XCL top tube questions- Mtbr.com
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  1. #1
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    XCL top tube questions

    1. Where the top tube meets the head tube there are 2 supports and on all the XCL frames it looks like the weld only goes around 3 sides and not the whole support. Just curious why.

    2. In a post on 9/7 a topic came up but was not really addressed. What is the difference between actual and effective top tube length. On Chumba's site they list the difference between a MED and LG as 23.5" VS 24" When I measure my frame from center of the seat quick release to center of head tube I come up with 23.5" is this effective or actual and do I have a MED or LG frame, not that I think the 1/2" would matter with seat and stem adjustments available.

  2. #2
    Nightriding rules SuperModerator
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    Quote Originally Posted by keefe
    1. Where the top tube meets the head tube there are 2 supports and on all the XCL frames it looks like the weld only goes around 3 sides and not the whole support. Just curious why.

    2. In a post on 9/7 a topic came up but was not really addressed. What is the difference between actual and effective top tube length. On Chumba's site they list the difference between a MED and LG as 23.5" VS 24" When I measure my frame from center of the seat quick release to center of head tube I come up with 23.5" is this effective or actual and do I have a MED or LG frame, not that I think the 1/2" would matter with seat and stem adjustments available.
    1. I am not sure why they don't weld it, but the other 2 welds on the sides should be enough to distribute the effort onto the tube, which is the purpose of that gusset...

    2. actual TT is the measurement that you did.......... effective TT is when you measure from the center of the headtube horizontally (parallel to the ground) to the projected centerline of the seattube (probably somewhere up your seat post)

  3. #3
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    Quote Originally Posted by keefe
    1. Where the top tube meets the head tube there are 2 supports and on all the XCL frames it looks like the weld only goes around 3 sides and not the whole support. Just curious why.

    2. In a post on 9/7 a topic came up but was not really addressed. What is the difference between actual and effective top tube length. On Chumba's site they list the difference between a MED and LG as 23.5" VS 24" When I measure my frame from center of the seat quick release to center of head tube I come up with 23.5" is this effective or actual and do I have a MED or LG frame, not that I think the 1/2" would matter with seat and stem adjustments available.
    For #1 - I believe that's what is called an open gusset. Here is the reason behind it from the EVO page.

    Open Gussets, so stress impact is more evenly distributed

    For #2 - the effective top tube measurement is a line (parallel to the ground) straight back from the top of your head tube to where your seat post would be. Actual top tube is the actual measurement of the top tube. The effective measurement takes into account the seat tube angle.


  4. #4
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    So, just to clarify...when Chumba says that a medium XCL as a 23.5" top tube length, is that the Actual or Effective? I would really like to know what the effective tt length is.

    Thanks.

  5. #5
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    Medium XCL's effective top tube is 23.5". The actual TT on mine measures out to be around 22.25".

  6. #6
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    Not welding that part saves them cost on the manufacuring.

  7. #7
    Mmmm Rocks Good
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    It saves them next to nothing in cost. I work in manufacturing and a good welder can weld those 4 or 5 inches total in about 2 minutes. The choice to not weld those ends has more to do with creating a potential stress riser across the area that is heat effected by the welding. Think of it like a pc of bamboo. It is easy to snap a pc of bamboo if you score across the grain of the bamboo. If you score with the grain of the bamboo you do not signifcantly weaken the total structure.

  8. #8
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    Cool-blue Rhythm

    I was just making a joke

  9. #9
    Mmmm Rocks Good
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    No problem!

    Quote Originally Posted by bit_lizard
    I was just making a joke
    No problem, I realized it as well but who knows if anybody else would get it and I was more interested in providing an explanation for the open gussets.

  10. #10
    Compulsive Bike Builder
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    It is what I like about Chumbas

    Another way to put this - that last weld does not contribute to the strength of the gusset. In fact, as an unneeded weld, the frame is actually weaker with that extra weld on it. This can be seen through computer analysis, which I know Ted does a lot of on his designs.

    It may not be much weaker, but you can see by looking at Ted's designs that he always goes with the option that makes the frame stiffer.

    It is sort of like being a weight weenie, which I am by admission. Lightening one part won't give you a light bike. But if you choose every component with light weight in mind, you can get a good result. Likewise with frame stiffness, every little bit adds up.
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