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Thread: What´s the reasoning behind dropped top tubes on a road bike?

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    Default What´s the reasoning behind dropped top tubes on a road bike?

    I find it ugly and a downgrade. It goes beyond aesthethics: a perfect geometric shape has effects on your psyche. No wonder certain structures and shapes were used in religious temples. Anyway.. i understand a dropped top tube on a mountain bike where standover is paramount. I understand curved top tubes on a cruiser which is about fun and taking it easy. A racing bike otoh is about grace and speed. A horizontal tube, parallel to horizon means balance and balance is necessary for grace in the face of risk. I could go on and on w/ this babbling.
    I know some serious designers like Kellog build w/ dropping top tubes so what´s the deal?
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    I think a “dropped” top tube often describes a level tube that sits lower between the head and seat tubes - think Pegoretti, etc.

    A “sloping” top tube or compact frame design is said to offer some different potential outcomes:

    A stiffer main triangle as the tubes are shorter, or lighter gauge or differently butted tubing could be used since the structure is inherently a little stiffer.

    A longer exposed seatpost can provide additional compliance in some planes.

    Pegoretti’s dropped design I think achieves a bit more stiffness, especially in larger frames. It doesn’t use substantially less material, but Pegs aren’t about frame weight.

    I have one sloping top tube frame in a household with 6 or 7 bikes. I understand your aesthetic impulses. But there is similar beauty in the total shape of some compact bikes. There are plenty of both compact and level top tube frames that are utterly horrid looking.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    They were made so tall riders like Urs Freuler and Edwig van Hooydonck would ride bikes with a nominally stiffer main section due to shorter tube lengths. I think aesthetics also played a role in creating a frame with slightly more normal proportions.

    These bikes predate sloping top tubes being widely accepted across the industry.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Some builders have their own ideas of frame geometry and fit. For example they may want you to ride the smallest, stiffest frame possible.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    It can be easier to make a frame to fit a smaller rider if the top tube is sloping.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    By dropped you mean sloping ?

    In that case the reasoning is often to have a stiffer frame while allowing for compliance in the seat area. I think you overthink a bit too much the psychological thing. Some frames with a sloping geometry look goofy other look great. You may obsess about the parrallelism of the top tube to the road, others would say they want the stem in the same angle as the top tube while avoiding spacers or extended top tube. There are a lot of ways to think about it aesthetically and I wouldn't say there is a definite answer.

    Also, for small 700c frames a bike with an horizontal top tube often looks goofy as the seatpost extension end up being very small. I'd tend to think bikes smaller than a 50/S should have 650b or 650c wheels but for some reason the industry doesn't seem to agree.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by colker View Post
    I find it ugly and a downgrade. .....
    Assuming we are talking about sloping top tubes -
    Personally I find them attractive and to my eye make a road racing frame "look" aggressive and fast.
    To each, his/her own.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by Bewheels View Post
    Assuming we are talking about sloping top tubes -
    Personally I find them attractive and to my eye make a road racing frame "look" aggressive and fast.
    To each, his/her own.
    Do a decent enough job matching the top tube angle to the stem angle (ballpark, not exact match) and they'll all look solid.
    "I guess you're some weird relic of an obsolete age." - davids

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    In regards to sloping TT frames being stiffer.....from Tom Kellogg:
    I designed it with a severe (17 degree) slope to ensure that any differences would be as obvious as possible. We had assumed that the new frame would be somewhat stiffer and lighter. It was lighter (about 4 ounces) but it was not appreciatively stiffer. Although we were able to measure a slight increase in stiffness, it was too slight to feel.
    All the way at the bottom of this page Spectrum Cycles | Geometry
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by choke View Post
    In regards to sloping TT frames being stiffer.....from Tom Kellogg: All the way at the bottom of this page Spectrum Cycles | Geometry
    Yes, though I wonder if Tom has a notion to share on achieving his stiffness/flex goals on larger frames? He doesn't ride a 62cm, AFAIK, and in that blog post he's talking about tube stock available in 1998. I'm curious how these interdependencies may have changed with modern steel alloys, butt profiles, and diameters? That said, it's interesting to think about what the rider perceives as useful stiffness or un-useful flex? Is it the chainstays and rear dropouts flexing relative to the BB? Is it the BB flexing side to side? Head tube out of plane with the BB as a result of downtube stiffness? I would imagine that these factors aren't influenced a lot by the height of the seat cluster, relatively speaking.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Some have mentioned more compliance from the seatpost. Otoh David Kirk is using longer stays. He says it´s about more rear wheel traction. Ritchey used a similar concept w/ the nexus stays. It should act like a coil. Instead of a single long tube flexing everywhere the builder can dictate where the flex goes w/ longer stays. A longer tube dissipates shock and road noise as well. Time (Moser leader ax, later Gaulzetti, speedvagens) went for an extended seat tube and less seatpost taking away all it´s flex and no one asked for more comfort.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Sure, though I think the characteristics of a frame are the totality of the system. Dave Kirk talks about his terraplane stays' ability to help keep the rear tire touching the ground on rough pavement.

    Could you achieve similar qualities by designing a rear triangle with specific flex characteristics working with tubing gauges and butt profiles and the shorter length seat stays typical of compact frames? All of which are related to where the riders' weight is carried relative to the wheels and BB center, etc. etc.

    re: seatmasts, I think the same idea is at work. The builder can specify the tube diameter and thickness and not have to account for a seat lug or a clamp at an area of intense brazing or welding. Whether or not the end result is stiffer or lighter than a similar elevation of the saddle with a traditional seatpost and hardware depends on the design and materials?
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    To each his own on the asethetics. I just had TK build me a steel bike to his design based on my contact points and in the concept of a do it all high performance steel road bike. It has a sloped top tube. Some of us bigger folks, and even TK talks about this on his website, notice a difference in feel particularly out of the saddle with a sloped top tube. I personally like the aesthetics very much. It's challenging to make a big bike (I would need a 63-64 stock bike) look anything but ungainly even with a level top tube. Or like my former Pegoretti Marcelo with the dropped top tube, you end up with very large headtube and seattube extensions, which have their own aesthetic issues. But whether I'm on my level top tube Sachs or slope top tube Spectrum or whatever, I'm really not fixating on the top tube or feeling compromised in motivation to ride by a couple of angles and tubes. If I'm fixated on the top tube its because I'm spent and probably dripping sweat all over it, at which point the angle really doesn't matter.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by choke View Post
    In regards to sloping TT frames being stiffer.....from Tom Kellogg: All the way at the bottom of this page Spectrum Cycles | Geometry
    You left out the rest of that paragraph, and the key part:
    "The big change came when I stood to accelerate or climb. As I stood up, the bike appeared to loose three pounds. The inertia of the bike as I rocked it back and forth was reduced so much that I felt as though I was on a twelve-pound bike. Interestingly, when seated, a compact frame feels exactly like a traditional design. The compact design has no effect on handling beyond the increases responsiveness during climbing and accelerating."

    I ride a 60-ish size frame and the Pegoretti style or slightly sloping TT work well for me. Allows a bit more seatpost to show. Otherwise, my bikes look like they're out of the 80's, when the longest seatpost Campy made was around 180mm.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by thomas View Post
    You left out the rest of that paragraph, and the key part:
    "The big change came when I stood to accelerate or climb. As I stood up, the bike appeared to loose three pounds. The inertia of the bike as I rocked it back and forth was reduced so much that I felt as though I was on a twelve-pound bike. Interestingly, when seated, a compact frame feels exactly like a traditional design. The compact design has no effect on handling beyond the increases responsiveness during climbing and accelerating."

    I ride a 60-ish size frame and the Pegoretti style or slightly sloping TT work well for me. Allows a bit more seatpost to show. Otherwise, my bikes look like they're out of the 80's, when the longest seatpost Campy made was around 180mm.
    I believe it ..coming from someone who is not about hype but pure substance like Kellogg. Otoh it does not make sense to me: power is generated at the BB and transfered thru chainstays. Both, bb and cstays, stay the same no matter how short are the other tubes.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by Matthew Strongin View Post
    Do a decent enough job matching the top tube angle to the stem angle (ballpark, not exact match) and they'll all look solid.
    Balance is the name of the game. One thing Craig may chime in on here but stuck with me on my Pavaix: Try to get the headtube length and exposed seatube length to be roughly the same. That balance also really helps with aesthetics and one of the reasons my Pavaix has a slightly sloping top tube.
     

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by theflashunc View Post
    Balance is the name of the game. One thing Craig may chime in on here but stuck with me on my Pavaix: Try to get the headtube length and exposed seatube length to be roughly the same. That balance also really helps with aesthetics and one of the reasons my Pavaix has a slightly sloping top tube.
    It´s a way of thinking it but a JP Weigle won´t build like that and it looks balanced. A line parallel to the horizon traditionally means or brings balance. Cycling is all about geometry, structure, math, levers, force and speed results from balance.
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by colker View Post
    It´s a way of thinking it but a JP Weigle won´t build like that and it looks balanced. A line parallel to the horizon traditionally means or brings balance. Cycling is all about geometry, structure, math, levers, force and speed results from balance.
    Each of us has a different metric regarding what looks balanced. That's why convention (bicycles with double diamonds and level top tubes) left the building by the time the 1980s rolled around.

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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by Matthew Strongin View Post
    Do a decent enough job matching the top tube angle to the stem angle (ballpark, not exact match) and they'll all look solid.
    Lines used to flow from stem to handlebar and brake levers. Bars were parallel to stem and top tube. Tubes were slender and structure looked delicate while it was engaged in speed through maximum human effort. Colors from clothing and bicycle played together. Does it matter if it does not flow anymore and each part of the bicycle seems plugged to another like plumbing?
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    Default Re: What´s the reasoning behind dropped top tubes on a road bike?

    Quote Originally Posted by colker View Post
    Lines used to flow from stem to handlebar and brake levers. Bars were parallel to stem and top tube. Tubes were slender and structure looked delicate while it was engaged in speed through maximum human effort. Colors from clothing and bicycle played together. Does it matter if it does not flow anymore and each part of the bicycle seems plugged to another like plumbing?
    People used to talk to each other too. Now it's text this and DM that.
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