Path Analysis.

A Bicycle Rear Suspension Analysis Method.

Theory, text, illustrations, and editing by Ken Sasaki.

4-bar path analysis by Peter Ejvinsson.

Spanish Version translated by Antonio Osuna
Additional translation and edition for the web y José Rubio

 “Linkage” suspension simulation by Gergely Kovacs.

© Kenneth M. Sasaki 2001, all rights reserved.

{The authors welcome the reposting or reprinting of this page or any part of it, so long as full credit is given to the authors.}

Contents (links provided).     

Introduction.

I.    Primary Concerns.

1)    Objectives.

2)    Main Conclusions.

A)   General Comments.

B)   Non-URTs.

i) Paths and Shock Absorption.

ii) Paths and Pedaling.

iii) Compromises.

iv) Paths and Braking.

C)   An Open Letter.

II.   Some Useful Suspension-Related Mechanics.

1)    Some Important Concepts.

A)   “Reference Frames”.

B)   “Degrees of Freedom”.

C)   “Nature Varies Smoothly” (NVS).

D)   “Approximation”.

E)   “Center of Mass” (CM).

F)   “Coaxial Condition”.

G)   “Instant Center” (IC).

2)    An Intuitive Look at Forces and Torques.

3)    Suspension Rate.

III.   Path Analysis.

1)    Path Analysis Main Assertions.

2)    P.A. Basics.

A)    Mass Approximation.

B)   Forces Between Linearly Constrained Particles.

3)    The Natural Mirror Bike.

4)    Paths and Performance.

A)   Mono-Pivot and 4-bar Rear Axle Paths.

B)   Shock Absorption (“coasting” situations).

C)   Pedaling (Non-URTs only).

D)  Compromises.

E)   Braking.

IV.   Wheel Path Analyses of Some Existing Models.

1)    Typical Horst Link Designs.

2)    The Giant NRS.

3)    The Rocky Mountain ETSX-70.

4)    The Cannondale Scalpel.

5)    The Virtual Pivot Point (VPP).

6)    Additional Linkage Data.

V.   Flawed Theories and Bogus Marketing.

1)    “Brake Induced Shock Lockout” (BISL).

2)    False Claims for Floating Brakes.

3)    “Special Point” Theories.

A)   “Pivot at the Chain Line” (PCL).

B)   Ellsworth’s “Instant Center Tracking” (ICT).

i) Test number 1.

ii) Test number 2.

iii) PA thus passes this third test, while ICT shows its fourth flaw.

iv) Ellsworth adds

4)    “Internal Force” Theories.

A)   “i-Drive” – A Perpetual Motion Machine?!?!

B)   “Chain Line Does Not Matter in a URT”.

5)    Bogus Marketing.

Appendices.

A)   PCL Problems – Some Further Calculations.

B)   Glossary.

About the Authors

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