Seat Tube Angle Preference

[Tmogul]

How did all of you with custom frames decide upon a seat tube angle? There was a reply to dirtdigger's post about how his bike looks better with the layback post than his original thomson (purely aesthetics). Obviously you need to first set up the fore/aft position but there would still be maybe a couple degrees to play with depending on the type of post chosen right? (thomson vs easton) So assuming no wheel clearance problems (meaning no change to chainstay length/wheelbase/front center unless they will always change with STA?) how would the STA affect the ride of the bike or is this just negligible? I hear slacker STAs make for a more comfortable ride. So did you choose an angle to get the post and looks you want or for some sort of ride quality or handling difference if it exists? Thanks

[CNote]

The builders could answer your question better, I hope, but it's complicated because you must consider all the other aspects of geometry. If there were only one seatpost available with a certain amount of setback, then nailing down the STA would be more critical. I think it's mainly an issue of center of gravity. A steeper seat tube moves the center of gravity forward and a more slack seat tube moves it back. However, this isn't the only way to affect center of gravity, as it can also be altered by changing the chainstay length and/or front-center dimension. Finally, I think the builder, not the client, ultimately decides on the STA after considering everything else.

By the way, I had a slacker STA on a bike once, but it just didn't do anything for me! :banana: :banana: :banana:

[Tmogul]

I realize I need to hear from some builders who I wouldn't expect to give input until the weekend is over...hopefully. The CG would not change in my hypothetical situation because the saddle and bar never moved. This all assumes that the STA pivots at the BB and so steepening it would simply lengthen SS and decrease HT length or vice versa for slacker STA and leave everything else alone (wheelbase/reach etc). I can't see how this would not be possible to compenate for seatpost choices but then the question is does it do anything for handling or comfort. If the builders choose then do some builders make a design for straight post or setback. I realize its more complex but hey I thought I'd throw this out there.

I brought this up because I have read in other forums that slacker angles make for more comfortable ti bikes. Myth?

[woolly]

Along with a whole slew of other measurements (including current bike & setup, & several body measurements), Don Ferris wanted to know what saddle & seatpost I wanted to use on my custom Anvil Chisel. He used these to determine a seat tube angle that would allow for the saddle to be clamped in the middle of the rails. Since I had planned to use a no-offset Thomson or Syncros, he ended up making the seat tube a bit more slack than if I was planning on using a post with set-back. Beautiful.

As far as how that angle affects ride, I couldn't tell you. But my suspicion is that it's another example of inappropriately looking at one aspect/measurement in a vacuum, and there are soooo many other inter-dependent variables that make up the overall fit, handling, and ride of a bike. I find broad sweeping generalizations such as "slacker STAs make for a more comfortable ride" somewhat amusing at best.

For myself, I found the best approach to a custom (my first one, anyway)was to answer all of my builders questions as accurately as possible. Some were objective, such as body measurements, existing bike measurements, and intended component choices. Other questions were more subjective, such as "what do you like best about your current bike's fit/ride/handling", or "What changes are you looking for in fit/ride/handling?" Once the Q&A was done, I figured the next best thing I could do would be to resist as much as possible the urge to "help". I trusted my builder to figure out what tubing, geometry, etc would satisfy the objectives, and I ended up being extremely satisfied. I think of the key factors here is that I was able to articulate what I liked and did not like about my current bike - if I were not able to do this, I probably would not have pursued a custom.

Now, for my Habanero, I knew EXACTLY what I wanted, and was very specific in the specs. I was extremely satisfied with this as well, but I was not starting from a clean sheet of paper.

As always, YM (and seat tube angle) MV

- Chris

[Peter]

I think seat tube angle is not as important as it's made out to be. I also think ST angles had "settled down" at least a couple decades ago, though the numbers settled upon were based on SETBACK seatposts. Zero setback posts throw the numbers much out of whack, in my opinion, and I find it hard to imagine easily locating a similar position with a zero setback post on a frame designed around setback posts, though I haven't delved into the precise numbers to see what the differences are.

On custom frames I've owned I merely chose a common STA based on my frame size, or experimented +/- a degree. Then I'd slide the seat all the way back because that was the "Euro" thing to do! As of late I've been sliding the seat towards the middle of the range believing if I did this I would be experiencing how the framebuilder wanted the bike to handle if I was centered over the fore/aft adjustment i.e. weight distribution. I can't tell much difference, though it's seemed to address some longstanding funkiness in the way I sit on the bike and pedal.

I'm of the opinion that the seat angle can't influence ride comfort because the frame doesn't flex in the vertical plane, even with these fancy/schmancy rear ends, Serotta included. Yeah; setback posts just "look right". You might want to consider seat tube angle in regards to tire clearance, etc. though. Changes in weight distribution over the rear wheel are minimal, in my opinion. Try this experiment: Put a bathroom scale under one wheel and level the other wheel. Climb aboard the bike and record the numbers of the weight over each wheel. Then slide your seat full forward/rearward and repeat. Then ask yourself if the differences are meaningful to you.

[Dr. Doofus]

put a setback post on the raspberry pimp today just out of boredom...the seat setback is the same, 7.5cm, it just looks different...

whatever

*dead smiley*

[musgravecycles]

We use the customer's saddle and post in the build process to determine STA. In the design process we use a set up fixture to design the frame on (really nice because you can visualize what the frame will look like). We can bolt the customers actual post and saddle onto the fixture (I tend to clamp the saddle in the middle of the rails). Using a customers setback requirements with this method pretty much dictates where the STA is going to end up.

Depending on your post choice you will have a small range of adjustment where the STA will fall.

My own personal opinion on posts has changed quite a bit in the last few years. I'm not quite sure why, but when I built my current bike 5 years ago I'd fallen into the 'thomson' craze. I think it was because the post and head were one piece and thus stronger...or something like that...anyway I built the frame for a thomson post (slacker STA). Now I've come full circle and much prefer to build a bike with a campy or shimano post. It looks MUCH more balanced to my eyes. I've started working on a new bike for myself and I've got a Chorus Ti post for it. Now if I just had more time to work on my own projects...

[Tmogul]

Thanks musgravecycles,

That was exactly what I thought. I am partial to thomson contrary to you but I do see what you mean about the chorus or dura-ace posts looking less chunky. I like the thomson for strength reasons (heavy guy). Although if chorus is made of ti......I'll have to look into that. Dirtdiggers bike did look better without the thomson but then who sees the post when you're riding right? Thanks for your response and get that bike of your made. :banana:

[musgravecycles]

That was exactly what I thought. I am partial to thomson contrary to you but I do see what you mean about the chorus or dura-ace posts looking less chunky.

It's not the chunkyness that I don't like, It's the proportion of saddle hanging over the front and rear of the post when standing back to look at it. Look at the first few pics of Dirt's Legend in the thread below to see what I'm talking about. It (the saddle) just looks front heavy over the post even though it's centered on the rails (draw and imaginary line along the ST up the post and through the saddle).

http://forums.thepaceline.net/showthread.php?t=7333


I like the thomson for strength reasons (heavy guy). Although if chorus is made of ti......I'll have to look into that.

You can't really find a Chorus Ti anymore I had to look HARD to find one (I had to pay retail :crap: and got it at Cycles by Kyle if I remember correctly, might check on ebay now and then). The new Centar post is alloy though. It should be plenty strong enough, how heavy are you? I'd stay away from the Record/Chorus carbon for a big guy, but alloy should be plenty strong. The Dura-Ace post is pretty nice as well.

Dirtdiggers bike did look better without the thomson but then who sees the post when you're riding right?

For me it's not about what you can get away with, but striving for perfection. It's about trying to make that perfectly balanced, visually stunning bike. If I wasn't striving for perfection then I wouldn't have much motivation to build, and would go buy a Trek (no offense to any trek owners!). The bike is going to ride the same either way but wouldn't you want to ride a 'special' bike if you could (see the what makes a special bike special thread)?