Frame Designs Print E-mail
Friday, 21 October 2005


The difference in ride between a poor quality frame and a good quality frame is enormous. We have couples who have changed tandem and immediately gone from struggling to keep up to leaving everyone else behind! The main criteria is a stiff frame to ensure that all the energy goes into making the tandem move forward rather than bending the tubing!

The geometry of the forks is also crucial to making the steerers life easy - if it is wrong the slightest movement of the stoker will send the tandem off in an unplanned direction! Look for a steep head angle (73° or greater) and a good amount of bend in the forks (rake).

Marathon  
This design offers a good compromise for touring between stiffness and comfort. Ideal if both riders have similar power outputs. Additional stays reinforce the rear triangle.
Double Marathon  
The strongest and stiffest design, very time consuming and difficult to manufacture and therefore expensive. Generally used for the largest and heaviest riders, racing or for extended heavy touring. The design is also used when light weight is required as very strong, stiff and light frames can be built.
Direct lateral  
Probably the easiest design to manufacture so very popular. Most "Off the peg" tandems are built to this design. It is also a good solution when the stoker is significantly lighter or less powerful than the steerer, and is particularly suitable for fitting kiddy cranks.  The performance of this frame design has improved considerably with the introduction of oversize tubes.
Double Diamond  
This design is basically two normal diamond frame solos joined together. The design is more flexible than the others which can make climbing hard work, however the flexibility does reduce the shock from bumps in the road.
Open Frame  
Not for serious use, but fine for short trips. Very flexible and heavy as strong tubes are required to compensate for the lack of bracing.

Frame Sizing

There are many different theories about frame sizing, and general rules always find someone who is an exception and needs something different.

The following tables are a guide for conventional touring style frames and has been taken from Tony Olivers excellent book "Touring Bikes" (ISBN 1 85223 339 7) which should be on every serious cyclists bookshelf.

These dimensions are a guide and individual wants need to be taken into consideration. The sizing of the top tube refers of course to the front of the tandem. The distance from the stokers handlebar centreline to the stokers seat tube will be similar to the top tube length added to the stem length, however stokers do have a tendancy to sit up straighter.

Inside
Leg
(in)
Frame
Size
(in)
Crank
Length
(mm)
Bracket
Height
(in)
28 19 162.5 10.125
29 19.75 165 10.25
30 20.75 165 10.25
31 21.5 167.5 10.375
32 22.5 170 10.5
33 23.25 170 10.5
34 24.25 172.5 10.625
35 25 175 10.75
36 26 175 10.75
37 27 177.5 10.875
38 28 177.5 10.875
 
Torso
arm &
Body
(in)
Top
Tube
(in)
Stem
Length
(mm)
39 20.0 60
40 20.2 70
41 20.4 75
42 20.6 80
43 20.8 90
44 21.0 90
45 21.3 95
46 21.6 95
47 21.9 100
48 22.2 100
49 22.5 105
50 22.9 105
51 23.4 110

Note the frame size refers to the seat tube length, and is measured from the centre of the bottom bracket to the top of the top tube. Continental frames are measured from the centre of the bottom bracket to the centre line of the top tube, and mountain bike frame size measurement depends on the manufacturer!

For alternative views on sizing, try www.sheldonbrown.com/harris/index.html

 

This page last updated 28/12/01

 
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