View Full Version : Top Tube Length Question
tcrush
06-02-2006, 09:37 PM
Okay folks, this one has me stumped. I'm looking at carbon framesets (really honey, just looking) and the Time geometry has me puzzled. Geometry wise, I'm normally very comfortable on something with a 58.5 to 59.5 top tube and as I look at the geometry table the Time frames max out at 58.0 (XL and XXL). Everyone else seems to size it up. Is the answer a setback seatpost and a Jerk-approved stem or simply ignore them for all eternity? They are difficult to find for a test ride, especially in the bigger sizes. Thanks in advance.
obtuse
06-02-2006, 09:49 PM
check the setback....by the "time" you get the seat in the right place; the overall reach isn't much different that other framesets which have th toptube length you are used too. any bike in the sizes you are discussing is balanced and designed around 130mm+ stem.
obtuse
(but maybe you should ask bumblebee dave. he is a far better and more knowledgable authority when it comes to bicycle geometry and race bike design.)
the top tube measurement may not be that telling
unless the head and seat angles are the same. if
the seat is shallower than the head and/or vice versa,
the rate of speed at whcich the saddle assy and stem/bar
assy leave their respective ports will yield a longer "cock-
pit" than the actual tube number suggests. above all, do
only use a setback seatpost. it's de rigeur and apropros
if this frame is to fit you as its design is intended. otoh,
for a good coup d'etat, the non-setback post comes in
handy atmo.
obtuse
06-02-2006, 10:01 PM
the top tube measurement may not be that telling
unless the head and seat angles are the same. if
the seat is shallower than the head and/or vice versa,
the rate of speed at whcich the saddle assy and stem/bar
assy leave their respective ports will yield a longer "cock-
pit" than the actual tube number suggests. above all, do
only use a setback seatpost. it's de rigeur and apropros
if this frame is to fit you as its design is intended. otoh,
for a good coup d'etat, the non-setback post comes in
handy atmo.
he should probably still ask bumblebee dave.
but atmo is right atmo. top tube length is a resulting measurement from the important ones....that's why the cool kids sometimes make bikes with strange non-prime numbers for tt lengths.....
try a time;stevep is giving them away. its like a french meivici but not as good. but hey, from pucc its free.
jerk
try a time;stevep is giving them away. its like a french meivici but not as good. but hey, from pucc its free.
jerk
pucc is away for the weekend getting his therapy.
The TT length does not tell the whole story. For a given frame size, it's the reach which determines the stem length required. Reach is the TT length minus the setback. Setback is the cosine of the STA times the c-c frame size (to a horizontal TT). Although reach is a great indicator of fit, it's only valid when comparing two frames of exactly the same c-c size. Comparing different brands, you won't find exactly the same size very often and reach comparisons can be off by 5mm or more. I noticed this on the Cervelo website, where they list a 54cm as having 1cm more reach than a 51cm, but the TT length is 1.5cm longer with the same STA. The discrepancy comes from measuring the reach at different vertical heights. It seems to defeat the value of using the reach measurement, if you're considering two different sizes.
As a rough guideline, when comparing two frames with different STAs, add 1cm per degree to the TT length of the frame with the steeper STA.
As for the setback seatpost, that's a given with nearly every frame on the market today.
Nothing wrong with a 130 stem on a large frame.
92degrees
06-03-2006, 09:24 AM
As for the setback seatpost, that's a given with nearly every frame on the market today.
interesting that the '06 Serotta catalog seems to illustrate so many bikes with zero setback posts...both Ottrotts, the Nove, the Concours, the CDA...
Tailwinds
06-03-2006, 09:28 AM
It really is about much more than TT-length as I learned the expensive way. I bought a Colnago (mail-ordered it) and didn't figure how much shorter the TT would have to be for its steep seat tube angle. It was a painful mistake, but one I'm glad I made -- 'cause it led me to my KIRK! :banana: :banana:
So as you know, it's not all about top tube length, but when you get all the other stuff right -- AND you have the right top tube length -- OH MY! :cool:
Just make sure your bike needs a straight seatpost. :p Straight seatposts are cool.
stevep
06-03-2006, 09:45 AM
the time ride long. even if the number is shortish.
i ran out of free ones yesterday...too bad i did not hear from you.
obtuse, the jerk, the wife of the jerk, obtuses wife,
friend of obtuse, obtuses other friend, obtuses enemy #1033, atmo, atmo lite, atmo heavy got the last 10 frames...
funny, they all needed xl frames. random statistics can be funny sometimes...and even the same ship to...very odd.
Fat Robert
06-03-2006, 11:46 AM
interesting that the '06 Serotta catalog seems to illustrate so many bikes with zero setback posts...both Ottrotts, the Nove, the Concours, the CDA...
and the bars are just about even with the seat, too -- so what's the point?
a straight post is either an inelegant solution to a stock geometry (robbie mcewen on a carbon ridley...check out his scandium this year, ahem), or an inelegant solution to a "problem" that doesn't need fixing (achieving kops at the cost of sensible weight distribution).
with a straight post, you either have to use longer stays if the frame is designed around a setback post, you give up tire clearance on that frame designed around a setback post (more frame setback without lengthening the stays), you're on the wrong size frame (because you're using a setback post to move you 2cm forward), or you're jerking around your weight distribution in the name of kops, which is just moronic. straight posts are all about inelegant compromises.
its another north american solution to a problem that doesn't exist for the old italian and french guys who figured all this junk out a long time ago.
its another north american solution to a problem that doesn't exist for the old italian and french guys who figured all this junk out a long time ago.
click (http://www.wfrchurch.org/amen/images/AMEN%20Logo%20Transparent3.png) click (http://www.snowaddy.net/brothersreachingout/images/BRO-Splash-Page.gif) atmo
Fat Robert
06-03-2006, 11:59 AM
click (http://images.google.com/imgres?imgurl=http://www.pucciplus.com/pressImages/ppjoe/P05.jpg&imgrefurl=http://www.pucciplus.com/gallery/gallery16.html&h=400&w=300&sz=50&tbnid=fJg1GjR2zQKz9M:&tbnh=120&tbnw=90&hl=en&start=8&prev=/images%3Fq%3Dpeter%2Bpucci%2B%26svnum%3D10%26hl%3D en%26lr%3D%26sa%3DN) click (http://www.snowaddy.net/brothersreachingout/images/BRO-Splash-Page.gif) atmo
forget the lobster
the double-chili-cheese-slaw-fries-burgers are on me
(fries on your burger are the new setback posts, fatmo)
It really is about much more than TT-length as I learned the expensive way. I bought a Colnago (mail-ordered it) and didn't figure how much shorter the TT would have to be for its steep seat tube angle. It was a painful mistake, but one I'm glad I made -- 'cause it led me to my KIRK! :banana: :banana:
So as you know, it's not all about top tube length, but when you get all the other stuff right -- AND you have the right top tube length -- OH MY! :cool:
Just make sure your bike needs a straight seatpost. :p Straight seatposts are cool.
A steep STA (like 74-75 degrees) makes the reach longer, not shorter. Many people get this backward. The steep STA requires the saddle to be moved further back and increases the reach.
The only frame I've ever had where I used a straight-up post was on my LOOK 381. In all sizes, a laid back 72.5 degree STA is used. This shortens the reach, so the 54cm TT length fits the same as a frame with a 74.5 STA and 52.3cm TT.
A steep STA (like 74-75 degrees) makes the reach longer, not shorter. Many people get this backward. The steep STA requires the saddle to be moved further back and increases the reach.
the reach is the reach - but a steeper seat tube angle
will make a top tube effectively shorter than it measures.
atmo = :confused:
Serpico
06-03-2006, 12:54 PM
this frustrates me a bit--why did my Serotta dealer tell me to use a non-setback post? (stem is a 110)
he had me in some wackass upright position too, but I changed that
Fat Robert
06-03-2006, 12:57 PM
this frustrates me a bit--why did my Serotta dealer tell me to use a non-setback post? (stem is a 110)
he had me in some wackass upright position too, but I changed that
the two points are related
probably, he had been shaken down by KOPS on the take
shop guys often dig out the zero setback to "get knee over spindle"...well...kops has been questioned and outright bashed by many in the industry (as if that was important...but sometimes a post will come up and some moron will say "gee, I guess you guys know more than the industry"...)...and few in europe pay any attention to that alleged biomechanical advantge.
also, there can be a bias in serotta-style fits towards a more upright position, that lines up kops and a short, high stem. that makes sense with the majority of their demo, but it may not always make sense for a rider....
anyway
top tube length can't be taken out of the context of the other factors in the bike design. frame setback and ht angle also have to be figured in to line up the points where they should be. and any time a ST angle stays the same in a company's size range, something is wack...the 56-57 bikes are probably ok but anything bigger or smaller is pretty obtuse...fatmo.
saab2000
06-03-2006, 01:04 PM
Don't take everything a Serotta dealer tells you as gospel truth. They sometimes have preconceived notions about how a bike should fit/look/ride based on their own preferences.
The only time I seriously thought about getting a Serotta new was just before I got my CIII. I brought my Merckx in to show them what I like and the guy was aghast at the position. He wanted a steeply sloping top tube with about 3 cm of spacers in order to get the bars up near the saddle. My Merckx has quite a drop.
I am not ranting against Serotta or their fit, but make sure you clearly define what you want to do with the bike. Tell them.
I will say that the Serotta fit cycle is pretty cool.
Serpico
06-03-2006, 01:04 PM
the two points are related
probably, he had been shaken down by KOPS on the take
keystone KOPS...:cool:
I don't mind fidgeting with the bars and stem, but I am leery about moving the saddle back further--will this really mess up my pedal stroke (switching to a setback post)??
advTHANKSance
saab2000
06-03-2006, 01:14 PM
These threads about the effects of changing angles and lengths are cruddy because they show me how little I know about bike design. :crap:
Trying to learn something here.
top tube length can't be taken out of the context of the other factors in the bike design. frame setback and ht angle also have to be figured in to line up the points where they should be.
'
92degrees
06-03-2006, 01:32 PM
that's a zero offset post. atmo
92degrees
06-03-2006, 01:35 PM
and the bars are just about even with the seat, too -- so what's the point?
:confused: they don't jack up their saddle for the garage door photos?
that's a zero offset post. atmo
let's talk about it at lunch atmo.
92degrees
06-03-2006, 01:40 PM
let's talk about it at lunch atmo.
K. i'll buy as soon as i get the w.mass mud off of the bike. riding today was...obtuse?
the reach is the reach - but a steeper seat tube angle
will make a top tube effectively shorter than it measures.
atmo = :confused:
TT length is measured from the intersection of the head tube and TT centerlines, along a horizontal line, to the intersection point of the TT and seat tube centerlines. The STA has no effect on this measurement - it is what it is.
When the bike is fit to a rider, the saddle will have to be moved further back to produce any given saddle position relative to the BB, compared to a frame with a more slack STA. This makes the reach longer, not shorter and will require a shorter stem.
In a previous post, I gave a perfectly accurate example of how a 51cm c-c frame with a 72.5 STA and 54cm TT will fit the same as one with a 74.5 STA and 52.3cm TT. If you can't understand this, I can't help it.
If you can't understand this, I can't help it.
thanks for trying.
Grant McLean
06-03-2006, 04:00 PM
TT length is measured from the intersection of the head tube and TT centerlines, along a horizontal line, to the intersection point of the TT and seat tube centerlines. The STA has no effect on this measurement - it is what it is.
When the bike is fit to a rider, the saddle will have to be moved further back to produce any given saddle position relative to the BB, compared to a frame with a more slack STA. This makes the reach longer, not shorter and will require a shorter stem.
In a previous post, I gave a perfectly accurate example of how a 51cm c-c frame with a 72.5 STA and 54cm TT will fit the same as one with a 74.5 STA and 52.3cm TT. If you can't understand this, I can't help it.
yo dave.
I think you meant to say...hey Richard, I know you undertand what we're
talking about here... but you typed it the wrong way around.
Am I "dead" right? Or do we need to insult each others smarts' some more first?
g
yo dave.
I think you meant to say...hey Richard, I know you undertand what we're
talking about here... but you typed it the wrong way around.
i thought i got it right the first time (http://forums.thepaceline.net/showpost.php?p=215466&postcount=3)
through. i'll stick to my original post atmo.
Chief
06-03-2006, 04:06 PM
he should probably still ask bumblebee dave.
but atmo is right atmo. top tube length is a resulting measurement from the important ones....that's why the cool kids sometimes make bikes with strange non-prime numbers for tt lengths.....
try a time;stevep is giving them away. its like a french meivici but not as good. but hey, from pucc its free.
jerk
See what I mean about split personalities--obtuse now thinks he is the jerk. Where will it end?
See what I mean about split personalities--obtuse now thinks he is the jerk. Where will it end?
where will it end?
we want you to come into the closet with us,
not you making us come out of the closet.
Grant McLean
06-03-2006, 05:10 PM
i thought i got it right the first time (http://forums.thepaceline.net/showpost.php?p=215466&postcount=3)
through. i'll stick to my original post atmo.
word. we're all saying the same thing.
and doing it politely.
g
word. we're all saying the same thing.
and doing it politely.
g
cool -
thanks from...
merckx
06-03-2006, 08:19 PM
TT length is measured from the intersection of the head tube and TT centerlines, along a horizontal line, to the intersection point of the TT and seat tube centerlines. The STA has no effect on this measurement - it is what it is.
When the bike is fit to a rider, the saddle will have to be moved further back to produce any given saddle position relative to the BB, compared to a frame with a more slack STA. This makes the reach longer, not shorter and will require a shorter stem.
In a previous post, I gave a perfectly accurate example of how a 51cm c-c frame with a 72.5 STA and 54cm TT will fit the same as one with a 74.5 STA and 52.3cm TT. If you can't understand this, I can't help it.
This is correct.
This is correct.
well it's not entirely true and that is why i
expressed doubt. we don't know if said
top tube length and seat angles will yield
a longer reach or necessitate a shorter stem
because we don't know what the head angle
is and how that affects the overall (ya' know,
that g word...). so - that is why i'm using that
:confused: guy again and saying that you need to know
all the specs to realize what effect the actual top
tube length has once all the parts leave the frame
and set up a cockpit measurement atmo.
Chief
06-03-2006, 09:11 PM
where will it end?
we want you to come into the closet with us,
not you making us come out of the closet.
The Chief is not going into a closet with any forum member.
Not that there is anything wrong with that.
well it's not entirely true and that is why i
expressed doubt. we don't know if said
top tube length and seat angles will yield
a longer reach or necessitate a shorter stem
because we don't know what the head angle
is and how that affects the overall (ya' know,
that g word...). so - that is why i'm using that
:confused: guy again and saying that you need to know
all the specs to realize what effect the actual top
tube length has once all the parts leave the frame
and set up a cockpit measurement atmo.
Of course you should not ignore the HTA difference completely, particularly if it's a large difference like 74 to 72 degrees, but this is rare. More often the difference will be 1 degree or less.
Consider that the pivot point is the TT/HT intersection point. Even with a large 3cm stack of spacer, the top of the stem will only be about 13cm above the pivot point. The amount that the stem moves would be 13cm x (cos72-cos74) = 4.3mm. For a 1 degree difference, it would only be 2mm and .5 degree it would be 1mm. Unless I see a HTA difference greater than 1 degree, I tned to ignore the effect of HTA. With most stems only available in 10mm increments, there's not a lot you can do about a 2mm difference in reach, other than move the saddle fore/aft or perhaps make a small change to the brake hood position.
Of course you should not ignore the HTA difference completely,<cut>
as far as this thread goes with the OP concerned
with the tt lengths available on the frame(s) in
question, HTA is one third of the equation wrt to
the issue at hand: reach. the other two thirds are
STA and the actual measurement of the tt atmo.
obtuse
06-04-2006, 09:30 AM
as far as this thread goes with the OP concerned
with the tt lengths available on the frame(s) in
question, HTA is one third of the equation wrt to
the issue at hand: reach. the other two thirds are
STA and the actual measurement of the tt atmo.
this thread is stupid. of course the seat tube angle and the head tube angle effect the reach...so does the stem length and the saddle setback...none of which should be looked at independently from saddle to stem drop....and this is just discussing position not frame design, or balance or anything else.
as for the guy who thinks his look frame is a variation and that production tolerences vary that much; you're wrong. there's something else going on there and my obtuse guess is that it has to do with the angle of the stem. a 1cm longer stem harldy ever translates into exactly a one cm longer reach....you know head angles, stem angles and trigonometry and stuff.
for what its worth....a 73,5 sa with the seat pushed all the way back and a 73 degree ha and a 58cm top tube with a 150mm stem works fine for me. your results may vary yo.
obtuse
Kirk Pacenti
06-04-2006, 12:30 PM
for what its worth....a 73,5 sa with the seat pushed all the way back and a 73 degree ha and a 58cm top tube with a 150mm stem works fine for me. your results may vary yo.
obtuse
What size frame do you ride ( c.t.c. assuming a horizontal TT)?
obtuse
06-04-2006, 12:36 PM
What size frame do you ride ( c.t.c. assuming a horizontal TT)?
it's a 55 c-c but it's got a longish headtube for its size (165mm with an integrated hset.) it's a bit lower than what i've typically ridden/raced....but with hoods getting higher and bars getting shallower in terms of drop the thing works.
obtuse
Where's e-Richie in this thread? And Dave K?
There are a number of issues that contribute to the complexity of top tube measurements. Here are just a couple more:
1. A difficult one: Part of what you're trying to accomplish (and especially what your framebuilder is trying to do) is to get you balanced on the frame fore and aft and, to a certain extent for various body parts, vertically. The same bike can handle very differently if a new rider buys it and has his/her mass positioned differently over the bike. Frankly, a bike that started out as an amazing handler for one owner can be quite a dog for someone else. You don't necessarily see as much of this issue riding in a straight line on the flat, but try doing descending turns at speed, or look for liveliness riding ascending hairpins. On descents your bike won't feel stable and taking the steep part of a hairpin ascent your bike will feel like a slug.
So what your builder is trying to do is to anticipate how you'll be perched on the bike, what kinds of roads you'll be riding, how much climbing or ascents, how you like to climb (and descend), etc. etc. You may not really be able to get the perfect amount of comfort distance from saddle to bars, but you may get the overall body positioning that lets you ride fast and securely.
2. If you ride with a relatively aerodynamic position, you are compressing your diaphragm into your rib cage and limiting your ability to breathe. While you want that aero position, you start losing significant lung capacity. A partial response to that is to ride more on the tops and save the drops for sprints and the like (this is the standard Euro solution). Another solution they use (and this is part of where Jerk comes from ... and me) is that you can increase your stem length. It doesn't move much of your body mass forward so your center of balance on the bike doesn't change, but it stretches your rib cage a bit and relieves pressure on the diaphragm. It can also, depending on your position, rotate your hips a bit more and give you better access to your hip flexors, which increases power.
3. A simple one: If you have your saddle significantly higher than your bars, you are creating additional saddle-to-bars distance by doing so both by the height and because the saddle is still traveling backwards as you raise it, while the bars aren't. Your riding style -- whether you use the drops a lot -- has a similar contributing effect to the correct top tube length. So does whether you have the flexibility to rotate your hips a lot in your cycling position, and whether you ride the rivet or sit back on your saddle. It's always interesting to watch riders who scream for enormous seat post setback and then ride on the very tip of the saddle.
obtuse
06-04-2006, 02:04 PM
Where's e-Richie in this thread?
he's at red lobster with the jerk. you should come on by.
obtuse
Where's e-Richie in this thread?
i'm already posting atmo.
hint - http://forums.thepaceline.net/member.php?u=4974
as far as this thread goes with the OP concerned
with the tt lengths available on the frame(s) in
question, HTA is one third of the equation wrt to
the issue at hand: reach. the other two thirds are
STA and the actual measurement of the tt atmo.
If you look up the Time geometry chart, I think you'll find the XL and XXL sizes have the same 73 degee STA, same 58cm TT, same 73.5 degree HTA and same 604mm front-center The only significant difference is the XL has a 2cm shorter HT and a 2cm shorter ST.
The OP mentioned nothing about the STA or HTA of any frame he wanted to compare with, so this whole thread is a waste of time unless he wants to chime in with some specifics.
The OP mentioned nothing about the STA or HTA of any frame he wanted to compare with, so this whole thread is a waste of time unless he wants to chime in with some specifics.
he mentioned that he was comfortable with
a 58.5 to 59.5 and all that was available was
a 58. we tried to help him by explaining in
quite succinct terms (http://forums.thepaceline.net/showpost.php?p=215466&postcount=3) that there was more
to determing reach than simply the linear
measurement of the top tube atmo.
for what its worth....a 73,5 sa with the seat pushed all the way back and a 73 degree ha
obtuse
This set up is working for me, too (but with a way shorter stem), which prompts a question that's at least tangentially related to this thread. What if obtuse and I had bikes with 73 or 72.5 seat angles and our seats a little farther forward? Assuming that the contact points were the same, is there any reason to prefer one set-up over the other? I ask because I'm thinking about investing in a new Coeur.
This set up is working for me, too (but with a way shorter stem), which prompts a question that's at least tangentially related to this thread. What if obtuse and I had bikes with 73 or 72.5 seat angles and our seats a little farther forward? Assuming that the contact points were the same, is there any reason to prefer one set-up over the other? I ask because I'm thinking about investing in a new Coeur.
contact points may be static, but your flexibilty
and fitness levels may differ. from what i hear,
obtuse is flying right now seeing as how he just
got a frozen shipment of these bad boys (http://www.cok.net/photos/misc/food/burrito.jpg) straight
from durango.
Kirk Pacenti
06-04-2006, 05:02 PM
imagine you didn't have a seat tube.....
obtuse
06-04-2006, 05:04 PM
contact points may be static, but your flexibilty
and fitness levels may differ. from what i hear,
obtuse is flying right now seeing as how he just
got a frozen shipment of these bad boys (http://www.cok.net/photos/misc/food/burrito.jpg) straight
from durango.
yup. straight from the obtuse source.
obtuse
imagine you didn't have a seat tube.....
are you channeling lennon again atmo?
Kirk Pacenti
06-04-2006, 07:24 PM
are you channeling lennon again atmo?
yeah. he says that a slammed back saddle is in fashion, but a saddle centered on your post shows real style.....
Fixed
06-04-2006, 07:47 PM
bro kirk your bike fits me great I raised the saddle a little that's all .
thanks 5 hours today .
obtuse
06-04-2006, 09:12 PM
yeah. he says that a slammed back saddle is in fashion, but a saddle centered on your post shows real style.....
no way. new school obtuse eye-talian style places the saddle firmlky slammed back all the way. it's the only way to roll.
obtuse
Fat Robert
06-05-2006, 05:33 AM
no way. new school obtuse eye-talian style places the saddle firmlky slammed back all the way. it's the only way to roll.
obtuse
the cat man is right
those durango delights is messin wid cho head, prima donna boy
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