March 12, 2014
Launching a Series
Here is the second of a series of posts exploring wheel design. You’ll recognize them by rhyming titles and the word “Right.”
Wheelbuilding’s strong design tradition is riddled with misconception and superstition, so let’s blow away some myths. Independent wheelbuilders (IWB) need to design with confidence.
As you may be aware, the role of spoke tension is often misunderstood and misrepresented. Hence, my earlier post “How Tight is Right?” The rest of this series will illuminate the underlying dynamics of various design features so you can choose effectively in a market with zillions of choices, contradictory claims, and a steady stream of unique riders and bikes.
We’re going to ignore some important wheel characteristics, design choices about which you don’t need my advice and around which there is little confusion. Color and price, in particular. What I want to discuss are elements that are invisible or hard to perceive - intangibles, you might say. Tension, weight, aerodynamics, and feel are my favorite four. Today, we’re onto weight.
A Huge Mix-up
While we all fundamentally know how to navigate features and benefits, the market is so shrill with emphatic claims and overstatement, we regularly fall victim to mass confusions. Few such confusions are so imbedded in cycling than the relationship between price and weight. It is almost unique to cycling because, in design at large and other vehicle industries, the issue is hardly blurred.
Have you noticed, the lighter a bike the more it costs? The lighter a wheel, the more it costs. This is a fraud and we don’t have to go far to see why. Do airplane makers charge less for light planes than for heavy? Are light trucks more expensive than heavy? Is a light hammer more expensive than heavy? No, of course. Since lightness is a virtue, the only reason to add weight is because requirements are greater. A 747 carries more than a 737. It is heavier for a reason and costs more. The same design standards apply to both planes. The heavier one is not less well made.
In cycling, cheap bikes are heavy. There’s no doubt but never confuse weight and price the way our industry has. In a simplified world, heavier bikes are meant to have features lighter bikes cannot: strength, comfort, longevity, accessories, versatility, portability, etc. To compare a cheap, heavy bike to a light bike that happens to be expensive is a big mistake, apples and oranges they say. The comparison is not valid. Designers need to be smarter than generalizations that come from flawed comparison.
So STOP giving companies credit for charging lots for light wheels that lack features. In fact, they’ll use expensive materials to increase the price because they are afraid you will reject them if they are not expensive. There are loads of inexpensive wheel designs just as light as the brands. Brands know the weight/price relationship is so totally misunderstood they must charge more. It’s as bad as believing that gray haired war veterans are wise and trustworthy. Sure, often. But look at the Senate. Doesn’t always apply, right?
The independent wheel builder is, first, a designer and second, a constructor. In your design role, know your way around the myth of weight and price.
In certain very limited situations, wheel weight has huge effect. Aggressive acceleration, as in road or CX racing, involves increasing wheel rotation. Lighter wheels take less energy to accelerate. This produces a dazzling impression on riders, especially initiates. Like autos where power = thrill = luxury => victory => fulfillment. Lighter wheels sprint great but do not produce victory. Most models suggest weight in wheels is about twice as important as other vehicle weight during sprinting.
More important, sprinting is a tiny, tiny portion of your ride. Despite their vivid impression, super light wheels do not get you from A to B appreciably faster. Don’t get me wrong, they’re fun, like horsepower. But fun does not equate to achievement.
The Dynamics of Climbing
Light wheels also climb great. Why? If you do the math, the lower mass of the wheel = less weight to carry up the grade. But the difference in weight between the heaviest and lightest wheel sets in the market is about 1kg. Vehicle weight (bike + rider) could be 89kg. Here wheels could bring a maximum 1.1% decrease in total mass. A 1% difference is negligible compared to accessories, morning meal, shifting decisions, and a normal wattage variation from day to day. So why such a vivid impression when climbing?
The key to efficient climbing is tempo. Maintaining ultra smooth pedal stroke and even crank rpm translates to constant road speed. Why is that good? At the lower speed of climbing a reduction in effort or pedal speed means an immediate, unrecoverable loss of momentum (road speed). No coasting effect that we enjoy at 30kph. Jerky climbing costs watts.
If you are an inefficient climber, then you are suffering these power losses due to uneven tempo. Every time you slow down and notice, you speed back up to pace. The lighter wheels feel good during these recovery moments. But they shouldn’t be happening in the first place! The more uneven one’s climbing technique, the greater benefit from light wheels.
Even for a crummy climber there’s a liability to low wheel weight. The low flywheel effect of light wheels makes a speed loss swifter. One might have fun constantly varying speed, feeling quick on recovery with light wheels. But the clock will show mediocre results. Just like gunning a powerful engine when driving. Feels impressive but not nearly as quick as driving with finesse.
So, What to Do?
(1) Never forget cost and weight are not directly linked in wheel design. That impression is a media event you must deflect as an IWB.
(2) Light wheels feel great but rarely make significant contributions to speed. Moments when they are important (sprinting) are short. Times when they feel great (climbing) are mostly illusory and often the result of poor technique.
(3) This doesn’t mean heavy = better! Lightness is always a virtue, especially in a fuel challenged world. But it is just one design element, not the holy grail.
(4) Be glad you aren’t stuck in a major wheel company, knowing all this but pandering to the warped expectations of the market, expectations largely driven by greedy, group-think advertising.
(5) Keep an eye on breaking news. Occasionally new technologies appear that may be overlooked by the industry or years from commercialization. The inventive spirit of the cycling world is unstoppable
Next, I’ll address pricing and aerodynamics. Navigating those quagmires takes some data and tact!
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