SunTour Accushift alpha-4050
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Category:  Rear Derailleurs
Name:  SunTour Accushift alpha-4050
Brand:  SunTour
Primary Group:  4050
Model:  RD-4050
Years:  1988 - ?
Country:  Japan
Added By: JFischer on 07/31/07
Updated By: peterbman on 05/05/18
Additional Photos - click for full size
SunTour Accushift alpha-4050SunTour Accushift alpha-4050SunTour Accushift alpha-4050
Outer Plate MarkingsSunTour Accushift 4050Inner Plate Markings
MaterialAluminum AlloyDesign CategorySlant parallelogram
Attachment Bolt Size5mm Allen KeyCable Attachment Bolt Size5mm Allen Key
Shifting SystemsSunTour AccuShift
Friction
Cable AdjusterYes
Cage LengthShortMax Cog Size24
Max Chain Wrap  
General Information
One of the 6sp Accushift derailleurs produced by SunTour during their race to catch up with Shimano in the indexed shifting race.  Mid-to-Upper-range derailleur in their sport/rec offerings lineup.  SunTour recommended a max cog size of 24t when using it in indexed mode, but will easily handle up to 28t in a friction shifting setup. 
Quality:Rarity:
 
 
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Resources:Reference & ChartsCatalogsExternal Resources
Component VariationsView Detailed List  Manage Variations
Variations of Component exist (Component is 1 of 2)BrandGroup
SunTour Accushift Edge (4050, Accushift Plus)SunTourEdge
Component Groups
Primary Group NameBrandQuick InfoBrowse Group Components
4050SunTourSport & RecreationView 2 Components
Brand Information(click to expand)

SunTour (Maeda)

SunTour derailleurs have a two-letter date code. On rear derailleurs the code is stamped on the back side of the inner parallel arm. On front derailleurs it is stamped on the back side of the inner cage.

The first letter represents the year. Larry Osborn and I believe O (Oh) is 1972, V is 1979 and A is 1984. As with Shimano, the second letter is the month code, where A is January and L is December.

SunTour Year Code

N
O
P
Q
R
S
T
U
V
W
X
Y
Z
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
 
A
B
C
D
E
F
G
H
I
1984
1985
1986
1987
1988
1989
1990
1991
1992

SunTour Month Code

A
B
C
D
E
F
G
H
I
J
K
L
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

The earliest Suntour derailleur I have found with a code is marked OF. A rear derailleur marked OD (corresponding to April of 72) was reported by Leighton Walter. I have a bike that dates from between 1970 to 1972 that has the original SunTour derailleurs. These derailleurs do not have date codes on them, so I believe the coding started sometime between 1970 and April of 1972.

(source: vintage-trek.com)

 
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