Previously in the past all of my adjustments to my bikes have just been to change stuff until it starts to "feel just right". Hardly an exacting method, however I'm thinking I really ought to take this more seriously. Not wishing to go so far as spending the expense of getting a proffesional fitting (although did consider that, but I thought I'd best get something like that when I'm no longer a poor starving student etc.....). So is there any advise or websites I could be directed to so I could embark upon this myself? Bearing in mind that cycling wise the only races which I really have as goals for myself this season (as it was for last season, and most probably will be for next season etc...) are long distance triathlons (namely the Auckland Half Ironman and Ironman NZ).
01-01-06, 07:41 PM
Below is an article about bike fit. It was written as instruction for coaches, so read it in that contet when it says "make sure that your clients...". Feel free to email me at CoachKen@erols.com with a quick question.
Bike Fit for Time Trials and Triathlon
© 2003 by Ken Mierke
Sometimes when I consider what tremendous consequences come from little things … I am tempted to think there are no little things.
- Bruce Barton
Position on the bike is critical for any racer, but establishing optimal position for time-trial racing may be much more critical, complicated, and dynamic than developing optimal position for road or mountain bike racing. Small adjustments in time trial position may make enormous differences in speed and efficiency. A few years ago, Quintana Roo had an add saying that the difference in aerodynamic drag between their bikes and a Kestrel more expensive aero frame is equivalent to sticking out your pinky finger. While that is true, the ad did not tell riders that a pinky finger’s worth of aerodynamic drag makes a huge difference in performance. When a few seconds can be the difference between first and fifth, attention to detail is important.
Colby Pierce set national records years ago pedaling in an extremely aerodynamic position and time trialing with wattages that were mediocre at best. One of my clients could sustain more than a hundred watts more than the national record-holder. That really opened my eyes as to how important aerodynamic positioning is.
Individual differences play an even greater role in time-trial positioning and optimal position will change more over time. Aggressive aero positions take time for a rider to adapt to and I think we should regularly reevaluate optimal position and work toward improving aerodynamics without compromising power output. Optimizing position is a long-term process. Lance Armstrong used to be beat in time trials by Raul Alcala, a 125 pound rider that Lance could climb with. Lane has worked every year to refine his position to what we see today and it has made a huge difference. Even as one of the world’s best at the time trial, he continues to work to improve his position. For many riders, specific exercises as part of their training program will enable more aggressive positioning over time.
In the late 1980s, aerodynamics became a fad and many time-trialists and triathletes went crazy trying to develop the most aero position possible, frequently at a great cost of economy and power production. Every magazine had articles about how much each component could cut from your 40K time trial split. I remember seeing 1-hour time 40K time-trialists riding with their stems so low that they struggled down the road at an extremely aerodynamic 23 miles per hour.
Then Dan Empfield developed a bike specifically for the aerobar and for time trial and triathlon racing. His bikes were the first to use forward positioning and steep seat tube angles. Unfortunately, many athletes took this to an extreme. We saw frames with extremely steep seat tube angles – up to 90 degrees. I have to plead guilty here myself. On the wall at my office hangs a beautiful custom aero frame with an 83-degree seat tube angle, never raced and with a total of about a hundred miles on it. On the flats, I could fly, but a 1 degree incline became a huge climb.
I also remember Steve Bauer riding the Tour Dupont on a 60-degree frame developed to simulate the Nautilus Dual Leg Press machine he used for weight training. I thought we did weights to help our cycling and not the other way around! John Cobb is now advocating his “slam” position for some riders. The real key here is “for some riders”. While some riders may ride best in fairly aggressive forward positions and others far behind the bottom bracket, a great majority will ride best with a position that is not extreme in either direction.
Saddle height is the first adjustment that should be made. Warm up well. Have him/her pedal and note ankle angle (dropped heel, neutral, toes down). Ask the rider to stop with his/her leg fully extended, where the crank is parallel to the seat tube, and measure the rider’s knee angle using a goniometer. Set the pivot point over the lateral epicondyle (knee’s axis of rotation) and line the arms up with the lateral maleolus and the greater trochanter. This angle should fall between 25 and 30 degrees. Research shows that pedaling economy is optimal anywhere in this range. I recommend saddle heights at the higher end of this range for athletes with poor hip flexibility and those for whom force is a major limiter.
When measuring knee angle, be very careful that the measurement is taken with the rider’s ankle angle set as it is when he/she pedals. Correct saddle height may be quite different for two riders with identical leg lengths if one pedals with slightly pointed toes and the other drops his heel.
Determining optimal torso angle is the single most critical step in aero positioning. Lowering torso position toward the horizontal decreases drag, but may also reduce pedaling economy and decrease power production dramatically. Each rider will have a minimum torso-femur angle at which they can produce power effectively. Generally there is a point at which he/she can produce good power, but lowering the stem just ¼ cm reduces pedaling efficiency dramatically. Finding this position is critical.
For riders who must sit relatively high on the bike, a specific program of stretching and strengthening may enable a more aerodynamic position in the future.
Flexibility plays an important role in this. Riders with tight hamstring and/or low back muscles will not produce power effectively in low positions. Riders with tight hip muscles will not be able to maintain a pedaling position that stays in the correct plane – their legs will bow outward, which affects both power production and aerodynamics.
Hip flexor strength and endurance also play a role in optimal torso height. Tight torso-femur angles require the hip flexors to work through an extreme range of motion to unload the pedals on the upstroke. This can be improved dramatically with an effective program of strength and muscular endurance training for these muscles, enabling efficient power production a lower, more aerodynamic position.
Each coach should have some means of measuring optimal torso height for their athletes. I have the riders pedal with a relatively high handlebar height on a Computrainer, using wattage slightly below LT, and measure ventilation. This is repeated after slightly lowering the handlebar a number of times. What I find is that ventilation increases slightly with each lowering of the bar, but at some point ventilation increases dramatically with a very small change in handlebar height. I set the height one notch higher than produces the ventilation jump. A similar test using heart rate and perceived exertion could be very effective. I do recommend using a relatively high wattage. I have seen bike shops have a rider pedal in a very light gear and ask “how does that feel?” A rider may be able to spin smoothly and comfortably at very low power output even if the position is much to low.
A more forward position allows a low torso position while maintaining a relatively open torso-femur angle. Most riders cannot pedal efficiently with a horizontal torso position on a bike with a traditional 73 degree seat tube.
The two primary power producers in cycling are the quadricep muscles (front thigh) and the gluteus maximus. The quadriceps extend the knee and the glutes extend the thigh. These two muscle groups produce maximum power during different phases of the pedal stroke. The ideal time-trial position produces a horizontal torso with a maximal overlap between the power phases of the quads and glutes.
Flexible riders will be able to use a more aft position, while riders with tight hamstring, low back, and hip muscles will ride better in a more forward position. Riders who prefer lower cadence will be effective in an more aft position, while spinners will be able to produce good power further forward.
I generally start about 2 cm forward of the knee-over-pedal-spindle position and adjust forward or backward from there. Almost every road cyclist time trials better forward of his/her road position.
After changing fore-aft position, it is important to reset saddle height. Saddle height has both vertical and horizontal components, so moving the saddle forward will reduce height and aft will increase it. Usually the adjustment is about one-third of the fore-aft adjustment. If you move the saddle forward one cm, raise the seatpost by 1/3 cm and vice versa.
Terrain of the priority races also plays a role in saddle fore-aft position. While an aggressive forward position may allow efficient power production in an aerodynamic position, power production will fluctuate more through the 360 degrees of the pedal stroke in a forward position. On a flat course, this is a good tradeoff for aerodynamics. At high speeds a rider can coast through dead spots in the pedal stroke and high peak wattage along with minimal drag make up for even with excessive dead spots in the pedal stroke. This is not true on climbs where a rider is not moving fast enough for momentum to carry him/her through dead spots in the pedal stroke effectively. A more aft position is preferred for hilly courses.
The Q-Factor is the horizontal-lateral distance between the pedals. Most riders time-trial most efficiently with a low Q-Factor. This makes pedaling with the knees in close to the top tube more natural. Wind tunnel studies indicate that pedaling with a wide knee position increases aerodynamic drag significantly. Wide knees not only disturb more air, they unnecessarily increase airflow into the seatpost, seat tube, and seat stays, which are aerodynamically messy areas of a bicycle.
Low profile cranks are widely available and several new pedal systems have adjustable Q-factor. I generally prefer relatively narrow Q-factors form my riders, but some report climbing more effectively at low cadence with wider spacing.
Most riders should learn to ride with relatively narrow elbows. Wind tunnel studies have shown that time-trialists with shoulders positioned above hip height (95% of us) minimize drag by bringing the aero pads as close together as possible, ideally with the forearms touching. The arms can then act as a fairing, redirecting airflow around the chest. This position may cause bike handling difficulties and should be gradually adopted. Elite riders with extreme flexibility and very effieicnt pedal strokes are able to ride with a lower torso position and may benefit from wider elbow placement.
A rider who is able to pedal efficiently with a perfectly horizontal torso will have the least drag with elbows and hands exactly the width of the legs so that the thighs can draft the arms and the arms present a minimal frontal area. Since the chest is not presented to the wind, redirecting airflow is secondary to minimizing frontal area. Few athletes have the level of flexibility to produce power efficiently from that low a position. Most athletes will ride faster sitting up slightly and getting narrow.
Lowering the head between the shoulders can cause a significant reduction in drag. This does not mean tilting the head downward. A rider should always keep their eyes up on the road in front of them, but gently squeeze their head downward. This feels like the scapula are being raised toward the sky. Try setting your bike up on a wind trainer in front of a mirror and noticing how much you reduce your frontal area with a correct head position.
Saddle Tip to Handlebar Distance
Most riders position has a saddle tip to handlebar distance that is too great. Road bikes are designed for an athlete to grip the handlebars with his/her hands and time trial bikes are designed to be ridden on the elbows. This dramatically reduces the required length - by the length of the rider’s forearm.
The elbows should be kept as much under the shoulders as possible, instead of more forward, for two reasons. The more a rider’s elbows are in front of his/her shoulders, the more the shoulder muscles must contract to hold the body up. This can be uncomfortable and, more importantly, uses oxygen that should be delivered to the legs.
Secondly, the thighs draft behind the arms and the closer they are, the greater the effect. Saddle tip to handlebar distance should be set long enough to encourage torso extension, but not enough to extend the elbows well in front of the shoulders.
Make sure that your athletes take their aero positions seriously. Work with them not only to develop their optimal current aero setup, but to improve physical qualities that keep them from producing power efficiently in an even more aero position. Remember that most of our athletes are VERY high up their diminishing returns curves as far as fitness. Improving aerodynamics by the equivalent of ten watts may possible when producing ten more watts isn’t. We need to help them take advantage of every bit of “free speed” that is available. Optimal aero positioning is a very large area of free speed.
Dan Empfield's tome on tri bike fit:
Then Dan Empfield developed a bike specifically for the aerobar and for time trial and triathlon racing. His bikes were the first to use forward positioning and steep seat tube angles. Unfortunately, many athletes took this to an extreme. We saw frames with extremely steep seat tube angles – up to 90 degrees. I have to plead guilty here myself. On the wall at my office hangs a beautiful custom aero frame with an 83-degree seat tube angle, never raced and with a total of about a hundred miles on it. On the flats, I could fly, but a 1 degree incline became a huge climb. Why would a 1 degree incline become a huge climb? Why should there be such a difference in cycling up a 1 degree slop as opposed to on the flat?