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Originally Posted by oldbobcat
(Post 14418003)
Actual top tube and actual seat tube are virtually useless unless you like to ride bikes that are too large for you.
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Back to the OP, since I didn't see it amongst the arguing, I use a spreadsheet to calculate stack and reach using the geometry given by the makers. It is within 1mm of those who also provide stack and reach along with their HTL, TTL, STA, HTA measurements. Usually it's off because I have to guess the fork length. The spreadsheet uses trig lifted from sites where stack and reach are discussed with adjustments to account for fork offset. It's come in very handy when I want to compare frames with surprising results every now and then.
Assuming the TT length is correct this is your Habanero: (HTL includes the bottom headset cup) [TABLE] [TR] [TD]Stack [/TD] [TD]622 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]Reach [/TD] [TD]363 [/TD] [TD]mm [/TD] [/TR] [TR] [TD] [/TD] [TD] [/TD] [TD] [/TD] [/TR] [TR] [TD]ETT [/TD] [TD]547 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]HTL [/TD] [TD]221 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]FL [/TD] [TD]370 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]FO [/TD] [TD]45 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]HTA [/TD] [TD]73.5 [/TD] [TD]deg [/TD] [/TR] [TR] [TD]STA [/TD] [TD]73.5 [/TD] [TD]deg [/TD] [/TR] [TR] [TD]BBD [/TD] [TD]68 [/TD] [TD]mm [/TD] [/TR] [/TABLE] And this is the integrated headset Nashbar frame: [TABLE] [TR] [TD]Stack [/TD] [TD]603 [/TD] [TD="width: 65"]mm [/TD] [/TR] [TR] [TD]Reach [/TD] [TD]392 [/TD] [TD]mm [/TD] [/TR] [TR] [TD] [/TD] [TD] [/TD] [TD] [/TD] [/TR] [TR] [TD]ETT [/TD] [TD]565 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]HTL [/TD] [TD]205 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]FL [/TD] [TD]370 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]FO [/TD] [TD]45 [/TD] [TD]mm [/TD] [/TR] [TR] [TD]HTA [/TD] [TD]72.5 [/TD] [TD]deg [/TD] [/TR] [TR] [TD]STA [/TD] [TD]74 [/TD] [TD]deg [/TD] [/TR] [TR] [TD]BBD [/TD] [TD]68 [/TD] [TD]mm [/TD] [/TR] [/TABLE] |
Originally Posted by kaliayev
(Post 14418438)
It is also important if you have a body build with a long torso and shot inseam.
OK, if your legs are super-short, you like sitting upright, and you have an aversion to long stems. |
Originally Posted by Bacciagalupe
(Post 14418135)
Given the situation, I don't think anything really has changed. Again, you just have to look for "effective top tube" with the compacts.
It is, but my recollection is that road bikes have largely settled on the 72º-74º range for seat tube angles. (E.g. the seat tube angle on the Roubaix and Tarmac are nearly identical.) And a 0.5º difference over 580mm only results in a 5mm difference. I think you'll see a lot more variation with head tube height, trail, wheelbase and the like than seat tube angle, and you'd only see something like a 77º ST on a dedicated TT bike. I'd think that if he needs a radically non-standard seat tube angle, that's going to alter his weight distribution on the bike, and you're almost certainly back in Custom Geometry Land to really get everything right. |
2 Attachment(s)
Originally Posted by rruff
(Post 14418239)
What this tells me is that bikes have a lot of adjustability. The puzzling thing is why you think ETT is important.
If you want to get the "right" frame size... which means you have standard parts in "aesthetic" adjustment ranges... the most important aspect to look at is head tube length. This analogous to the old frame sizing method of looking at seat tube length when top tubes were horizontal. |
Originally Posted by mmmdonuts
(Post 14418487)
Back to the OP, since I didn't see it amongst the arguing, I use a spreadsheet to calculate stack and reach using the geometry given by the makers. It is within 1mm of those who also provide stack and reach along with their HTL, TTL, STA, HTA measurements. Usually it's off because I have to guess the fork length. The spreadsheet uses trig lifted from sites where stack and reach are discussed with adjustments to account for fork offset. It's come in very handy when I want to compare frames with surprising results every now and then.
Assuming the TT length is correct this is your Habanero: (HTL includes the bottom headset cup) [TABLE] [TR] [TD]Stack[/TD] [TD]622[/TD] [TD]mm[/TD] [/TR] [TR] [TD]Reach[/TD] [TD]363[/TD] [TD]mm[/TD] [/TR] [TR] [TD] [/TD] [TD] [/TD] [TD] [/TD] [/TR] [TR] [TD]ETT[/TD] [TD]547[/TD] [TD]mm[/TD] [/TR] [TR] [TD]HTL[/TD] [TD]221[/TD] [TD]mm[/TD] [/TR] [TR] [TD]FL[/TD] [TD]370[/TD] [TD]mm[/TD] [/TR] [TR] [TD]FO[/TD] [TD]45[/TD] [TD]mm[/TD] [/TR] [TR] [TD]HTA[/TD] [TD]73.5[/TD] [TD]deg[/TD] [/TR] [TR] [TD]STA[/TD] [TD]73.5[/TD] [TD]deg[/TD] [/TR] [TR] [TD]BBD[/TD] [TD]68[/TD] [TD]mm[/TD] [/TR] [/TABLE] And this is the integrated headset Nashbar frame: [TABLE] [TR] [TD]Stack[/TD] [TD]603[/TD] [TD]mm[/TD] [/TR] [TR] [TD]Reach[/TD] [TD]392[/TD] [TD]mm[/TD] [/TR] [TR] [TD] [/TD] [TD] [/TD] [TD] [/TD] [/TR] [TR] [TD]ETT[/TD] [TD]565[/TD] [TD]mm[/TD] [/TR] [TR] [TD]HTL[/TD] [TD]205[/TD] [TD]mm[/TD] [/TR] [TR] [TD]FL[/TD] [TD]370[/TD] [TD]mm[/TD] [/TR] [TR] [TD]FO[/TD] [TD]45[/TD] [TD]mm[/TD] [/TR] [TR] [TD]HTA[/TD] [TD]72.5[/TD] [TD]deg[/TD] [/TR] [TR] [TD]STA[/TD] [TD]74[/TD] [TD]deg[/TD] [/TR] [TR] [TD]BBD[/TD] [TD]68[/TD] [TD]mm[/TD] [/TR] [/TABLE] I am aware that the Nashbar does not exactly fit me, but it's within a couple cm and with my goofy body that's not bad. Actually, if the Habanero were to fit me PERFECTLY it should have a HT and ST approx 2 cm longer....but then my choices in forks would be severely limited. That's why I have to resort to a slightly flipped-up (or unflipped, in 41 parlance) stem. |
Originally Posted by Campag4life
(Post 14417973)
STA however is a pretty big deal. The reason is...indeed reach has to be satisfied as you believe...and stack...beauty of why we like our Roubaixs....but STA is very important for fore/aft weight distribution which is really the starting place or cornerstone of fit.
STA in turn affects net reach...especially if deviating from a stock seatpost which some need, including me for optimal balance on the bike. For the Roubaix...Spesh sells two varieties of seat post...a single bolt with 21mm of setback and a 2 bolt post which is 25mm. So depending on which post your bike came with...Sworks has been sold with either, on clamp center, your net reach will be affected by 3mm. Neither are enough for me to balance my weight however. Many amateur rides including pros like Hincappie, Schleck, Boonen etc prefer in excess of 100mm of setback...saddle tip to BB center. I am long legged and ride with my Speedplay cleats a bit rearward therefore I ride with a slightly lower saddle height for my leg length. This reduces setback even fruther with the stock post that came on my bike of 21mm. My 58 Roubaix has a sta of 73 deg...and I believe Colin your 61 has a sta of 72.5 deg. Ideally I have the leg length which works better with a 72.5 deg STA like you have....but a 61 Roubaix is a hair big for my overall size...you are a bit taller. So...I run a 32mm setback post...see pic below. I ride it just forward...about 3-4mm of center for a net setback of 28-29mm or so...or about 5-8mm over stock. This dramatically changes the weight distribution on the bike and for the better. But by having a stock 73 deg STA and increasing setback, this effectively elongates my effective top tube length. This btw is OK in my case as I ride with a 120mm stem...I have long arms to match my long legs and choose to ride with a higher handlebar which effectively shortens reach. Reach should always be served independent of what bar height you ride. Most importantly over and above reach...is fore/aft weight distribution must be served for any chance of a good fit. This is a function of STA and saddle setback as it relates to net reach and why so vitally important to answer your question. The thing about fit is...it is much more complex than just 'top tube' or head tube height. STA really affects overall reach but most importantly, it affects fore/aft position on the bike AND effective reach to the handlebars. So STA is significant. Hope that makes sense. There are 2 things with replicating a fit - getting the saddle where it needs to be relative to the bottom bracket, and putting the handlebars where they should be. So the first question becomes, can you get the saddle where it needs to be on a 72.5 STA or a 74 STA bike? The answer is yes. The answer to my earlier question was - there is a 2cm difference between a 72.5 and 74 STA for an 82cm BB-saddle length (for most riders, this number will be less, as they'll have a shorter saddle height and possible less extra variance in STA). This is easy enough to achieve with by sliding the saddle back/forward or by swapping the seatpost. Now on to the second part of the fit - putting the handlebars where they need to be. You are correct - sliding the saddle back/forth to compensate for the difference in STA will affect reach, as the reach to the head tube changes. A 565 ETT on a 72.5 STA frame isn't the same reach as a 565 ETT on a 74 STA frame. However, unless you are riding in an extreme position (stem maxxed out), you can offset this by choosing a different stem. So the answer to the second part is: yes, you can get the handlebars where you need them as well, by changing the stem length. In short, you can get your bike set up exactly the same way, regardless of the STA and HTA. Yes, it will affect weight distribution - no one is saying that a bike with a 72.5 STA is going to handle exactly the same as a bike with a 74 STA. Duh. But we were talking about replicating a particular FIT. As long as you pick a frame based on your preferred ETT and HT, and you don't ride in an extreme position on this bike, then you can get the frame to be built up to replicate your desired fit. That isn't "BS", as you had claimed in your initial post. |
Originally Posted by rruff
(Post 14418239)
What this tells me is that bikes have a lot of adjustability. The puzzling thing is why you think ETT is important.
The ETT figure gives me approx reach - yes, this is going to be affected by the STA and, to a lesser degree, the HTA. But as mentioned in my post earlier, the variation caused by STA is typically manageable in terms of setting up the bike to replicate a particular riding position. Taken in conjunction with the HT length, the ETT lets me know if the dimensions of the frame are within the range that will fit me or not. I know that if I have a bike in the 565-570mm ETT and a 175-185mm HT, I can get it set up exactly the way I want, b/c these numbers give me a fit that is right in the middle. OTOH, if I have a bike with a 575-585mm ETT, or with a much lower HT length, then I know that the fit will require extreme measures to get it to work - and that is where STA will make a difference (a 72.5 STA bike with a 575-580 ETT may work, a 74 STA bike will definitely not). |
Originally Posted by datlas
(Post 14414288)
I have been an avid road cyclist for more than 25 years.
I would like to think that I have a good basic understanding of frame geometry, but with the movement towards compact frames I feel like my knowledge is moldy. I still think in terms of Top Tube, Seat Tube, Head Tube lengths...and HT angle/ST angle. However I have been hearing more lately that since manufacturers are lying about their geometries it makes more sense to look at "stack" and "reach." I want to learn a bit more about this but I suspect it will require a change in my thinking. Anyone know a good website to help me convert my old math (geometry) thinking into the 21st century?? There on the left side is an index. Try "Engineering" then click onto "Geometry & Fit" http://cervelo.com/en_us/engineering...presentations/ |
Originally Posted by Garfield Cat
(Post 14420112)
the Cervelo website explains their thinking on stack and reach. www.cervelo.com
There on the left side is an index. Try "Engineering" then click onto "Geometry & Fit" http://cervelo.com/en_us/engineering...presentations/ |
Originally Posted by Garfield Cat
(Post 14420112)
the Cervelo website explains their thinking on stack and reach. www.cervelo.com
There on the left side is an index. Try "Engineering" then click onto "Geometry & Fit" http://cervelo.com/en_us/engineering...presentations/ thank you for that link. I had not previously seen it, but C4L needs to read it (maybe he will) and understand it (:P) and agree with it (:lol:).
Originally Posted by guadzilla
(Post 14420049)
In short, you can get your bike set up exactly the same way, regardless of the STA and HTA.
Yes, it will affect weight distribution - no one is saying that a bike with a 72.5 STA is going to handle exactly the same as a bike with a 74 STA. Duh. But we were talking about replicating a particular FIT. As long as you pick a frame based on your preferred ETT and HT, and you don't ride in an extreme position on this bike, then you can get the frame to be built up to replicate your desired fit. That isn't "BS", as you had claimed in your initial post. it's so simple. the STA, HTA and other things C4L is hung up on do matter for handling, and they're critical for framebuilders. but when we're talking fit, they matter not.... assuming that you intelligently and properly adjust your saddle (including seatpost setback) and stem to achieve proper bar height and saddle position relative to the bottom bracket. it isn't "rocket surgery". ;) |
The OP and others curious might find this stack & reach calculator quite helpful:
http://bb2stem.blogspot.com/ |
Originally Posted by guadzilla
(Post 14420072)
The ETT figure gives me approx reach - yes, this is going to be affected by the STA and, to a lesser degree, the HTA. But as mentioned in my post earlier, the variation caused by STA is typically manageable in terms of setting up the bike to replicate a particular riding position.
There really is no substitute for figuring out where you want your saddle and bars relative to the bottom bracket, and then breaking out the HS geometry book and seeing what it will take to connect the dots. For instance, I'm 6ft with average proportions, but like a lot of drop from the saddle to bar. Because this is "unusual" it is the controlling factor in sizing. I ride a 54cm frame with a 145mm head tube, 130mm -10 stem (no spacers), and 20mm offset post with the saddle back about as far as it will go. If I didn't want so much drop I could ride a 56, 58, or even a 60 quite easily. |
Originally Posted by guadzilla
(Post 14420049)
This post is a little more useful than your earlier attempts at being snarky - stick to content next time: you do better there. Witty put-downs aren't exactly your forte.
There are 2 things with replicating a fit - getting the saddle where it needs to be relative to the bottom bracket, and putting the handlebars where they should be. So the first question becomes, can you get the saddle where it needs to be on a 72.5 STA or a 74 STA bike? The answer is yes. The answer to my earlier question was - there is a 2cm difference between a 72.5 and 74 STA for an 82cm BB-saddle length (for most riders, this number will be less, as they'll have a shorter saddle height and possible less extra variance in STA). This is easy enough to achieve with by sliding the saddle back/forward or by swapping the seatpost. Now on to the second part of the fit - putting the handlebars where they need to be. You are correct - sliding the saddle back/forth to compensate for the difference in STA will affect reach, as the reach to the head tube changes. A 565 ETT on a 72.5 STA frame isn't the same reach as a 565 ETT on a 74 STA frame. However, unless you are riding in an extreme position (stem maxxed out), you can offset this by choosing a different stem. So the answer to the second part is: yes, you can get the handlebars where you need them as well, by changing the stem length. In short, you can get your bike set up exactly the same way, regardless of the STA and HTA. Yes, it will affect weight distribution - no one is saying that a bike with a 72.5 STA is going to handle exactly the same as a bike with a 74 STA. Duh. But we were talking about replicating a particular FIT. As long as you pick a frame based on your preferred ETT and HT, and you don't ride in an extreme position on this bike, then you can get the frame to be built up to replicate your desired fit. That isn't "BS", as you had claimed in your initial post. STA is very important pal and to not consider it in the equation of overall reach once fore/aft postion is established is perhaps the biggest mistake any fitter could make. In summary, all your writing suggests you don't get it. You will never get it I am afraid, so pardon me if I balance my boredom with you with some humor. |
You and rruff clearly are not reading the links we are providing and are clearly not interested in any learning, merely spouting your antiquated and ill-advised positions. You have plenty of time to post on BF (as do I) so I know you have time to read the links.
Apparently even source material from Cervelo's engineering group isn't worth your attention. If it were, you'd learn something. |
Originally Posted by ColinL
(Post 14420677)
You and rruff clearly are not reading the links we are providing and are clearly not interested in any learning, merely spouting your antiquated and ill-advised positions. You have plenty of time to post on BF (as do I) so I know you have time to read the links.
Apparently even source material from Cervelo's engineering group isn't worth your attention. If it were, you'd learn something. OK...carry on. As you were :) |
Jesus Christ, man! Your Smug-Level is off the charts! It's disturbing.
As for the OP, I was fitted on a M/L Giant Defy in the store. This is a compact frame, and it has a 56cm effective top tube. So when I was looking for a cheap single speed from Nashbar, I just bought the standard frame in a size 56 hoping it would work. It did. I have the fit almost exactly the same between both bikes. I believe I have "normal" proportions though. From my own experience so far, I know that I either need a standard frame with a 56cm top tube, or a compact frame with a 56cm effective top tube. |
Originally Posted by rruff
(Post 14420285)
ETT doesn't give you meaningful reach, since the STA effects it quite a lot...
in addition to HTA and HT. Most people don't realize that HT length effects reach on two frames that otherwise have the same STA and ETT. That's one reason why "stack" and "reach" are not so great for sizing. A 30mm HT difference is ~10mm in reach. For instance, I'm 6ft with average proportions, but like a lot of drop from the saddle to bar. Because this is "unusual" it is the controlling factor in sizing. I ride a 54cm frame with a 145mm head tube, 130mm -10 stem (no spacers), and 20mm offset post with the saddle back about as far as it will go. If I didn't want so much drop I could ride a 56, 58, or even a 60 quite easily. |
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Originally Posted by Campag4life
(Post 14420667)
I am sorry not to take you seriously
I need less than a 72.5 deg sta to achieved a balanced position on the bike with a stock seatpost. With proprietary aka areo posts on many bikes, then best position isn't achievable if sticking to your range of 'adjustment'...which also affects net reach. STA is very important pal and to not consider it in the equation of overall reach once fore/aft postion is established is perhaps the biggest mistake any fitter could make. In summary, all your writing suggests you don't get it. You will never get it I am afraid, so pardon me if I balance my boredom with you with some humor. If you ease up on the self-fellating self-congratulations, you'll realize that you are not actually addressing anything I wrote. Re-read my post to rruf. But somehow, I doubt if you'll let facts come in the way of your one-man circle jerk, so carry on. |
Originally Posted by guadzilla
(Post 14421113)
I know my comprehension on the subject is limited and I might add you are more than worthy of your mantle on Mt Olympus. Please be tolerant as I am trying to learn.
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Originally Posted by ColinL
(Post 14420677)
You and rruff clearly are not reading the links we are providing and are clearly not interested in any learning
I haven't said anything "incorrect". It's as basic and unassailable as math and geometry. |
Originally Posted by ColinL
(Post 14420677)
Apparently even source material from Cervelo's engineering group isn't worth your attention. If it were, you'd learn something.
A better method would be to locate the vertical point for measuring reach at some arbitrary stack value, rather than measuring it at the top of the head tube. |
Originally Posted by rruff
(Post 14422688)
Hey... say that to my face!
I haven't said anything "incorrect". It's as basic and unassailable as math and geometry. but one of their points is that they design frames so that stack and reach *do* linearly grow and shrink together as you move up and down sizes. other brands often do not decrease reach linearly as you go down, making their bikes smaller than 54cm seriously jacked. |
Originally Posted by rruff
(Post 14422723)
Cervelo's presentation is very good, but they do not mention that stack and reach are dependent on each other.
However, I think you are making it a little more complicated than it needs to be. The purpose of Stack and Reach is to standardize bike dimensions. I am not sure why you keep saying that S/R are not the best values for determining a frame's geometry for sizing. If I know my current bike's S/R and it fits, all I need to do is get another bike with comparable/close enough S/R numbers and I know I'll get it to fit. My current TT bike has a stack of 523 and a reach of 418. The reach is a little more than I'd prefer, and the stack a little lower than I'd like (I have a mountain of spacers there). The Shiv has a stack of 540 and a reach of 405. This bike is going to put the bars closer and higher - which is perfect for me. Yes, I will still need to do some measurements to get the fit right, but simply by reading the numbers, I know that the Shiv is going to require less futzing around to make it work. A better method would be to locate the vertical point for measuring reach at some arbitrary stack value, rather than measuring it at the top of the head tube. |
I completely agree with the above. If you know the location of 3 key points and the adjustment range for 2 of those then any frame within that range can fit. Knowing the stack/reach and STA values will help you fine tune that selection if you are worried about saddle setback, stem length, and stack height.
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