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  1. #1
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    Fiberglass frame..?

    I'm in the early stages of building a custom recumbent bike for cruising around town and riding around the lakes a few times a year. I have a jig made and I'm working on the foam plug now (using a mold in case I want to make 2 or a revision). But I was wondering something ..

    The plan was hand layed Carbon Fiber over a foam frame. I was about to order my resin and I ended up reading about home made personal aircrafts like the Cozy ect. They mostly use Bi/Unidirectional woven fiberglass cloth. This quality cloth is available for around $5 a yard (50" wide), even cheaper in bulk. Quality Carbon Fiber is around $20-25 from what I've found, and the rolls are 20-30" wide. Using the same aircraft quality resin as I would with CF, would this fiberglass cloth hold up well enough?

    Before you say flat out "no", I should say more about my design. I have allready designed more surface area than most bikes built. A rear fender is incorporated into the frame which gives more support to the rear wheel. It's a LWB design with an extra thick nose piece. I'm not afraid of making extra thick layers. I'm a casual rider and I'm not worried about weight/racing/hillclimbing. I just want something that will hold together and ride like a Buick (Another reason for the LWB).

    If I do use fiberglass, all load bearing areas can be backed up easily with wood... I think.

  2. #2
    11,134 posts WTF
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    EEEE I don't Know

    Quote Originally Posted by e_fractal
    I'm in the early stages of building a custom recumbent bike for cruising around town and riding around the lakes a few times a year. I have a jig made and I'm working on the foam plug now (using a mold in case I want to make 2 or a revision). But I was wondering something ..

    The plan was hand layed Carbon Fiber over a foam frame. I was about to order my resin and I ended up reading about home made personal aircrafts like the Cozy ect. They mostly use Bi/Unidirectional woven fiberglass cloth. This quality cloth is available for around $5 a yard (50" wide), even cheaper in bulk. Quality Carbon Fiber is around $20-25 from what I've found, and the rolls are 20-30" wide. Using the same aircraft quality resin as I would with CF, would this fiberglass cloth hold up well enough?

    Before you say flat out "no", I should say more about my design. I have allready designed more surface area than most bikes built. A rear fender is incorporated into the frame which gives more support to the rear wheel. It's a LWB design with an extra thick nose piece. I'm not afraid of making extra thick layers. I'm a casual rider and I'm not worried about weight/racing/hillclimbing. I just want something that will hold together and ride like a Buick (Another reason for the LWB).

    If I do use fiberglass, all load bearing areas can be backed up easily with wood... I think.
    Dude I admire your creativity but there's a reason every manufacturer has a cf bike in their line and not fiberglass. Hey Colnago never did it Merckx never did it DeRosa never did it Pinarello never did it. Even Trek hasn't done it, and that's saying something. It would ride like wood as it is reinforced with it and that is what people use to describe a bad cf frame. Stick with what is known and proven. I'm not trying to be rude but i don't want you to spend all that money on a frame you don't like and probably won't last long.

  3. #3
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    I appreciate any info or opinions, good or bad.

    I have been pondering what you stated too. Why havn't the big companies made fiberglass frames yet? Anyone know?

    Most of what I have read has been more directed at aviation. Proper fiberglass cloth will have higher impact strength than CF, but less tensile strength (pulling). But still, the tensile strength is nothing to worry about as its very close to CF and more layers can make up for it. Again, I will be using the same Epoxy resin with either material.


    I know CF is better for bikes, don't get me wrong. I'm just wondering if it will work, and if not, why?

    Edit: http://nbhaa.com/indexBowden.html . The rear half of this bike is exactly the same as my design. I would love to have one of these. This is the only commercial attempt I found, and it failed horribly like most good things do
    Last edited by e_fractal; 02-15-2006 at 11:12 PM.

  4. #4
    Downhill Juggernaut
    Reputation: Chris H's Avatar
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    Don't know how it relates exactly to building a bike out of it, but when I was a hard core fly fisher my first rod was fiberglass. Insanely heavy and very whippy and not very lively. Consequent rods were made of graphite. Light stiff and responsive.

    Doesn't mean that your bike will whip about like an antennae, the cloth should add some stability, but if you want the bike to be as heavy as a Buick... fiberglass seems to be the way to go.
    If running were a person I would try to sabotage their life so that they were poor and drunk and living in the gutter pulling half smoked cigarettes from ashtrays in front of the Target. - Joe Daddio

  5. #5
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    Fiber glass will work. As you have stated, glass doesn't have the tensile strength or the modulus of carbon, but the main reason it isn't used in the industry is its weight. You can make a equally performing frame with glass, but the frame may weigh a pound or more than a carbon frame. Glass does have better impact resistance than carbon.

    I say go for it! If weight is an issue look for S2 glass which is stronger, therefore you can use less of it and reduce your weight slightly.

    By the way, "white carbon" is aluminized glass used as a decorative facing on typically ugly unidirectional carbon lay-ups.

  6. #6
    Resident Dutchbag
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    Quote Originally Posted by centoweed

    By the way, "white carbon" is aluminized glass used as a decorative facing on typically ugly unidirectional carbon lay-ups.
    "White carbon" is a term sometimes used for fiberglass, the aluminized stuff is in fact carbon.
    Originally posted by thatsmybush:
    I can only speak for my self, but if Fergie wanted to rub her lovely lady lumps on me, I could play the role of "human stripper pole."

  7. #7
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    Go for it

    A lot of wheel companies made fibreglass disc wheels (Mavic, Wolber, Fir, TTD Max, Ambrosio) before introducing carbon to their wheels in the late eighties. Fibreglass wheels were plenty stiff, but they were also quite heavy relative to carbon. The success/failure of your recumbent project seems not to be contingent on weight. So I say go for it and post the pics once you've made your recumbent. I'm interested.
    G

  8. #8
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    Like some others have posted, fiberglass will work fine, but will be a bit heavier. If you are not worried about the weight, and/ or this is going to be your first attempt fiberglass is the call.

    S2 is going to be more expensive then conventional E-glass and is slightly stronger. However, you may actually find E to work better for what you are talking about as S2 only performs better in certain layups. You can always mix and match your layers of material, you could use any glass, kevlar, carbon combo. Kevlar can be nice, but its hard to cut and doesn't laminate very well.

    It sounds like you may be set on your foam and resin system, but there can be huge strength and weight gains in these departments. You may consider laminating 1/4" Airex or Baltek Mat on top of the foam you have and then do your layers. What is your base foarm, EPS?

    If you have a good idea of what the load path will be you could push 1 or 2 carbon tubes through your foam and have them tie into your exterior laminate.

  9. #9
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    Fiberglass will work but it's heavier and not quite as strong as carbon

    When LOOK first strarted making frames in the late 80's, their cheaper models used a fiberglass/carbon mix. The KG56 was 70 percent glass and 30 percent carbon.
    Dave Hickey/ Fort Worth

    My 3Rensho Blog: http://vintage3rensholove.blogspot.com/

  10. #10
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    In high-tech production, the nod goes to CF. For your purposes, fiberglass will likely be equally strong and light as CF. Do spend the extra for S-glass. S2 would be even better, but probably isn't worth the price difference for this application.

    Just tossing a fiber into a resin, the functional difference is minimal between CF and glass. CF starts to shine when you begin to optimize the cloth/resin ratios, as its higher density allows it's fibers (which are functionally somewhat weaker than glass) to align better, decreasing their inherent stress less than the glass. In essence, more of each fiber's strength can be utilized, as they are less stressed by being bent out of shape by the weave of the cloth.

    To phrase this another way, the weight in a composite is in the resin, and CF allows for higher compaction and a lower resin/fiber ratio, because CF fibers can be pulled finer than can glass.

    As a practical matter, hand/homebuilt composite methods usually don't develop enough compaction to make CF function better than quality glass. Experienced, quality vacuum bagging can begin to make CF the better choice, but for strict hand-layup glass will function as well with no meaningful weight penalty. Given that you aren't enginneering the layup, weights, and tows precisely, there's no meaningful advantage to CF.

    To those who imagine themselves composites engineers: Yes, I took some shortcuts to make this vaguely readable. The bottom line is unless one has an engineered layup with optimized resin/matrix ratios, S-glass layups have generally equivalent to sometimes higher strength/weight ratios as compared to CF. It's exactly why the aircraft mentioned use glass rather than CF - there's not a practical way for a builder to create the needed pressure on the composite on such a large-scale item.

    Besides, it's just an opinion based on wide assumptions. If the OP can develop the needed pressures and design the layup appropriately, I'm all wet.
    A good habit is as hard to break as a bad one..

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