Why are chainrings indexed?
01-06-05, 02:35 PM
#1
Senior Member
Thread Starter
Join Date: May 2004
Location: Southern California
Posts: 2,191
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 114 Post(s)
Liked 119 Times
in
92 Posts
Why are chainrings indexed?
I have Shimano and Bontrager triple mountain cranksets and I've noticed the chainrings have an index marking. The index mark could be a small post, or cut-out. Out of habit, I always align these index markings with the adjacent crankarm. But why?
In the old days (like late 1980's) oval or elipitical chainrings were popular. Because the shape was ergonomically fit to the pedal position, you had to ensure the chainring was positioned with respect to the crankarm.
However, I am pretty sure chainrings nowdays are circular.
The reasons I could think of why they're still indexed are:
1. Holdout feature from the eliptical chainring days (but doubt the added cost to add the feature is worth it).
2. The shifting ramps on the chainrings need to be positioned with respect to the crankarm and pedal position. If so, is the chain position during a shift event that critical?
3. Tradition.
Any others?
In the old days (like late 1980's) oval or elipitical chainrings were popular. Because the shape was ergonomically fit to the pedal position, you had to ensure the chainring was positioned with respect to the crankarm.
However, I am pretty sure chainrings nowdays are circular.
The reasons I could think of why they're still indexed are:
1. Holdout feature from the eliptical chainring days (but doubt the added cost to add the feature is worth it).
2. The shifting ramps on the chainrings need to be positioned with respect to the crankarm and pedal position. If so, is the chain position during a shift event that critical?
3. Tradition.
Any others?
01-06-05, 02:56 PM
#2
Senior Member
Join Date: Jan 2004
Posts: 9,428
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 2 Times
in
2 Posts
Originally Posted by MudPie
I have Shimano and Bontrager triple mountain cranksets and I've noticed the chainrings have an index marking. The index mark could be a small post, or cut-out. Out of habit, I always align these index markings with the adjacent crankarm. But why?
In the old days (like late 1980's) oval or elipitical chainrings were popular. Because the shape was ergonomically fit to the pedal position, you had to ensure the chainring was positioned with respect to the crankarm.
However, I am pretty sure chainrings nowdays are circular.
The reasons I could think of why they're still indexed are:
1. Holdout feature from the eliptical chainring days (but doubt the added cost to add the feature is worth it).
2. The shifting ramps on the chainrings need to be positioned with respect to the crankarm and pedal position. If so, is the chain position during a shift event that critical?
3. Tradition.
Any others?
In the old days (like late 1980's) oval or elipitical chainrings were popular. Because the shape was ergonomically fit to the pedal position, you had to ensure the chainring was positioned with respect to the crankarm.
However, I am pretty sure chainrings nowdays are circular.
The reasons I could think of why they're still indexed are:
1. Holdout feature from the eliptical chainring days (but doubt the added cost to add the feature is worth it).
2. The shifting ramps on the chainrings need to be positioned with respect to the crankarm and pedal position. If so, is the chain position during a shift event that critical?
3. Tradition.
Any others?
01-06-05, 03:00 PM
#3
I couldn't car less.
Join Date: Nov 2003
Posts: 4,397
Bikes: Ritchey P-series prototype, Diamondback, Nishiki Triathelon Pro.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
2: yes, some are ramp\pinned. Some rings have angled teeth different high\low points for chain take up.
:yes it's important if you have ovaled or ramped\pinned rings.
If your ring are round (I've rings from doubles that are) run them anyway.
The middle ring will be the most altered by teeth peaks, ramps.
A non ramp, mono ring like my 38T Blackspire Epic, has no index mark.
:yes it's important if you have ovaled or ramped\pinned rings.
If your ring are round (I've rings from doubles that are) run them anyway.
The middle ring will be the most altered by teeth peaks, ramps.
A non ramp, mono ring like my 38T Blackspire Epic, has no index mark.
01-06-05, 05:46 PM
#4
Shimano Certified
In many newer designs it is better to have it indexed to the arm. This is because a lot of designs have a protruding pin that keeps the chain from going beween the arm and the ring in an overshift. It is a rare problem but a very nasty one. So far as performance goes, they design the ramps/pins to corespond to eachother to make the shifting reliable. To a certain degree they position these points along the predicted power stroke, so it can be dependent on index position.
To answer the question, yes it will work unindexed. It just wont be the best.
To answer the question, yes it will work unindexed. It just wont be the best.
