Grams-to-dollars ratio explained!
(Author's note: (written November 2006) I haven't reread this in a while, but I have a nagging suspicion I wouldn't agree with all of it anymore. I'm going to leave it up anyway, for "historic" purposes, for now. -- Ace)
Not long ago I decided that I wanted to try to knock two pounds off my wife's bike and one pound off of mine, and I decided I could spend a maximum of about $500 to do it. This number was decided upon arbitrarily, but it had something to do with a discussion over lunch about $700 cranks. They were a fancy composite material, and knocked off a good half or 3/4's of a pound from the weight of even fairly good cranks. Definitely trick. I had torn out the article about them and showed it to my wife, and we started thinking about what we could do to save weight on the bikes, and spend no more than about $500, which we figured would be the street price of the cranks. We decided there were much better ways than buying cranks (though I still want the cranks.) We ended up not doing all the work, instead we went all-out and bought my wife a new bike, but the exercise of figuring out what I would have done was quite useful.
It turned out to be pretty easy to come up with a better group of things to buy, and it was definitely a worthwhile exercise, since it gave us some rules to live by when trying to reduce bike weight. The final result: A general grams to dollars ratio for buying lighter bike components! This ratio will be different for everyone since in most cases it depends on available money, but for this article, it came to average about 30 cents a gram. Before going on I must explain that the ratio varies considerably depending on where the component is situated on the bike. I'll explain that later in the article. We came up with 30 cents this way:
First, a really good bike, with really good components, might cost $4,000 and weight 27 pounds, which is a little over 12,000 grams (about 12,247) A pound is roughly 450 grams (453.6 is closer). Since I wanted to knock off a total of three pounds, that's about 1350 grams altogether. For $500.00 that's about 30 cents a gram (27 cents a gram, but close enough.) You could just go out and buy components using this as a ratio, but that's incomplete: The real calculation is to decide what factor the weight savings has on the handling.
Good handling depends on many factors, of course. Angles of tubes, ratios of things, and balance being a few of them. Another important factor concerns the bike's resistance to change. The flywheel effect of a weight (in this case a wheel) spinning quickly (or even fairly slowly) causes that thing (the wheel) to resist change. It does so, for those keeping track, at the square of the distance from the center of the wheel. This means you have to work harder get it to turn. Also once turning it will tend to keep turning. And finally, it will be harder to stop turning.
The improvements we made were designed to improve weight without sacrificing stiffness or other good handling qualities of the bike. If you have a lot of endos, you should do one thing, if you tend to run off the trail, something else may need doing. If you can't brake well, it's something else, and if the rear end slides out from under you when you brake in a turn, that's something else altogether. It's true: you have to become one with your bike, and only do improvements which help overall. But saving a little weight off a bike can make a big difference.
My wife and I ride fairly often, averaging around 50 miles a month, all of it off-road. We began riding in 1992 and as of this writing (1996) are now on our second generation of mountain bikes (my wife's third generation bike is on order). Since we each have fallen bad enough to end up at the emergency room (okay, just barely, nothing serious) we figure we have a pretty strong desire to stay in this sport. In fact, one could say we are often head over heels in love with it.
Her current bike is a Cannondale M400 with a Manitou III front shock, and mine is an Answer Manitou System FS, a full-suspension frame also based on the Manitou III shock in front and a similar shock in the rear. We were going to upgrade my wifes bike, but decided instead to get her a full suspension bike with all new XTR components. Since my wife will be moving up to full suspension soon, we won't actually be doing this work to her current bike. Theoretically at least, let's proceed.
There are approximately five main kinds of weight on your mountain bike. Each component fits into one or more of these five categories of weight, and the first thing to do is to place the component in the appropriate category. Usually a component falls into several categories.
First, there is rotational weight. That's the most important. That would be tires, tubes, rims, spokes and hubs. To a lesser degree, the cranks and pedals are rotational weight, but generally they rotate slower and on downhills and rough terrain, they often don't rotate at all. Your two wheels act as two big flywheels, and if you've ever held your front wheel in your hands and then spun it, you know that it resists motion. This is not good for handling! It can help a little in balance at high speeds, but that 'help' is far outweighed, I think, but the resistive element. You need to be able to throw the bike around underneath you. The further from the center of rotation a given weight is, the greater the effect it will have on handling. It's importance varies with the square of the distance from the center, so clearly the most important weight you can ever reduce on your bike is in your wheels, including spokes and even hubs. Rotational weight savings has another advantage as well: Your ability to change speeds is more dependent on reducing rotational weight than any other weight. Light wheel assemblies mean you can slow down more suddenly for a technical section, and then get up to speed again quickly afterwards.
If you consider the importance of rotational weight, one thing comes clear: Panaracer GreenLite or some other Polyurethane inner tube is a great way to save important weight. Even though these are five or six times the cost of a regular inner tube, the 2 to 4 ounces they save over regular butyl, even lightweight butyl tubes is very significant. In fact, for the first $100.00 of the $500.00 we planned to spend, we bought five of these tubes. Why five? One of us (me) carries a spare tube. The spare is not rotational weight, but it is "high weight" which is also important and which I explain later. At a grams to dollars ratio, these tubes clock in at a whopping 5 grams to a dollar, not only well under the 30 cent average we're looking for, but it's rotational weight at the far end of the rotating part (the wheel), making it the most important and cost-effective weight savings available! We recommend lightweight tubes to anyone who ever bought so much as one component in their life with any consideration to weight. (You'll want to switch everyone you ride with over to them, since you need a different patch kit.)
Get lightweight kevlar tires to complete the picture. They are about twice as expensive as "regular" tires but it's all-important rotational weight. Panaracer Smokes and Darts (mine are Magics) are our choice. but I don't like the lip on the edges of the Panaracer front tire. The sharp edge of the lip makes them squirly in a turn.
Different people with different riding styles like different tires, but everyone likes light ones. You will too. Hubs, being at the very center of the rotation, are not nearly as important for weight considerations, though a good hub can add stiffness and reduce weight on a suspension system.
The next most important type of weight is steering weight which is weight on the front of the bike, like handlebars, shifters, brake grips, bar ends, front brakes and stems. This is a very important area for mountain bikers since again, you are constantly "throwing the bike around underneath you" and to turn the handlebars, they should be as light as possible. Also, lightening this area helps the bike jump up when needed when your front wheel hits a big rock. And on steep downhills lightening this area means more of the weight is still behind the front wheel.
Last but definitely not least lightening the "steering weight" helps you hold your course when something tries to knock the handlebars out of your hands. Letting go of the handlebars, I contend, having studied hundreds of accidents including several dozen of my own, is the single greatest cause of severe accidents in this sport. (But that's a topic for another article.) The further away (in a perpendicular direction) from the headset a component is, the more important the weight is. Light barends are several times more important than a light stem is, though no barends is even better if you ask me.
The handlebar itself should be as light as possible, but it's not a good place to sacrifice strength! I use Answer Hyperlites because they are reported to have the best test results in strength tests. They're inexpensive (about $45.00) and they're real light. Easton aluminum is such a wonderful thing! My wife, who weighs nearly half what I do, can probably be perfectly safe with a pair of the new Scott brand thermoplastic handlebars, which are even lighter than the Hyperlites, but I'll stick to Hyperlites. Broken handlebars produce some of the nastiest accidents you'll ever see. Figure $50 for the handlebars and save maybe 100 grams over what she's got now, which is a stock Cannondale handlebar. $.50 cents a gram. Not 30 cents, but close enough since it's turning weight.
The third most important type of weight is unsuspended weight. That would include all of the wheels, which are also of course, rotational weight. Unsuspended weight also includes any components attached to the wheel side of your suspension. It is important to reduce unsuspended weight because when you bounce over rocks and ruts, this weight goes ballistic, literally. It flys through the air with a life of it's own and that's not good for single-track-minded riders.
On an unsuspended bike all the weight is, of course, in this category, and on a front-suspension bike like my wife's, the weight closest to the unsuspended rear is largely unsuspended weight. On her bike, as you get further toward the front of the bike, a smaller and smaller percentage of a given component's weight is unsuspended weight. Unsuspended weight is important, though not nearly as important as turning weight and rotational weight. The brakes, the skewers, and the suspension fork crown are all unsuspended weight even on a full-suspension bike. Skewers are a cheap place to save weight. A pair of "lightweight" quick-release skewers can save around two ounces off stock ones. Salsa makes some nice steel front/titanium rear ones with excellent high-leverage handles. Some people feel that titanium skewers are less rigid than steel ones, which is most important in the front, hence the combination. And rigidity is basically a good thing. At a cost of about $50.00 for steel skewers, good ones are above the agreed-on 30 cents a gram, but since it's fairly important unsuspended weight and, for the front skewer, it's also turning weight, we think they're worth it.
Next there is high weight which is weight that is high above the ground. High weight includes first and foremost, the seat and the seat post, since these are indeed the highest part of most mountain bikes, though sometimes the stem and headset are a little higher. The importance of this weight is that as you get further above the base of the bike, a partial loss of balance of the bike becomes harder to fix. Imagine a five pound weight on a pole that ran vertically straight up the center of the bike. As you move that weight up the pole it will become more and difficult to correct the bike's balance, eventually (if you had a tall enough pole) the weight would always topple the bike and not even Hercules (in New York) could keep the bike up. That's really high weight, but the next best (real) thing is the seat and seat post. Short people can cut most seat posts with a hack saw (be sure to debur it afterwards) and still have a safe amount inside the seat tube (at least four inches is normally recommended, but I'm not making recommendations here-ask a local expert.) The seat post should be aluminum or titanium, and the seat kevlar with titanium rails. We figure to save nearly a pound on my wife's bike for about $200.00 for the seat and the seat post. Grams to dollar ration: about 40 cents a gram. Close enough since it's high weight.
The next type of weight is, for lack of a better term, jiggling weight. A lot of people might not consider your tool kit to be a component, but if you wouldn't leave home without it, it's a component. And if it is sitting in a bag that can bounce around, or if it can bounce around inside of the bag, you have jiggling weight. Try to stop jiggling weight from jiggling if possible. Jiggling weight is bad, because it's essentially unpredictable. It makes your bike do seemingly random movements of it's own. You may not recognize it, but it's there. I lost two ounces of jiggling weight when I opened my pack and realized I didn't need to carry a separate spoke wrench, since most multipurpose tools have a spoke wrench built into them.
The last type of weight is basically anything that doesn't fit into any of the other categories, which I call dead weight. It's anywhere you can find that weight can be saved for a fair price. Generally the further from the bike's bottom bracket a component is, the more important it's dead weight factor is. The rear brake, the water bottle cages, and the front derailer are all dead weight. The anti-chainsuck thing if you have one and the seat post quick release are also examples of dead weight. Dead weight should be removed if it's cost-effective to do so.
If we did all the work, my wife's bike would be about two pounds lighter than it is now, and mine will be over a pound lighter. Does this make a difference? On a 27 pound bike, one pound is nearly 4% of the weight. Unless you do something strange, that means the bike is probably going to be at least 4% easier to handle. If the weight is in the right places, like rotational weight, it will make an even greater difference. The changes we've made so far have improved handling significantly already. If we find $1400.00 we don't know what to do with, we'll save a little more weight by buying two pairs of those composite cranks. But until then, these are the next best thing, and doing these calculations provided us with a guide to what would be worth doing.
All of these calculations about weight make the assumption that you have already lost all the weight off your body that you can. And a few other big assumptions as well, but at least these are some things to consider when trying to perform weight savings on your mountain bike.
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