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Thread: why are MTB stems so short?

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    Default why are MTB stems so short?

    I have some theories. What do you think?

    popular ideas include:
    • steering dynamics
    • weight distribution over the front axle
    • fitting
    Jonathan - Austin, TX

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    Default Re: why are MTB stems so short?

    Because when riding down steep angles and drops your weight distribution feels correct.
    XC bikes generally have longer stems.
     

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    Default Re: why are MTB stems so short?

    the moment you take a 8-10" bike off a big drop it all makes sense.
     

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    Default Re: why are MTB stems so short?

    I am an idiot so take with salt, though one impression I have is that short stems maintain the same reach on a bike that has a much longer front center. While chainstays remain short and wheelbases try to remain in the ballpark, slack head tubes and long TTs stretch out the part of the bike the rider "experiences" and the stem compensates to maintain normalcy.
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by zambenini View Post
    I am an idiot so take with salt, though one impression I have is that short stems maintain the same reach on a bike that has a much longer front center. While chainstays remain short and wheelbases try to remain in the ballpark, slack head tubes and long TTs stretch out the part of the bike the rider "experiences" and the stem compensates to maintain normalcy.
    That's what I thought too. Back in the day, mountain bikes were just glorified touring bikes without the slack head tube angles that came later. We made them handle better on single track with longer stems and stupid narrow bars (because that's what Tomac did). My Coconino hardtail has a 70mm stem, my Raleigh Chill had a 150mm Tioga stem.
    Weight Doper

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    Default Re: why are MTB stems so short?

    It's to cope with a revolutionary geometry change. A revolution happens every other year or so.
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by mack_turtle View Post
    I have some theories. What do you think?

    popular ideas include:
    • steering dynamics
    • weight distribution over the front axle
    • fitting
    i ran a 120 stem on a ti hardtail with pretty steep headtube (vs. "modern" geometry)...i went over my bars with regularity

    doesnt happen anymore with a short stem and slack front end
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by funcrusher View Post
    i ran a 120 stem on a ti hardtail with pretty steep headtube (vs. "modern" geometry)...i went over my bars with regularity

    doesnt happen anymore with a short stem and slack front end
    is it the head tube angle, the reach, or the front-center that changed? or all three? if one were to build a bike with a relatively slack HTA but a short reach, would the rider still want a short stem? would a bike with a long reach and a relatively steep HTA then need a longer stem?

    just trying to open discussion to narrow down what the real issue is. I am not trying to prove anything, just curious about what is fact and what is pseudo-science.
    Jonathan - Austin, TX

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by mack_turtle View Post
    is it the head tube angle, the reach, or the front-center that changed? or all three? if one were to build a bike with a relatively slack HTA but a short reach, would the rider still want a short stem? would a bike with a long reach and a relatively steep HTA then need a longer stem?

    just trying to open discussion to narrow down what the real issue is. I am not trying to prove anything, just curious about what is fact and what is pseudo-science.
    Likely similar total reach to old stretched xc positions, but now the tt is longer.
    I've become a fan I think as long as things aren't crazy slack. I ride my xl mtb w/ a 50mm stem (493 reach) and my 58cm gravel bike (406 reach) has a 100/110mm I think. Definitely different setup than older bikes I've had.
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by mack_turtle View Post
    is it the head tube angle, the reach, or the front-center that changed? or all three? if one were to build a bike with a relatively slack HTA but a short reach, would the rider still want a short stem? would a bike with a long reach and a relatively steep HTA then need a longer stem?

    just trying to open discussion to narrow down what the real issue is. I am not trying to prove anything, just curious about what is fact and what is pseudo-science.
    everything changed..."modern" geo is long/slack...so shorter stem to compensate...definitely stabler on descents

    and no trade-off because steep seat angle helps for climbing
     

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    Default Re: why are MTB stems so short?

    It's the classic try before you buy scenario based on your local trail needs. As for me, I did not find with modern bikes that there was "no penalty" when climbing. The length of the front center made it feel very long ... like piloting a Cadillac, so if you ride twisty, classic trails, and technical, rooty climbs, buyer beware. Railing series of berms downhill ... sure, sign me up for the Cadillac, but that's not my area. I tried two modern bikes, one modernish, a two or three year old Trek FS, and the other a 2020 Santa Cruz Tallboy, which is much more "modern". Though I'm a likely hardtail customer til I'm older or ride gnarlier stuff, I thought I'd see what the fuss was about. Couldn't handle the wheel flop or wandering front end on the TB when trying to get up climbs, though back end traction was really impressive. The steep, steep seat angles have you sitting in the middle of the bike - you don't seem to do as much body English or sliding your weight back, it seems mostly about getting low. As for me, I wound up sticking with what I know, as I felt like I was still learning and enjoying classic "get your weight back"/"keep your front end low to aid front-end traction", etc. type techniques and didn't want or need to depart from that for the time being. So, I stuck with a hardtail with old school XC geo, but all the trails I ride are XC oriented - tight, twisty singletrack, rooty, old school singletrack climbs, gently undulating terrain, etc. I went with a low BB, 90mm stem, and thus configured, the 71.5 head angle still feels marvelous both uphill and down. That's road bike geo to contemporary riders, but it has all the precision and snap I like from the front end while climbing. It's been fine downhill - I, for one, quit going over the bars when I switched from 26" to a 29er, though I'd be willing to try maybe a 70 HA. YMMV, horses for courses, etc.

    Let us know what you try.
     

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    Default Re: why are MTB stems so short?

    Stability and leverage.

    Short stem + wide bars = bumps and objects don't knock you off line, you don't endo anymore, handlebars don't flop over sideways once turned, and you have the power to hold the bars still no matter how rough the terrain. Same reason BMX does it, but they don't need a hold a comfortable pedaling position for hours so the rest of the geometry doesn't have to follow.

    Really really strong pro riders can even do narrow-ish bars and short stems and not have to deal with width challenges, but only because their upper bodies and cores are so strong that they don't need as much leverage help.
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by zambenini View Post
    It's the classic try before you buy scenario based on your local trail needs. As for me, I did not find with modern bikes that there was "no penalty" when climbing. The length of the front center made it feel very long ... like piloting a Cadillac, so if you ride twisty, classic trails, and technical, rooty climbs, buyer beware. Railing series of berms downhill ... sure, sign me up for the Cadillac, but that's not my area. I tried two modern bikes, one modernish, a two or three year old Trek FS, and the other a 2020 Santa Cruz Tallboy, which is much more "modern". Though I'm a likely hardtail customer til I'm older or ride gnarlier stuff, I thought I'd see what the fuss was about. Couldn't handle the wheel flop or wandering front end on the TB when trying to get up climbs, though back end traction was really impressive. The steep, steep seat angles have you sitting in the middle of the bike - you don't seem to do as much body English or sliding your weight back, it seems mostly about getting low. As for me, I wound up sticking with what I know, as I felt like I was still learning and enjoying classic "get your weight back"/"keep your front end low to aid front-end traction", etc. type techniques and didn't want or need to depart from that for the time being. So, I stuck with a hardtail with old school XC geo, but all the trails I ride are XC oriented - tight, twisty singletrack, rooty, old school singletrack climbs, gently undulating terrain, etc. I went with a low BB, 90mm stem, and thus configured, the 71.5 head angle still feels marvelous both uphill and down. That's road bike geo to contemporary riders, but it has all the precision and snap I like from the front end while climbing. It's been fine downhill - I, for one, quit going over the bars when I switched from 26" to a 29er, though I'd be willing to try maybe a 70 HA. YMMV, horses for courses, etc.

    Let us know what you try.
    You need to borrow my Chameleon. Think it's a 67.3HA/50mm stem. Its flat enough here that old school still works fine but in the steep (WNC) and the new stuff comes into its own. As per my other thread my next bike will land between 66 and 67 HA trying to balance our local flat terrain with trips back home to AVL.
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by Jason Musgrave View Post
    You need to borrow my Chameleon. Think it's a 67.3HA/50mm stem. Its flat enough here that old school still works fine but in the steep (WNC) and the new stuff comes into its own. As per my other thread my next bike will land between 66 and 67 HA trying to balance our local flat terrain with trips back home to AVL.
    That I do! Let's make this happen soon. I also suspect that I might be curious about a larger bike, kind of like that one time I rode your road bike and did not mind the longer reach whatsoever.
     

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    Default Re: why are MTB stems so short?

    Also handlebar width. At 780 or 800mm, there’s a ton of reach just being generated by the bars. You have to shorten the stem, quite a bit, to compensate for that as well.

    Cheers
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by Lionel View Post
    It's to cope with a revolutionary geometry change. A revolution happens every other year or so.
    How about adding a sarcastic "tongue in cheek" emoji with that?!

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    Default Re: why are MTB stems so short?

    I agree that ideal head angle, fork rake and top tube length have influenced neccesary stem length, but I also think many people are now riding a stem that is too short for them.
    Stem length should still be fit driven- Just maybe not a stretched out as what used to be the norm.

    I am 5'10 and currently riding a size large Orbea Oiz. Top tube length is 619mm. Reach is 446mm, Stack is 608mm. I use a 90mm -8 degree stem without spacers and 740mm bars. Why? Because it fits me.
    People call out a 90mm stem as if it was an old school 150mm Control Tech!
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by boots2000 View Post
    People call out a 90mm stem as if it was an old school 150mm Control Tech!
    If it works for Kulhavy...

    This R14, monster is the most epic bike at this year’s Cape Epic

    db8c351c36344936a72cbbee904bc049.jpg

    bb99f6e5fc0f4d78806aa0d6a5d12537.jpg
     

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    Default Re: why are MTB stems so short?

    Quote Originally Posted by boots2000 View Post
    I agree that ideal head angle, fork rake and top tube length have influenced neccesary stem length, but I also think many people are now riding a stem that is too short for them.
    Stem length should still be fit driven- Just maybe not a stretched out as what used to be the norm.

    I am 5'10 and currently riding a size large Orbea Oiz. Top tube length is 619mm. Reach is 446mm, Stack is 608mm. I use a 90mm -8 degree stem without spacers and 740mm bars. Why? Because it fits me.
    People call out a 90mm stem as if it was an old school 150mm Control Tech!
    I prefer to think of the short stem/ wide bars less a fit thing and more of a handling thing. I also prefer to keep stem length and fork rake close. So I put people who prefer wide bars and modern bikes with 37mm (27.5" bikes) to 44mm rake (29ers) on 40 or 50mm stems. "Fit" is addressed through reach which means getting them on the right frame.
    Got some cash
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    Default Re: why are MTB stems so short?

    first argument
    Lee McCormack on steering-hands offset

    p3pb16749349.jpg

    Steering-Hands Offset (SHO) is the distance of your hands in front or or behind your bikeís steering axis.
    Iíll bet youíll like a SHO in the 0-20mm range, and the closer you get to zero the yummier your bike will feel.
    second argument
    Naked Framebuilder's Notes on a Prototype- this article featuring Sam Whittingham used to be on handbuildbicyclenews.com but that site appears to be down. in it, he discusses designing a hardtail with the longest-front-center possible. I saved it and can still paraphrase it here: actual head tube angle is unimportant and people need to stop obsessing over it. It's a red herring for the real issue: front-center. a long front-center achieved by a slack HTA creates wheel flop, which is why you design around the shortest stem possible. Sam says that hands should be about lined up with the steering axis.

    three
    Gene from Better Ride (written in 2010)
    Your stem is a not a bike fit device, it greatly effects the control of your bike. ... So for a more controlled ride go with a 50 to 80mm stem and 27″-32″ wide bars.
    four
    Richard Cunningham on stems and steering
    In reality, your hand position, relative to the forkís steerer tube are the only components in the equation that matter. ... handlebar-adjusted stem length around 20 millimeters would be as short as youíd want.
    Contrarian views provided by Pete Verdone:
    stupid about stems
    This shows us that arguments for short stems, that donít put them into a system, are almost universally false.
    On Reach just relevant

    Bars, stems, and spacers


    I think there are another PVD article on the topic I'll try to find later, but his point seems to be that getting the hands where they need to go relative to the BB is crucial, and that hands/ steering axis is unimportant. the short stems are the result of building bikes with long front-center measurements that keep the from being enormous.
    Jonathan - Austin, TX

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