Stack Height Issue- Mtbr.com
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  1. #1
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    Stack Height Issue

    Hi, all!

    I've finally joined this forum after reading for a good, long time, but now I've got a question to ask that I haven't been able to find an answer for.

    I've been out of the mtb/xc scene for nearly a decade following a somewhat serious accident that scared me out of it. After being on the road for most of that time, I've decided to get back into the mtb scene, however I'm older now and decided to build up a bike, rather than buy one and ride it.

    I've built a couple road bikes and I've never come into this problem before; the issue is as follows:

    Fork Steerer is 6.6550 inches (169mm) long
    Head Tube is 4.33 inches (110mm) long

    Which leaves me with roughly 2.32 inches (59mm) for headset + stem. Zerostack headsets won't work with my frame. From some reading that I've been doing I've found that a bit of a space between the top of the stem and the top of the steerer is okay. I've been looking at getting a Cane Creek 40 traditional headset which has a stack height of 28mm, which leaves me with 31mm for a stem.

    I've been reading that it's good to have the top of the steerer 3mm below the top of the stem, but if I'm putting a 41mm stem in, that gap grows to 10mm.

    *phew*

    Ok, so, is a 10mm gap okay, or do I have to keep hunting for a a lower stack headset + stem?



  2. #2
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    Personnally, I'd try to reduce that gap. Its going to put a lot of stress on the stem clamping area to keep it tight enough. And you don't want that failing when you're going downhill at 40mph. If its a 40mm stem, and you're only clamping on 30mm, you're using 25% less clamping area than it is designed for.

    When I'm setting up a new fork, I put a 3mm spacer ontop of the stem. That way there is full contact between the stem and the steerer tube.

    You may have trouble finding a stem with a lower stack height though. Maybe you'll have to consider selling your forks, and getting some with a longer steerer tube.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
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  3. #3
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    If I could find a shorter stack stem (FSA XC stem is 35mm as I just learned) would leave me with a 4mm gap. That should be alright, you think?

    For some reason I never thought to look for low-stack stems.

  4. #4
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    Yeah, 4mm gap would be fine.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
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  5. #5
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    pics would be good for this thread...

  6. #6
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    Quote Originally Posted by thefragger
    If I could find a shorter stack stem (FSA XC stem is 35mm as I just learned) would leave me with a 4mm gap. That should be alright, you think?

    For some reason I never thought to look for low-stack stems.
    Crank Bros headsets have a stack ht under 21mm. Would give you more stem options.
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  7. #7
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    I've been reading about the Crank Bros heatsets--while they sound like a good design to keep things low, in practise, from what I understand, the bearings can't be replaced since they're integrated into the cups. And there's been some rust issues.

    Some photos are below. The frame is a mk.ii Misfit Psycles diSSent XL and the fork is a 2008 Rock Shox Tora 318 Solo Air. I've bought derailleur-capable dropouts from Misfit to run in a 1x9 configuration.

    I'm a student and also have a lot of years in a machine shop (plus a fancy technologists' diploma), so I don't have a lot of cash and I plan on making a bunch of tools for myself (I'll share), aaand I'm not afraid to hack stuff up right proper.

    Photos!









    Last edited by thefragger; 04-19-2011 at 06:30 AM.

  8. #8
    55rpmasher
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    I just had the same issue. Get the lower stack stem. I ended up with a Ritchey Superlogic Logic Headset. It was the lowest stack headset i could find (26.9) that was high end and not a Crank Brothers. That headset and the FSA stem you were talking about will get you 3mm or less. Good Luck.
    Last edited by 55rpmasher; 04-21-2011 at 07:13 AM.

  9. #9
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    The Crank Brothers headsets aren't that bad if you get the stainless one. The carbon steel one will rust if you ride in bad weather. But, CB was always good about replacing it for me.

    They have a stack height just under 21mm and that will give you a lot more options in the stem department.

    You can always go with a Thomson X2 if you don't mind the -10 deg angle, they have a really low stack height. THe FSA or a Syntace F109 also have a low stack height and give you more options as fas as angles go.

  10. #10
    55rpmasher
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    I actually tried the CB stainless headset. During installation I dropped it on the shop floor. The floor has padding. The cup chipped on impact. I removed the bottom cup and sent it off to warranty. I have not had good success with alot of there products. I say look elsewhere.

  11. #11
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    I ran into a stack height problem a year ago while helping a friend. We took a two-pronged approach: 1) Crank Brothers heads, and 2) Truvative AKA stem.

    The Truvative stem had a shorter stack height than any of the other stems I had on hand. We went from being about 5mm too short in the steerer tube to having about 5mm extra.

  12. #12
    It's carbon dontcha know.
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    Here's a reply I gave to a friend with similar issues.
    Quote Originally Posted by 6thElement
    With 30mm of steerer, the Sunline will work fine then allowing for the 3mm of space for top cap?

    My XC-1 has 32/33mm stack height, I bought it from Chainlove for $30. They list the AM as 34mm.
    http://www.sixsixone.com/sunline.aspx

    $35 for the 90mm silver.
    http://www.departmentofgoods.com/sunline-v1-xc-stem
    Rolling on 29", 650b, 8.3" and 23mm

  13. #13
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    You need space between the top of the stem's bore, and the top of the steerer. Why? That's how you snug up the headset!

    Every headset mfr will tell you what amount of space to run for headset adjustment/preload.

    When you increase the spacing beyond what's suggested by the mfr, you are reducing the stem's ability to clamp onto something solid (the steerer) and at some point the stem's clamp can be compromised.

    Whether the 10mm spacing could work, well... I doubt I'd want to try it myself. I'd aim for a shorter height stem, or a shorter stack headset myself.

  14. #14
    mtbr member
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    PM sent.
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  15. #15
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    thanks for the offer, seat_boy!

    Has anyone on here every made their own stem? I've got a good stock of 6061 billet that I could use, it would look chunky as frak, tho!

  16. #16
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    Looking at an Avid SAAGO stem now--looks neat!

  17. #17
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    OK, I re-measured my steerer and it's 167mm long, my bad.

    So, the new math says 167 - 110 - 28 = 29mm. The SAAGO has a stack height of 31mm and wants a 2mm gap under it, which is perfect.

    Fingers crossed all the bits play nice when they all arrive!

  18. #18
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    Just a thought...if it all goes together this way, is it going to fit in a way that is comfortable? What will your resulting saddle-to-bars drop be?

  19. #19
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    Quote Originally Posted by canyonrat
    Just a thought...if it all goes together this way, is it going to fit in a way that is comfortable? What will your resulting saddle-to-bars drop be?
    Now, there's something I haven't seriously thought about. Still have yet to get a seat post + saddle.

    If I float myself over the frame approximately where the seat would be, and have my arms where the bars will be with the 100mm stem on, I'm pretty comfortable, but I've no numbers to back it up. Just a WAG for now that it'll be comfy.

    How would I go about working out my saddle-to-bars drop?

  20. #20
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    Bought a SAAGO stem and a Cane Creek 40 headset. The SAAGO stem instructions state that an additional 2mm should be cut off in addition to the exposed steerer tube when a dry-fit if performed.

    Updated calculations:

    Total steerer: 167.68mm
    Exposed steerer with the stem mounted: 135.88mm
    ==> 31.8mm stem stack height, minus 2mm ==> 29.8mm should be left for the stem

    This means that my stack height should be (135.88mm + 2mm =) 137.88mm for the stem to work correctly.
    110mm (head tube) + 28mm (headset) = 138mm <== looks good!!

    Verification:
    167.68mm (steerer) - 110mm (head tube) - 28mm (headset) = 29.68mm <== looks good!!


    It looks like all these parts were made for each other! Thanks for everyones help!

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