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  1. #1
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    Increasing stack height on carbon steerer

    Let's say I'm pretty interested in the new Trek Emonda ALR disc, but to get what I know is the right fit for me, I would need to shorten the stem to 90mm and raise the bars about 10-15mm more than what can be achieved with the stock 7° stem and the mfg recommended maximum 40 mm of spacers (long legs, comically short torso, awful flexibility). Considering that shortening the stem decreases the lever effect on the steerer, would it be safe to either use a more angled stem (17 or 24°) or riser bars (which raise the tops by 15mm)? Would one be preferable to the other?

    I'm 140 pounds, used to run a Synapse with 55mm of spacers, which looked stupid but was within Cannondale recommendations.

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    You should do what ever is best to get where you want to go. How ever you get there isn't going to matter. Shorter stem with risers or angled stem turned up.

    There will be some here that will claim it will change the handling and create issues. But putting riser bars, shorter stems, longer stems, etc. changes the handling so little; only at the edge of control will that come into play.

    On moto's, they change the risers, bars, mounting height, etc., you will get used to the changes after 5 min on the bike.

    I run a 50mm stem on my bike & went to short reach bars, I didn't notice any change and still pass everyone on the corners (going downhill).
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  3. #3
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    Stem and spacers. Bars should be selected because you like the shape not for positioning. But be mindful that bars have different reaches too if you do get new bars.

  4. #4
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    Quote Originally Posted by ToiletSiphon View Post
    Let's say I'm pretty interested in the new Trek Emonda ALR disc, but to get what I know is the right fit for me, I would need to shorten the stem to 90mm and raise the bars about 10-15mm more than what can be achieved with the stock 7° stem and the mfg recommended maximum 40 mm of spacers (long legs, comically short torso, awful flexibility). Considering that shortening the stem decreases the lever effect on the steerer, would it be safe to either use a more angled stem (17 or 24°) or riser bars (which raise the tops by 15mm)? Would one be preferable to the other?

    I'm 140 pounds, used to run a Synapse with 55mm of spacers, which looked stupid but was within Cannondale recommendations.

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    Sorry but I disagree with both previous posters. Stem length matters OP. You are ok with 90mm but don't go shorter.


    Going from 7 deg stem of 90mm to 17 deg 90mm stem =
    sine of (17 - 7 deg) X 90mm = 15.6 mm more rise

    This should achieve your objective of stack. Keep in mind, at the same steerer height, going from a 7 deg 90mm stem to 17 deg 90mm stem will shorten horizontal reach by only 1.3mm or so using law of sines.

    Reach for all intents isn't affected very much in the horizontal plane...but...as you, and I also with long legs and short torso know, 15.6mm in bar height makes a big difference because the handlebar is moved up much closer to the shoulder joints and true (rider) reach to the bars is really the hypotenuse of two legs of a right triangle comprised of stack and bike reach...bike reach being on a chart and true rider reach being a function of both stack and bike reach.

    Hope that helps.

    Stem angle chart below for further refererence.

    PS for a short torso to long leg length ratio, the H2 Emonda is a pretty good selection. I could own that bike as well. Another bike to look at for more analogous proportion to how you are built is the Domane with even shorter top tube to stack compared to the Emonda. The Domane is one of the tallest bikes in the industry relative to reach...similar to the Spesh Roubaix. People love both bikes, but I believe with the right frame selection, you can get the Emonda to work.
    Attached Thumbnails Attached Thumbnails Increasing stack height on carbon steerer-stem-ii-angle-chart.jpg  
    Last edited by 11spd; 10-16-2018 at 03:21 AM.

  5. #5
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    Toilet...HERE is a stem comparison tool to determine how a new stem will change bar height and reach.

  6. #6
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    Quote Originally Posted by 11spd View Post
    Sorry but I disagree with both previous posters. Stem length matters OP. You are ok with 90mm but don't go shorter.


    Going from 7 deg stem of 90mm to 17 deg 90mm stem =
    sine of (17 - 7 deg) X 90mm = 15.6 mm more rise

    This should achieve your objective of stack. Keep in mind, at the same steerer height, going from a 7 deg 90mm stem to 17 deg 90mm stem will shorten horizontal reach by only 1.3mm or so using law of sines.

    Reach for all intents isn't affected very much in the horizontal plane...but...as you, and I also with long legs and short torso know, 15.6mm in bar height makes a big difference because the handlebar is moved up much closer to the shoulder joints and true (rider) reach to the bars is really the hypotenuse of two legs of a right triangle comprised of stack and (versus bike) reach.

    Hope that helps.

    Stem angle chart below for further refererence.

    PS for a short torso to long leg length ratio, the H2 Emonda is a pretty good selection. I could own that bike as well. Another bike to look at for more analogous proportion to how you are built is the Domane with even shorter top tube to stack compared to the Emonda. The Domane is one of the tallest bikes in the industry relative to reach...similar to the Spesh Roubaix. People love both bikes, but I believe with the right frame selection, you can get the Emonda to work.
    Very detailed answer, thank you. I had already made some quick trigonometry calculations and figured that the 17° stem and 15mm riser bars would both put the hoods roughly in the same spot height and reach wise.

    My concern is that by doing so, I'm kinda cheating on what is the manufacturer recommended max stack height (max 40mm of spacers). If I were to stay with a 100mm stem, the hoods would be further from the top bearing, thus creating more leverage and more stress on the carbon steerer. But the shorter stem I require probably negates that effect.
    EDIT : not so sure about that, see post below.

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    Last edited by ToiletSiphon; 10-15-2018 at 08:52 AM.

  7. #7
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    Redid my calculations with the link provided above. Seems like going from a 100mm 7° stem to a 100mm 17° stem would shorten the reach by 8mm and increase stack by 15,which would be perfect. Going to a 90mm would not yield the same good results.

    Which brings me back to my original question, slightly modified : would a 17° stem put more stress on a steerer than a 7° stem of equal length?

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  8. #8
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    Quote Originally Posted by ToiletSiphon View Post
    Redid my calculations with the link provided above. Seems like going from a 100mm 7° stem to a 100mm 17° stem would shorten the reach by 8mm and increase stack by 15,which would be perfect. Going to a 90mm would not yield the same good results.

    Which brings me back to my original question, slightly modified : would a 17° stem put more stress on a steerer than a 7° stem of equal length?

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    you're missing point. They advise not to use xx amount of spacers. Period.

  9. #9
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    Quote Originally Posted by ToiletSiphon View Post
    Redid my calculations with the link provided above. Seems like going from a 100mm 7° stem to a 100mm 17° stem would shorten the reach by 8mm and increase stack by 15,which would be perfect. Going to a 90mm would not yield the same good results.

    Which brings me back to my original question, slightly modified : would a 17° stem put more stress on a steerer than a 7° stem of equal length?

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    Answer is no. In fact a 17 deg stem places less stress on the steerer compared to a 7 deg same length albeit fractionally less. 17+ degree stems are common for the simple reason they help an amateur rider get closer to handlebar height about the same as saddle height, i.e. French fit which works better for many and how I set up average riders who struggle with pain on the bike with a slammed stem.

    If you stay under the manufacturer stack recommendation beneath the stem, you are good. This is generally 40mm or so for a 'carbon steerer' carbon fork for many mfrs.

    HTH

  10. #10
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    Quote Originally Posted by duriel View Post
    You should do what ever is best to get where you want to go. How ever you get there isn't going to matter. Shorter stem with risers or angled stem turned up.

    There will be some here that will claim it will change the handling and create issues. But putting riser bars, shorter stems, longer stems, etc. changes the handling so little; only at the edge of control will that come into play.

    On moto's, they change the risers, bars, mounting height, etc., you will get used to the changes after 5 min on the bike.

    I run a 50mm stem on my bike & went to short reach bars, I didn't notice any change and still pass everyone on the corners (going downhill).
    I couldn't have said it better here. I think change in handling claims are way overblown unless you are into doing stupid s#!t on the bike.

    I run a 40 degree upright stem. No handling issues.

    Another way to get more upright is to tilt your bars up slightly. But experiment with this in small amounts because overdoing this may be a strain on your wrists.

    As far as spacers, as long as your stem doesn't come up above the end of the steerer, you are fine.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

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  11. #11
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    Quote Originally Posted by 11spd View Post
    Answer is no. In fact a 17 deg stem places less stress on the steerer compared to a 7 deg same length albeit fractionally less. 17+ degree stems are common for the simple reason they help an amateur rider get closer to handlebar height about the same as saddle height, i.e. French fit which works better for many and how I set up average riders who struggle with pain on the bike with a slammed stem.

    If you stay under the manufacturer stack recommendation beneath the stem, you are good. This is generally 40mm or so for a 'carbon steerer' carbon fork for many mfrs.

    HTH
    That makes a lot of sense.

    After some more calculations, another option that would give pretty much the same fit as a 90mm 17° stem would be a 90mm 7° stem with hover bars (raised 15 mm). Would this change anything on the stress put on the steerer?

    I'm inclined to think it wouldn't, and if it does the little additional stress VS 17°/90mm would still be less than what it is with the stock 100mm stem with the stock bars, which are longer reach and wider (420 VS 400) than what I would get.

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  12. #12
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    Quote Originally Posted by ToiletSiphon View Post
    That makes a lot of sense.

    After some more calculations, another option that would give pretty much the same fit as a 90mm 17° stem would be a 90mm 7° stem with hover bars (raised 15 mm). Would this change anything on the stress put on the steerer?

    I'm inclined to think it wouldn't, and if it does the little additional stress VS 17°/90mm would still be less than what it is with the stock 100mm stem with the stock bars, which are longer reach and wider (420 VS 400) than what I would get.

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    So much can be written on this. I am an engineer so look thru the lens of science, stress/strain, and why stem length matters. Engineers design framesets for a given head tube angle, fork rake, chainstay length, wheelbase and trail. The predicate is stem length which is typically a range depending on frame size. Generally for a medium frameset this is min. length of 90mm. For example, I am a better recreational rider and I ride a 58cm frameset with 130mm stem. Short = twitchier.
    I think you know that. When starting off and selecting a frame which is where you are I believe, you want to size the bike for a nominal stem length. Better riders tend to ride longer stems and slightly smaller frame.

    Any compulsion you have about steerer stress is nebula unless you are an Olympic powerlifter. Even with a 50mm stack under the stem and whatever stem and handlebar you choose, it won't break. So don't be concerned.

    We don't know much about you. Your height, weight, and inseam, your saddle height from BB to saddle top, and your overall fitness.

    In your shoes, if you are an average recreational rider with no physical problems, I would select a frame size that will give you a 110mm stem with about a 1 inch saddle to handlebar drop with about a 40-45 deg back angle with hands draped comfortably on the hoods.

    Sometimes this is hard to figure out on your own. We learn by trial and error as it turns out. Many riders...I see so many on the road doing it wrong. You can ride a road bike for 10 years in a bad position...either too upright or too slammed for your level of athleticism.

    Good luck

    PS: Below is a great position on a road bike. Many poorer riders tend to ride more upright and then they will end up having too much pressure on their hands because they are crowding the handlebar and with a high handlebar, the bar pushes back on the shoulders when the torso tries to find is proper angle to fit exertion level. Notice there isn't a lot of saddle to bar drop in the picture but the rider is comfortably stretched out. If you get close to this position you likely will be pretty comfortable for 'spirited' biking whereby pedal forces naturally unweight the torso for leaning over the top tube.

    By Contrast:
    I thought for best perspective, I would post a poor common endurance fit I see on the road. This rider has no chance to be comfortable. What separates the two riders? A lot. The second rider who is tallish is crowding the handlebar which is set high. Further his hoods are rotated rearward and his drops are unsupportive...very common. Rider isn't comfortable in the hoods because of too much hand pressure due to crowding the handlebar. What is the most common element of sitting too close to the handlebar? Poor posture. A rider has to slouch to shorten their torso when sitting too close the handlebar. What does slouching do? It promotes sitting on a saddle like a park bench with weight falling forward. The way to get proper weight distribution on the bike is with pelvis rotated position which promotes sticking out the bum and good lumbar posture...the opposite of slouching. This moves riders weight rearward and weight off the hands. Even with a lot more reach to the handlebar the first rider has much less weight on the hands even with a fractionally lower handlebar.

    Much of fit is counterintuitive and too complex for the average person to sort out. Many people need more reach to the handlebar and a longer stem and rotating the pelvis forward to move rider CG rearward. Good posture begins in the lumbar of the back which can only be accomplished with adequate pelvis rotation, this lengths the back not unlike good posture elongating the spine walking down the street. This requires more reach and why better riders prefer a longer cockpit because it supports their better posture. Posture and reach on the bike go hand in hand. Hard to have one without the other.
    Attached Thumbnails Attached Thumbnails Increasing stack height on carbon steerer-fit.jpg   Increasing stack height on carbon steerer-roubaix.jpg  
    Last edited by 11spd; 4 Weeks Ago at 10:24 AM.

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