloth. Thinner strips, more numerous laminations, 2-part epoxy, and cotton layers are recent enhancements to the historical manufacturing process which create substantially stronger and more stable rims. Visually, none of this can be readily detected and the rims are still entirely hand made. Ghisallo rims: traditional yet modern.


The spiral hoops are securely glued.


The basic rim shape is glued.


The glued hoop is fly cut on a horizontal routing machine.


After several cuts, the hoop assumes its final shape.


The rim is then precisely drilled for nipples in this dedicated machine. Once drilled, each rim is carefully sanded and finished with many coats of marine epoxy. The process is basic but many years of experience is necessary to produce rims with legendary performance. It's not a cheap process, but these rims are a match for the very best that have ever been made.