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  1. #1
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    Steel or Aluminium For My Fat Bike Frame?

    I'm looking to get a Fat Bike frame built and have to decide between 4130 cr-mo or 6061 alloy.

    What would you choose? I'm going to use mine mainly in a snow free area, riding trails and anything that looks like fun but I'm also going to race it in XC for a laugh from time to time. I'll probably also set it up as a single speeder at times as well.

  2. #2
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    Hey;

    To some extent, I don't think it matters, as long as your builder has their heat treat process really worked out properly. Given that, and if weight is an issue, then Al is the obvious choice. Steel is easier and offers more opportunities for customization. I doubt many small builders have the facility for manipulating aluminum very much. The differing ride qualities will not show so much on a squishy tired fatty. Steel is certainly tougher and easier to repair, where 6061 is basically throw-away if it fails. That might be less likely on that same squishy fatty.

    I went old school when I built mine. Working with Al is another level of skill altogether.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  3. #3
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    Steluminiumel

  4. #4
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    Ti > *

    But given those choices, I'd go with steel.
    Let the market decide!

    N42.58 W83.06

  5. #5
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    Go with aluminum if maximum performance (weight, stiffness) is what you're looking for, go with steel if durability is your priority.

  6. #6
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    A well built steel frame will not perform worse than an AL frame. Stiffness doesn't translate directly to speed and going too flexy or too stiff will both negatively impact bike performance. A custom built steel frame should be right in the sweet spot if your builder is on the ball.

    The weight difference will be negligible and not affect how fast you ride.

    If I was getting a custom fatbike built and my choices were AL or steel I'd take steel.
    Safe riding,

    Vik
    www.vikapproved.com

  7. #7
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    I went for an aluminum Mukluk which was great but if you ever want to take it touring or anywhere that's kind of rough in terms of transportation (eg, throwing it on top of a bus) then aluminum will more likely get wrecked. I took mine to Baja California and strapping it to the front rack of the Sportsmobile rubbed a gouge in the chainstay (I missed one rub point hiding under some padding). Luckily it doesn't seem to be in a critical location. But after that I sold it to my friend because I don't want to deal with that. He won't be loading it too hard or doing anything crazy with it, whereas I would, and don't want the hassle.

  8. #8
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    I would go steel if it's a custom frame. Reynolds 853, or if you have money to burn and want something unique and very cool, Reynolds 931 or 953

    Their 853 stuff is the light steel that people race on.

  9. #9
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    I really like the extra frame bag space a steel frame gives.
    laotzucycles.blogspot.com

  10. #10
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    Quote Originally Posted by daves4mtb View Post
    Why would aluminum be more likely to do that than steel, which is typically a softer metal?
    I believe the Brinnel hardness of 4130 chromoly steel is about 3 times that of 7005 aluminum. Aluminum tubing typically also has much thinner walls than steel tubing.

  11. #11
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    Aluminum frames achieve their stiffness by using larger diameter tubing, not by using more material.

  12. #12
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    Quote Originally Posted by daves4mtb View Post
    that doesn't mean an aluminum frame will be more susceptible to damage of the kind described. Or does it?
    It does. AL is a great material for mountain bikes in general, but there are some downsides.

    The metal on metal rubbing Mark described is certainly one concern if you need to transport your AL bike.
    Safe riding,

    Vik
    www.vikapproved.com

  13. #13
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    Hey;

    It is likely down to the difference between strength and toughness. They are NOT the same. Hardened Al has far greater strength than steel given the same tube spec, but NOWHERE NEAR the toughness. Al also work hardens, which makes it brittle and prone to failure unless annealed. A dent is a very localized form of work hardening. This is why AL frames have a finite fatigue life. It is not a question of if they will fail, but when, usually.

    Take a 6"x1" strip of 12ga steel and a like piece of 6061, put and inch of each in a vice, and start bending it back and forth at 90*. The AL will crack and fail very quickly. The steel will not. You will also note the difference in stiffness then. Then, try that with a piece of 5052 Al, which is a non heat treated alloy. It will have less strength than 6061 by far, and will bend many more times before it fails, but it will still fail sooner than steel. That's because it will work harden at the bend and then fail similarly to 6061.

    If steel fails, you fix it. If Al fails, you recycle it. Not a value judgement, just the facts.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  14. #14
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    Fantastic feedback guys. Is a lightweight steel tube set like Reynolds 853 as strong as say DB 4130 for instance? Not saying I can afford 853 though!!!

  15. #15
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    You can't anodize steel!

  16. #16
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    Quote Originally Posted by Kiwi19 View Post
    Fantastic feedback guys. Is a lightweight steel tube set like Reynolds 853 as strong as say DB 4130 for instance? Not saying I can afford 853 though!!!
    Any heat treated steel tube will be stiffer and stronger than generic 4130 CroMo. You can generally go thinner with it and save weight with equal strength and higher stiffness. Getting it to ride as well as the "soft stuff" is another matter, I would think.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

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