MATERIALS ENGINEERING

Welcome to the Department of Materials Engineering

Bicycle Frame Testing at the Open University

Introduction

Many cycle magazines run features on frames that have already been built into cycles and comment upon their relative "stiffnesses". Manufacturers rarely make quantitative comments upon frame stiffness. Hence we have decided to do some basic testing.

Method

The frames are tested with and without their intended forks by bolting them through their rear dropouts (suitably spaced) to a flat table and hanging masses from the bottom bracket as shown in the photographs. A total weight of 23 kg is suspended at 90° to the plane of the frame. This is equivalent to a 60 kg rider leaning the bike over by 27° as they stand on the pedals. It is well within the "elastic" range of the frame. The test is then repeated with forks fitted which also contain suitable axle spacers plus the front dropouts bolted to the table. The deflection of the bottom bracket relative to an unloaded reference bar is monitored with a dial gauge.

Origin of Frames

Because of a reluctance by manufacturers of frames and cycle shops to loan frames for testing it has been necessary to use frames that have been loaned by cyclists of the Bicester Millennium cycling club (www.bmcc2000.com) and employees of The Open University. Frames are as close to 55 cm in size as possible.

Results

The deflections with and without forks are shown below along with the weights of the totally stripped frames and forks. Also see comments at base of table.

Bottom Bracket Deflections at 23kg side load (90° lean)

Comments

As can be seen:-

1. The presence of the forks usually reduces bottom bracket deflection; however in oversize carbon frames fitted with carbon forks this increase is very small.

2. The type of fork influences the bottom bracket deflection and in the case of the titanium frame the aerodynamic carbon forks gave more deflection than the lighter conventional steel forks.

3. The oversize aluminium frame (GT) was not as stiff as the bonded Alan frame that used much smaller tube sections.

4. The stiffest frame tested to date is a titanium frame with a very oversized aero-section down tube.

5. A conventional 531 steel frame gave the third least deflection and was stiffer than almost all the modern frames, although considerably heavier.

Page 2 for Images of frame test set-up

Visit the departments Component Failure Museum for examples of bike part failures.

If you have any comments about these tests please contact i.norman@open.ac.uk .
Page last modified 15-Jan-2008