|Head tube angle's effect on reach?||swvegg|
Dec 28, 2003 2:43 PM
|Say two bikes have the bars at the same height, have the same top tube length, same seat angle, etc. basically same geometery, aside from the head tube angle. What would be the difference in reach, with everything set up the same, of a bike with a 72¢ª HTA and a bike with a 73¢ª HTA? (In mm, please)|
|those were supposed to be degree signs||swvegg|
Dec 28, 2003 2:44 PM
|Got screwed up.|
|how many spacers?||cyclopathic|
Dec 28, 2003 3:04 PM
|but even then if TT length is identical, the difference will be less then ~1mm. Problem is diff mfg have diff way of measuring TT length|
|how many spacers?||swvegg|
Dec 28, 2003 3:06 PM
|between 1.5 and 0 cm of spacers.|
Dec 28, 2003 3:27 PM
|with 80-100mm (including headset, stem, spacers and top of head tube) you'd be 1-1.5mm off. Ignore, if bike is from same mfg/builder. However the way diff builders measure TT may account well over 1/2"|
|re: Head tube angle's effect on reach?||e-RICHIE|
Dec 28, 2003 4:09 PM
|one degree could yield a 1cm diff in overall reach.
Dec 28, 2003 5:16 PM
|This is simple trig. The distance from the center of the top tube to the center of the stem would rarely exceed 10cm. The difference in reach would be 10 x (sin1)= .17cm.
More often the amount is 1mm or less.
|hey genius......||Arnold Zefal|
Dec 28, 2003 6:10 PM
|I'm guessing that Richard Sachs may have a little more practical experiance in frame dimensions then you. You may may be the "fit guru" on the internet, but I know that boy has actually cobbled a few of these things together in the real world.|
|no genius required....||C-40|
Dec 28, 2003 6:44 PM
|Well, you don't need to be a genius to solve a simple high school level trig problem. If you're so smart, prove me wrong. The pivot point from which the TT length is measured is the intersection of the top tube and head tube. For a 1 degree change in the head tube angle to create a 1cm or 10mm change in reach, the bars would have to be 1/.0174= 57.5cm above this point. Anyone who's analyzed frame geometry will quickly recongnize that this is the typical change in the TT length when the SEAT TUBE ANGLE is changed 1 degree, not the head tube angle.
I'd say that Richard mixed up his millimeters and centimeters, or the poster confused head tube angle with seat tube anggle.
|C-40 is right . . . yet again (nm)||Drone 5200|
Dec 28, 2003 10:08 PM
|Uhhh, I seriously doubt that was actually Richard Sachs...||russw19|
Dec 28, 2003 7:29 PM
|I have emailed Richard Sachs a couple questions on occasion and he has never answered anything that simply. He takes time to explain his answers to questions, which is exactly what makes him an asset when you need an answer.
I suspect that this is either just someone who works for Sachs, or just likes their bikes and threw the URL in for credibility.
But that's just my suspicion. If that was actually Richard's answer, I may stop asking him questions....
|Most likely it was...||Nessism|
Dec 28, 2003 8:13 PM
|I follow the framebuilders list and Mr. Sachs receintly explained that he doesn't focus on head angle so much as front center and rider reach to the bars. Maybe he was using a different perspective to answer the question? For example, maybe he's thinking in terms of how he builds a frame? Not sure. But, I am sure of one thing, he's no dummie.
|Wouldn't he post under "Richard Sachs"????||russw19|
Dec 29, 2003 3:35 AM
|If he wanted to have his posts establish the same credibility that his frame building reputation deserves them to have, I would think he would sign his posts as "Richard Sachs" instead of "e-RICHIE" but that's just me.
|Wouldn't he post under "Richard Sachs"????||e-RICHIE|
Dec 29, 2003 5:45 AM
i've been e-RICHIE on this and other boards and electronic mediums since 1998.
|Cool! Then welcome to the board!||russw19|
Dec 29, 2003 10:52 PM
|Uhhh, I seriously doubt that was actually Richard Sachs...||e-RICHIE|
Dec 29, 2003 5:57 AM
|don't doubt it!
i'll continue to take your personal emails. since all this is so anonymous, mebbe let me know your real name so i can recall the exchanges.
otoh, i think for a board like this, a simple answer can be -the- answer; no real need for multiple examples to make a point.
|Teo's Theory Simple Answers||teoteoteo|
Dec 29, 2003 6:27 AM
|Funny thing about bike guys and this board are that simple answers are best but there is always someone within earshot who knows more, or THINKS they know more--myself included.
They'll be compelled by their own ego to jump into the converstion and begin to talk just so they can hear their own head rattle. Luckily for us all sometimes they do know what they are talking about. Maybe I'll start whispering advice when I am at the shop...now all I have to do is whisper online.
Gotta go now, I hear a slight reverberation beginning in my head (laughs)
|Uhhh, I seriously doubt that was actually Richard Sachs...||russw19|
Dec 29, 2003 11:14 PM
|Ok... my real name is Russ Williams, I live in Gainesville Florida and I have emailed you a couple silly questions which you were kind enough to take the time to try to explain to me. One was a question about why top Euro (and a few American) frame builders use the suits of a deck of cards as their symbols and what the significance of it was.
Another I asked you about was Joe Bell paint jobs, as I was looking to have him repaint a bike of mine and wanted to see if you were happy with his work. You had nothing but glowing reviews for his work.
And the last question I asked you and carbon copied Sheldon Brown asking if you remember the first Shimano Dura-Ace STI prototypes that Andy Hampsten rode in the 1988 Giro... was it 7 or 8 speed? I don't remember getting a reply to that one from you, but Sheldon didn't know.
Thanks for your input in this thread. It's always good to get a good frame builder's perspective on some of these questions. I have built a frame before, but even I wouldn't ride it and I surely wouldn't sell it to anyone. My frame was a far cry from yours.
Hope you frequent this board more often, it's good to get input from guys like you.
Dec 29, 2003 5:42 AM
|without blaspheming the trig industry, my post is based in fact; all my frame's tubes are fixtured and, before any measurements re "uppper body reach" are set in stone, i often refer to the possibilities of altering tt length, head angle, and proposed stem length to determine the current balance. my experience has yielded that, keeping tt length and stem constant, a 1 degree increase in head angle will cause a 1cm-ish gain in overall reach. i also have a st installed at the correct vertical height and lean along with a surrogate saddle assembly to verify these measurements with a tape measure. i stand by the 1cm reply.
major-ly big and small frames may propotionately different results.
Dec 29, 2003 5:43 AM
|This is silly....||C-40|
Dec 29, 2003 7:00 AM
|We apparently have some sort of miscommunication going on here. If you are Richard Sachs, then you obviously know what you're talking about, but it's not the same thing that we are talking about.
We are talking about nearly identical STOCK frames, prebuilt, with only a 1-degree difference in the head tube angle. With an identical seattube angle and toptube length, the headtube/toptube intersection point will be in exactly the same place. Trigonometry can easily be used to calculate the change in reach due to a difference in head tube angle.
The head tube's pivot point is the intersection of the toptube centerline and the headtube centerline. Draw a vertical line through this point to the height of the stem centerline. A horizontal line from the end of this line to the intersection with the headtube centerline represents what you might call the "setback" of the stem, due to headtube angle (just like seattube setback). A vertical headtube would have zero setback for instance. The true difference in the position of the stem (and reach) is defined by the equation: stem height x (cosA-cosB) where A and B are the two angles.
Even if the stem was set quite high, like 15cm above the toptube/headtube intersection, the result from the above equation is .25cm, comparing 72 and 73 degree angles. Using the more simplistic estimate of sin1 x 15cm yields a nearly identical answer of .26cm. Most folks don't have their stems set that high, so the difference is usually much less.
Dec 29, 2003 7:48 AM
|but, otoh, i understand the original question and i replied based on real world experience - and in saying that i do not mean to disparage the trig industry.
if i fixture, for example:
12cm surrogate stem
and i alter the head tube by 1 single degree, the distance from the saddle nose (a surrogate saddle/seatpost assy is installed in the st during the preliminary setup...) to the stem will increase by a cm.
(btw, not to go off point, but ed was correct: i don't measure the head angle per se as a control; i let it be a resultant measurement based on the choices needed for a balanced upper body position, balanced steering, and balanced front centers. but, my fixture "is" calibrated so i do know when one angle becomes another angle.)
Dec 29, 2003 11:08 AM
|I assume Richard Sachs means that while building a frame, if you change the head tube angle from 72 to 73 you'll end up with A LONGER TOP TUBE (roughly 1cm longer, depending on frame size). But if you are comparing two frames with identical seat tube angles and top tube lengths, a 1 degree difference in head tube angle makes essentially no difference in reach.|
Dec 29, 2003 11:38 AM
|gtx wrote: "But if you are comparing two frames with identical seat tube angles and top tube lengths, a 1 degree difference in head tube angle makes essentially no difference in reach."
that's my point. that was the initial query and i replied to that hypothetical. i maintain (and i even doublechecked it this a.m. by playing with the frame fixture here...) that, indeed, if the st height, setback, and tt remain constant, a 1 degree change in the head angle will affect a 1cm gain in overall reach, assuming also that the saddle and stem placements are untouched.
|anyway, I still know one thing||gtx|
Dec 29, 2003 11:52 AM
|I still want one of your frames--have since I saw one at age 16 in 1984. I just haven't figured out where the money is going to come from, and what color I want. Right now I'm thinking white/red for my 40th birthday/midlife crisis. But I'm afraid that if Campy keeps making their parts out of plastic I might have to break with tradition and built it up with DA. ;) Thanks for dropping by our silly forum.|
|can i sign your post gtx?||colker1|
Dec 29, 2003 2:00 PM
|change age crisis (add some more yrs) and there's me. i want a sachs road bike! mine in black and white.|
|Where are the two of measuring "reach"? (nm)||TFerguson|
Dec 29, 2003 12:03 PM
|There is no trig industry||Frith|
Dec 29, 2003 11:29 AM
|There is a body of knowledge and fact studied and proven beginning sometime b.c. by guy's like Newton. These equations can be easily used to draw conclusions about questions like the one posted here with zero margin of doubt. So on one hand we have thousands of years of research and on the other we have the memory of a very fine frame builder who may have mismeasured or recalled incorrectly some practical experience. You make amazing frames but my money's on Newton for this one.|
|i know that...||e-RICHIE|
Dec 29, 2003 11:45 AM
"There is no trig industry"
yes, i know that! i was using levity.
otoh, your thoughts aside, there is no mistaking my setting up a prescribed frame geometry in my fixture, locking everything down, and simply measuring with a ruler the gain in overall reach yielded when the head tube assy is adjusted for a 1 degree increase. my memory is not in question; i do this daily in real-time at 100% scale. the tape measure is not lying.
|with all due respect....||C-40|
Dec 29, 2003 12:07 PM
|If you are Richard Sachs, I amazed that you apparently do not understand trigonometry, which by the way is a mathematical discipline, not an "industry". This discussion can never be resolved, because you don't understand the language.
The situation can be carefully drawn to scale or calculated and both methods will prove that you are incorrect.
If you are rotating the head tube in the lug, which is close to the headtube/toptube intersection, the position of the stem will not change more than .25cm due the short length from the point of rotation to the top of the stem.
A similar situation occurs when the seattube angle is changed by 1-degree. In this case the seat tube is much longer and the horizontal change at the top of the seat tube can be calculated with the formula: setback = seattube length x (cosA-cosB). With a 58cm seat tube, a change from a 74 to a 73 degree STA would change the setback by .97cm. It's hard to imagine how the same angular change to the head tube could displace the much shorter stem by this same amount.
Trig is also useful in calculating the seattube angle from the setback. In your example, a 58cm seat tube with a 16cm setback has an angle of: inverse cosine 16/58 =73.99 degrees.
If you have even a basic understanding of trigonometry, it's clear that two members of substantially different length cannot both be rotated by 1 degree and produce the same horizontal displacement, but that's essenttially what you are claiming.
|with all due respect....||e-RICHIE|
Dec 29, 2003 12:23 PM
|thank you, C40.
it's true, i don't understand trig because i did not take it in school. but, alas, i don't need it or use it to build frames. everything here is done at 100% scale and my original reply was based on experience (30 plus years) as well as addressing the issue with a tapemeasure in my daily work.
re the "trig industry" reference - yes, i know there is none; see my other reply and my reference to use the term lightheartedly. i did not mean to get under your skin with the term.
i think the best way i can stand my ground here is for me to direct you to the jpg of my frame fixture, so conveniently pasted by another, and "imagine" the original hypothetical whilst using the fixture as periscoping/telescoping "ouiji board" if you will. that image was set up for a photo shoot. normally there would also be a surrogate saddle assy and stem installed so that i can make the correct decisions re tube cuts BEFORE the frame is heated.
|hey C-40 it is not about trigonometry||cyclopathic|
Dec 29, 2003 12:41 PM
|it is about how jig operates and frame is built. When HTA adjusted there're more then one change to front triangle geometry made. In "ideal" world if TT effective length remain constant and pivoting point was at TT/HT junction you and I were correct. In reality it doesn't even if Richard believes it does since he didn't cut/replaced tubes.
look at the pic of frame in jig below, you'd understand what I mean.
|change top tube for front center and it makes sense:||colker1|
Dec 29, 2003 7:49 AM
|2 bikes with the same front center but different head angles. the one with slacker angle will have a shorter top tube. the rider of the slack front bike could use a longer stem and place his bars closer to front axle. "colnagos are designed with longer stems in mind..." as i read floating around here, starts making sense. the short tubed colnagos are built w/ longer stems and voila: no more cramped riders on them.|
Dec 29, 2003 7:53 AM
|the original query from swvegg was not about that hypothetical.
|I think I know what's going on||cyclopathic|
Dec 29, 2003 11:19 AM
|if you look at the Richard's bike below, you'd see that TT isn't parallel, it actually slops down to headtube. I'll bet when he changes HTA in jig he maintains the same TT (and downtube?) and adjusts TT (effectively changes seattube/TT angle).
If that's the case the "pivot point" isn't at at all TT/HT intersection, it is way below. To get 10mm change in reach on 1deg require 573mm, and with avg fork height around 363-375mm it is more like front center as colker1 said.
|here's another pic||cyclopathic|
Dec 29, 2003 11:34 AM
|as you see rear triangle is already built, and head tube isn't cut, I was correct. HT will be cut after HTA adjusted, and it will be the only tube cut. TT/HT lug will slide up for final HTA adjustment.|
|here's another pic||e-RICHIE|
Dec 29, 2003 12:06 PM
|that's a FULLY fixtured frame and there IS a headtube pinned to those head lugs!!!!!!!
thanks for pasting that image.
now - if you imagine all things on that fixture being constant, and you then INCREASE the head angle 1 degree, the net effect will be a 1cm increase from the saddle (which is not installed for the sake of the photography...) to the stem (which is also not in this image...)
a tape measure between the 2 points will address my 1st reply; the overall reach is increased by 1cm if the ONLY change made in the hypothetical is a 1 degree increase in head angle.
Dec 29, 2003 3:11 PM
i was nudged offlist to clarify this. that jpg shows extra head tube length above the headlug. that small amount is nt part of the finished frame. it's part of the set-up and gives me an area to sweat braze material towards during the heating cycle. the top of the lug is where the frame ends; the excess head tube will be trimmed off.
|I'm hopelessly confused by this thread...||Ray Sachs|
Dec 29, 2003 11:40 AM
|...but I sure like looking at that picture :)
-Ray (no relation) Sachs
|well they've been talking apples and bananas for a while||cyclopathic|
Dec 29, 2003 11:49 AM
|look at the jig pic above. C-40 knows trigonometry and Richard knows how to build bikes. Apparently both find opposite confusing and can't explain themselves well to be understood, I'll leave it at that.|
Dec 29, 2003 11:55 AM
|this isn't confusing to me. but what more do you need than a full on frame fixture, some surrogate stems & saddles, the original hypothetical, a tape measure, and fifteen minutes to check & re-check this at 100% scale?!
Dec 29, 2003 11:50 AM
|the top tube is level and parallel to the horizon. the picture was shot with the front wheel nearer to the viewer and the bicycle, too, was leaning away from the viewer. for the sake of the shot, this stance accomplished more than a true 90 degree side shot would. studio photography has its own demons; shooting a bicycle to get all components and perspectives 100% is not always possible.
|re: not quite...||cyclopathic|
Dec 29, 2003 11:59 AM
on my commuter (KHS Flite 300) TT is slopped same way, 1.3deg. For all purposes it looks parallel to horizon, walking around/no pic taken. I didn't know 'till I looked at geom charts. I'd bet you don't measure it, and sometimes don't realize.
PS. just tell me this: do you slide top lug up when you adjust HTA or you cut downtube?
|re: not quite...||e-RICHIE|
Dec 29, 2003 12:10 PM
|"PS. just tell me this: do you slide top lug up when you adjust HTA or you cut downtube?"
i am not sure i undertand your question. the top tube REMAINS level at all times; the fixture has it set at 180 degrees. the intersection between a level top tube and the prescribed head tube "tells me" where the lug goes.
Dec 29, 2003 12:25 PM
|when you change HTA this 1cm change in reach has to come from somewhere, right?
you can get it by sliding TT out of lag, sliding top lug up and slightely adjusting TT orientation of TT to horizon or by filing down downtube.
Now, if you're saying that top and downtube remain fixed while you adjust HTA, and you don't effectively change HT height after adjustment there must be a gap btw HT and TT inside top lug.
C-40 (and myself) made trig under assumption that there's no variable gap btw HT and TT and TT orientation fixed, really fixed.
PS. btw the pic of your bike taken from angle close to 90deg, compare the size of front and rear wheel. TT is slopped down.
|re: not quite...||crankset|
Dec 29, 2003 10:30 PM
|Well, for those doubting if this is Ricard Sachs, do a search for his name and e-RICHIE and you will find out this IS RS.
Maybe this answers something that puzzled me for a while. I bought a small TCR. It has a 74 degree STA and a 53.5 effective TT with a 72 degree HTA. Well, I kept hitting the stem with my knee and could not figure out why. My regular bike has a 55cm TT, 73HTA, and 73.5 STA and going by trig, the Giant's TT is only supposed to be 1cm longer so I figured a longer stem would take care of that but reading what Richard writes, it is more around 2cm. Not sure if that is why but that Giant's TT really looked short when riding it. I really liked the bike but the cockpit was too short. On top of that I had the stem quite high which makes things even shorter.
You know that's why we should leave certain things to experts. We think we know about something by just reading about it but a minute of real world experience counts more than a day of reading. I know this from being a car mechanic. You can seat all day in a classroom and learn all about a certain aspect of car repair and it seems simple enough but when you go out there to a real car and try to apply what you just learned you figure out real quickly that what you learned in the classroom will only take you so far. Experience counts for so much more than head knowledge.
For example, you are told that if you test an alternator and it gives you a certain result, it needs to be replaced. To do this all you have to do is unhook the battery, remove the electrical connections at the alternator and the two bolts holding it. Then you go to the Honda Accord in the garage and what do you find? That to get to the alternator, you have to reach it from the bottom of the car and if you don't know what you are doing, you will remove the CV axle to get it out. Sounded pretty simple in the classroom but it's quite different when you actually put your hands on it. And that's of course if the bolts don't break off or the CV axle is not frozen in the hub, etc.
Sorry for the long post but I have always believed, like I said before, that there is absolutely no substitute for experience and this thread is a perfect example of that.
Thanks for your input Richard.
|I think I know what's going on||koala|
Dec 29, 2003 7:20 PM
|If you use tt/ht center as pivot and keep tt length the same you alter the downtube length. If you pivot from the dt/ht intersection, you lengthen the top tube and thus the reach. You cant effectively change ht angle and keep every other aspect of the frame the same....|
|re: I think I know what's going on||cyclopathic|
Dec 30, 2003 8:24 AM
|the point is you can't use neither TT/HT nor DT/HT as pivot point b/c you'd effectively change STA (fork length stays the same) THat's why the effective pivot point in jig is somewhere around front axle.|
|re: I think I know what's going on||koala|
Dec 30, 2003 8:30 AM
|O.K., got it. Which explains Mr. Sachs getting a centimeter difference...Thanks.|
|THIS SHOULD ANSWER THE OFT ASKED QUESTION||Fez|
Dec 29, 2003 12:38 PM
|Should I get stock or custom?
I'm not going to comment on who's right or wrong here, but it emphasizes the importance of communication.
With so much potential for miscommunication, the best thing may be an educated consumer armed with all the specs and info and then making an educated decision.
If you know what you want and can't find it, then find a builder you can effectively communicate with.
Dec 29, 2003 2:13 PM
|I doubt you'd go wrong with a Richard Sachs frame, but it's hardly your "typical" custom frame. From his web site:
"What I offer isn't customit's made to measure," Sachs says. He compares what he does to clothing. A custom suit is one made to your spec, while made to measure is a custom-fitted suit that's made to the tailor's design."
|what i learned from this thread is||colker1|
Dec 29, 2003 2:28 PM
|that is possible to find something real beyond mystique, smoke screens, hype and technonological (most of the time silly) theatrics that surrounds us in this road bike addiction we have. actually... this thread is the best, most cool ever! hey, santa claus does exist!|
|Wow those are some pretty bikes. Anyone here want to fess||Fez|
Dec 29, 2003 3:23 PM
|up and admit to owning one of these? Post a picture and some details.|| |