Mountain Bike Reviews Forum banner

1 - 10 of 10 Posts

·
650b me
Joined
·
1,486 Posts
Discussion Starter #1
Especially as it relates to hardtail bikes. Sure, it makes for good copy when the big manufacturers rave about how their steeper seat tube angle aids in climbing the steep stuff, but what about all other terrain? To be blunt, I'm skeptical. But then again, that's my nature with most new trends in MTB. It took me a long time to come around to dropper seatposts, but now I'm completely on board.

So, especially amongst the experienced builders out there on this forum, what are your thoughts on seat tube angles in the 76/77 degree range? I can't see (without riding one) how this could possibly be a good all-around setup.

EDIT: I should add that my most recent personal frame build inadvertently ended up with a seat tube angle of approximately 71 degrees. I say "approximately" because the seat tube is bent so it's hard to get an exact measurement off of the bike. If you believe the current hype, you would think this bike would be unrideable. But I love it, and I only ever notice the slack seat angle on the steepest of climbs. In all other terrain it feels great.
 

·
Registered
Joined
·
968 Posts
My experience (3-4 different frames with different SA). Steep terrain is better suited to steep SA.

Flatter I don't want as steep because it may not be as comfortable (too much pressure on my hands).

However, bikes are a system and chainstay length, reach, handlebar position etc etc all play a role and it's hard to break bikes down to 1 angle.

Your experience with a "slacker" seat angle actually matches what we (Little_Twin) and I have discovered recently. He built a bike that should be terrible (per the internet), but it feels really good) And, you can counteract that slack SA by having longer (440 instead of 420) chainstays.

Note, I am not an experienced frame builder but have been riding a variety of frames with different SA, thinking about how it feels, and then having the next one built with a change for a specific reason.

So, just supporting your "I am skeptical statement." I think that's a reasonable place to be.
 

·
Registered
Joined
·
3,692 Posts
If you live where it is flatter, steep seat angles are terrible. Basically, anywhere where you have a lot of traversing. I live in the SF bay area and ride the real stuff. I tend toward a 74.5 to 75 degree effective seat angle on a hardtail. On a full suspension, 76 to 76.5 degrees.

Manufacturers are doing them more everywhere as it makes bike manufacturing easier and cheaper.
 

·
650b me
Joined
·
1,486 Posts
Discussion Starter #4
I hear you guys on how the terrain that you ride matters. And Peter I agree that hardtails should dial it back a bit since the head angle can only ever get steeper, unlike full-sus bikes.

But don't we all ride trails that have flat spots, rollers, and steeps? Anyway, I'm looking for a good all-purpose frame geometry, realizing that it won't excel in all terrain.
 

·
Registered
Joined
·
214 Posts
I see this dimension being one of the most subjective to where you ride, and how you ride.

If you want to over-simplify it: Steep angles are better for steep climbing, slack angles are better for slack riding.

If you want to get into everything else that is also involved, then don't forget: does the rider climb hills mostly out of the saddle? Does the rider have a lot of traversing terrain? Do they have a dropper post? Are they on a singlespeed? All of those things factor in.

Yes, there is variation in any of the terrain we ride, but that affects everything. We just try to average out what works the best in the most scenarios for us, and go from there.

The Industry likes to tout every new feature or geometry change as being the best for everyone, but obviously that doesn't make sense. But The Industry is used to catering to consumers who for the most part know very little about the product they're buying. So they just say, "buy this, it works great" and most customers do.
 

·
Registered
Joined
·
746 Posts
On the "how you ride" side of things, foot positioning seems to be an often ignored factor for what's "optimal" for STA.

Because your feet wind up further forward relative to the seat, midfoot pedal positioning can make a bike feel like the seat angle is slacker than the numbers would suggest.
 

·
Registered
Joined
·
396 Posts
Thought I'd add my input here too....

As mentioned steeper is not always better.
If you don't change anything else, then steeper actually cramps up the cockpit of the bike very quickly.
I build my bamboo frame with an 80deg STA. (planned 79deg, but the jig settled at 80 and I ran with it).
Most of my riding is not super steep climbs or descents, its mostly relatively flat trails.
Since my reach was 500mm, it actually has a similar cockpit feel to my old alloy frame when saddle up and climbing.
The biggest difference I find is that your body position CoG is more forward and less upright, since the BB is further back under you and your hips are rotated forward slightly due to this.
Some people would hate this feeling, but where I ride mid-foot pedal position with flats it actually suits me better.
It gets very close to personal ergonomics at this point, as certain people have preferred lower back/hip angles that they prefer and find most comfortable to ride with. Saddle angle can assist/help this slightly, but not as much as you might think, as most of the body weight is actually going through the 2 sit bone pressure points.

Yes, when riding along the flats this more forward position does have the negative effect or more bodyweight through your bars\arms.
This is where compromises and personal preference should always prevail over "the latest" trends. And is also why most new geo reviews out there will state that it really rewards an aggressive rider. (read that as not the best for all round riding ;) )

Where the bike does shine is when things get faster, and steeper. So it does push me to ride a bit more aggressively. And this is what a lot of reviews of frames I took the inspiration for the geo from said. Climbing, it's really nice to be more forwards with the body position. Descending it's great when it speeds up, but can be a handful when it gets slow, steep and technical.

Octane One prone 29er L, running 160mm fork and 27.5 wheels, with 72deg STA, and 440mm reach was my comparison frame if anyone's interested.

My experience has also taught me that yes you can go too far, and I went slightly over.
As much as my bamboo bike is a nice ride, it is a bit stretched out for general riding and due to the long reach takes a lot more body language to get the front wheel up.
So even though the cockpit feels nice, it isn't as evenly balanced for slower playful riding as my alloy frame is.

The key measurements to note when looking at actual bike fit are:
1: saddle to grips (at climbing height)
2: BB to Grips
3: hip angle
Hip angle is the one that is dependant on personal measurements, torso length, and arm length. And also crank length, and leg proportions.
There are a lot of bike ergonomics studys you can find regarding road, but not that many about for MTB.

So horses for courses, take inspiration from other frames geometry. But do read the reviews and you should be able to take a rough judgement and find something that is right for you.
 

·
Registered
Joined
·
70 Posts
Especially as it relates to hardtail bikes. Sure, it makes for good copy when the big manufacturers rave about how their steeper seat tube angle aids in climbing the steep stuff, but what about all other terrain? To be blunt, I'm skeptical. But then again, that's my nature with most new trends in MTB. It took me a long time to come around to dropper seatposts, but now I'm completely on board.
I'm a rider who has lived through the last 30 years of MTB development, still own my 1990 hardtail alongside a 2020 'Enduro' full suspension bike. Looking at STA in isolation from chain stay length, reach and stack is just a nonsense, regardless of the terrain/riding style the bike is designed for. Change any one number and you have to change many others to end up with a bike that rides nicely.
The steeper STA lets you lengthen the wheelbase while keeping your seated weight centred, so you can weight your front wheel through corners despite the HTA being slacked out. Because you have lengthened the wheelbase, the bike is also a more confident descender.
 

·
Registered
Joined
·
101 Posts
I'm not a frame builder but I can tell you that my l45 disk is disintegrating and my bike with 77 sta helps it and my bike with 74 probably actually hurts it.
 

·
Registered
Joined
·
19 Posts
An experiment with steep seat tube angles on a recent gravel project proved to be a winner. Works just as nicely as it does In mountain bikes.

1918045
 
1 - 10 of 10 Posts
Top