Teaching an Old Material New Tricks
The first bike was invented in 1817 using the highest technology of the time, a wood frame and wheels held together with nails and pegs...no pedals. Since then wood bikes have been manufactured for sale off and on worldwide through the late 1940's with some advances, but virtually none have been hollow nor were they engineered for performance. Renovo introduced technology to wood bikes in 2007, 190 years after the first wood bike, and thanks to technology, there has been progress.
Renovo's founders are not woodworkers of any sort...they chose wood for its outstanding engineering properties. Our background is composite aircraft design, engineering and manufacturing, the tools in our box are CAD/CAM, or Computer Aided Design and Computer Aided Machining. Our background in aircraft design plus a simple engineering analysis of potential frame materials led us to wood, and with state-of-the-art adhesives, finishes and manufacturing techniques we have produced high performance, lightweight wood bicycles so durable and beautiful they'll become treasured heirlooms.
The all wood, English DeHavilland Mosquito, introduced in 1940. The fastest plane in the world when introduced, it was the most successful fighter bomber of WWII. 8000 were built.
From Calfee Designs, one of the original carbon frame producers..."As bicycle companies compete in the arms race to make even lighter, stiffer bikes, safety and durability are pushed to the limit. High modulus (66 Msi and greater) carbon fiber is being used to make stiff yet thin walled tubing. When slightly damaged from a pebble thrown up by a passing car, or an unfortunate event during a group ride or race, a thin walled tube can rapidly degrade to an unsafe condition". Calfee's very popular carbon repair business is evidence of this common failure.
A Renovo is perhaps the most durable of frames. Our relatively thick-wall hardwood frames are extremely damage resistant and the easiest, least expensive frames to repair as shown to the left. They withstand Northwest rain, Desert heat, Alaska cold and Belize humidity. We know because we have customers in all these places.
"Yesterday I was driving to ride at the Chico Wildflower Century. Driving down a backroad at about 50MPH, my hitchmount rack broke, dumping my bike to the pavement. The end of the carbon bar was broken, the pedal and rear deraileur were scraped, the hanger was bent and the frame had 2 dings where it struck the hitch. I am certain if the frame had been carbon it would have been unridable. Here's a pic of the damage." Eric Olsen Eric rode the bike for some 6 months after the accident before sending it back for the repair pictured is to the left.
As you read the following, consider the repeated and substantial stress endured by wooden diving boards. Many modern boards still favor wooden cores.Frame life is determined by the fatigue resistance of the particular frame material, that is; its ability to absorb cyclic loads, the amount of material to absorb those loads, and finally, the actual loads the frame sees; racing, abuse, accidents, etc. Wood is one of the most fatigue resistant materials on earth, simply because it used to be a tree, resisting the constant bending and twisting in the wind for their entire life, which for some windblown trees such as the bristlecone pine, is nearly 5000 years. As a result, wood has a remarkable fatigue life that exceeds steel and aluminum and rivals carbon, so we can design our frames with adequate margins to assure a long life against normal loads, and still have a light-weight frame. But not fragile-light. An authoritive source on wood fatigue is ANC-18, the 1951 Army-Navy joint publication titled, 'The Design of Wood Aircraft Structures', wherein they simply state 'wood is less sensitive to rapidly repeated loads than are the more crystalline structural materials (metals), resulting in a higher endurance limit in proportion to the ultimate strength." Echoing ANC-18 are the products and testing done by the Gougeon Brothers who manufactured (among other things), 100' long wind turbine blades of epoxy bonded wood which withstood 400 million fatigue cycles over a 30 year life span, and epoxy-bonded wooden boats. They developed the West Epoxy system and wrote the book on epoxy-bonded wooden boat construction.
The image above is a frame load test with a hydraulic ram pulling down on the frame bottom bracket with a load of 3008 pounds (1367kg), the weight of our Volvo Station wagon. The 1 inch steel bar in place of the fork is bending with the load.
Bonding We use four different epoxy formulations from two suppliers to meet our requirements of withstanding high temperatures, resisting moisture and bonding complex joinery. Our adhesives are moisture proof and the frames are oven cured to withstand the temperature and humidity range anywhere bikes are ridden on earth. We have bikes that endure extreme weather in Alaska, Norway, Belize, Singapore, Dubai and of course the rainy Northwest with never a failure from these conditions. To ensure consistent and good bond quality, we follow industry standard practice: meticulous surface preparation, good process control and good training—pretty much the same set of criteria to ensure good bonds on carbon bikes or good welds on metal bikes. All bonding is done in a climate-controlled room and the frames are oven cured to achieve the highest possible bond strength.
The Right Boards
The appearance of each bike is unique simply because grain, color and figure vary, even within the same board. Our wood selection process for each and every bike is painstakingly conducted by obsessive people. We spend ridiculous amounts of time at four different specialty lumber yards searching for and choosing the perfect lumber to achieve stunning, and much more time back at the shop deciding how to cut and match the 16 to 40 pieces of wood that make up a frame. But I confess, we love going to the lumber yard, it's an exciting treasure hunt every time. Way more fun than just ordering another Reynolds tubing set...
Our finish coating is two applications of at least three layers each two separate formulations of linear polyurethane, specifically formulated for use on aircraft, the toughest, most waterproof clear coat available. No other coating compares to our finish for blocking Ultraviolet damage and moisture.
Heat, Cold and Moisture are Not Problems
Wood, in a properly designed structure, properly sealed and bonded, is unaffected by hot, wet or cold outdoor environments; modern wooden boats live in the water, wooden aircraft and wooden propellers fly through it.
Metal Sleeves in the Frame
We use metal sleeves in the head tube, upper seat tube and bottom bracket. All bonded aluminum is abrasive blasted, acid etched and alodined for maximum bonding strength.
Before proceeding with the wooden frame concept, we made and tested wooden tubes of various species, wall thicknesses, shapes and sizes, with the goal of at least equaling the torsional stiffness, out-of-plane-bending, and weight of an Easton aluminum mountain bike down tube. We surpassed that goal and easily match carbon stiffness..
We test every stick of wood that enters our shop for stiffness, moisture content and other factors that affect the quality of our frames, then enter its index number in our woods database. This database enables us to forecast ride quality and stiffness for the riding style and weight of the owner. We also test each frame we produce for stiffness, which gives feedback on our predicted stiffness and also serves as a quality check on the bonding and joinery.
No more is required than any other painted bike, perhaps less. A scratch through the paint and epoxy could be a cosmetic problem if left unsealed, much like a steel frame—if the scratch got wet enough, often enough, the finish around the scratch might eventually blister. A quick fix is clear nail polish, although a properly done repair is simple and unlikely to require a pro.