What is Relevant in Track Bike Sizing? – Part 2

What is Relevant in Track Bike Sizing? – Part 2

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Kirsten Wild (NL) at the European Championships in Paris

In Part 1 of this article we discussed the relevance of stack and reach as key factors in sizing a track bike. In this article we look at the practical implication of this and the relevance of head tube angle in achieving a desirable position.

What is important in endurance track racing?

Track racing is all about speed – we know this. The key variables in any discipline where speed is the primary objective are power output and coefficient of drag (CdA). When optimising a rider’s position  for the track, we need to better understand the intensity the cyclist will be performing at and we want to look at reducing the surface area of the athlete.

Exercise intensity

Endurance track racing is dominated by high-intensity work and supramaximal intensity work. Put simply, these intensities can be defined as follows: .

High-intensity: By definition, high-intensity implies performance at close to the VO2max work rate. Such “above threshold” efforts can be sustained for between 3 and 5 minutes. In track cycling, this level of intensity represents the efforts performed when taking a lap, or a  sustained turn at the front of the group.

Supramaximal intensity: By definition, supramaximal intensity implies that the effort is above the VO2max work rate. As a general rule supramaximal intensity exercise is a bout performed at between 130 and 200% VO2max work rate. This type of efforts represents a solid acceleration through to a very hard, short-duration, sustained intensity effort at the front of the bunch.

The Link Between Bike Size and Exercise Intensity

When high-intensity and supramaximal intensity exercise define the demands of competition, the length of the bike is the vital factor in the overall fit and feel. When working hard, the tendency is for an individual to move forward on the seat while also lowering their torso. These changes in position improve mechanical efficiency and coordination when pedalling at a high work rate and high cadence. The change in torso inclination is favourable outcome as it has the potential to improve aerodynamic efficiency (reduce surface area).

The overall length of the bike makes an aggressive riding position either feel awkward and restricted (short) or when appropriately setup, facilitates the ease of performing high-intensity work. Again, length is the decisive factor in how well a track bike fits.

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Should You Replicate Your Road Bike Position on the Track?

This is one of the most common questions asked when working with athletes who compete in both track and road disciplines. Often saddle position can be replicated between bikes, but replicating the position for length is a lot more complex.

Firstly, given the shorter duration on the track events, we can forego some of the comfort requirements needed when setting up a road position in favour of what is conducive of speed. From working with many time trial athletes, we know that length is the vital factor in gaining free speed. Extending and flattening the torso promotes more favourable gains in aerodynamic efficiency than hunching. On the track bike we achieve this length (effective reach) through a combination of frame reach, stem length and handlebar reach.

Unlike road bikes, track bikes don’t have a shifter/brake lever body that forms the upper contact point of the handlebar. This component accounts for approximately 7.5% of the effective reach (frame reach + stem reach + handlebar reach + shifter reach). Thus, in order for a track frame to match a well-fitting road bike, it must be proportionally longer in reach measurement.  A track frame with well designed geometry will factor this in. In fact, there are a small number of well-known manufactures building track frames that are approximately 10% longer than their equivalent road frames.

The simple answer is “yes”. Length at the forward contact point is very similar between a road bike setup for competition and a well setup track bike. But the way that forward contact point is defined differs greatly. On the track, your forward contact point is the shifter/brake hood. On the track it is in the drops.

Madison of Melbourne Track Cycling

The Impact of Head Tube Angle and Fork Offset

It seems like such an insignificant consideration, but the head tube angle of a frame has a considerable impact on the stem length you can run. Refer back to Track Bike Setup Within the UCI Rules and rule 1.3.022:

“For endurance events the rules are fairly simple. The rules state that the distance between the forward most tip of the drop bars and the vertical axle plane must not exceed 50mm.”

Like most of the UCI rules there is a functional purpose for them being imposed. In this case, it is to ensure the distribution of body mass does not fall excessively in front of the front axle thus altering the handling of the bike in a negative way.

One factor that influences the position of the front axle is the head tube angle (steering axis) of the frame. Frame reach being equal, the steeper the head tube angle, the closer the front axle ends up being to the bottom bracket. The slacker the head tube angle, the further the front axle from the bottom bracket.

The second factor that influences the position of the front axle is fork offset. Greater offset puts the front axle a greater distance in front of the steering axis and further away from the bottom bracket. The slacker the head tube angle, and the greater the fork offset, the further the front axle ends up being in front of the bottom bracket and in front of the cyclists centre of mass.

Without getting into the implications on handling (that’s not the purpose of this article), these differences have clear implications for the stem length that you can run in competition. The exact outcome (stem length required) depends on the morphology of the individual in question and their specific requirements.

Niklas Larsen (DK)

A Look at Manufacturers Data

These are three of the common frames used at club and state level competition.

Measurement Fuji Track Elite (56) Felt TK 1 (57) Cervelo T4 (56)
Reach (mm) 413 426 433
Head Tube Angle (⁰) 74.5 74 72.5
Fork Offset (mm) 35 40 43

Not only is the Cervelo considerably longer than the competition, it has a slacker head tube and greater fork offset. The practical implications of this are:

  • At the extremes of the table there is 20 mm difference in reach measurement, the main determining factor in the length of the bike.
  • At the extremes of the table there is a 2 degree difference in head tube angle.
  • At the extremes of the table there is an 8 mm difference in fork offset.

Indeed, the geometry chosen by Cervelo allows for a longer position due to frame reach alone. By the time head tube angle and fork offset are factored in, the Cervelo allows for a further 30 mm in stem length, without breaching UCI regulations.

It is important to keep in mind, while an additional 30 mm of length may not be necessary, the freedom to explore these options without breaching UCI regulation 1.3.022 offers the athlete a distinct positional advantage, with favourable outcomes for both comfort and aerodynamic efficiency.

A note on aerodynamic efficiency: This will be discussed in an additional piece on MOMNIUM in the coming months. The authors of this piece invite specific questions on what the reader would like addressed when we investigate the topic of aerodynamic efficiency.

Conclusion

This article has presented a number of important considerations when determining the correct position setup for your track bike. It goes beyond frame stack and frame reach. We suggest that a rider’s position at the critical moments in competition needs to be considered and how an understanding of the frame’s front geometry can afford a rider maximum leeway to achieve the optimal racing position.

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