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Fitting a Cyclocross Bicycle

By Colby Pearce

Riders frequently ask me if there is a correlation between the fit of a road bike and a cyclocross bike. The process is not formulaic or necessarily simple, however there are some basic guidelines that can be useful in setting up a cyclocross bike using the road bike as a starting point.

The recommendations made below are assuming your road bike fit is dialed in. From my perspective, this means:

  • proper saddle setback, which puts as much weight as possible on the saddle given the mass distribution of the rider, the limb length, limitations lower back and hamstring mobility, flexibility and ability to generate symmetrical force while in a position of acute hip flexion.
  • proper bar height and extension which is set according to the mass distribution of the rider, the limb and torso length, limitations lower back and hamstring mobility, flexibility and ability to generate symmetrical force while in a position of acute hip flexion, and is set within context of the demands of the event the bike is being fit for (for example, longer road rides with lots of vertical gain vs. shorter, faster group rides).
  • proper saddle height set within the parameters of pelvic stability and pedaling technique.
  • proper arch support, foot correction and cleat position.

All bicycles can be placed on a spectrum in regards to their intended purpose. On one end of this spectrum, is we have time trial bicycles, especially those used in most US or UK races, which tend to be straightforward out and back events that typically lack hills or corners other than a single “U” turn. When setting up a rider’s position on an aero TT bike, very little concern is given to how the rider’s weight distribution impacts handling, because the events do not have many changes in direction or varying terrain. The parameters that dictate the setup of the bike are rider aerodynamics and generation of power. The rider’s center of gravity rarely changes in relation to the bottom bracket or wheel axles during these types of events, it is very fixed.

On the other end of this spectrum, we find downhill mountain bikes. The riders make huge accommodations to their positions in order to ensure the bike handles properly for the demands of the event, even at the expense of a rider’s power production. The saddles are set at ridiculously low heights (or dropper seat posts are used) to allow maximum adjustment of the rider’s center of gravity over steep terrain, stems are incredibly short to minimize bar “whip” over rocks and drops, bars are super wide to provide the largest possible hand stance, and cranks are short for ground clearance. Most riders probably cannot approach their true FTP on this type of bike, but a downhill race does not demand that they do so. The demands of this discipline require that handling over rough, steep, rocky terrain is more important than power production. A fast downhiller constantly changes the relationship between his or her center of gravity and the BB and wheel axles of the bicycle and in order to accomplish this, the cockpit must be “compressed”. If the distance between the bars and saddle is too large, it will limit the ability of the rider to manipulate the center of gravity in order to maintain tread contact with the trail at key moments.

Cyclocross represents an area of middle ground between the above examples of time trial and downhill MTB, and thus the cyclocross bicycle is set up to allow a rider to make adjustments of the center of gravity relative to the wheelbase and bottom bracket, but not on the scale of a downhill bike. Aerodynamics are not a consideration for cyclocross fit, as the average speed of competitions are not high enough for the coefficient of drag to be a significant factor in the outcome of the race.

Cyclocross riding and racing require some fundamentally different skills than road riding. In order for a rider to negotiate off road terrain at varying speeds, he or she must be able to shift their weight using the dimensions of the bicycle cockpit. Off road cycling requires dynamic weight placement on the bike to a much higher degree than road cycling. Changing weight emphasis, or moving the rider’s center of gravity, during off camber, uphill, downhill, grassy, rocky, sandy or other challenging conditions is essential to riding fast and staying upright. A rider whose bike is set up too stretched out, with the bars too low, or slammed too far back will not be able to perform these tasks effectively. Rider weight is shifted between all points of contact (front, middle or rear of the saddle, tops, hoods and drops on L and R sides respectively, and L or R pedals) to influence the contact patches of tire tread and drive the tread into the ground. This is how a rider negotiates the varying surfaces of a cyclocross course and stays upright.

Common cyclocross bike differences, relative to a road position, are listed below (in no particular order). These recommendations are based on the premise that the road position is reasonably aggressive, meaning that the road position is set up with some consideration to aerodynamics and that the rider has the functional ability to apply power smoothly in a position with a relatively large saddle offset, low bars, and long reach. If the rider’s road position is not very aggressive due to reduced anatomical function, the positional differences between a road and CX bike will be less or possibly none.

  • Stem length: typically shorter by 1-3 cm. This facilitates the ability to move over the bars when the rider needs more weight on the front wheel. This is crucial for the entrance to corners that require increased weight on the front axle. A shorter stem also reduces the length of the lever on the steering column, which creates a shorter radius to turn the wheel the same amount (in terms of angle relative to the top tube) in comparison to a longer stem (given the same bar width). During cyclocross races, more steering is required due to the low speed turns encountered on the course (in contrast to road riding, which requires more leaning at higher speeds).
  • Bar height: The handlebars are sometimes 1-3cm higher. Due to the lower average speeds of cyclocross races, aerodynamics are not a significant consideration in the parameters of the fit, and raising the bars allows for more variation in how the rider carries his or her weight on the front end of the bike. That said, in my opinion many cyclocross (and mountain) bikes are set up with bars higher than they should be. The concern many athletes have about setting up bars low on a CX or MTB is going over the bars on a steep descent. In most cases, this is pilot error as the butt must be far enough back over the BB to not let the weight launch forward over the front axle when negotiating steep descents. The most stable position with superior front wheel control is in the drop (as opposed to the hoods) and the drops should be used on steep descents. Additionally, a lower bar helps put more weight on the front wheel, which is generally desirable when setting up a cyclocross bike. I talk more about this below.
  • Drop angle: frequently I notice cross riders who neglect or ignore their drops completely, always choosing the tops or hoods for all conditions. In most cases, the drop angle of their bars is also incorrect. Typically, the rider finds the hood angle is too low over bumpy terrain and rotates the entire handlebar to move the hoods higher (instead of unwrapping the bar to the hoods and moving the hoods alone), compromising the drop angle in the process. When the drop angle is set correctly to maintain a neutral wrist, and the proper hood angle is preserved to do the same, the rider typically resumes use of both positions at the appropriate point on the course. When the wrist angle is neutral, it is much easier for the rider to apply effective cornering force to the front wheel tread by driving the inside bar down towards the ground.
  • Handlebars: typically one size (~2cm) wider. This allows for increased leverage during out of the saddle efforts in a high torque, low RPM situation (such as up a steep climb). Longer bars also allow for more leverage when pulling on the hoods or drops during seated, maximal efforts. The biggest argument for a narrow handlebar is aerodynamics, which does not apply to most events or rides in cross, so the benefits of a wider bar can be utilized without compromise.
  • Pedal stance: is typically the same or wider. Most cranksets used on CX bikes are the same as road cranks (with possibly different chainrings) but depending on the road bike and type of pedals used, a rider’s cyclocross bike may have a wider pedal separation distance. This may be desirable or not, depending on the rider. If the rider requires a very narrow stance, MTB pedals may not provide optimal cleat placement. Most MTB pedals have longer axles than road pedals, and most MTB cleats have less lateral adjustment than road pedals, thus a rider’s feet may be much father from the centerline of the bike than optimal. Keep in mind that pedal separation distance also effects the handling of your bicycle; the wider the stance, the easier it is to “steer” the bicycle over bumpy or loose terrain by weighting your feet. A narrower stance makes it more challenging to do this. Downhill riders prefer cranks with wider pedal separation distance to maximize the ability to stabilize the bike by planting the feet.
  • Saddle setback: is typically 1-4cm less than on a road bike. Again, this is to allow the rider opportunity to shift his or her weight in order to accommodate the greater variety of terrain encountered in a CX race relative to most road races. In road riding, the weight bias between front and rear axle must be very close. During a high speed sweeping corner on asphalt, if either wheel slides out it is usually a big problem. In contrast, during medium speed cornering over uneven terrain, the front wheel is more critical than the rear. If the rear wheel breaks loose, a good handler usually has no problem with a minor slide. However, if the front brakes loose, the rider must be very skilled to avoid going down. Thus, in off road terrain the weight bias changes to emphasize the front wheel. As we push the saddle further forward, we increase weight on the front axle (all other variables equal). This comes at the potential compromise of posterior chain muscle recruitment and support of the torso by the saddle. As the saddle comes forward, there is usually more reliance on quads to drive the pedals and more postural muscles will be recruited to support the weight of the thorax.
  • Crankarms: are typically the same length as used on a road bike, or sometimes shorter. Because of the punchy, acceleratory nature of cyclocross races, shorter cranks are desirable. A longer crank will tend to take away snap, which can have a big influence in the outcome of a CX race. If you are riding cranks which are considered “normal” for your road bike size, inseam length, foot length, type of racing and movement function, then you probably will use the same size on a cross bike. If you are pushing the envelope on your road bike, consider sizing down by 2.5mm. If you don’t know what length cranks you should be on, start by reading this article: http://www.stevehoggbikefitting.com/blog/2011/06/crank-length-which-one/
  • Cleat position: may be further forward. Depending on the rider’s stability (pelvicly) on the bicycle, and their road cleat position, it may be advantageous to push cleats forward, in particular if a rider is on Steve Hogg’s “method 2” cleat placement. “Method 1” will emphasize more snap and acceleration, and may also help the transition between riding and running. For information, see Steve’s article: http://www.stevehoggbikefitting.com/blog/2011/04/power-to-the-pedal-cleat-position/
  • Saddle height: will be the same or possibly slightly lower (by a few mm) on a CX bike. A lower saddle accommodates weight shifts towards the front and rear of the saddle more readily, without putting a rider extremely far out of their optimal range of leg extension. Because of the high torque/ low cadence nature of cyclocross, it tends to bring out any challenges a rider has towards pedaling smoothly. In many cases it is advisable to error on the side of slightly less saddle extension if this is true.

Keep in mind that you typically cannot measure directly the difference between road and CX saddle heights, because normally you are dealing with different shoes (and thus sole thicknesses), pedals, cleats, pedal separation distance, and sometimes saddles. The best way to set your CX saddle height is either by feel if you are sensitive to these types of adjustments, or by having an experienced fitter view you riding under pressure on both bikes to make a comparison and evaluation.

Note: a common mistake is to measure bar height from the floor on the road bike and then transfer this measurement to a cross bike. CX bikes frequently have higher bottom brackets than road bikes and you can inadvertently end up with more saddle to bar drop than you want with this method. Bar drop should be measured from a horizontal line (a four foot level) extended from the saddle on both bikes (the bike must be perfectly level for this measurement to be valid).

Some riders select shoes that have less rigid soles for the running portions of the course. In my opinion, this is not necessary. The time spent running during a cyclocross race is minimal in terms of the total length of effort on the majority of courses, it is rarely a selective element in and of itself, and most cyclists run like ducks anyway. For those who come from a running background or have good running technique, the runs in most cyclocross races are chaotic affairs and typically take place on muddy inclines or wooden stairs, so there is not much technique involved other than doing it as fast as possible without taking yourself out.

Also, be advised that your off road pedals and shoes may not provide the same stable platform as your road pedals and shoes. A major pitfall of most off road pedal systems is that the lateral stability of the shoe is dependent on the contact of the shoe lugs with the pedal. In some cases, lugs on certain shoes are not standard height, causing the foot to “rock” or the opposite, making it difficult or impossible to engage the pedal. Additionally, when you go running around all over the place in your MTB shoes, you wear down the lug height, which decreases the stability of the interface with the pedal. This can in some instances lead to knee pain or other problems for certain riders. To evaluate how effective your pedal and shoe combination are working, clip your shoe into the pedal and remove your foot from the shoe. Then rock the shoe back and forth (tipping it from side to side, not by moving the heel L to R but by rotating the pedal around an imaginary axis running from heel to big toe) and look at the lug/ pedal contact. If there is more than 1mm gap on either side, you are riding on an unstable platform, and this should be remedied.

Crank Brothers makes Contact Sleeves for their Candy and Egg Beater pedals, which allows you to adjust the play between pedal and shoe. These can also be used if a rider requires a shim under one shoe, with different heights being used on both sides (but only up to 3mm). They can be found here:

(found here: http://www.crankbrothers.com/accessories_sleeves.php)

All modern off road pedal systems are subject to this limitation (Shimano SPD, Crank Brothers, Time, Look) except one: the Speedplay Syzr. The design of this system places the stability on the interface of the cleat and pedal and is independent of the lug height of the shoe. This means the system is the most stable and solid platform available for off road riding. The cleat height is taller than the lugs on most off road shoes, which means during running most of the contact happens on the cleats. There are a few other quirks to this system but overall it is by far the best option for someone who seeks a stable interface between the cleats and pedal, or for any rider who wants to shim or wedge their cleats.

http://www.speedplay.com/index.cfm?fuseaction=home.syzr

Weight Balance

Setting up the proper weight balance on a cyclocross bike is necessary to maximize cornering ability on bumpy or slick terrain. This process can involve some trial and error, but it is relatively straightforward overall. The essence of cornering is that an increase in weight must be placed on the front wheel during the corner entrance. Exiting the corner, weight must be placed on the rear wheel to avoid fishtailing and allow tread engagement for acceleration. This does not mean 100% of a rider’s weight goes from front to rear during a corner; rather a subtle shift occurs during the cornering without abrupt transition.

If the bike is set up with too much saddle setback, the bars too high, or a stem that is too short, the rider will have a tendency to wash out the front wheel in corner entrances, and will have a tendency to brake more than necessary for corners as compensation. This is because too much weight is focused on the rear of the bike.

Conversely, if a bike is set up with too little saddle setback, a stem which is too long, or bars which are too low (or some combination thereof) a rider will have too much weight on the front wheel and will have a tendency to slide out the rear wheel, frequently after the apex of a corner. As a general rule, if you dump it on your CX bike, you should try to make note of which tire slid out and in what part of the corner, and after 3 crashes of the same nature, a change should be make to position, technique, or both. When making changes in saddle setback, bar height or reach, do it in 5-10 mm increments and change only one parameter at a time. After a few rides, you will have an idea if the variable changed was effective, or whether additional modification is needed.

Cyclocross is a bizarre, addictive and entertaining sport. Hopefully you will enjoy it all the more with a proper bike setup.

Ride fast,

Colby Pearce

 

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