Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

Stem shim question

Notices
Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Stem shim question

Old 11-08-16, 06:30 PM
  #1  
Senior Member
Thread Starter
 
Join Date: Sep 2014
Posts: 430
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Stem shim question

Hey everyone,

Sorry if it's a noob question but I was wondering if anyone has a moment and can help me out.

Can anyone explain what I believe to be called shims (circular parts with numbers +4, +2, 0 that go on the inside part) of the stem do. Right now the stem I have has some inserted.



1. What do they do?
2. How do they effect the position?
3. What does removing them do?
B1KE is offline  
Old 11-08-16, 06:35 PM
  #2  
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 109 Post(s)
Tagged: 1 Thread(s)
Quoted: 6556 Post(s)
Likes: 0
Liked 58 Times in 36 Posts
They affect the angle or "rise" of the stem. They raise or lower the bars with a smaller movement to the front or back by about 1/3 the amount of the change in height. Removing the shins sets the stem angle to it's base value.
__________________
Robert

Originally Posted by LAJ
No matter where I go, here I am...
rpenmanparker is offline  
Old 11-08-16, 06:36 PM
  #3  
Senior Member
 
exmechanic89's Avatar
 
Join Date: May 2015
Location: Richmond VA area
Posts: 2,713

Bikes: '00 Koga Miyata Full Pro Oval Road bike.

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 475 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
Unless I'm mistaken (quite possible) shims are simply adaptors that allow you to fit a stem, seat post, etc that wouldnt otherwise fit. They work in some applications but are not ideal - the right fit without the shim would be ideal of course.
exmechanic89 is offline  
Old 11-08-16, 06:38 PM
  #4  
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 109 Post(s)
Tagged: 1 Thread(s)
Quoted: 6556 Post(s)
Likes: 0
Liked 58 Times in 36 Posts
Originally Posted by exmechanic89
Unless I'm mistaken (quite possible) shims are simply adaptors that allow you to fit a stem, seat post, etc that wouldnt otherwise fit. They work in some applications but are not ideal - the right fit without the shim would be ideal of course.
I don't think that is the case here. See my post.
__________________
Robert

Originally Posted by LAJ
No matter where I go, here I am...
rpenmanparker is offline  
Old 11-08-16, 06:46 PM
  #5  
Senior Member
 
Join Date: Oct 2014
Location: Long Island NY
Posts: 111

Bikes: TREK Domane 5.2 Giant Defy Wilier Triestina Cento

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 35 Post(s)
Likes: 0
Liked 4 Times in 4 Posts
Actually they are not stem size adaptors, they are used to "fine tune" the angle of the stem as described in post#2 above.
qajaq is offline  
Old 11-08-16, 06:55 PM
  #6  
Senior Member
Thread Starter
 
Join Date: Sep 2014
Posts: 430
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by rpenmanparker
They affect the angle or "rise" of the stem. They raise or lower the bars with a smaller movement to the front or back by about 1/3 the amount of the change in height. Removing the shins sets the stem angle to it's base value.
Thanks for your help. The stem I have now has a 12 degree rise(not sure what that means) but I want to get it as horizontal as possible to extend my reach a bit when I take off the spacers I have the "shim" on the inside, I have the shim inserted and one side of the circular shim says +4 and on the other side of the same shim it says -4. How do I insert this and whch way to achieve the most horizontal angle?

If I take out the shim completely the stem does not fit on the steerer tube.
B1KE is offline  
Old 11-08-16, 07:00 PM
  #7  
Senior Member
Thread Starter
 
Join Date: Sep 2014
Posts: 430
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by qajaq
Actually they are not stem size adaptors, they are used to "fine tune" the angle of the stem as described in post#2 above.
Thanks for your help, how do I go about fine tuning the fit because the shim says -4 on one side and +4 on the other side. It seems like the only way to insert it is from the top or the bottom.
B1KE is offline  
Old 11-08-16, 07:08 PM
  #8  
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 109 Post(s)
Tagged: 1 Thread(s)
Quoted: 6556 Post(s)
Likes: 0
Liked 58 Times in 36 Posts
You know you can turn the stem over and make it -12. The shim can be used to either raise or lower the stem further. +4 raises the bars, -4 lowers it. Keep in mind the -17 is horizontal when your head tube angle is 73 deg.
__________________
Robert

Originally Posted by LAJ
No matter where I go, here I am...
rpenmanparker is offline  
Old 11-08-16, 07:11 PM
  #9  
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 109 Post(s)
Tagged: 1 Thread(s)
Quoted: 6556 Post(s)
Likes: 0
Liked 58 Times in 36 Posts
There should be a way to use the stem without the shim. It is supposed to be a 4 position system.
__________________
Robert

Originally Posted by LAJ
No matter where I go, here I am...
rpenmanparker is offline  
Old 11-08-16, 07:17 PM
  #10  
Senior Member
Thread Starter
 
Join Date: Sep 2014
Posts: 430
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by rpenmanparker
You know you can turn the stem over and make it -12. The shim can be used to either raise or lower the stem further. +4 raises the bars, -4 lowers it. Keep in mind the -17 is horizontal when your head tube angle is 73 deg.
Thanks for the reply, I'm learning a lot.

The head tube angle on my bike is 72 currently. Does the +4 or -4 come into effect depending on whether I flip the stem up or down? Because I only have one shim labelled +4, -4, where as in the specialized picture it comes with 3 different ones.
B1KE is offline  
Old 11-08-16, 07:24 PM
  #11  
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 109 Post(s)
Tagged: 1 Thread(s)
Quoted: 6556 Post(s)
Likes: 0
Liked 58 Times in 36 Posts
Four or six combinations. + or - 12 and + or - 4 or no shim so + or - 8, 12, 16
__________________
Robert

Originally Posted by LAJ
No matter where I go, here I am...
rpenmanparker is offline  
Old 11-08-16, 07:34 PM
  #12  
don't try this at home.
 
rm -rf's Avatar
 
Join Date: Jan 2006
Location: N. KY
Posts: 5,918
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 964 Post(s)
Liked 496 Times in 343 Posts
Originally Posted by B1KE
Thanks for the reply, I'm learning a lot.

The head tube angle on my bike is 72 currently. Does the +4 or -4 come into effect depending on whether I flip the stem up or down? Because I only have one shim labelled +4, -4, where as in the specialized picture it comes with 3 different ones.
This stem is sort of unusual, most stems don't have these adjustable shims. Basically, the stem is a little oversized, and the hole through the shim that fits the steerer is angled from top to bottom, either 4, 2, or zero degrees. (The top of the shim is thicker on one side, and thicker on the opposite bottom side.) A pretty slick design.


You need to have one of the shims installed. The photo shows +4,-4 and +2,-2 and +0,-0.
If you are missing the other two (is it a used bike?), you should be able to contact Specialized for replacements.

EDIT -- do you have that 17 degree stem in the photo? or one that's labeled 12 degrees? The discussion below is similar, just start with -12 instead of -17.

With the correct spacer, and flipped down, the stem can be set to any of these angles:
-17 -4 = -21 degrees
-17+4 = -13

-17 -2 = -19
-17 +2 = -15

-17 +0 = -17


So:
72 degree steerer on your bike. The "-17" degree angle is measured downward from 90 degrees straight out of the stem, which is +18 degrees from horizontal, since the steerer is tilted back. (90-72=18)

Then, starting from the bike's +18 degrees, a -17 degree stem is a 1 degree rise from horizontal, essentially flat.

See this Stem Comparison calculator, it's a lot clearer to see the stem angles. (I couldn't explain it until I looked at the calculator!)

You can plug in the 72 degree steerer, the stem angle, the number of spacers, and the stem length to compare two different settings. It will tell you how much the bar position will change by changing angles or spacers.

Flipping the stem
If you flipped the stem with the -4 spacer, it would be +18 +17 -4 = +31 degrees upward. Way up!

Most "flipped" stems are closer to 6 degrees, which would make them +18 -6 = +12 degrees, or +18 +6 = +24 degrees. Both of these could be usable for different riders.

Look at most modern bikes, you'll see that the stem angles up a little or a lot. It's rare now to see one horizontal, those are more often on racer's bikes.


Example:

Here's the stem, I guessed it was 110 mm (a typical length)
The red stem is -17
The blue stem is -21 (with your -4 spacer)
Attached Images
File Type: jpg
-17 stem.jpg (94.0 KB, 54 views)

Last edited by rm -rf; 11-08-16 at 07:57 PM.
rm -rf is offline  
Old 11-08-16, 08:30 PM
  #13  
Senior Member
 
exmechanic89's Avatar
 
Join Date: May 2015
Location: Richmond VA area
Posts: 2,713

Bikes: '00 Koga Miyata Full Pro Oval Road bike.

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 475 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
Originally Posted by B1KE
Thanks for the reply, I'm learning a lot.
Me too, lol!
exmechanic89 is offline  
Old 11-08-16, 08:40 PM
  #14  
Senior Member
 
PepeM's Avatar
 
Join Date: Apr 2015
Posts: 6,861
Mentioned: 180 Post(s)
Tagged: 1 Thread(s)
Quoted: 2739 Post(s)
Liked 119 Times in 59 Posts
All of that is explained in the stem's users manual btw.
PepeM is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
B1KE
Road Cycling
14
11-07-16 02:01 PM
TKJava
General Cycling Discussion
15
06-22-16 08:56 AM
kenshireen
Road Cycling
13
04-19-16 08:17 AM
Kzoo1
General Cycling Discussion
20
02-16-15 10:46 PM
Psychkle
Singlespeed & Fixed Gear
5
11-10-10 08:27 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.