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  1. #1
    Senior Member JeffOYB's Avatar
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    Do cross frames have to be heavier than road frames?

    What if a CX frame was made just like a road frame only it had slightly wider clearances, canti studs and a higher BB -- would it break?

    Such a frame might weigh a couple ounces more than a road frame just due to the canti studs and the fractional more mat'l required to widen the clearances a few mm's.

    What I see on the market for frames in comparable price brackets is that a CX frame of alum, say, often seems to weigh up to a pound more than its road-frame counterpart. The carbon frames often also seem to weigh a fair bit more.

    Does a CX fork have to be beefier?

    Are there known failure points for road bike frames, forks and parts when used for CX?

    When roadbikes were used for CX in the, say, 70's and 80's -- back when CX was much harsher -- were those bikes known to have shorter lifespans? ...And to break in certain known places that we now know to reinforce?

    I used to use a roadbike for CX back then and it held up fine until I started jumping it -- then the forks choppered -- but it was fine til then. I never heard of CX 'wrecking' a roadbike or even wheelset. These were 20-lb steel roadbikes with 26-28mm CX sewups.

    Do we know better today?

    I notice that the Giant TCX SL Aluxx weighs like a pound more than the comparable TCR. That's a +25% weight gain. Where did they put all that material? Can't be just studs and clearances. I don't see their marketing mat'l playing up any known points for reinforcement for CX frames. But that's just one example and it's hard to find exact weight info that always agrees. (It kinda looks like it's a half-lb in the frame and half-lb in the alum fork compared to TCR carbon fork.)
    Last edited by JeffOYB; 10-17-13 at 10:44 AM.
    Jeff Potter
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  2. #2
    coprolite fietsbob's Avatar
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    It is possible, in theory, to make a thing so perfect for purpose that is lasts just long enough

    to get you across the finish line and then collapse ,

    then you get a new one for the next time.

  3. #3
    Senior Member
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    Why a new thread? This is just basically a continuation of the old one.

    I'm with Bob, look at race cars. They are designed to last JUST the length of the race before the engines generally need to be completely rebuilt. The higher a performance a thing is, the closer it skates to the failure line in terms of ultra light weight and durability. And the much more expensive the parts are.

    Most ultra light full carbon race bike frames have weight limits of like 175 pounds for the rider. So companies have a balancing act. Cheap+durable but not light or Cheap+light but not durable or light+durable but very expensive. Companies want an insurance buffer in their commodity bike frames like the TCX. I imagine that they don't make it super light so it won't fail. Cyclocross is a hard sport yet Giant warranties their frames for a long time. I imagine that the cyclocross frames have thicker welds, maybe thicker tubing, etc to withstand the abuse and not fail so preventing warranty claims. Road biking doesn't suffer nearly the same harsh abuse that cyclocross frames do.

    Steel frames/forks are much more forgiving than carbon and alloy parts. Now look what I said, forgiving, not necessarily stronger. I believe that for the most part, a carbon part is quite a bit stronger and lighter than a steel part, the difference is the failure modes. A steel frame/fork will just keep bending and you can bend it back and keep using it. A carbon part will withstand the abuse that bends the steel but when it gives way, it just breaks like a piece of glass. Alloy is kind of in the middle. An alloy frame will bend a little bit unlike carbon but it will eventually just crack.

    So even though people back in the old days used steel road frames, they were much more forgiving to the abuse than modern road frames.
    Apples and oranges comparing road to cyclocross frames. A similar priced road vs cyclocross frame? I would not be surprised one bit by the cyclocross frame being heavier and designed to withstand the abuse. You want a super light cyclocross frame? Pay much more money and be happy.
    Last edited by bobotech; 10-17-13 at 12:38 PM.
    "When dealing with stuff like this consider that this is a bicycle, not a spaceship." -- FBinNY

  4. #4
    idc
    idc is offline
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    I think the basic answer is "yes". Look at how touring bikes (even lighter touring bikes) are spec'ed, and they don't even bunny hop barriers, get thrown around on remounts, or get air - but they do need to be reliable and carry heavy loads.

  5. #5
    Team Water Andy_K's Avatar
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    It's hard to find an apples-to-apples comparison point, but try this:

    A. Whiskey 7 straight blade road fork



    Claimed weight: 375 grams

    B. Whiskey 7 straight blade cross fork



    Claimed weight: 491 grams

    I suppose the canti studs add some weight, maybe 30-50 grams. The cross fork is also 29mm longer. So is the CX fork really that much "beefier"? Probably not, at least in this case.

    FWIW, the Bike Rumor review of the Whiskey 7 disc fork (would you really buy a fork that could be described as "Whiskey disc"?) had it 60 grams over the advertised weight.

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    The chainstays and fork are longer so, yes, a cross bike is necessarily heavier, all else being equal.

  7. #7
    Team Water Andy_K's Avatar
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    The other thing I'd like add is that having watched a CX race that featured a 180 degree turn at the bottom of a downhill stretch of pavement and observed that you can actually see, from 20+ feet away, a carbon fork shudder under hard braking, I wouldn't want a CX fork that was any less beefy than what's available.

  8. #8
    Senior Member Jiggle's Avatar
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    I can see how forks would need to be heavier because of the higher moment of canti mounts vs road caliper mounts. But frames? Is the stress on a frame greater jumping a cx barrier than it is bunny hopping curbs or hitting road potholes? I think not much. Top road frames are in the 700g range right now with weight limits around 110kg. I'd like to see at least a 900g cross frame with a weight limit of 100kg.

  9. #9
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    Quote Originally Posted by Jiggle View Post
    I can see how forks would need to be heavier because of the higher moment of canti mounts vs road caliper mounts. But frames? Is the stress on a frame greater jumping a cx barrier than it is bunny hopping curbs or hitting road potholes? I think not much. Top road frames are in the 700g range right now with weight limits around 110kg. I'd like to see at least a 900g cross frame with a weight limit of 100kg.
    I don't know many people who bunny hop or intentionally ride their nice road bikes through pot holes. Cross racing is just much more harsh than normal road riding. Watching the cross race last weekend made me realize just how much more abuse the track dishes out compared to riding on the streets.
    "When dealing with stuff like this consider that this is a bicycle, not a spaceship." -- FBinNY

  10. #10
    Senior Member Jiggle's Avatar
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    Doesn't matter if they are more harsh because road frames are overbuilt anyway for a rider of non-fat size.

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