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Frame question: Seat tube angle & climbing


June Bug
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How much difference does seat tube angle make in ease  and efficiency of climbing (grinding along climbing, not steep and technical climbing) and power to the pedal on a hardtail?  Mostly for bike touring/dirt roads/mellow single track bike packing. 

 One frame has a seat-tube angle of 73.2 degrees, and the other  75 degrees. 

Edited by June Bug
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  • June Bug changed the title to Frame question: Seat tube angle & climbing

JB, for what you're talking about in my opinion it's a lot more about the physiological relationship between seated position and the crankset - however that comes together from the combination of saddle, saddle mount, seat tube angle & length, crank length, distance from saddle to h-bars, etc. etc., in comparison to the rider's physiology.

To me that grinding along climbing is more akin to needing good pedalling position like a well fitted road bike so that the muscle effort is well balanced in the legs and torso, the upper body is in a neutral and supported position, which includes balanced front wheel pressure.

So, that 1.8d difference in seat tube is more likely accommodated by the fore-aft position of the saddle .. or just a well fitting bike.

Probably not a really helpful response, even with a lot of words.

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1 hour ago, ATXZJ said:

FS MTB the minimum for me would be 76*. IMHO, STA effects climbing more than HTA on full suspension bikes

Whatever happened to the art of just sliding your ass forward until the nose of the saddle is right up your taint? A little bob from the FS just makes it all the more rewarding! 🤣

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I used to laugh at the people that obsessed about things like seat tube angle. Then I demo’d a ripely and felt like I was over the bars. Tried an Occam and found a couple degrees of seat tube angle have a huge impact. 
 

My advice is to ride the bike. As Neil once said “numbers don’t add up to nothing”. But, then that was after he shot a guy, so your mileage may vary. Ride he bike, it will tell you if it is right or not.

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2 hours ago, throet said:

Whatever happened to the art of just sliding your ass forward until the nose of the saddle is right up your taint? A little bob from the FS just makes it all the more rewarding! 

Dude, that is so MOJO.   T'aint a full suspension,  it's a rigid hardtail and and not for super steep technical climbing and will have a fairly upright riding position. 

Anyway, the topic of my post may be a moot point because "Santa" may have ordered the HT w/ the 73.2 degree seat tube angle. We'll see what happens and I'll let y'all know.  

4 hours ago, bear said:

JB, for what you're talking about in my opinion it's a lot more about the physiological relationship between seated position and the crankset - however that comes together from the combination of saddle, saddle mount, seat tube angle & length, crank length, distance from saddle to h-bars, etc. etc., in comparison to the rider's physiology.

Hey, Bear.  Hope you and the missus are doing well!   Still in Raleigh?  This is a great reminder to get a good bike fit.  

2 hours ago, mack_turtle said:

I don't understand the question. when I am climbing, my butt is almost never on the saddle.

 Let's say you're pedaling along for 20 minutes with a relatively mellow grade or for 10 minutes or much longer on a  little steeper grade.   Seated pedaling. 

 

 

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12 hours ago, June Bug said:

Dude, that is so MOJO.   T'aint a full suspension,  it's a rigid hardtail and and not for super steep technical climbing and will have a fairly upright riding position.

Sorry about that. I was responding directly to ATXZJ's comment about needing a minimum 76 STA on a FS bike.  

12 hours ago, June Bug said:

Anyway, the topic of my post may be a moot point because "Santa" may have ordered the HT w/ the 73.2 degree seat tube angle. We'll see what happens and I'll let y'all know.  

Joking aside, I was serious about the art of climbing and how with old-school geo it was essential to scoot forward in the saddle on long, sustained climbs. When I was racing XC on my Orbea Alma HT in the Cascades, some of those races started with a 5-mi or more climb. I'd find that forward position in the saddle where there was just enough weight on the rear-wheel to maximize traction, then bring my chest down and grind. Even being far forward on the saddle, it's actually not an uncomfortable position because your bike is pointing up and your pedals are supporting your weight. I think you will be just fine with 73.2 degree STA. 

Edited by throet
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I was just noticing on my gravel bike, with it's slack seat tube angle and offset seatpost, that fitting is a package deal. the front-center of a drop-bar bike is much shorter than on a mountain bike due to the short, rigid fork and steep head tube angle, but the effective reach is must longer when you consider the forward bend of the handlebar and the way the hoods stick out. you might think that one should move the saddle forward to shorten the effective reach, but the opposite is true. shifting your saddle forward would throw off your balance and you'd slide forward on the saddle, bracing your arms to prevent that, and the result would be too much pressure on your hands. sliding the saddle back cantilevers more of your weight over the center of the bike and that's what it's all about.

I like John Weirath's approach to saddle position, which is similar to Steve Hogg's. you body weight should be mostly in the pedals. I can pedal my bike with my butt just barely touching the saddle and my hands only loosely holding the bar on both of my bikes because I figured this out. 

on a modern mountain bike with a longer fork and resulting long front-center, a steeper seat tube angle helps to center your weight between the wheels. dropper post or not, this helps you keep the front tire down without the old school "sit on the nose of your saddle" approach, which might not ever be enough on a bike with a long, long front-center. also relevant: https://www.handbuiltbicyclenews.com/c23-bicycles/328-nakeds-framebuilder-notes-on-a-prototype

If sitting on a bike with the saddle further forward doesn't work for you, you need to consider the other dimensions of the bike because forward geometry is a whole-bike deal, or the bike is just not designed for the way you are used to riding. It might also not be designed for the kind of terrain we have here, which is likely when you consider how PNW riding is fettishized everywhere. You can chose to adapt or just ride a different bike.

Edited by mack_turtle
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STA decreases with seatpost extension. Guys with long legs suffer from this the most. Combine that with the current ultra short chainstay fetish, and you've got a wheelie machine on the climbs. HTA were blamed for poor climbing the past, but having owned / ridden multiple bikes with 62-64* HTA can say it's nowhere near unmanageable.

Thankfully manufacturers are now steepening STA by quite a bit, and lengthening CS in relation to frame sizes. 

 

 

 

Edited by ATXZJ
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@mack_turtle - what he said about center of gravity between wheels - i've been telling people for years and still believe that the neutral position should be with CoG centered between wheel contact patches. So, up/down-hill, turning, whatever, gives the rider the most easy control on keeping that center based upon the dynamic conditions. There's a LOT of tolerance for moving off that when conditions are "easy" but if you have dynamic situations with lots of change then being stuck biased in one direction or the other leads to loss of control (or, rider panic and increased heart rate and blood pressure).

@June Bug - yes, we're stlll in Raleigh, probably for at least 2+ more years, ask me again in '23 who knows what will be going on. There's reasons and stuff and Adulting to be done between now and then.

And a lot of Western NC mountain biking to be done too ... and some Arkansas riding ... and if I can at least 1 more trip to ATX ... been too long already.

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14 hours ago, bear said:

@mack_turtle - what he said about center of gravity between wheels - i've been telling people for years and still believe that the neutral position should be with CoG centered between wheel contact patches.

I've seen people actually test this by putting scales under a stationary bike to see how the front and rear weight bias plays out. some say there should be about a 60/40 balance rear/front, but there's really not a single approach that suits everyone, nor is there consensus on this. it is helpful to play with wheelbase, front and rear, on bike design to change this dynamic. but as far as I am concerned, the distance between your feet and your hands and your saddle height should not change much. that leaves chainstay length and the elements that make up front-center length as variables.

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On 12/20/2021 at 7:39 AM, throet said:

Sorry about that. I was responding directly to ATXZJ's comment about needing a minimum 76 STA on a FS bike.  

Joking aside, I was serious about the art of climbing and how with old-school geo it was essential to scoot forward in the saddle on long, sustained climbs. When I was racing XC on my Orbea Alma HT in the Cascades, some of those races started with a 5-mi or more climb. I'd find that forward position in the saddle where there was just enough weight on the rear-wheel to maximize traction, then bring my chest down and grind. Even being far forward on the saddle, it's actually not an uncomfortable position because your bike is pointing up and your pedals are supporting your weight. I think you will be just fine with 73.2 degree STA. 

I much prefer the old school geometry on STA. I found the new geo put me too far forward. I dont mind scooting up on my seat. maybe those steep STA are designed for the 10 mile climbs they have in actual mountains.

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TLDR: depends on reach

"Modern" geometry (slack HTA, long reach, steep STA) is for going up and down. The long wheelbase of slack HTA long-reach bikes gives great pitch stability for steep descents, but they have to steepen the STA or the top tube will be too long for size. This puts your COG farther forward, which counters the rearward COG shift from an incline so it's good for climbing too. The trade-off is it's bad on flat ground because it puts your COG in front of the bottom bracket which puts too much weight on your arms/hands.

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