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  1. #1
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    seat angle geometry madness

    I've recently been following this thread, among others, and read a lot of reviews discussing "modern geometry", and there seems to be a lot of misunderstandings and misinformation and conflicting statements. I'm not going to claim to be an expert, but a lot of what I've been reading just doesn't pass the smell test, and some of it is just complete nonsense. What am I missing, here?

    First, there is reach. Reach is the horizontal distance from the bottom bracket to the top of the head tube.

    Then there is stack. Stack is the vertical distance from the bottom bracket to the top of the head tube.

    Reach and stack are way more important than the effective top tube measure for bike fit. In fact, I don't even look at ETT. Stack and reach are independent of seat tube angle and head tube angle; they only depend on bottom bracket, which is where your feet are.

    Easy peasy, right?

    Things get weird when you throw in the seat tube angle and start saying things like "modern bikes will have steeper seat tube angles to improve climbing". That doesn't compute. Here's why....

    Pedaling power output is optimized by adjusting saddle fore-aft to get somewhere around KOPs (Knee-Over-Pedal). This is relative to the bottom bracket position. I'm not going to argue whether KOPs is correct, specifically, but in a general sense, you don't want to be far off from that, unless you're only going one direction: up or down.

    A steeper seat tube angle with the saddle centered on the post is equivalent to pushing the saddle towards the bars. You aren't changing reach, you are only changing the saddle position relative to the bottom bracket. If I move to a bike with a steeper seat tube angle, I'm going to move my saddle back to maintain the same fore-aft position relative to the bottom bracket.

    A bike with a steeper seat tube angle does not climb better. Sure, with your saddle moved forward relative to the bottom bracket, you might be in a better position to climb steep stuff, but then you suffer on the flats and the downhills.

    Likewise, you can't reduce the reach from the saddle to the bars with a steeper seat tube angle because you should be adjusting your saddle position relative to the bottom bracket.

    What am I missing?

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  2. #2
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    missing? dunno, but there's a lot going on in the discussion in this thread :

    https://forums.mtbr.com/general-disc...n-1102571.html
    All the gear and no idea.

  3. #3
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    Quote Originally Posted by BmoreKen View Post
    What am I missing?
    Test riding one for yourself and seeing what all the hype is about.

    The steepest STA I've ridden was 78.3 ish. It shrinks the ETT when seated, but as soon as you stand up or lower the dropper the Reach goes back to feeling nice and roomy.

    Modern geo: steeper STA, shorter chainstays, longer reach, slacker HTA. All for the better so long as the BB doesn't get too low which is way too common for my liking.

    Edit: that steep of a STA isn't necessary and doesn't work on all bikes. It's just an extreme example. However when reading an article recently about bike reviews/comparisons someone asked the test riders what STA they though was the best. Most were in the 77 degree range, though these were mid-long travel trail bikes.
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  4. #4
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    I think it's pretty simple. On a given wheelbase there is a balance point for overall bike handling. If you increase the front center and keep chainstay static the seat tube angle must steepen to handle the longer front center. Many companies, Yeti for example, just employed longer chainstays to maintain this balance. Their new SB designs have longer front centers and shorter chainstays. Therefore the balance point had to move much further forward (seat tube angle) as the BB is much futher back relative to WB.

  5. #5
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    Isn't "reach from the saddle to the bars" that you're talking about up there actually ETT that you claim isn't worth talking about?


    Steeper seat tube angle makes reach and ETT more similar. Slack seat tube angle makes them more different.


    Some people have been wanting them more similar. For one thing it gives you a longer reach without a crazy long ETT so you can be comfortable climbing and descending.

  6. #6
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    I prefer to have my knee position 2" in front of the crank arm, with steep STA it is now possible without reversing a laid back post or moving a saddle so far forward on the rails it compromises the saddle. I disagree also on position, it is a stronger position to be in on flats for power output (look at TT bike fits) and with dropper posts the descend does not come into play.

  7. #7
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    In one post ride chill time a couple weeks ago, I saw a guy try to tell another guy that enduro bikes have super slack seat tubes. The other guy was confused and kept trying to tell him about the concept of effective seat tube angle. The argumentative guy wouldn't hear it, kept getting more and more angry. It was pretty pathetic.

  8. #8
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    Quote Originally Posted by mik_git View Post
    missing? dunno, but there's a lot going on in the discussion in this thread :

    https://forums.mtbr.com/general-disc...n-1102571.html
    Ah, no shit. Didn't see that....

  9. #9
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    Quote Originally Posted by LargeMan View Post
    I prefer to have my knee position 2" in front of the crank arm, with steep STA it is now possible without reversing a laid back post or moving a saddle so far forward on the rails it compromises the saddle. I disagree also on position, it is a stronger position to be in on flats for power output (look at TT bike fits) and with dropper posts the descend does not come into play.
    The vast majority of people produce less wattage in a TT position compared to any other position on the bike.

    It is slower for climbing (lower power output) but faster on flat to rolling TT courses because it lowers the CdA of the rider enough that it more than compensates for the loss of power.




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  10. #10
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    I could have sworn my Chameleon had a steeper seat tube angle than my stumpjumper.

    Quite the opposite actually
    Stumpy=74*
    Chameleon=72.6*

    From the time I sat on the Chameleon I've had a feeling so different in that when I press down on the pedal my foot wants to slide off on the down stroke. That's a bit of an exaggeration but it explains what I mean.
    I FEEL like I have way better power delivery on the Stumpjumper, apparently because I'm pressing downward more directly.
    Maybe what I'm feeling is my foot slipping forward on the Chameleon, not slipping off more downward.

    I haven't measured from seat post/seat intersection horizontally to the BB to compare, but it is definitely something I notice. I can say, however, the seat is slid nearly all the way forward on the Chameleon to make up for the 18mm longer reach it has over the Stumpy.

    I don't notice it too much now since I'm familiar with both bikes. I've had the Stumpjumper a few years and the Chameleon since December. Just after getting a feel for the stock Chameleon I got back on the Stumpy and it felt like the bars were in my lap -rolled back and shorter reach. I wouldn't change it for the world, I've taken time to get the comfort and efficiency just right. I've since rolled back the Chameleon bars to what feels go and seems to be set now, but they aren't in my lap as the Chameleon is.

    I strayed a bit from the original question, but I think it's a good example of how the bike has a whole works together. I don't know if I'd feel as comfortable on the Chameleon with a laid back seat tube, likewise I think a steeper angle on the Stumpy would be awkward.
    Of course saddle position could change for 'comfort' but then the handling characteristics would be altered as well.

    Ugh. I'm just gonna ride and not do the math in my head on my next ride.

  11. #11
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    My two cents: steeper seat tube angles provide a more consistent reach throughout, i.e. slack angles and droppers suck for my knuckle dragging gorilla arms, as changing seat height screws with my reach, whereas a steeper angle makes my knees very happy and results in better riding (pleasurable and fun, zero shitz given to climbing efficiency, only climbing comfort) overall.

  12. #12
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    Quote Originally Posted by BmoreKen View Post
    Sure, with your saddle moved forward relative to the bottom bracket, you might be in a better position to climb steep stuff, but then you suffer on the flats and the downhills.

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    There is a limit to how steep a STA I want on an all-round MTB that I pedal on flatter trails, but for bike intended for steep climbs and steep descents, itís great. Thereís no limitation on the descent, because youíre not seated.

    The reason I like a long stroke dropper is to have additional height when Iím perched on the nose of the saddle. Higher than Iíd want it for a normal pedaling position, in other words.

  13. #13
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    So it seems the view is that a more forward saddle position provides a better climbing position, while not penalizing you on descents since youíre standing (saddle position doesnít matter, saddle likely dropped anyway).

    There might be something to this. At least if you are riding where it is all either up or down.

    MTB is definitely more up/down than road, so I can see an argument to move away from road bike geometry constraints.

    But Iím still not convinced. Maybe because my local trails have lots of flats in between those hills. And if itís really steep, Iím out of the saddle, anyway (there goes that argument for a forward saddle position).



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  14. #14
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    For some of us the really steep say 75+ tends to make the seated length just too short given our physical body dimensions-or with some just preference-I have found both the Smugler and the new Ripley to be in this category---for others they are fine-----shows one has to test ride a bike to see what works

  15. #15
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    Pinkbike article on STA. Maybe inspired by this thread?

    Opinion: Why Is Everyone Talking About Seat Tube Angles?
    https://www.pinkbike.com/news/opinio...be-angles.html

  16. #16
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    Quote Originally Posted by BmoreKen View Post
    So it seems the view is that a more forward saddle position provides a better climbing position, while not penalizing you on descents since youíre standing (saddle position doesnít matter, saddle likely dropped anyway).

    There might be something to this. At least if you are riding where it is all either up or down.

    MTB is definitely more up/down than road, so I can see an argument to move away from road bike geometry constraints.

    But Iím still not convinced. Maybe because my local trails have lots of flats in between those hills. And if itís really steep, Iím out of the saddle, anyway (there goes that argument for a forward saddle position).



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    For what it's worth, I went from a Ripley LS V3 with a 73* seat tube angle, to a Ripmo with a 76* seat tube angle. I live in Florida, so my trails are primarily flat with very short punchy ups/downs and man made features; I also took it to NC a couple weeks ago on a 9 day trip. Everywhere I've ridden that bike, the geometry is better for me, and the pedaling efficiency felt incredible despite it being 145mm travel vs. 120mm on the Ripley. I feel that by shifting my weight forward, front wheel traction is improved on flats and I felt more balanced overall, and I feel this also had a positive effect on reducing pedal bob in the rear shock by distributing weight more evenly.

  17. #17
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    Quote Originally Posted by BmoreKen View Post
    So it seems the view is that a more forward saddle position provides a better climbing position, while not penalizing you on descents since youíre standing (saddle position doesnít matter, saddle likely dropped anyway).

    There might be something to this. At least if you are riding where it is all either up or down.

    MTB is definitely more up/down than road, so I can see an argument to move away from road bike geometry constraints.

    But Iím still not convinced. Maybe because my local trails have lots of flats in between those hills. And if itís really steep, Iím out of the saddle, anyway (there goes that argument for a forward saddle position).



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    And where do you find yourself relative to your saddle when you stand to attack those steeps? Closer to where the steeper STAs put you to start. This let's you stay seated more often and conserve energy on more climbs ( plus, many bikes maintain best traction when you can sit and spin).

  18. #18
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    KOPS is 100% bullshit. It means nothing.

    edit: KOPS might be a useful reference point, but it goes out the window on technical singletrack. It's more useful on road bikes.

  19. #19
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    Quote Originally Posted by mack_turtle View Post
    KOPS is 100% bullshit. It means nothing.
    People get obsessed with what they've come to think of as the right way to do things.

  20. #20
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    Quote Originally Posted by Forest Rider View Post
    I could have sworn my Chameleon had a steeper seat tube angle than my stumpjumper.

    Quite the opposite actually
    Stumpy=74*
    Chameleon=72.6*
    Remember, you cannot directly compare static (unsagged) STA's between a F/S bike and a hardtail.

    Why?

    Your hardtail, at sag (when you sit on it) gets steeper. Both for HTA and STA. It's usually approximately 1.5* steeper.

    So your Chameleon will have a sagged STA of 74.1*

    Your Stumpy, on the other hand, will get slacker in STA when you're climbing a steep slope (weight shift will cause the rear to squat and the fork to compress less).

    So what you've "felt" while riding the two makes sense!
    I like 'em long, low, slack and playful

  21. #21
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    seat angle geometry madness

    So that article inspired measuring of actual or effective STA on two recent bikes. Prior bike had one of those bent seat tubes, so with my long legs the effective STA was 70! Now itís 75. So it really is effected by rider measurements and in my case whether bike has bent sent tube. The ďSTA madnessĒ in my situation was the older geometry.

  22. #22
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    I don't have a power meter but I do track my climbing times. Having moved to bikes with steeper STAs has not slowed me down and I am more comfortable climbing. I don't ride flay trails but do go on some flat gravel roads where my times are faster. It's probably my femur length but I love the steep STA, longer reach, so I can have a good saddle position and not be too close to the bars. Your body dimensions and terrain are going to be the deciding factor.
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  23. #23
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    Quote Originally Posted by BmoreKen View Post
    a more forward saddle position provides a better climbing position, while not penalizing you on descents
    If on the same bike, yes. But on a new frame, a more forward saddle will also improve descending because it allows for a longer Reach and Front Center.

    If ETT = Forward Reach + Rearward Reach, the new geo shortens RR and increases FR, forcing you to assume a more "rider forward" position. A dropper becomes mandatory.

    Saddle position renders RR and ETT measurements incidental, making Forward Reach ("Reach") the holy grail of bike fitment on the horizontal plane.

    Quote Originally Posted by BmoreKen View Post
    if itís really steep, Iím out of the saddle, anyway (there goes that argument for a forward saddle position).
    Somewhat true but a more forward saddle means you don't need to stand as often, the cockpit doesn't shrink as much when you stand, and alternating between sitting/standing is more natural.

    Quote Originally Posted by BmoreKen View Post
    my local trails have lots of flats in between those hills.
    Then maybe avoid the more severe rider-forward designs. Horses-for-courses still applies - just better options now.

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