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Thread: modern geometry / seat tube angle

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    Default modern geometry / seat tube angle

    My old frame cracked last weekend so it's time for something more contemporary. (This is not a "what frame should I buy" thread.)

    I get the whole longer, slacker thing happening and I want another full suspension bike. But looking at geometry specs I'm seeing seat tube angles of 76º & 77º. With a zero offset dropper post the saddle is going to be really far forward on these bikes. One of the bikes that intrigues me is a more understandable 74º.

    Is this an attempt to compensate for the longer reach? I still like to pedal my bikes (uphill, downhill, and often to the trail head) so I want a relatively normal pedaling position. I embrace the right tool for the job theory and this isn't a road or TT bike, but what's going on here? I'd appreciate some insight to help my decision making.
     

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    Default Re: modern geometry / seat tube angle

    I am in same cracked frame boat and in as of a few hours ago the same seat angle question boat. I am only smart enough to understand what the HA does to the handling and don't have granular enough math thinking to add in SA. Then I started looking at Tyler's new Evil The FOllowing MB geo chart and noticed the SA,...

    ... and so yes, please, VS, help.
     

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    Default Re: modern geometry / seat tube angle

    I didn't know the trend was to silly steep seat angles. That's absurd. Run, don't walk, toward more rational seat angles.

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    Default Re: modern geometry / seat tube angle

    Have not ridden any of the new school bikes from what i hear those bikes are built w/ a dropper in the equation. SEated pedalling is for climbing only. Head angle is around the 66 degr. mark and the front wheel is way out front. You need to move your weight as much forward as possible to compensate the head angle. It sounds stupid but everyone loves it when riding down steep and rough terrain.
    I came here for the socks.

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    Default Re: modern geometry / seat tube angle

    Firstly, when you're talking about longer front centers and slacker head angles, the steep STA not only works, it's an important part of the handling equation.

    Essentially, the role of the steep STA is to force you to get weight up on the front wheel to compensate for what would have been a heavy rear-wheel biased weight distribution. The way some of us ride bikes has changed and the way we fit on them has changed too.

    Some data points. Other than getting heavier, I'm still pretty much the same shape I was 25 years ago. 5'11", 34.5" inseam. In 1995 I rode what would have been a 19" bike. Let's say it had a 600mm ETT (it was actually a bit shorter than that) with your standard 71/73° angles. The REACH on that bike would be ~ 425mm, the Front-Center ~650mm and the WheelBase ~ 1070mm. Let's ignore STA and use saddle setback instead because you can accommodate for slight variations in seat post, STA and so on. My setback was ~75mm and stayed that way for a long time. Chainstay lengths at that time were 420-430mm and a lot of folks would run the bars a few inches below the top of the saddle.

    Right now, the bike I ride most of the time has a 65°HTA, 483mm reach, 821mm F-C, 1253mm WB with 435mm stays. You can see that straight away the REACH is 58mm longer, and the F-C is 173mm longer. You can already imagine how the weight balance is moving rearward. Of course my stem length is significantly shorter now, biasing the weight even further rearward. My saddle setback is currently ~35mm and the tops of my grips are about level with the top of my saddle.

    Moving the saddle forward is forcing you to put more weight on the front wheel when you're seated. With the long front center and slack HTA, this does a lot to keep the front wheel from wandering all over the place while climbing. Longer stays help calm that handling trait as well. 25 years ago, we had to fight hard to get back far enough over the rear wheel when riding steep downhills. A lot of modern bikes reward an aggressive position with your body centered over the bike so you can get enough pressure on your front tire in fast corners to keep it hooked up. If you try to get back too far, the front tire is more likely to wash.
    Sean Chaney
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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by VertigoCycles View Post
    If you try to get back too far, the front tire is more likely to wash.
    This would explain a lot. I was still running a 100mm stem on my rigid SS (more traditional geo), but I was over the moon about it when I finally slammed it and got my bars lower (had the effect of rotating me forward a little bit, too. It felt completely more connected with the trail; I felt better about traction, etc.).

    So, why the trend toward a shorter stem, if weighting the front wheel is the goal with new geo trends? Or am I missing something. Thanks again, Sean. That dropper still rules, btw. Thank you.
     

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by zambenini View Post
    This would explain a lot. I was still running a 100mm stem on my rigid SS (more traditional geo), but I was over the moon about it when I finally slammed it and got my bars lower (had the effect of rotating me forward a little bit, too. It felt completely more connected with the trail; I felt better about traction, etc.).

    So, why the trend toward a shorter stem, if weighting the front wheel is the goal with new geo trends? Or am I missing something. Thanks again, Sean. That dropper still rules, btw. Thank you.
    Handling a shallow angle front w/ lots of travel on a shorter stem is much better. That´s all i know.
    I came here for the socks.

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    Default Re: modern geometry / seat tube angle

    Well we've got things like wide bars, dropper posts, and tyres with grip these days and that's changed a lot of things. Modern trail bikes are the best-riding bikes that mankind has ever created, and they're the best fit for their intended purpose of any cycling discipline.

    Get the young grom at the shop to pick the right size and go for a spin on a modern 130mm bike - simply amazing.

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    Default Re: modern geometry / seat tube angle

    As another 'old timer' this is an interesting topic because while I get the longer TT/shorter stem/wider bar I have been perplexed by the steeper ST or shorted setback.

    The original poster was pointing out that traditional ST angles allowed for traditional pedaling position as it relates to hips/knees/feet. The newer ST angles/setback place these body point more forward.
    It is very common to position myself on the tip of the saddle while climbing steep pitches to get the right weight distribution (enough weight on the rear for traction and enough weight on the front for steering). However not all climbs are steep enough to warrant this and whether riding to a trail or simply riding dirt roads between challenging sections does not require this weight distribution and tips the scale back to being able lay power into the pedals like any road bike.

    Is it simply a matter of putting the emphasis on the time spent on the more technical riding?

    I know the answer is to go ride a sampling of the newer bikes but shops around me no longer have demo bikes or even rentals. Instead everyone seems to rely on the traveling factory demo days. While this makes sense at some level it requires that everyone's schedule aligns and weather is cooperating....different topic.
    Brian McLaughlin

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by Bewheels View Post
    As another 'old timer' this is an interesting topic because while I get the longer TT/shorter stem/wider bar I have been perplexed by the steeper ST or shorted setback.

    The original poster was pointing out that traditional ST angles allowed for traditional pedaling position as it relates to hips/knees/feet. The newer ST angles/setback place these body point more forward.
    It is very common to position myself on the tip of the saddle while climbing steep pitches to get the right weight distribution (enough weight on the rear for traction and enough weight on the front for steering). However not all climbs are steep enough to warrant this and whether riding to a trail or simply riding dirt roads between challenging sections does not require this weight distribution and tips the scale back to being able lay power into the pedals like any road bike.

    Is it simply a matter of putting the emphasis on the time spent on the more technical riding?

    I know the answer is to go ride a sampling of the newer bikes but shops around me no longer have demo bikes or even rentals. Instead everyone seems to rely on the traveling factory demo days. While this makes sense at some level it requires that everyone's schedule aligns and weather is cooperating....different topic.
    IMO, the reduced saddle setback doesn't take away from the parts of riding that are non-technical. I've been using Strava for the past several years to track all my rides and power output on my normal 3.5mi climb between my old school and new school bikes are very similar. There's certainly an adjustment period when transitioning to one or the other and I'll say that I much prefer the longer bike and shorter setback. Just as another data point. Saddle height and saddle tip to bar are identical on both bikes. My bar relative to the saddle is about 1/2" higher on the new school bike but the position is surely more forward with a more open hip angle.
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: modern geometry / seat tube angle

    [QUOTE=zambenini;975827]This would explain a lot. I was still running a 100mm stem on my rigid SS (more traditional geo), but I was over the moon about it when I finally slammed it and got my bars lower (had the effect of rotating me forward a little bit, too. It felt completely more connected with the trail; I felt better about traction, etc.).

    I have a long answer, but the short answer is that I don't know. It's a trend right now. It works for some, but not for others and it'll depend on who you are, how you ride, where you ride and how hard you're pushing your own limits. I learned this year that I can't ride a 35mm stem, but 55mm works for me. Perhaps if I rode steeper terrain more often, 35 would work, but I don't and it doesn't. That's just me though.
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: modern geometry / seat tube angle

    When getting back to MTB a few years ago I ran across Lee McCormack. Besides his great in person coaching, his approach to fitting really works for me. My current Trek Remedy is setup with his RAD approach and uses a 40mm stem. They way I position myself now on an MTB is totally different than road. I don't even measure my saddle setback any longer. The STA for me is all about getting weight forward when climbing. If I were riding XC primarily (or riding gravel bikes on single track) the approach would be different.

    This is worth checking out if you haven't seen it.

    Make it RAD
     

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    Default Re: modern geometry / seat tube angle

    So with a 77deg STA your knees are much farther forward. I know that I am pretty sensitive the knee position and really not sure that I could pedal a 77STA for a long time without pain.
     

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by Lionel View Post
    So with a 77deg STA your knees are much farther forward. I know that I am pretty sensitive the knee position and really not sure that I could pedal a 77STA for a long time without pain.
    Isn´t it like out of the saddle climbing or seating on the tip of the saddle? I understand these bikes are made w/ not much of extended climbing as the plan. In that case you would ride a xc 29er. I find the mtb quiver options a bit confusing and too focused on specifics.
    I came here for the socks.

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by colker View Post
    Isn´t it like out of the saddle climbing or seating on the tip of the saddle? I understand these bikes are made w/ not much of extended climbing as the plan. In that case you would ride a xc 29er. I find the mtb quiver options a bit confusing and too focused on specifics.
    For me, my aperture opened up when I compared it to skiing. For a long time, skiing was what we think of now as XC with a free heel. Lift served terrain changed everything. Heck, even XC bifurcated.

    Having lift served (all be it very short vertical) in my backyard changed everything. Including how I ride the trails that are not lift served. These days, skiing means a lot lot more than a heal that's not attached to the ski and MTB means a whole lot more than XC bikes.
     

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    Default Re: modern geometry / seat tube angle

    It is worth mentioning that different bike manufacturers measure STA different ways. Because the seat tube is very rarely straight on a modern FS bike, different manufacturers might both say 75* STA, but when you look at the way they’re measured, they are completely different bikes.

    I’ve been on a Hightower LT for a couple of years now for my “brappy bike” and I really like it. Admittedly it doesn’t climb like a classic geometry steel hard tail... but the difference on the descent is night and day. The Hightower is point and shoot... and hang on. I have to be much more careful about getting weight back on the older bike.

    On the Stravaaaaa.... my uphill times are pretty much the same, but downhill, the new school bikes are ahead by a landslide.
     

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by Lionel View Post
    So with a 77deg STA your knees are much farther forward. I know that I am pretty sensitive the knee position and really not sure that I could pedal a 77STA for a long time without pain.
    This is something that I want to learn more about because I'm curious about it. Again, let's disregard the STA because it's inconsequential to where the saddle is placed. I understand you're tall, and am assuming that your bikes have ~100mm of saddle setback. At its essence, the saddle has a radial relationship with the BB center. In a very general sense, fitting a TT bike is like taking a road bike position and rotating it forward around the BB. The saddle is forward, the bars are forward and lower. Hip angle is generally similar. Do people who spend a lot of time on TT bikes have more knee problems than those who don't? I legitimately don't know the answer to that, so anyone with experience, please chime in.

    Fitting yourself to a new-school MTB is similar. You're essentially rotating forward from the BB but your hip angle opens up a bit as there's no real incentive to drop your bars. So this leads me to question WHY your knees hurt. The 4° difference in STA is relative to the ground, but inclination is changing all the time, hopefully a great deal more than 4°. It makes me wonder if knee pain would be more likely if you maintain a static bar position and get cramped on the bike rather than a new bike with a longer F-C, longer Reach and forward saddle to preserve your saddle to bar distance.

    I don't want to imply that my experience will be the same as anyone else. I have pretty bad arthritis in my left knee, and have had a minor meniscus tear for 16 years because apparently there isn't enough material to scope it out. It's also lead to a popliteal cyst about the size of a golf ball. That's a long way of saying that I have an extremely sensitive left knee. I noticed that if I moved the saddle more than 5mm from my happy place on my old bike - BAM! Crippling knee pain for 4-7 days. On the new bike (see geo comparisons above) the saddle is much farther forward compared to the old one, but my saddle to bar distance is preserved and my knee hasn't been any worse.
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: modern geometry / seat tube angle

    Modern mountain bike trail bikes aren’t road bikes anymore.
    Don’t try to make them road bikes.
    Get a pair of modern trail clipless shoes where you can slam the cleats all the way back in the slots. You’ll need to do that anyway if you want to be able to descend with any conviction(or bloodflow to your calves).

    If you live in a place where all the mtb trails are smooth and fast and rolling and you want to be able to replicate your road bike fit, the options for gravel bikes are nearly endless.
    Most gravel bikes have nearly identical geometry to xc hardtails from 10 years ago.

    Most modern trail bikes make non-technical riding boring, to say the least.
    I doubt the industry will ever go back to mountain bikes that have the same capabilities as gravel bikes.
     

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    Default Re: modern geometry / seat tube angle

    Quote Originally Posted by suspectdevice View Post
    Modern mountain bike trail bikes aren’t road bikes anymore.
    Don’t try to make them road bikes.
    Get a pair of modern trail clipless shoes where you can slam the cleats all the way back in the slots. You’ll need to do that anyway if you want to be able to descend with any conviction(or bloodflow to your calves).

    If you live in a place where all the mtb trails are smooth and fast and rolling and you want to be able to replicate your road bike fit, the options for gravel bikes are nearly endless.
    Most gravel bikes have nearly identical geometry to xc hardtails from 10 years ago.

    Most modern trail bikes make non-technical riding boring, to say the least.
    I doubt the industry will ever go back to mountain bikes that have the same capabilities as gravel bikes.
    It's interesting, I recently read a bunch of reviews on the Ripley v4, The Yeti SB130, new Trek Fuel EX. I think these bikes fall into the "very modern" geo with super slack HTA and super steep STA, 2cm stems, 820mm bars etc... All the reviewers are commenting on how "great" these bikes are at climbing or rolling. What you are describing about seems to make more sense. I will try to ride the new Ripley one of these days.
     

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    Default Re: modern geometry / seat tube angle

    Some great information in this thread. It's that time of year (getting colder) when I drag my old school geometry Turner Sultan out of the shed and start riding it again. I would really like a new bike but also wonder about all the geometry changes. My biggest hang up is the bottom bracket height of everything new seems really low. We have a lot of rocky technical single track and I don't want to be smashing my pedals all the time.
    I rode with a friend yesterday who upgraded his 10 year old Specialized Epic to a new Santa Cruz Tallboy 4. He really likes the bike and said it makes technical terrain much easier but, he did get a lot of pedal strikes on the rocks.
    Dan Bare

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