Calculating stem length when getting a wider bar- Mtbr.com
Results 1 to 14 of 14
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jun 2012
    Posts
    72

    Calculating stem length when getting a wider bar

    I have an older bike which, believe it or not, has a 21-inch wide flat handlebar. I'd like to swap it for a 27-inch riser bar and anticipate trying a few stems before finding the right fit for me (5-9, 160lbs). Increasing the width of the bar obviously increases the reach, which means I'll need to compensate with a shorter stem. My question is how do I calculate how much? It is a basic high school geometry problem (height of an isosceles triangle) and while I've found great calculators for comparing stems and other bike geometry, I've exhausted all the search queries I can think of to find one to easily calculate this.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Jul 2012
    Posts
    6

    help

    o need help k

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    2,673
    You'd have to take your shoulders into account since your hand position relative to your shoulder determines how far forward your body would be pulled.

    But ultimately you need to try some and determine what works for you. Trying to exactly replicate your body position from your narrow bars may not be what is really best for you. Plus, you may find that you want to trim a little off the 27-inch bars once you start riding them. Or you may even find that you want something even wider.

    My strategy has been to build a collection of various size/rise stems when I find them on sale/clearance. I don't always have the right stem, but after trying a few, I can narrow it down quite a bit and order the right one.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  4. #4
    mtbr member
    Reputation:
    Join Date
    Jun 2012
    Posts
    72
    Yeah, I figure it will take some trial and error. I used this online calculator to calculate that a 27-inch bar will increase the height of the triangle my arms would make if I was sitting straight up by 1.33 inches. So I'm going to start with a 90mm stem with 10 deg rise and try from there. This is about 40mm shorter than the stem I have now, but with more rise, so it won't be 40mm closer. BTW, my shoulders are about 17-18 inches apart.

  5. #5
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    2,673
    Just to make sure you understand how to measure a stem.
    When you're measuring your stems, the length measurement is the distance from center (of steerer tube) to center (of bars) on a line running at 0 degrees. So a stem with more rise will be physically longer than one with less rise but the same reach.
    You can also look on the existing stem to see if the length is stamped on it (some are, some aren't).
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  6. #6
    mtbr member
    Reputation:
    Join Date
    Jun 2012
    Posts
    72
    Oh, good tip, I was measuring it wrong. Thanks.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    2,673
    let me add that that is the proper way to measure a stem, and most stems are measured that way. But, you may find some that measure physical length of stem rather than reach.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  8. #8
    Bicyclochondriac.
    Reputation:
    Join Date
    Jan 2004
    Posts
    14,172
    Quote Originally Posted by Bjdraw View Post
    I have an older bike which, believe it or not, has a 21-inch wide flat handlebar. I'd like to swap it for a 27-inch riser bar and anticipate trying a few stems before finding the right fit for me (5-9, 160lbs). Increasing the width of the bar obviously increases the reach, which means I'll need to compensate with a shorter stem. My question is how do I calculate how much? It is a basic high school geometry problem (height of an isosceles triangle) and while I've found great calculators for comparing stems and other bike geometry, I've exhausted all the search queries I can think of to find one to easily calculate this.
    Just to be clear on how stems are usually measured (since this is how they are usually labeled when you buy them): They are measured along the length of the actual stem, at whatever that angle is. If you are looking at a 15 degree stem, it is measured from the center of the steer tube to the center of the bar ALONG THE STEM ITSELF.

    "Reach" is something else. That is how much it lengthens or shortens the horizontal distance from the saddle to the bars. So a 100 mm 15 deg stem is going to have a shorter reach than a 100mm 0 degree stem.

    I use this chart to easily visualize how different length and angle stems affect the height and reach. You need to account for the head angle of the bike when using this, so I just use the "+20 deg" line for a 0 degree stem (I'm rounding the head angle of the bike to 70) and go from there.

    If you want to be stupid precise, try this one.

    I think that you are just going to have to do a bit of experimenting with some cheaper stems. That is a HUGE jump in width (though 27" is not all that wide by today's standards) and you are likely going to be changing how you position yourself in the cockpit.
    15mm is a second-best solution to a problem that was already solved.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    2,673
    Quote Originally Posted by kapusta View Post
    Just to be clear on how stems are usually measured (since this is how they are usually labeled when you buy them): They are measured along the length of the actual stem, at whatever that angle is. If you are looking at a 15 degree stem, it is measured from the center of the steer tube to the center of the bar ALONG THE STEM ITSELF.

    "Reach" is something else. That is how much it lengthens or shortens the horizontal distance from the saddle to the bars. So a 100 mm 15 deg stem is going to have a shorter reach than a 100mm 0 degree stem.
    .
    I was under the impression (maybe wrongly) that "reach" was the normal measurement used as "length" with stems, though I've seen them both ways. I have a bunch of older 130mm stems that I don't use anymore that I know were measured as reach. Most of the stems I've purchased in recent years have very little rise so the difference is not really measurable".

    It can make a big difference on a higher rise stem though , so it's obviously important to know exactly how the stem you are buying was measured if your getting a higher rise stem.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Feb 2007
    Posts
    3,048
    I believe that I heard that for every inch wider the bar, the stem should be shortened by 1/2". So if your bars are 6" wider, you should shorten your stem by 3" to keep the same reach, provided rise of the stem and bars are equal, as mentioned above.

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jun 2012
    Posts
    72
    Interesting, that would put me right at about 55mm vs the 90mm I was estimating. That seems to be at either end of the spectrum, so perhaps it makes sense to get both and figure out which feels better.

  12. #12
    Trail Tire TV on blogger
    Reputation: thomllama's Avatar
    Join Date
    Oct 2007
    Posts
    4,237
    Quote Originally Posted by trailville View Post
    ............
    My strategy has been to build a collection of various size/rise stems when I find them on sale/clearance. I don't always have the right stem, but after trying a few, I can narrow it down quite a bit and order the right one.
    I went through all this, trying to figure it out... have since help a few friends.. found I'd just hit Pricepoint, Bluesky, what ever online place and buy a bunch of the super cheapo ones with diff lengths and angle.. try them for a few rides till I find the one I like.. then go get the nice Thompson or Easton or what ever once I was sure and ebay or just hang onto the cheapos for the next build, or when a friend wants to try a new one..

    if you are thinking 90mm.. I'd get a 110, 90, 70... and go from there..

    can also hit the local shop and see what they have in their junk box for an assortment.. Did that once with my local shop.. he just gave me a few junkers and told me to come back with them when I was ready to order.. worth the few extra bucks I paid for the one I got in the long run...
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  13. #13
    mtbr member
    Reputation:
    Join Date
    Jun 2012
    Posts
    72
    Just wanted to follow up on how this ended. I contacted JensonUSA support and they told me it was an acceptable use of their return policy to order three stems and return the ones I didn't like -- had to pay return shipping. They said it was so I ordered 80, 90 and 100mm with 8 degree rise. After trying all three, I settled on the 100mm, but ended up sending all three back because I didn't like how there was no faceplate on the CrankBrothers stems. So I ordered a 38.1mm 100mm Thomson and am very happy with the upgraded stem and wider handle bars.

    Thanks for all those who replied for your help.

  14. #14
    mtbr member
    Reputation: Trail_Blazer's Avatar
    Join Date
    May 2012
    Posts
    2,162
    Congrats!

Members who have read this thread: 0

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2020 VerticalScope Inc. All rights reserved.