Help me understand ST angles

[BdaGhisallo]

Originally Posted by Mark McM

Only the builder of the frame (who has to cut the tubes to length) needs to worry about the length of the top tube. The people who have to use the frame (or to fit the frame to the user) only need to be concerned with REACH (horizontal distance between BB and head tube) and STA.

Have a gander back at the OP's original post.

He referenced top tube lengths and STAs. It doesn't appear that he had the relevant reach numbers on hand for what he needed or for the frame he was looking at.

Without the understanding of STAs and how they affect frame reach, when the top tube length is fixed, that his friend brought to light, he would have ended up with a frame that didn't fit him so well.

[benb]

Originally Posted by BdaGhisallo

Have a gander back at the OP's original post.

He referenced top tube lengths and STAs. It doesn't appear that he had the relevant reach numbers on hand for what he needed or for the frame he was looking at.

Without the understanding of STAs and how they affect frame reach when the top tube length is fixed that his friend brought to light, he would have ended up with a frame that didn't fit him so well.

That's the whole takeaway of the thread.

If anyone is confused and thinks ETT & STA can only be changed exclusively of each other they need to learn that's not true. If they adjust one # they will adjust the other accordingly. Assuming it's a good bike builder.

[fourflys]

I think maybe part of the discussion is that, over the last few years, we've been told over and over again that stack and reach are the end all/be all for figuring out if a bike will fit you.. and many of us might be in a part of our life where we want a taller stack and short enough reach.. so if you are looking at a bike with a stack you like and the reach just barely works, you may not realize if the bike has a slacker seat tube that will effectively cause a longer stretch to the hoods, assuming you have the saddle where you want it, which, as others have said, is often farther back for folks who sit more upright/has less or no bar drop (those of us who can't ride 250 miles a week due to family and work commitments).. maybe I'm misinterpreting what I've read over the last few pages, but..

certainly this thread has schooled me up on STA and how it interacts with the other aspects.. and I'm certain a custom builder would take all of that into account and adjust each metric to work with the others.. but I'm not convinced all off-the-shelf bikes have that factored in since many, many still think we all need/want to ride a bike that's long and low like the pros..

I think a much better measure than reach as described in this thread is the actual reach from a known point on the saddle (I like to use 120mm from the rear to account for different saddle lengths) to the middle of the bars (or you could hoods as well, or both).. that way, assuming your saddle is in a good spot, you can see if the new bike can replicate that placement.. at least that makes sense in my head..

[Mark McM]

Originally Posted by fourflys

I think maybe part of the discussion is that, over the last few years, we've been told over and over again that stack and reach are the end all/be all for figuring out if a bike will fit you.. and many of us might be in a part of our life where we want a taller stack and short enough reach.. so if you are looking at a bike with a stack you like and the reach just barely works, you may not realize if the bike has a slacker seat tube that will effectively cause a longer stretch to the hoods, assuming you have the saddle where you want it, which, as others have said, is often farther back for folks who sit more upright/has less or no bar drop (those of us who can't ride 250 miles a week due to family and work commitments).. maybe I'm misinterpreting what I've read over the last few pages, but..

If the saddle is where you want it, than any frame with the same Stack & Reach will fit the same. The STA won't affect the reach the handlebar, it only affects the seat post offset and saddle rail position required to get the saddle where you want.

Originally Posted by fourflys

I think a much better measure than reach as described in this thread is the actual reach from a known point on the saddle (I like to use 120mm from the rear to account for different saddle lengths) to the middle of the bars (or you could hoods as well, or both).. that way, assuming your saddle is in a good spot, you can see if the new bike can replicate that placement.. at least that makes sense in my head..

You can't really describe a frame size with respect to a saddle, because there are a variety of saddles that can be fitted to any given frame, and the saddle can be at a variety of different heights and setbacks, not to mention that a rider may be shifted forward and back by how they sit on the saddle.

Bikes have a variety of different dimensions - heights, lengths, angles, offsets, etc. that all affect fit. The Stack & Reach system simplifies finding a frame that fits by breaking it down to a 3 step process:

1. First get a fitting to find the best contact points for good fit and handling. This will define the saddle and handlebar positions with respect to the fixed point of the bottom bracket.
   
2. Second find the Stack & Reach that accommodates the handlebar position found from above fitting.
   
3. Finally, determine the STA (or range of STAs) that allows the desired saddle setback for the saddle position from step one.

[Wakatel_Luum]

Originally Posted by vespasianus

His long femur length is legendary and his slack seat angles are one of the reasons why some people did not get along with his line of bikes.

Greg says in his 'Cafe' ride on youtube that he was too far back then and no longer uses 175mm cranks so his opinion has 'relaxed' in that ideal.

[Wakatel_Luum]

Originally Posted by Nomadmax

But if you set the saddles to the same height/set back on both frames, won't it be the same?

What I mean to say is that on a frame with slacker STA you'll have to move the saddle forward to get the same setback relative to the BB.

The issue I found is when bike companies do not list the TT length there is no way to establish whether the bike can fit you. Stack and reach is too limiting, STA is not so much an issue but the idea that you can choose a frame size with only Stack/Reach I find impossible.

Factor Bikes do this and I cannot work out a frame size out that would be appropriate...

[BdaGhisallo]

Originally Posted by Wakatel_Luum

Greg says in his 'Cafe' ride on youtube that he was too far back then and no longer uses 175mm cranks so his opinion has 'relaxed' in that ideal.

It was Cyrille Guimard who put Greg in that position. Greg had to raise his saddle an inch and a half when he turned pro with Renault and Guimard changed his position.

[MikeD]

Originally Posted by Wakatel_Luum

Greg says in his 'Cafe' ride on youtube that he was too far back then and no longer uses 175mm cranks so his opinion has 'relaxed' in that ideal.

That's interesting. I used that position when I first started cycling and the result was I experienced hamstring pain. I now use the saddle setback position that resulted from a Retul bike fit, which moved my saddle forward more.

[Mark McM]

Originally Posted by Wakatel_Luum

The issue I found is when bike companies do not list the TT length there is no way to establish whether the bike can fit you. Stack and reach is too limiting, STA is not so much an issue but the idea that you can choose a frame size with only Stack/Reach I find impossible.

Factor Bikes do this and I cannot work out a frame size out that would be appropriate...

Please explain what TT length can tell you that Stack & Reach cannot (no credit given if you don't show your math).

[Dave]

Originally Posted by Wakatel_Luum

The issue I found is when bike companies do not list the TT length there is no way to establish whether the bike can fit you. Stack and reach is too limiting, STA is not so much an issue but the idea that you can choose a frame size with only Stack/Reach I find impossible.

Factor Bikes do this and I cannot work out a frame size out that would be appropriate...

I've bought 6 frames using only stack and reach and they fit just as expected. You're doing something wrong. STA only affects the seatpost setback that I choose. None of the frames varied enough to use anything but my normal 25mm. All also used 110mm stems, but one used a -17 and the others use -6 to -8 with no choice of angle.

The ostro vam in a 52 would fit me perfectly. I see nothing particularly unusual.

[Wakatel_Luum]

Originally Posted by Mark McM

Please explain what TT length can tell you that Stack & Reach cannot (no credit given if you don't show your math).

I am 179cm tall, I require a TT of at least 56cm CTC and a ST length of approximately 52-53cm CTT with a sloping TT. I use a 120mm stem currently with a drop from the saddle to the top of my handlebars at about 130mm.

I have a long upper body with shorter legs. The reach on the Factor Bikes geometry chart for example does not provide a TT length which I require. A ST/HT angle slight variation is fine. Reach only provides a portion of the space I require to feel comfortable on a bike otherwise I have to compensate with a longer or shorter stem..

[fa63]

If ETT is important, calculating it is simple trigonometry if you know the frame reach/stack and the STA.

[slowpoke]

Originally Posted by fourflys

I think maybe part of the discussion is that, over the last few years, we've been told over and over again that stack and reach are the end all/be all for figuring out if a bike will fit you..

I don't think anyone is saying all you need is stack and reach. They're good replacements for top tube and seat tube length, but you still want to know the STA and HTA (and BB drop/height, and fork offset, and chainstay length...).

[bob59]

BdaGhisallo Pal - you nailed it, thank you.....all the extra discussion has been en-lighting. ....thanks again to my Pal who alerted me to the 72'STA - I was a deer in the headlights when I saw 54.5TT with a tall HT Kirk, interesting it is still for sale. ....this place is great, thank you PL.

I hope by the time I have enough nickels saved, DK will still be buildings frames.

[BdaGhisallo]

Originally Posted by bob59

BdaGhisallo Pal - you nailed it, thank you.....all the extra discussion has been en-lighting. ....thanks again to my Pal who alerted me to the 72'STA - I was a deer in the headlights when I saw 54.5TT with a tall HT Kirk, interesting it is still for sale. ....this place is great, thank you PL.

I hope by the time I have enough nickels saved, DK will still be buildings frames.

Cheers.


A really easy way to understand the effect of STA on things is to assume a fixed top tube length and compare two hypothetical frames - one with a STA of 45 degrees and one with a STA of 90 degrees.

Those two frames will have very different sizing and will fit very, very differently, with the front wheels ending up in very distinct places.

Once the lightbulb has gone off on this understanding, you'll never think of frame geometry the same again.