Bicycle Fit Dynamics and Ride Oscillations

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Ground Vehicle Systems  ·  Difficulty: Advanced  ·  Setup: School Lab  ·  Time: Full Year

The Hook

A bike can feel smooth at one saddle height and shaky at another. That is not just comfort, it is physics. Small fit changes can change how vibration moves through the frame and into your body. You can measure that instead of guessing.

What Is It?

This project looks at how a rider and a bicycle move together as one system. When you ride, the bike frame, wheels, saddle, bars, and your body all affect each other. Think of it like two linked springs. Push one side, and the other side responds.

You can use motion sensors, such as IMUs, on the seat post and handlebar to track vibration and oscillation. An IMU, or inertial measurement unit, measures acceleration and rotation. From that data, you can find which motions happen most often, which ones die out fast, and which saddle heights change the pattern most. Then you fit a Lagrangian model, which is a math model built from energy, to match the data.

The goal is not just to say, "this bike feels better." The goal is to turn fit into numbers. You can compare how the rider-bike system behaves at different saddle heights and ask which setup reduces unwanted oscillation or transfers less vibration.

Why This Is a Good Topic

This is a strong science fair topic because you can change one clear variable, saddle height, and measure real mechanical effects. It connects to bike fit, comfort, safety, and performance, which makes the work feel practical. You also get room for real engineering analysis, including vibration data, model fitting, and comparison across conditions. A motivated student can start with simple sensors and still build a serious project.

Research Questions

• How does saddle height change the dominant oscillation frequency of the rider-bike system? ?
• What is the effect of saddle height on vibration amplitude at the seat post and handlebar? ?
• Does a more upright rider posture reduce coupled oscillation between the rider and frame? ?
• To what extent do different road surface textures change the response of the same bike fit? ?
• Which saddle height best reduces transmitted vibration while preserving stable steering motion? ?
• How does rider mass affect the fitted parameters of a Lagrangian model of the bike-rider system? ?

Basic Materials

• Bike with adjustable saddle height.
• Helmet and basic safety gear.
• Two IMU sensors or smartphone motion sensors with mounting straps.
• Tape measure or ruler for saddle height.
• Marking tape for repeated setup positions.
• Digital scale for rider mass, if needed.
• Laptop or tablet for data download and analysis.
• Notebook for trial notes and fit settings.

Advanced Materials

• Bike with adjustable saddle height and repeatable fit markings.
• Two or more calibrated IMUs with data logging capability.
• Rigid sensor mounts for seat post and handlebar.
• Cadence sensor or wheel speed sensor.
• Force sensor or pressure sensor for saddle contact, if available.
• High-speed video camera for motion comparison.
• Lab stand or bike trainer for repeatable loading.
• Computer for model fitting and signal processing.

Software & Tools

• Python: Processes acceleration data, finds oscillation frequencies, and fits model parameters.
• Excel: Organizes trials, plots trends, and compares fit settings.
• ImageJ: Measures motion in video frames when you want to compare sensor data with visible movement.
• MATLAB: Helps with signal analysis and system identification if your school has access.
• GeoGebra: Lets you sketch simple mechanics models and visualize relationships before coding.

Experiment Steps

1. Define the exact fit variable you will change first, such as saddle height, and keep every other setup detail fixed.
2. Choose your sensor placement so the seat post and handlebar give separate views of the same ride dynamics.
3. Plan a repeatable test route or trainer setup that gives each trial the same kind of motion input.
4. Design a data plan that lets you extract frequency, amplitude, and damping from each trial.
5. Build a simple Lagrangian model of the rider-bike system and decide which parameters you will estimate from data.
6. Compare model predictions with measurements, then test whether the pattern changes across different fit settings.

Common Pitfalls

• Mounting sensors loosely, which adds fake vibration that looks like real rider-bike motion.
• Changing saddle height without rechecking leg extension, which confounds fit with rider posture.
• Comparing trials from different road surfaces, which hides the effect of the fit change.
• Recording data at inconsistent speeds, which shifts oscillation frequency and makes trials hard to compare.
• Fitting a model with too many free parameters, which can make the math look good without explaining the system.

What Makes This Competitive

A class-level project might only compare comfort ratings or raw vibration graphs. A stronger project goes further and links those measurements to a real dynamics model. You can stand out by testing whether the model predicts changes in oscillation across different rider sizes, fit settings, or road inputs. Careful calibration, strong controls, and clear parameter estimates make the work feel much more like engineering research.

Project Variations

• Compare suspension seat posts versus rigid seat posts using the same rider and sensor setup.
• Test how handlebar height changes vibration transfer from the frame to the rider's hands.
• Compare two riders with different body masses to see how rider-bike coupling changes the fitted model.

Learn More

• NASA NTRS: Search for papers on vibration, human motion, and system modeling in the NASA Technical Reports Server.
• PubMed: Search for review articles on cycling biomechanics, vibration exposure, and comfort.
• Google Scholar: Search for papers on bicycle dynamics, rider-bike coupling, and modal analysis.
• MIT OpenCourseWare: Look for dynamics, vibrations, and systems modeling course notes.
• ASME Digital Collection: Search for peer-reviewed papers on bike dynamics, vibration, and human-machine systems.