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Thread: Top tube?

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    Senior Member tntom's Avatar
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    Top tube?

    What is the difference between a level top tube and a sloping top tube? How do they change the way a bike rides?
    Thanks Tom

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    Senior Member Retro Grouch's Avatar
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    If everything else is equal I don't see why there should be any difference in ride. Problem is, everything else never seems to be quite equal.

    When the bike companies started producing "compact frames" with sloping top tubes, many of them took that opportunity to substitute multiple or adjustable stems and reduce the number of frame sizes. Then they fed us a bunch of bologna about how having a lot of additional seat post sticking up was going to make the bike "stiffer". I think the big motivation was simply to make the bikes cheaper to produce.

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    No change in handling. Those characteristics are determined by: wheelbase, head tube angle, seat tube angle, fork rake and trail and length of chainstays. Possibly a stiffer ride, but I doubt that as well.

    Slopping top tube bikes are what is known as Compact Geometry bikes, and are (mostly) a gimmick by the manufacturers to convince you - the consumer, that there's a weight savings and increase in ride stiffness. In reality, it allows manufacturers to assemble fewer choices in frames sizes, going S, M, L, XL etc... in place of 49,51,53,55,57,59, cm seat tube length bikes, as example (saves money in manufacture). The theory with CG is you adjust seat post length for saddle height and stem length to get correct reach. Works OK for a lot of riders, but you can only make up so much with stem length before the stem becomes either too long, or too short, either of which CAN negatively affect handling, as you find yourself stuck between frame sizes. Thus having better choices in TT length increases the chances that the stem, and thus the bike, will fit and handle correctly.

    Unfortunately, the straight TT bike is going the way of the Polar Bear.

    SB

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    Small Member maddmaxx's Avatar
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    Compact frames provide a little more standover height for a given virtual top tube length. The smaller triangle probably stiffens the frame a little as would the smaller rear triangle on many TT or Tri bikes. Marketing stressed standover height for sizing frames for new riders so many people were getting bikes that were too small for them.

    I think that some of the compact frame ideas for modern road bikes are a result of design ideas spilling over from the MTB side of the room. As with all things, the proper frame depends on the needs of the rider. At 6' in height with a 30" inseam 31" standover height properly measured I live in the world of compact frames. I need the long virtual top tube of a 57cm frame with some sembalance of standover height. My MTB is so extreme that a full size water bottle will not fit on the seat tube. That may not however be the answer for everyone. WSD frames tend toward just the opposit as women are more likely to have longer legs than men in relation to a given height.
    Last edited by maddmaxx; 10-07-07 at 10:07 AM.

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    Time for a change. stapfam's Avatar
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    In general- the "Normal" and "Compact" frames have no difference in handling. The compact Frames did away with "Standover Height" and left the choice of size of frame to suit the Reach of the torso and arm length to the rider. Claims that it is cheaper to manufacture-Cuts down on Sizes that have to be made- or better handling for one of the other frame can be believed or disproved as you wish. The difference is in the feel of the frame once being ridden. And only you can tell that.
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    gone ride'n cyclinfool's Avatar
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    Material characteristics have more to do with bike stiffness, the wall thickness of the tubes and the type of material used. Wheel base and angles effect tracking and stability as stated previously. My latest purchase is a sloping TT, compact geometry CF frame. My other ride is a level TT classic geometry lugged steel (columbus SLX) frame. They both absorb road vibrations about the same but the CF frame is definately stiffer when cranking on the pedals. Is that the geometry or the material, my guess is that it is the material. I don't notice the lower stand over height. Luckily I am a very average size and proportioned person so I am in the middle of the fit bell curve and take to a stock frame nicely so rider position works equally as well for me on both stock sized frames. If you have a wierd body size I would suspect you would have difficulty with any stock frame size and might need to go custom.
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    Senior Member Wildwood's Avatar
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    I didn't read every post above completely.
    There are traditional and compact frames but then there are varying degrees of slope in the top tube from 2 deg up to ??. Some sloping top tubes serve the purpose of a taller headtube for getting the handlebars more level with the saddle.
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    Cycling Anarchist Trsnrtr's Avatar
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    Quote Originally Posted by tntom View Post
    What is the difference between a level top tube and a sloping top tube? How do they change the way a bike rides?
    Thanks Tom
    One's a girl's bike and the other isn't.

    Just kidding, but that's what I always tell a friend of mine that owns a compact frame.
    Dennis T

  9. #9
    feros ferio John E's Avatar
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    Quote Originally Posted by tntom View Post
    What is the difference between a level top tube and a sloping top tube? ...
    As a highly biased retrosnob, I say the former looks correct/proper/good/etc.

    The latter reduces manufacturing and retailing costs by allowing a given size to accommodate a wider range of sizes of riders.

    Ride something that fits you comfortably and which serves your needs and desires.
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    Unfortunately, the straight TT bike is going the way of the Polar Bear.

    Then with all the holiday wrapping paper I found in the attic this weekend, I will be able to retire when my traditional frame bikes are classics and worth a fortune on scambay!

  11. #11
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by John E View Post
    As a highly biased retrosnob, I say the former looks correct/proper/good/etc.

    The latter reduces manufacturing and retailing costs by allowing a given size to accommodate a wider range of sizes of riders.

    Ride something that fits you comfortably and which serves your needs and desires.
    Said some one would say this.

    All a frame is- is something to hang the rest of the bits on. If it was critical on dimensions-materials- sizing- then there would only be one frame size and all the same critical angles. Bikes differ and so do the people that ride them. One of the reasons I ride compact is that I started on Mountain bikes and Distance between the crotch and the top tube is Critical. The further the two can be apart- the better. But a Compact frame also gives a different ride. The bike is stiffer- the rear triangle is smaller and stiffer and this does give an advantage when pedalling power is changed to forward movement. Stiffer frame = less flexing = less power loss from pedalling effort. Then there is the "Chuckability" of a small frame on technical parts of a ride. That small frame- even though it may weigh more (Which mine don't)-is easier to manoeuvre.

    When I transferred over to road bikes- I went with the compact frames as this is what I know. I am used to the frames and although I don't often have to Bunny hop logs or Swerve round many trees on the road- I do feel that I can do it if necessary.

    So get out and ride a few compacts and a few normal frames and see what you like.

    Attachment is of the 3rd type of frame- Sloping Tube
    Attached Images Attached Images
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    Sloping top tubes - just look wrong!

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