The How of Fitting
The Bicycle Source
Riding with high comfort and efficiency requires a properly fitted bike. There is a lot of misinformation floating about, saying that none of your weight should be your arms, or that saddle height doesn't matter, or that the handlebars should be as high as the seat, but the information here comes from well-researched books and studies by experts.
While everyone is different, and these recommendations only represent the norms, these are the best estimates from experts who have done experiments involving hundreds of people, so give the standard settings a good long trial before changing them.
Does Perfect Fit Ever Change?
QUESTION: I've been reading a lot about bike setup. Here are two things that I still can't sort out: ---If there is one "best" position, does it change over a season after I've ridden more miles or done a stretching program? ---I've been told to move my cleats back on the shoe sole to alleviate "hot foot." If establishing proper cleat position requires tape measures, plumb bobs and a little bit of astrophysics, how can I just slide the cleats back with impunity? -- Ann S. COACH FRED: First, I think the concept of "perfect" bike fit is overrated. The theory says that everyone has an ideal fit for a specific type of riding or event. Fit is right when it reduces injuries while increasing power potential. But perfect fit can vary with time, circumstance and a host of other factors.
Most experts now agree that there's a "fit window" -- a range of acceptable positioning. The leeway is about one centimeter for variables such as saddle height and reach to the handlebar. If you get accustomed to riding in a certain position in your window, you'll adapt and not get injured.
Consider this, too: Lots of riders switch from their road bike to their mountain bike or hybrid without suffering dire consequences even though these bikes put them in different riding positions.
As for sliding cleats to the rear, this does change other position variables, seat height being one. The key is to move cleats a small amount, about 2 mm, then ride in that position several times. Then slide them another 2 mm. Keep this up until you have the cleats where you want them. The body doesn't like sudden changes. It can adapt quite easily to slow, incremental changes.
The height of the seat can have a very significant impact on the efficiency of riding. In one study of short-term total power output, saddle height was optimized at 109% of the inseam length (the distance between the bone in the crotch and the ground, in bare feet). While the experiment was quite specific in focus and there is individual variation, on average an alteration of saddle height of only 4% affected power output by approximately 5%, or 84 seconds on a 28 minute, 15 kilometer time trial. By comparison, a guy I know spent some $600 on new wheels with streamlined, 16-hole rims and bladed spokes to shave 59 seconds off of his time.
Like most adjustments on a bike, the issue of saddle height is not a simple one. Cycling is a repetitive activity where the longtime cyclist becomes strongly accustomed to a saddle height, so changes should be made in small amounts and at long intervals, such as 1/4" each month, towards the formula result. Large variations in saddle height can be compensated by the degree and even direction of ankling.
In general, you want to extend your leg as much as is possible without completely straightening it, which disrupts your pedaling and probably the health of your knees as well. Similarly, if you rock back and forth in the saddle, the saddle is too high. On the other hand, a saddle set too low misses the optimum extension of your leg muscles, where they are strongest at near their maximum extension (albeit the details are highly specific to the activity). Women, with their longer legs, will want a higher saddle than a man who is just as tall.
When you find your perfect saddle height, mark your seat post and periodically check it, as your seat post will slowly sink into the tube over time.
The rails on a seat allow you to set it towards the front or rear, which is a complex and important optimization. The position of the seat with respect to the handlebars and pedals make the main difference between the steep 74 degree seat tube of a racing bike and the 71 degree tube of a touring bike.
Moving your saddle back puts you in a lower posture, which is more aerodynamically efficient, allows you to use all of your leg muscles, and is better for your back and breathing in the exact same way as dropped handlebars. The best way to achieve this may be to lower your headset and get one which extends farther, however, as sliding the seat back this can mess up your leg geometry. The farther forward your are, the more total power output you have available -- hence the steep seat-tube angle on racing or sprinting bikes -- and farther back allows you to "ankle" more effectively and is conducive to long-haul output.
Older riders generally prefer seats towards the back of the usual 1 3/4" to 2 1/2" range from the nose of the saddle to a vertical line through the crankset.
Start out with the saddle parallel to the ground. Mine was set with a carpentry level, which is what you should use, and I find it great. Before it was leveled, on the other hand, I kept slipping around uncomfortably.
Sometimes cyclists tilt their saddles very slightly upwards, which helps the rider to put more of his weight on the saddle and less on the arms. Women riders will generally want as little weight as possible on the saddle, and many men find the upward tilt uncomfortable.
Of more frequent concern are downward-tilted saddles. These cause the rider to constantly slide forward, or brace themselves with their arms as long as they're in the saddle. Forward-tilted saddles do not add to comfort, so set it to dead level.
The frame size is measured from the seat lug at the top to the center of the bottom bracket. To calculate your correct frame size, divide your height by three, or subtract 9 inches from your inseam length (measured from crotch to floor, in bare feet).
Regardless of the calculations, the frame should be easily straddled with both feet flat, with perhaps an inch of clearance. While a smaller frame can be compensated with a higher seat and headset, of course, a frame which is too large for adequate groin clearance should be avoided at all costs, for the inevitable is inevitable. If you can adjust the seat and bars properly with two different sized frames, the smaller one will be stiffer and absorb less of your pedaling power in flexing. As men have proportionately shorter legs than do women, your frame and seat will usually be higher than a man of the same height.
Most bikes have a 72 degree seat tube and head tube angle. This provides an excellent combination of road holding, shock absorption, and power transmission, and is great for bumpy streets. Racing frames are steeper or "tighter," at 73, 73.5, or 74 degrees, or a combination like 73 head and 74 seat, for a stiffer ride and better power transmission. The main great thing about suspension and shock-absorbent materials like titanium and carbon fibre is that more efficient setups like steeper frames or higher tire pressures become tolerably comfortable.
The headset (vertical) should be higher and the stem (horizontal) should be shorter on a women's bike than on one for a male of the same height, as both are determined by arm length. Arm length varies substantially between women and men, so the optimal bar placement varies a great deal as well. While the lower and farther that you are able to comfortably reach, the better in terms of aerodynamics, don't get stuck with handlebars in the wrong spot just because you're a girl.
While the headset's vertical height can be adjusted, the length of your stem is fixed, so buy one of the correct size the first time. Or, better yet, use an adjustable stem until you find the right length. The height and length settings are related, of course, so they can compensate for one another to an extent.
Handlebar position is generally set by the nose being directly above handlebars when down on the hooks. A second rule of thumb is when riding in you normal position, your front hub should appear hidden by or a bit behind your handlebars. Alternately, sit on the bike in your normal riding position while someone holds it steady. Without changing position, remove one hand from the bars and let it relax and dangle freely. Without stretching, rotate your arm in a large arc. As it comes back to the bar, if it comes ahead or behind your other hand, your handlebars need to be moved.
Just as you support your torso with your arms when bent over to catch your breath, it is normal to have some of your weight rest on your arms, at least when using dropped bars or another well-designed, efficient arrangement.
The straight bars, often nearly as high or higher than the seat, on mountain bikes so hopelessly retard your riding that it barely matters where you put them to minimize the damage they do to your breathing, back, aerodynamics and comfort. On the better-designed of mountain bikes, you will note that the handlebars are very much lower than the seat, and are far enough forward to promote the optimal 45 degree back posture. Get your handlebars as low as possible on a mountain bike that you can still manage a downhill, or change it if you won't be around hilly trials for a while.
Many of the advantages of using dropped bars apply to setting your hybrid or mountain bike's bars to a height which promotes a similar effect.
Lowering your bars gives you more power, as jerking on your bars as you pedal will add to the torque generated, without the unwanted side effect of pulling the front wheel off of the ground. The lower bars also let you move your saddle forward with respect to the pedals, which puts it in a sprinting position.
Are Your Legs Symmetrical?
For almost everyone, you'll find that one leg is longer than the other. If the difference is as slight as a half centimeter you probably needn't worry, but at some point you will want to make your bike fit. There are three major ways to adjust your bike.
If the difference is mostly in your thighs, you'll want to compensate in your crank length. It isn't easy or cheap to order an odd crank of a different size, but it will do the trick.
If your lower legs are different, the pedal cage height is the measurement to change. Shimano makes drop-center pedals, which can be fitted to some cranksets. The shorter leg uses a conventional pedal, possibly using a an adapter in the crankset.
Another option is to use orthopedic pedals set to different cage heights. France's T.A. makes a set, and a good bike shop can order them for you.
For more information on fitting your bicycle, stop in to our store for a personal consultation, and if needed, a custom fitting by the experts. We use Body Scanning for a perfect fit between man and bike.
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