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Alloy or Carbon - What would you do?



  • SeeFarr wrote:
    Vinnyc19 wrote:
    I'd have no hesitation with a carbon road bike, I was sold on carbon a while back when i saw this ... t-lab.html

    A reassuring video, nice find.
    Yes I saw that and was convinced too until I sent the link to a keen cyclist boffin friend who suggested the following, some of which I quote from and other parts are paraphrased :

    The tests are impressive but don't replicate real life riding conditions. The screwjack test replicates perhaps only front wheel braking from immense speed. The other test replicates hitting something front on – which is when you actually want the frame to distort (without breaking and absorb part of the impact and protect you / the rider, from the full force of the impact (like the crumple zone in a car). For this you would be better off with steel and especially the manganese molybdenum alloys that are 531, and the chromium molybdenum alloys(e.g. 725 (or 4130 in the aircraft industry)) that are so prevalent today (when steel is used); and which aluminium alloys do reasonably well .

    In the second test a steel 'device' appears to have been inserted into the headtube. It seems unlikely that any road or MTB fork would transmit those loads to a frame without themselves breaking / failing – which therefore also render the tests meaningless. And where are the comparative tests, even with the same front fork replacement devices, on steel and aluminium frames? Where are the benchmarks, the control subjects?

    When ridden, the top tube of a bicycle is in compression, and the down tube in tension, both the result of an upwards force acting through the front axle which tends to rotate the forks forward. Neither test replicates that – in both, the top tube is put in tension and the down tube in compression – and neither test replicates the reciprocating actions that are characteristic of bicycling – either the continual up-and-down loads transmitted from passage over the road / track surface, or the very complex patterns of on-off loading generated throughout the entire machine (including handlebars and stem / extension) by pedalling action. These actions are again something that steel alloys accommodate extraordinarily well, and aluminium alloys do reasonably well. Remember also all the problems that aeroplanes over the years have had with metal fatigue through continual flexing / loading/unloading action, especially aluminium alloys.

    Going back to the tests: drop the weight on the back of the forks, or stretch rather than collapse the frame and you might have tests that begin to be relevant. But they didn’t do either. So, whilst these tests have all the appearances of being scientific and are very spectacular, I think they do no more than make Santa Cruz feel good about themselves and give them an edge in marketing – a very clever edge: “look how scientific we are”, “look how open we are”, etc.. But why are they bothering, if their machines are so good in the first place? For me, their tests do quite the opposite: the very fact that they don’t replicate riding persuades me that they are actually ignorant of the engineering principles involved .

    So, there you have it. I do believe he knows what he's talking about on this one and is clearly anti carbon. All this said I still find it hard to believe that so many major bike companies would continue to produce increasing ranges and numbers of carbon bikes if there was a significant problem and risk to the customer?
  • rolf_frolf_f Posts: 15,969
    dwanes wrote:
    Components take a long time to deteriorate, majority of these people tend to sell their bikes well before this would ever happen anyway.

    They take a long time to deteriorate depending on when you use them. If you are out daily in the kind of weather we've had over the last couple of weeks, they don't take long to deteriorate at all. I reckon about 90% of the wear and tear comes in the bad weather of December and January. I've worn chains and cassettes out in shockingly short times despite very regular cleaning.

    Parts for my old touring bike generally cost less than half the price of those of my more modern bikes. £150 spent on a second hand bike for winter is economically a no brainer.
    Faster than a tent.......
  • You only have to ask yourself one question, if carbon failed that easily then why has virtually every bike manufacturer used it on their top bikes? Carbon is everywhere, the pro peloton is full of it, so if it was bad would they use it?

    Seriously, the days of alu v carbon are long gone. Theres nothing wrong with both materials and just comes down to personal preference. Ive got 2 bikes, an alu that i used for 5 years no problem on the road and now being used on the turbo still going strong and my road bike of four years a carbon job thats taken everything thrown at it.
    Im not against either, but if was me i would use an alu in winter and a carbon any other time, purely because alu tends to be cheaper so a cheap winter road bike keeps the carbon beauty ready for spring-summer-autumn.

    Oh and i weigh the best part of 19stone, rugby player, and both bikes have barely creaked under me. Same with the wheels, not a single set have gone out of true, and they were basic Shimanos RS20 on the alu and Eastons on the carbon. Despite all the talk of fatigue, good products in my experience last a lot longer than given credit. Unless you bin it down a ditch ever week of course.
  • Still pondering which way to jump on this. Does anyone know what frame/fork guarantee Giant & Cube offer? (& other makers come to that) Have heard contradictory stories with Giant ranging from 4 years to lifetime...
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