Wednesday 29 February 2012

Quattro Gearing


The original Quattro gearing was a triple chainring and an extended Capreo block with a custom derailleur. Although this worked OK, I didn’t trust it to take me all the way across the USA.
Custom Derailleur

Tensioner
I decided to fit a standard short cage 105 derailleur, with an extra custom tensioner to take up the slack.
The gearing for ROAM was 72T, 60T & 45T chainrings and a standard Capreo 9 speed block, 9T, 10T, 11T, 13T, 15T, 17T, 20T, 23T & 26T.
Front Wheel Drive
This gives a top gear of 72x16/9 = 128” (10.3m) and a bottom gear of 45x16/26 = 27.7” (2.23m), which is a range of 462% but I was badly over-geared on hills over 10%.
Sliding Gears
What I would like to try is a single chainring and a straight chain line. The extended block slides left and right on some kind of spline and the tensioner is fixed.
Aiming for a gear range of 500% based on the Capreo block, there are three relatively simple options.
Gear Number
Capreo 9 Speed Block
Shimano HG61 Block
Custom Sprockets
Result
1
9


9
2
10


10
3
11


11
4
13
12

12
5
15
14

14
6
17
16

16
7
20
18

18
8
23
21

21
9
26
24

24
10

28

28
11

32

32
12

36

36
13


40
40
14


45
45
This gives some nice close ratios for racing but I discard most of the expensive Capreo Block.
Alternatively
Gear Number
Capreo 9 Speed Block
Custom Sprockets
Result
1
9

9
2
10

10
3
11

11
4
13

13
5
15

15
6
17

17
7
20

20
8
23

23
9
26

26
10

30
30
11

34
34
12

39
39
13

45
45
This gives slightly wider ratios but is physically narrower and nothing is discarded.
Alternatively
Gear Number
Capreo 9 Speed Block
Shimano Sprocket
Custom Sprockets
Result
1
9


9
2
10


10
3
11


11
4

12

12
5
13


13
6
15


15
7
17


17
8
20


20
9
23


23
10
26


26
11


30
30
12


34
34
13


39
39
14


45
45
This gives nice close ratios for racing and as many gears as a Rohloff Hub!
They all give a top gear of 72x16/9 = 128” (10.3m) and a bottom gear of 72x16/45 = 25.6” (2.06m).
For any future tours I would probably reduce the chainring to say 65T.
Giving a top gear of 65x16/9 = 115.6” (9.31m) and a bottom gear of 65x16/45 = 23.1” (1.86m).
9T Selected

 
45T Selected
It was easier to make an MDF mock-up of the tensioner shape and position, than to try and draw it on the computer.