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Because a longer travel, higher sag (>30%) bike sinks further into its travel than a 100-120mm bike at 20% sag.


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This.
Once sagged, all the good modern bikes, XC to Enduro, end up with very nearly identical seat tube angles.

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I'm on a Trance 29 and love it, but the seat tube angle is "effective" seat tube angle. It's the angle from the BB to the top of the seat tube which is a tube with a bend in it. The angle from there to the seat itself is much slacker. The longer your legs, and the higher you have your seat, the slacker the "effective" angle becomes. I suppose there must be seat tubes that are straight lines so the angle is the actual angle. It remains the same as the seat is raised.
The "seat tube angle" can be a bit of an inconsistent measure, so I'm just not sure how important that particular bit of data is. It's not important to me, but I have a friend who has really long legs in proportion to his torso. For someone like him, the way in which the angle is measured may be more important than the angle itself.
There are enough nuances to bike design that I don't really look at these measurements as being very helpful, at least individually, in picking out a bike.
 

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Can't wait for the 90+ degree seat tube angles on future bikes! Sure, pedalling on flat ground is nearly impossible, but those 70% grades will be a piece of cake.

On a more serious note, it seems like a lot of ultra-modern geometry for trail/Enduro bikes is built around the assumption that you're either climbing or descending, with literally nothing in between. Let's make the seat angle super steep so climbing is good, then the dropper gets it out of the way for descents. Who needs to be comfortable when pedalling on level ground for long periods? This is mountain biking!

My arms/hands get a bit numb on 30-40mile rides on my XC Hardtail, with 74 degree seat tube angles. SE Michigan so there's not a lot of major elevation changes. Mostly flat with some short punchy climbs. I don't think my arms would last with an 80 degree ST...
 

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My arms/hands get a bit numb on 30-40mile rides on my XC Hardtail, with 74 degree seat tube angles. SE Michigan so there's not a lot of major elevation changes. Mostly flat with some short punchy climbs. I don't think my arms would last with an 80 degree ST...
Yep. My hands would hurt on my hardtail (GG Pedal head) with a 74.5° STA too. My FS bikes with 76° STA's are much more comfortable with less pressure on my hands. 74° is kinda steep for an XC hardtail. As mentioned the STA with no context is a useless number.
 

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Trail Ninja
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That could just be mere correlation, regarding STA and excessive pressure on the hands. I have excess pressure on my hands riding one 75 degree STA bike, and none riding another 75 STA bike. One's a bikesdirect AM FS with crap geo (excessively long CS) and pedal-assist, and another is a high-end enduro bike with very short CS (Jekyll 27.5), both with gravity casing tires. Guess which one has more hand pressure issues? I'll give you a hint, it's the one that has plenty of weight on the front wheel from the long CS + short front end and has me pushing away from the bars.

Bikes with steep STA put more weight on the front. Bikes with long CS put more weight on the front, moreso if you size down on these bikes. It's a combo of many issues, including the seat-to-grip drop difference and spine-angle + pelvic tilt.

The true root cause is the strategy you use to carry your upper body weight. Lots of muscles are involved in carrying this burden. The neck can get exhausted enough to have you staring at the ground instead of focusing aghead. An adult head weighs about 11 lbs by itself. Add another 2.5 lbs for a FF helmet, and maybe another 1/2 lb for goggles and 1/2 lb for GoPro. For example: tilt your body forward to look at your screen and rest some weight on your arms and elbows right now, then take note of the pressure. If you're sitting, maybe rest your elbows on your quads. Now let your upper body fall limp like if you were going to sleep, but catch that weight with your arms. There should be a lot more pressure on the arms as a result. The point of this exercise is to show that there are a lot of muscles besides the arms supporting the weight of the upper body. The lower back is generally one that tires out quickly on a long ride and feels painful, which then leaves its burden to the butt and arms to carry the weight that it used to be responsible for. Actively managing this strategy to split the burden can manage to extend your endurance without pain.

I personally fixed my problem by getting a comfier saddle on relying on it more to carry the load of my upper body weight, leaving less burden for my arms and core.

As an aside, the comfy saddle strategy fit my style of heavy-feet and light-hands. I noticed that a huge difference between slack STA and my 83° STA bike was that I would tend to "plop" into the seat on a slack STA bike like it were a couch. It took enough effort to get out of the saddle to be reluctant to do it. Combined with long crank arms, I was encouraged to drop a lot of weight on the saddle and sort of uncouple my legs from my upper body, in order to allow it to spin more freely. I could allow everything under my pelvis to sort of work subconsciously like a motor, and use my shifter to keep it efficient, turning my focus to my upper body control. On my 83° bike, I wanted to emulate a similar style of pedaling, where I can let the legs spin without holding carrying the weight of my upper body, but allowing me to put weight into pedal strokes. Enter mega short crankarms. They turned the spin motion into a stair climb motion. If I plopped my weight on the saddle, I would be moving my legs up and down like a set of pistons. It made me conscious of the weight of my shoes and kneepads. It felt a lot better hammering out of the saddle--it was a lot easier to find the "sweet spot height" to keep my hips in order to sprint out-of-the-saddle without my upper body bobbing up and down and without needing to rock the bike side-to-side excessively. Anyways, I think the bike world is way too conservative. Lots of different paths to explore, but people keep wanting something familiar and blaming/hating things they don't understand, being afraid of failures rather than seeing them as a way to learn.
 
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Unpredictable
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I'm on a Trance 29 and love it, but the seat tube angle is "effective" seat tube angle. It's the angle from the BB to the top of the seat tube which is a tube with a bend in it. The angle from there to the seat itself is much slacker. The longer your legs, and the higher you have your seat, the slacker the "effective" angle becomes. I suppose there must be seat tubes that are straight lines so the angle is the actual angle. It remains the same as the seat is raised.
The "seat tube angle" can be a bit of an inconsistent measure, so I'm just not sure how important that particular bit of data is. It's not important to me, but I have a friend who has really long legs in proportion to his torso. For someone like him, the way in which the angle is measured may be more important than the angle itself.
There are enough nuances to bike design that I don't really look at these measurements as being very helpful, at least individually, in picking out a bike.
Wow it took a very long time for anyone to see this and state it. The "real" STA is the line from the top of the seat tube straight down to the CS, not to the BB. 76 degrees on one bike may have you way behind 75 degrees on another. If that line is just inside the inner edge of the rear rim, it's a good STA for climbing and general riding. Some steeper STAs are way farther back. Seat tube angles like statistics can confuse.
 

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Wow it took a very long time for anyone to see this and state it. The "real" STA is the line from the top of the seat tube straight down
Then the "real" seat tube angle would always be 90°. You could express it as a horizontal distance from some point but that would depend on saddle height...so you can see why traditionally (when effective STA equaled actual STA) they used angle from the BB. Even if you expressed it as a distance or distance ratio, it's still going to change with sag so the 'real real' seat position would have to be expressed as a horizontal distance at sag but... even still, different height and weight riders will cause the bike of a give leverage rate to sag in different ways on different grades so the 'real real real' seat position will need to include all of that. You could express the seat position as a formula that no one could understand or you know, use seat tube angle. It would be nice if manufactures used a stand method of calculating effective STA. Santa Cruz has started listing different effective STA's for each size to give a bit more realistic idea of what to expect.
 

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Discussion Starter · #28 ·
Santa Cruz has started listing different effective STA's for each size to give a bit more realistic idea of what to expect
So how does that work out? Smaller sizes have steeper effective STA's? If so, would that correlate to every bike design or just SC (the smaller the frame, the slightly steeper the STA).
 

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So how does that work out? Smaller sizes have steeper effective STA's? If so, would that correlate to every bike design or just SC (the smaller the frame, the slightly steeper the STA).
Yeah the smaller sizes have a steeper effective STA. Typically across brands, the actual STA is slacker so the higher the seat the slacker the effective STA.
 

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My 110/130mm bike has a (measured) seat tube angle of 72 degrees since I use a setback seat post. One day I went backwards up an enduro line and was able to climb grades that were as steep as my rear tire would give traction. All I had to do was flatten my back, which is easy because it's a natural climbing position that helps engage the glutes. All this 77+ deg sta brouhaha is utterly ridiculous. I can see a few more degrees for longer travel bikes. iirc my 160mm bike has a 75 sta, climbs fine. I find a consistent (flat curve) antisquat is a far more important value to have for steep or technical climbing.
 

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You guys making it sound like the saddle is fixed onto the seapost and can't be moved. 😁
 

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Elitest thrill junkie
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Are you a wizard?
 

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I was kidding.
I was also aboard the “just kidding” train :).

That said, actual seat tube angles make a big difference. My bike has an advertised 76 degree effective seat tube angle. But the “actual” seat tube angle is something like 67 degrees. I’ve got a pretty long inseam (~35in), and super short chainstays on this bike (425mm).

And my local trail system has some really steep climbs (measured at 32%grade on one of them). And the front end most definitely gets light on those.

I think I could definitely use a steeper seat tube angle on those climbs, but I’d like to try one first.

Another thing I’ve not heard discussed here though is the effect of stack height in regards to hand pain. If you have hand pain because of a steeper seat tube angle, then increasing the effective stack height should help that issue.
 

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I was also aboard the “just kidding” train :).

That said, actual seat tube angles make a big difference. My bike has an advertised 76 degree effective seat tube angle. But the “actual” seat tube angle is something like 67 degrees. I’ve got a pretty long inseam (~35in), and super short chainstays on this bike (425mm).

And my local trail system has some really steep climbs (measured at 32%grade on one of them). And the front end most definitely gets light on those.

I think I could definitely use a steeper seat tube angle on those climbs, but I’d like to try one first.

Another thing I’ve not heard discussed here though is the effect of stack height in regards to hand pain. If you have hand pain because of a steeper seat tube angle, then increasing the effective stack height should help that issue.
People have tried that. Moving the saddle forward 20mm plus adding height to the handlebar will give you a hunchback seated position. If you raise the handlebar with spacers...that'll will effectively shorten the cockpit even more.
 

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Can't just steepen the STA on old-school-style bikes and expect good results. Bikes with short wheelbase need the slacker STA. It pairs naturally with long CS for comfort, with much of the wheelbase reduction coming from a steep HTA and short fork. It promotes a riding style that spends the vast majority of the time pedaling in the saddle.

Steepening the STA is the right call when combined with longer reach and longer wheelbase (when much of the wheelbase gain is from a slacker HA). It makes for a bike that can handle gravity, yet still climb. It pairs naturally with a short CS and a riding style that gets out of the saddle more.
 
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