Optimizing Pedaling Mechanics in the TT Position: A Case Study with 165mm Cranks

Optimizing Pedaling Mechanics in the TT Position: A Case Study with 165mm Cranks.

Angela Naeth, MPT, BHS, Professional Triathlete and Coach
Author’s Note:

I’ve been using 165 mm cranks on my TT bike since 2014. Over the years, I’ve collected a range of data using Garmin Cycling Dynamics, which allows me to dive into how my pedal stroke performs under different conditions. I’ve done multiple ride analyses to better understand my power phase and how it aligns with my position on the bike. This case study shares a snapshot of that data, supported by research, to offer insights into pedal stroke mechanics in the time trial position.

Abstract

Understanding the biomechanics of the cycling power phase is essential for optimizing performance, especially in time trial (TT) positions. This article explores current research on power phase timing, crank length effects, and muscular activation patterns during the pedal stroke. Using a case study approach, I share my own data as a professional triathlete riding 165 mm cranks on a TT bike at 5'5", demonstrating how equipment and position can influence pedal dynamics. Supported by peer-reviewed studies, this article provides practical implications for athletes and coaches aiming to enhance pedaling efficiency and reduce joint strain in aggressive positions.

Introduction

In cycling, the power phase refers to the segment of the pedal stroke where positive torque is applied to the cranks—typically from ~60° to 120° crank angle. Peak power often occurs between 90°–110°, especially in trained cyclists. Efficient force application during this phase is tied to muscle recruitment patterns, crank length, rider position, and biomechanical fit.

While research has explored upright cycling biomechanics extensively, fewer studies address the impact of aero TT positioning and crank length on force application and muscular efficiency. As a professional triathlete, I’ve tested various crank lengths and positions. I currently ride 165 mm cranks on a TT bike, and at 5'5", this setup has improved my hip clearance, comfort, and pedaling efficiency.

This case study explores how crank length (165 mm) in a TT position influences power phase timing and muscle engagement patterns.

Understanding Peak Power Phase vs. Power Phase

Before diving into the results, it’s important to clarify a key concept in pedaling dynamics: Peak Power Phase is a subset of the broader Power Phase.

• The Power Phase encompasses the entire portion of the pedal stroke where positive torque is applied to the crank — typically a wider angle range such as 40°–220° depending on the rider and conditions.
• The Peak Power Phase, by contrast, represents the most effective section of that power phase — the crank angles where you're generating the highest torque during each stroke.

Garmin Cycling Dynamics defines this range with specific start and end crank angles for each leg and reports the arc length of this peak effort. In this case study, we’ll be focusing on this Peak Power Phase, as it provides critical insight into neuromuscular coordination and pedal efficiency in the TT position.

Methods

Note on Data Collection This case study is based on an average of data collected from approximately 20 sessions, both indoors and outdoors. These sessions were performed in training environments without interference or artificial adjustments. Across these sessions, Garmin Cycling Dynamics data showed a consistent power phase pattern with less than ±1% variance, providing confidence in the repeatability of the results.

Case Study Setup

• Rider Height: 165 cm (5'5")
• Crank Length: 165 mm
• Bike Type: TT bike in aggressive aero position
• Power Phase Range: 73° (start) to 114° (end)
• Peak Power Zone: ~95°–105°
• Data Tools: Dual-sided power meter with crank-angle analysis (Garmin Vector 3 w/ Garmin Cycling Dynamics)
• Cadence: varied in multiple settings 
• Environment: multiple unmodified outdoor training sessions to capture real-world data, and indoor sessions. 

Literature Review

1. Ideal Power Phase Timing: Korff et al. (2007) identified peak torque in trained cyclists between 90°–110°, aligning with gluteus maximus and quadriceps activation. Bini et al. (2014) noted that in TT positions, closed hip angles lead to increased hamstring and glute engagement, shifting torque slightly earlier.

2. Crank Length and Joint Kinetics: Baxter et al. (2016) showed that crank lengths from 145 mm to 195 mm affect joint-specific power distribution. Shorter cranks (like 165 mm) preserved total power output while improving hip clearance and earlier power onset—ideal for TT setups.

3. Power Phase Efficiency in Elite Cyclists: Macdermid & Edwards (2010) found that elite cyclists exhibit narrower and earlier power phases, correlating with better neuromuscular efficiency and reduced fatigue.

Muscle Activation in the Power Phase

• Gluteus Maximus: Initiates power early (~60°–90°); enhanced in aero due to hip flexion.
• Quadriceps (Vastus Lateralis/Medialis): Peak activation ~70°–110°, driving primary knee extension.
• Hamstrings: Assist in maintaining posterior chain engagement; activation increases in aero due to hip angle.
• Gastrocnemius/Soleus: Assist near bottom of stroke but less relevant in TT due to limited ankle motion.

Results: Case Study Interpretation

My Garmin Cycling Dynamics data reflects an average across approximately 20 training sessions, both indoor and outdoor. Across these rides, the peak power phase remained consistent within ±1%, indicating a reliable pedaling pattern. On average, I generated a peak power phase from 75° to 115° on the left and 73° to 114° on the right, each with a 41° arc length—matching optimal parameters seen in elite riders. Power balance was even at 50% left / 50% right, indicating a highly symmetrical and coordinated stroke in my TT position.

Discussion

The 165 mm crank length in a TT position provides several biomechanical advantages:

• Reduces hip compression at top dead center.
• Facilitates earlier and smoother power delivery.
• Decreases knee and hip joint strain by promoting a more neutral stroke.

These adjustments allow for a more aerodynamic position without sacrificing power. My own metrics reflect this benefit: an early-start, compact power phase that minimizes wasted motion and improves cadence control.

Crank Length Comparisons: 160 mm vs 170 mm

I've personally tested:

• 160 mm cranks: Felt “too short.” While hip clearance improved slightly, I lost some leverage and felt disconnected during high-torque, low-cadence intervals.
• 170 mm cranks: Caused hip impingement in aero position, delayed power onset, and felt harder to maintain smooth cadence.

Studies like Too & Williams (2000) support the idea that 5 mm crank length changes don’t drastically affect power, but do change biomechanics—especially joint angles and feel.

Does Rider Height Matter?

Yes—but so does femur length, flexibility, and positioning goals. Riders under 5'7" often benefit from 160–165 mm cranks to reduce hip/knee strain and improve cadence fluidity. Ultimately, your crank length should optimize your comfort, biomechanics, and position—not just power output.

Limitations

This is a single-subject case study (n=1) based on my own cycling position and biomechanics. Results may not generalize to all athletes. Power phase data was collected using multiple sessions—indoors and outdoors—and averaged with a ±1% margin of variation. However, this analysis was not conducted in a controlled lab environment.

Coach’s Insight: Applying This to Your Setup

When working with TT athletes—especially women or smaller riders—I often recommend testing 165 mm cranks. Benefits include:

• More aggressive positions without sacrificing comfort
• Improved joint clearance
• Better cadence stability at race effort

Use tools like Garmin Cycling Dynamics to track stroke mechanics over time. Look for:

• Earlier torque onset
• Smoother cadence across zones
• Reduction in left/right imbalance
  
  
  

Key Takeaways for Athletes & Coaches

• Shorter cranks (160–165 mm) improve hip clearance, aero positioning, and joint loading.
• A compact, early-start power phase suggests high pedaling efficiency.
• Crank length affects joint angles and pedaling rhythm more than raw power.
• Track your power phase data with compatible power meters for deeper insights.
• The "best" crank length is the one that fits your goals, anatomy, and position.

How to Find Your Own Peak Power Phase Data: If you’re curious about your own pedal stroke dynamics, many modern power meters and head units can help. Here’s how to get started:

• Use a dual-sided power meter
• Pair your power meter with a Garmin Edge head unit or compatible device that displays Pedal Stroke Analysis, including:
• Peak Power Phase Start/End Angles
• Power Phase Arc Length
• Left/Right Balance
• After your ride, sync with Garmin Connect to review crank-angle data and trends over time.

This data can help you:

• Evaluate timing and symmetry in your pedal stroke
• Test how position or crank changes affect your mechanics
• Understand which crank angles you produce maximum torque

Whether you’re a coach, athlete, or just bike-nerd curious about performance, analyzing your peak power phase is a valuable tool to refine your fit, efficiency, and long-term sustainability on the bike.

References

1. Baxter JR, Piazza SJ. Crank length and muscle kinetics affect joint-specific power during cycling. Journal of Biomechanics. 2016.
2. Korff T, Romer LM, Mayhew I, Martin JC. Effect of pedal type and power output on pedaling technique. Med Sci Sports Exerc. 2007.
3. Bini RR, Diefenthaeler F, Carpes FP. Lower limb muscle activation during cycling in different positions. Journal of Science and Cycling. 2014.
4. Macdermid PW, Edwards AM. Biomechanical analysis of the pedal stroke using different power outputs and cadences. Eur J Sport Sci. 2010.
5. Too D, Williams C. The effect of crank length on oxygen uptake and power output during submaximal and maximal cycling. Ergonomics. 2000.

1. ositions. Journal of Science and Cycling. 2014.
2. Macdermid PW, Edwards AM. Biomechanical analysis of the pedal stroke using different power outputs and cadences. Eur J Sport Sci. 2010.
3. Too D, Williams C. The effect of crank length on oxygen uptake and power output during submaximal and maximal cycling. Ergonomics. 2000.