Category Archives: Bike fit

Top 5 lessons from the Symposium on Cycling Optimisation

1.  Aerodynamic drag versus Gravity drag

You’ve probably heard that the power required to increase your speed goes up disproportionately with the increase in speed.  Here is how the power required to push you and your bike through the air is calculated.

  • Power = ½ρV² x CdA
    • ρ = air density
    • V = Velocity
    • Cd = Coefficient of friction
    • A = Frontal area

Energy model for ITTKnowledge is power, and Sebastian Weber, Sports Scientist at Cannondale-Garmin, explained how they model aerodynamic drag and gravity drag on a parcours to determine their equipment and race strategy. For example, based on the amount of climbing to be done and the expected wind conditions, they decide whether to use their lightest wheels or those that are most aerodynamic.

In fact, they run the model for each rider on each parcours, as their riders’ power/weight and power/CdA differ greatly.  They use this modelling to determine which riders they will use in a one day race and the role each rider will play each day on a multi-day stage race.

For non-professionals, we can select the races or sportives we ride based on analysing our own power/weight and power/CdA.  We can also figure out pretty quickly that pushing hard on a downhill to go from 30 mph to 31 mph is a VERY poor way to use our energy.  We will be MUCH better served by using our energy to go from 10 mph to 11 mph when climbing!

2.  Don’t waste money on an aero road bike  

(We can gain you 1 – 3 mph without a wind tunnel)

The number 1 thing we can do to make you faster on the vast majority of courses is reduce your profile and resistance in the wind.  If you look at the variables we can control in the equation above, there isn’t much we can do about air density, and we want to go as fast as our power will take us, so the things we can control are our frontal area and the drag created by our clothing.

cervelo-S5-review-front-rear-streamline-view02What percentage of the frontal area on the rider to the right is the rider, and what percentage is the bike? (over 80% of aerodynamic drag is from the rider, and, of the remaining 20%, half the drag is from the wheels) Now, how much money should you be spending on buying a bike with more aerodynamic tubes versus improving your own aerodynamic position on the bike?

Dr Andy Fronchini, who consults with British Cycling and many professional teams on aerodynamics, put together a list of the top 100 things you can do to go faster through the air.  Number 1 is improve your position on the bike, and number 100 is buy an aero road bike.  In other words, aerodynamic tubes, the positioning of your brakes, and other bike tweaks are the most marginal of marginal gains.  Of the aero losses due to your bike, 50% comes from the wheels, so if you’re going to spend money on faster equipment, spend it on the wheels.

Tommy's aero position comparisonThe bottom line is you should spend your money on improving your aerodynamic position.  If you do time trials, then TT bikes are optimised to get you as aero as possible.  How you are set up on your TT bike, however has to be optimised for the type of time trial you are riding.  You must be able to sustain your position for the duration of your race to benefit, so you can be much more aggressive in your position for a 10 mile TT (25 minutes) than you can for an Ironman triathlon (6 hours).

On road bikes, use your drops and get your head down.  We use an iPad app that allows us to accurately measure the area uncovered in the photo.  In top image it was 0.163 square meters, and in the bottom image it was 0.129 square meters.  This is only the rider’s head, arms and torso, so, conservatively, we improved the total area including his legs and the bike by 10%.

In this case, we are working to improve his speed in the sprint at the end of a race, so he is already travelling over 50 kph (30 mph).  With every thing else fixed, a 10% decrease in frontal area means he needs 10% less power to reach the same speed.  So, using the formula above, keeping the same power will increase his speed by 2.8 kph (1.7 mph).  That can easily be the difference between winning and coming fifth.

For you, we can improve your frontal profile and quantify the benefit it will deliver.  At Sportive speeds, you’ll gain up to 5 kph (3 mph).  We have added this service to our business, and at £75 it’s the most effective money you will ever spend on going faster.  So, rather than buy that aero bike you were thinking about, get a proper aero fitting and invest in some fitness testing and structured training!

3.  Periodising Nutrition can train fat burning

Your aerobic system is what powers over 90% of your cycling effort, and it burns a mix of fats and carbohydrates. However, your fat burning system will atrophy if you continuously fuel the aerobic system with carbs.

Feedzone-BooksWe have all been influenced by the sports nutrition companies into believing we must fuel our cycling with products we buy from them.  It turns out that simply isn’t true, and by continuously feeding our bodies carbohydrates, we can actually harm our long term development as athletes.

Team Sky and Cannondale-Garmin have both publicly acknowledged they periodise their nutrition strategy to optimise fat burning.  In the off-season, they use fasted and bonking rides to force the riders’ bodies to burn fat.  This stops once racing begins,  but even then they prepare “real food” and supplement that with gels and powders, rather than the other way around.  The books pictured are co-authored by a chef who works for professional teams, and they are filled with recipes for real food to fuel your riding.

For you, think about what and when you eat on the bike.  Your body stores enough glycogen in your muscles and liver for around 90 minutes of sub-threshold effort, so you don’t need any food for rides under 2 or 3 hours if you’ve had a meal before you ride. Occasionally, you can ride beyond your glycogen stores (bonking) and force your body to burn fat exclusively.  It’s not the most pleasant experience, but it will improve your fat utilisation for subsequent rides and your racing/sportive season.

4.  How differences in Women’s anatomy affect their bike fit

male and femail pelvisesYes, we all know there are differences between women’s and men’s anatomies, but it the bits you can’t see that make the difference between women’s and men’s bike fitting.  The two primary factors are the differing shapes of their respective pelvises and women having greater joint mobility than men.

While I knew women’s sit bones were further apart than men’s, I wasn’t aware that women’s sit bones are far less pronounced, and their pubic arch comes lower.  As a result, women carry more weight on their pubic bone than men, and, in general, women cannot not get as aerodynamic as men.  To help address this, saddle choice is vital for women, and the nose of the saddle must offer more pressure relief.

women's bar widthWhen it comes to joint mobility,  correct handlebar width is critical with women. Bars that are too wide require more work from the muscles and tendons to hold the rider’s upper body in position.  The measurement to the end of the shoulder blade should be matched by the centre line to centre line measurement of the handlebars.  With the arms reaching straight out from shoulders down to the handlebars, bone structure takes far more of the load, and that will help eliminate the upper back and neck pain many women cyclists experience.

5.  Shorter Cranks is the answer.  What was the question?

Power versus crank lengthAccording to Dr Mark Timmerman, who consults with Trek Bicycles on medical issues associated with cycling, shorter cranks help alleviate or prevent a variety of knee, leg and hip problems.  I’ve quoted him in the heading for this section, “Shorter cranks is the answer. What was the question?”

But don’t longer cranks help you generate more power? Tradition is a difficult habit to break, and traditionally cyclist have used cranks ranging from 170 – 175 mm in length.  A seminal study by Dr Jim Martin at the University of Utah,, concluded that shorter cranks actually offer a benefit in power production.

So, hip flexion and knee angle at the top of the pedal stroke, which are vital for your health and performance, are both are improved with shorter cranks without compromising power. In addition, shorter cranks allow you to get lower over the front of your bike by reducing the amount by which you close your hip angle, so you can be more aerodynamic.

Improved power, better aerodynamics and less likelihood of injury all result from shorter cranks.  I’m riding 165 mm cranks now, and hopefully you’ll soon be using shorter cranks soon as well.

Myth Busting & Tips from Team Sky’s Head Physio

Custom Saddles, Bike Fitting, Training, Coaching Tips
Phil Burt – Head Physio at Team Sky and British Cycling

Phil Burt, Head Physio at British Cycling (BC) and Team Sky, has been working with the world’s top cyclists for nearly a decade, and he has committed his learning and experience to paper in his new book, Bike Fit. There is a great deal of cause & effect analysis in the book, and his perspective and experience have led to a number of cycling’s “facts” being turned up as myths.

I went to his presentation in London last night.   In to discussing the book, he presented highlights from recent academic research into cycling physiology, which further busted some long held “truths” and introduced some great new training tips. Finally, he shared a few stories from working with folks like Bradley Wiggins, Chris Froome and Mark Cavendish over the years. Here are highlights from Phil’s presentation.

  • Marginal gains are irrelevant until you get your own weight and fitness where they need to be.  In 2010 Bradley Wiggins had every benefit BC and Sky sports science could provide at the Tour de France, but he wasn’t fit enough.  After that, Team Sky made a rule – no salary payment for any rider until all their month’s power meter data had been uploaded.
  • 70% of the R&D budget for Sky/BC goes into aerodynamics.  Above 18mph, 80% plus of energy expended goes into pushing you through air, so that’s where they’re finding the best return on investment.
  • BC has designed their own women’s saddles, as standard models were creating major soft tissue damage on many of the women riders.  (If you’re having an issue, we can help )
  • Proper resistance (weight) training also increases endurance, but you have to commit to it throughout the year, not just during a two month “off season”.  The focus is on functional strength for cyclists, by the way, not building biceps.
  • There is no “correct” crank length, as there is no appreciable difference in power output between 150 – 180mm cranks
  • There is NO difference in muscle group recruitment between 80 – 120 rpm with your cadence
  • There is NO benefit, and even a loss of efficiency, in pulling up with your hamstrings during your pedal stroke.
  • Speedplay are the most “knee friendly” pedals
  • There was an epidemic of knee problems at Sky/BC when another pedal manufacturer made a small (and un-announced) increase in the spring tension in their cleats
  • Bradley Wiggins suffers for his success.  He may look smooth on his time trial bike, but that position is NOT comfortable.
  • Saddle Fit is the single most important element of a Time Trial fit.  If you cannot hold the aero position for the full race, what’s the point?  Discomfort on the saddle is the primary reason people get out of their tuck.
  • The most common cycling injuries he works with are knees, back and neck, in that order
  • It is NOT true that knees should track directly up and down viewed from the front.  If they do, fine.  But as long as you’re not having any pain, don’t try to fix it.  Every knee has its own bio mechanics, so only alter the knee movement if there is knee pain.
  • Wiggins’ recent advice to neo-pros going to high altitude training camp, “Bring your own porn boys, there’s no internet at the hotel”

Are you average? 3 reasons why bike fits get it wrong

Many bike fitters get it exactly wrong by simply relying upon the precise measurements of their fitting systems and fitting guidelines from the manufacturer. Here are 3 reasons why they often get it wrong based on our case studies.

before and after1. Saddle fit is ignored. You can place a rider in their ideal position for 5 minutes but will they stay there for 5 hours? This rider suffered from neck and shoulder pain. It’s easy to see on the left she is riding with straight & stiff arms and her shoulders are in her ears. However, the traditional fix, a shorter stem to reduce reach, won’t address the fundamental problem.

Pressure map nose heavyHer arms are straight and locked in order to rotate her hips and push herself up off the nose of her saddle, which is causing discomfort.  This saddle pressure map shows how the majority of pressure is on the nose of the saddle.

In order to get the rider comfortable in a position they could sustain on the bike, we had to change the saddle and move the saddle forward.  Again, traditional thinking is that moving the saddle forward will automatically move the rider’s position forward.  If fact, many riders will actually move back on their saddle to keep the same position of their knee relative to the pedal spindle.  In this case, we were able to get the rider comfortable on her saddle, and then the straight arms and hunched shoulders were eliminated.

Polar Chart comparison2. Historic injuries.  While measurements of leg lengths and flexibility may show a rider to be be symmetrical, those with historic injuries may sub-consciously compromise their position on the bike in order to protect the old problem.  You can see in the upper diagram (a Wattbike power “polar chart”), this rider had significantly less power on the right pedal stroke than they did on the left, and there was an alarming dip in power part way through the down stroke on the right leg, which is the flattening of the curve between 1:00 and 2:00.

Original pressure mapIn order to diagnose this asymmetry in power output, we used the saddle pressure map to understand how the rider was sitting on their saddle.  It turned out they were rotated anti-clockwise, and they had more pressure on the left side of the saddle.

Using a “shark” saddle, which forces the rider to sit straight on their saddle through the use of a “fin” at the back, we eliminated the dip in the power they generated with their right leg (see the lower Wattbike polar chart, above).

The rider was completely unaware they were not straight on the saddle and unaware they had a power asymmetry.  They had, however, disclosed in the pre-fit discussion they had an historic injury of the right knee.  Subconsciously, they had adjusted their position to “protect” that knee.  They are now riding with a Shark saddle to ensure they are straight on the saddle, which addresses the dip in power, and they are working to strengthen the right leg to reduce the total power difference.

3. Your body changes,so your fit needs to change.  Our bodies are wonderfully adaptable.  We change in response to stimulus.  For example, training that stresses our muscles results in the body adding mitochondria to supply energy to the muscles more efficiently.  The body also increases capillary density to bring more blood to muscles, and we understand these changes as “getting fitter”.

Unfortunately, our bodies also adapt in negative ways.  If you work at a desk 8 – 10 hours a day hunched over a computer, your body will adapt to that stimulus.  So, a bike fit for a 50 year old office worker new to cycling should be VERY different to the fit for a 24 year old amateur racer working in a bike shop to support their racing habit.  Where is the “average” between these two profiles?

old versus young

If you have a bike fit when you are just starting serious cycling, that fit may no longer be correct for you after you’ve trained for six months.  Your body has changed.  You’ve gotten stronger, and the balance between your muscles has altered.  For example, if your quads are stronger relative to your hamstrings than they were, then your ideal seat height may be different.  Think of your bike fit as dynamic, not a one-off static event.

How will a professional Bike Fit improve my cycling?

Bike Fit, KOPS, Bike Fitting
Knee over Pedal Spindle

When you’re comfortable on the bike, you’ll ride with more power and confidence, but the top benefit of a quality bike fit is avoiding injury.

You turn you legs over around 10,000 times every time you ride two hours, so cycling can be a recipe for repetitive strain injuries.  All three contact points (pedals, saddle and handlebars) can be adjusted to find YOUR ideal fit and avoid the most common cycling injuries. 

Knees, lower back, feet/ankles wrists, shoulders and hips are the most common areas for injury.  Pre-existing problems, such as poor flexibility, previous injuries, leg length imbalance, collapsed arches, can be accommodated through your bike fit if they are correctly diagnosed and understood. 

Andy Pruitt wrote the definitive book on bike fit, “Complete Medical Guide to Cyclists”, and here are his top three rules.

  1. Make the bike fit the body, don’t make the body fit the bike:  While improvements can be made in flexibility over time, it’s vital to make the bike fit you and not the other way around. Importantly, it’s not just the bike, the angle of your cleats and the arch support provided by your shoe affect the tracking of your knee, and the top injury among cyclists is patellar tendinitis, the inflammation of the tendon structure supporting the knee cap.
  2. Dynamic bike fit is better than static bike fit:  When you are pedaling, your are constantly moving on the bike. As you pedal the angle of your foot changes throughout your pedal stroke.  Can you replicate the exact angle at the bottom of your pedal stroke when you static on the bike?  Angle measurements taken while your sitting motionless can vary dramatically with those taken while you’re pedaling.
  3. Remember the fit window.  What works for a svelte 25 year old professional cyclist with a physio and masseuse may not work for you.  Systems that fit you to a prescribed set of angles do not take into account critical variables, such as previous injuries, flexibility and the natural orientation of your feet (straight ahead, toe in or toe out).  As a result, their recommendations are not sufficiently customised for you.

We can also you find the ideal balance between aerodynamics and comfort.  Michael Hutchinson, author of Faster and winner of over 50 national titles explains, “Most of the drag comes from the rider, not the bike, and just because were fashioned by evolution for every purpose other than aerodynamics, doesn’t mean you don’t have to make the best of it”  

AerodynamicsThere is little point putting you into your most aerodynamic position, however, if you are unable to breathe properly and lose 20% of your power and endurance.  By adjusting your position and simultaneously measuring your power output and heart rate, we can objectively determine a balance point.

If aerodynamics are particularly important to reach your goals, we can experiment with more aggressive positions and give you body a chance to adapt to a new position over a period of weeks before measuring your power output again.