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  1. #26
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    Quote Originally Posted by busdriver1959 View Post
    The part that confused me and some others was the change in seat tube angle without the seat following it. I think most would use seat tube angle to put your butt where it needs to be with the seat roughly centered on the rails. Reach is achieved with top tube and stem length. Changing reach with ST angle is a little bit backwards.
    Hmm....

    I was just saying as a result of changing the ST angle, I was told by Sam at Singular Cycles that the effective reach would also change so long as my saddle position remained the same as it is on my current set up. I know how reach is achieved, but for me changing the reach is not the ultimate goal by changing the seat tube angle. Although, I do see it as an advantage.

    Right now, I can't adjust the saddle to middle of the rails (and sit in the middle of the saddle where it's comfy) without feeling pushed too far over the crank and too much of my upper body weight on the handlebars. Changing the reach isn't going to solve that. Changing the ST angle would. Yes, I need an inch off the reach, but more on that in a minute.

    Here's the article by Grant Peterson I read: https://www.google.com/url?sa=t&rct=...57967247,d.eW0

    Another thing, as frame sizes start getting smaller in reach/ETT, they almost always get shorter in height, as well. For me, that's a problem because of my leg length. It forces me to resort to more awkward methods of getting the handlebars up to saddle height. You know, like lots of headset spacers, or extreme rise on the stem, or a really tall quill stem.....like the Nitto Technomic. All well and good, I suppose. Many people do that, but it's kind of a weird way to do it, IMO. It just looks strange. But, it seems someone like me is forced to do that because there's no choice due to off the shelf frame designs.

    I would just like to be able to use normal equipment like what most people use to get a good fit. Normal seat post set back, normal/middle of the rail saddle adjustment, normal length/height stem, normal handlebars.....meaning more options that just compact bars with really short reach, no huge stack of spacers, no stem that reaches skyward, and no seat post that looks like it was bent in a wreck and costs $90 unless I can find a great deal on ebay. Even then, good luck finding one to fit a vintage frame.

    In the end, my original question was if there would be a problem having a more slack ST angle and steeper head tube angle. And, it doesn't seem that there is.

  2. #27
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by unterhausen View Post
    the seat tube angle isn't all that important except in its role in fit and weight distribution. Small frames are always a compromise, pay no attention to them unless you want to design a small frame.
    +1 this.

    And once the frame is smaller than about 50cm, you should really consider using smaller wheels rather than tweaking the geometry.

  3. #28
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    Quote Originally Posted by thook View Post
    I don't think comfort exclusively means raising the handlebars. I already have them at saddle height as it is. I really believe my problem has been weight distribution. When I move back on the saddle end, the weight comes off of my hands a great deal. Of course, it will.
    OK. You are on a performance bike, not a comfort bike, so no you are not trying to go easy chair on us.

    Why are you trying to get your weight off your hands? Are you just getting hand sensitivity? If so I wouldn't blow my fit for that, I would approach it directly. And also through fitness. Do you cycle braced arms, or do you have a lot of elasticity in your torso. Anyway, weird conditions either count for custom approaches (pro fitting), or as you are doing a lot of noodling to figure out what you need.

    If the saddle position relative to the BB doesn't change, yet you tip the ST back while the HT angle remains a constant, the top tube is going to move backwards latitudinal thereby drawing the handlebars backwards towards the rider.
    I hear you. We design in a different way than that. We place the parts in space, and make adjustments that move only one thing at a time. with what you are suggesting everything would be moving around at once. But I hear what you are saying.


    Grant Peterson explained in the article I mentioned that when you change the angle even by one degree, at a certain height....I don't remember that height, either.....but, it was right about where I do have my saddle height currently...... reach has effectively changed by one cm. Is he correct? I assumed he would be since he designs frames. I guess that's what I've been going by. And, it's probably why most of his frames have a slack seat tube. Even with small ones.
    Yeah, 1 cm is .4" as I mentioned, I don't know what length you are talking about, but it sure sounds ballpark. One thing is that traditionally frames had like 56 cm ST, and 56 cm TT. If in that circumstance you tipped the ST back, you would pull the bars back also. But normally the seat moves back at the same time, so reach doesn't change. If you keep the seat in the same place your balance won't change.

    The fixed tube length way of building bicycles never worked for me because we have cad and frame jigs, and they all work from the discrete changes method. I wonder at times about these traditions, whereby larger frames have short TTs, relatively, etc... In some cases the market wants some fixed number on wheel base, but doesn't make sense to me.



    Lastly, I read somewhere (not by Mr. Peterson or Sam) that a change in HT angle wouldn't change reach much. Atleast, not compared to a change in seat tube angle. Something about the angles' point of origin starting from different horizontal planes? Man, that was a while back. I'm probably totally wrong about that.

    Edit: Well, when I look up there at that frame chart, I guess I was right. They do have different points of origin.
    I agree with that, I never said it was a lot, just that I didn't understand how it got to be shorter, which I now sorta get, though I am unclear as to your whole balance angle thinking in practice. At least we are drawing our lines the same way.

  4. #29
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    I don't know why GP is setting his frame geometry slacker, but one reason is if you like the old leather seats, they were design around lower st angles.

  5. #30
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    Quote Originally Posted by Canaboo View Post
    I made this bamboo frame with a ridiculously laid back seat tube to prove a point and made the HT steeper to compensate for the old steel fork that has an almost chopper like rake to it.
    When the seat is moved into the into the right position it's hard to really notice any quirks in handling etc. because of those features.
    It does seem like there is considerable leeway in a frame geometry that can be compensated for by what you actually mount on the frame as far as the fork and seat go.
    Making a steeper HT to compensate for a lot of rake seems contrary to my understanding. More rake= faster handling, more HA = faster handling. Am I missing something here?

  6. #31
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    Quote Originally Posted by JohnDThompson View Post
    +1 this.

    And once the frame is smaller than about 50cm, you should really consider using smaller wheels rather than tweaking the geometry.
    I definitely understand what you're saying there with frames that small. It does make a lot of sense. At 5'7, I don't believe I'll need to go less than 53cm on the TT. 54cm C-C on the ST is ideal for me on a horizontal TT. Nevertheless, it's funny you should say that because I'd actually like to go with something smaller than 700c, anyway. Most likely 650a or b.
    Last edited by thook; 12-12-13 at 11:17 PM.

  7. #32
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    Quote Originally Posted by Fred Smedley View Post
    Making a steeper HT to compensate for a lot of rake seems contrary to my understanding. More rake= faster handling, more HA = faster handling. Am I missing something here?
    I could be wrong, but the consequent amount of trail when wheel diameter is factored in might have something do with it.

    Am I right or am I wrong? Anyone?

  8. #33
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    Quote Originally Posted by MassiveD View Post
    I don't know why GP is setting his frame geometry slacker, but one reason is if you like the old leather seats, they were design around lower st angles.
    Yeah, I read a lot of leather saddles have a very limited amount of rearward rail adjustment. Brook's in particular. Selle Anatomica addressed it with really long rails. I think they're oogily, myself.

  9. #34
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    Quote Originally Posted by MassiveD View Post
    OK. You are on a performance bike, not a comfort bike, so no you are not trying to go easy chair on us.

    Why are you trying to get your weight off your hands? Are you just getting hand sensitivity? If so I wouldn't blow my fit for that, I would approach it directly. And also through fitness. Do you cycle braced arms, or do you have a lot of elasticity in your torso. Anyway, weird conditions either count for custom approaches (pro fitting), or as you are doing a lot of noodling to figure out what you need.



    I hear you. We design in a different way than that. We place the parts in space, and make adjustments that move only one thing at a time. with what you are suggesting everything would be moving around at once. But I hear what you are saying.




    Yeah, 1 cm is .4" as I mentioned, I don't know what length you are talking about, but it sure sounds ballpark. One thing is that traditionally frames had like 56 cm ST, and 56 cm TT. If in that circumstance you tipped the ST back, you would pull the bars back also. But normally the seat moves back at the same time, so reach doesn't change. If you keep the seat in the same place your balance won't change.

    The fixed tube length way of building bicycles never worked for me because we have cad and frame jigs, and they all work from the discrete changes method. I wonder at times about these traditions, whereby larger frames have short TTs, relatively, etc... In some cases the market wants some fixed number on wheel base, but doesn't make sense to me.





    I agree with that, I never said it was a lot, just that I didn't understand how it got to be shorter, which I now sorta get, though I am unclear as to your whole balance angle thinking in practice. At least we are drawing our lines the same way.
    I'll have to reply to this another time. I'm out of it for the moment...lol!

  10. #35
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    Quote Originally Posted by thook View Post
    I could be wrong, but the consequent amount of trail when wheel diameter is factored in might have something do with it.

    Am I right or am I wrong? Anyone?
    It appears that the Bamboo bike is sporting a 50mm +- rake fork with at least a 74 degree head angle. If anything that vintage fork fork was probably from a 27" bike and now is 700c. Seems outside the bounds of what is typically desired. IMO you would be wrong, at least in this example.

  11. #36
    Andrew R Stewart Andrew R Stewart's Avatar
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    Quote Originally Posted by thook View Post
    I could be wrong, but the consequent amount of trail when wheel diameter is factored in might have something do with it.

    Am I right or am I wrong? Anyone?
    Thook- Yes and no IME. I just did a review of the last two 571 wheeled bikes and last two 520 (ft) wheeled bikes I've built WRT trail.

    571- Both bikes had virtually the same trail, 57mm and 60mm. Both bikes were very well received by their riders, and my test rides showed a nice balance between quickness and stability. One bike had 71.5* HA with 40mm rake. The other was 72* HA and 40mm rake

    520- Both bikes had almost the same trail at 45mm and 47mm. Both bikes (for the same rider) were well received but were said to be a bit quick in their handling. (Same rider got the 57mm trailed 571 wheeled bike above and liked that handling better. But there were a few other fit changes so..) I always thought that the 520 bikes I've test ridden (I sold Terry's for years back in the 1990s) were quick handling but they never really fit me well. For the record the two bikes had 72* HA and 45mm rake and 72.5* HA and 40mm rake.

    If i were to do th 520 bikes again I'd likely increase the rake to around 55-60mm. But the take away I have is that a better fitting bike always feels better handling and this out weighs the trail being just so.

    BTW the designer with the most experience with these wheel sizes, Terry (with many hundreds of bikes made and sold), uses Bill Boston's Castor angle theory. In BikeCad Castor angle is called Arctan. Bill Boston's theory was to end up with what he called neutral handling and used a Castor angle of about 9-9.5*. I find most of my bikes end up with about 10-10.5* of Castor.

    Hope this helps. Andy.

  12. #37
    Andrew R Stewart Andrew R Stewart's Avatar
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    A follow up on my above post. I mentioned that a better fitting bike handles better. perhaps I should have said that it feels better.

    When i made my first small wheel bike it was for my wife who was riding a Trek 720. The trek was a classic touring bike in the smallest size they made, 49cm. My wife had little post showing, being only 5' 1.5" tall. She used the tops of the bars almost all the time, unless she was needing to brake, then she shifted to the hoods. Obviously the bikes approx 52+cm TT length was too long a reach.

    The bike I made for her was a 600A ft wheel (the size that Bill B and Terry were using and what was available in 1986). 600A has a 540 rim diameter. This bike had a 47mm trail, 72.5*HA and a 43mm rake.

    This bike was far better handling and with the 50cm TT, the reach was far better. But what I didn't expect was my wife's down hill average speed increase. I expected the flats' speed to be maybe a touch faster and the up hill more so (now that she could use the bar's outer curves and open up her chest more as well as stand with more control). But now she was able to descend with her hands on the hoods which gave her a LOT more confidence. This confidence let her carry more speed and not feel the need to shift to the hoods and be unsteadily braking (as was the case with the Trek).

    I have seen this increase of speed/handling comfort again with others and i have felt this is because the rider is more confident and feel within their ability zone with a better fitting bike, regardless of the new bike's steering geometry (to a large degree). Andy.

  13. #38
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by thook View Post
    @Road Fan

    My current ride has a seat tube angle of 73*. The seat post has 25mm of set back and I have the saddle at the furthest backward adjustment. I still find myself on the back end of the saddle to feel balanced with the weight off my hands when I'm cruising for long periods.

    After trial, error, suffering, expense, and much web researching I finally....finally....understand that point; weight relative to BB axis. My hands and wrists used to go numb to the point I could not WAIT to get off the bike after a long ride. That was on a bigger frame, though. It's not that bad since I went to smaller one.......though, even this one is still a bit too long.

    Anyway, I've got a pretty strong core. I do a lot of lifting and handsplit my firewood atleast half of the year. Still, it's hard to hold oneself up when riding long distances if you're not balanced. After about 30 miles, I start wishing I hadn't ridden out quite so far...hahaha! Can't do anything about it right now, though. I have the frame I have. But, I have a lead on a frame with 54cm square geo and a ST angle of 72.5*. Ain't quite there for me, but it'll be better, hopefully. My current frame has a 55cm TT and I figure I need to come off about an inch of the total current reach. So, switch the 54cm frame, use an 80mm stem (current is 95mm), and possibly the only compact bar I could find with 70mm reach. My current is at 80mm's. That would come to more than an inch off, but not much. I'm not how much 1cm will make a difference. I suppose I could lower the bars a little if I feel to cramped on that theoretical set up. Right now, I have the bars at saddle height.

    Speaking of calculating, do you have a resource you like to use for that? I've use Leonard Zinn's calculator for frame fit. I'm probably gonna retake some measurements and review.

    Oh, I don't suppose you have any comments on the ST angle being slacker than the HT angle? I'm wondering since I don't see anyone doing it, there might a good reason. But, then again, maybe not.
    Pretty much the same experience, and I think the ST to HT relationships are not in general connected. ST angle affects saddle setback, and HT angle affect steering geometry and hence steering behavior.

    In order to calculate I have a leg up - being a trained and dinosaur engineer I just grab my iPhone and use the scientific calculator app I downloaded. If it was 35 years ago I'd just grab a piece of paper, a pencil, and a slide rule. Or now I might program it in Excel, but I tend not to make and save libraries of little tools like that.

    Zinn is a very smart guy and also mathematically trained. If he's got some little tools on his site, I'd guess they're good, though I have not checked them.

    As you look for frames that might help you, it's good to think of how much saddle setback you really need - looks like you don't know that, at least based on this post (#4). One saddle that is pretty good for helping to sort this out is a Selle Anatomica, due to it's extremely long saddle rails. Combined with your 25 mm setback seat post, you might just push it back a few mm at a time until you reach the kind of balance point you think will help you. Take notes on what worked and does not, and you can figure out an estimate of your target angle. It'll be useful data when you talk to a custom frame builder. Also, take before and after pics to share. Good builders will want to understand why your odd request is the right thing for him to do. The ones with a scientific background will want a good story (school of hard knocks!).

    Plus, if you find the balance and take down the numbers, I can help you with the calculations. I don't build frames, but I can run a calculator (and sometimes pedal a bike!).
    Last edited by Road Fan; 12-13-13 at 02:58 PM.

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