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  1. #1
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    DH front triangle tubing size

    I'm looking to purchase straight gauge chromoly tubing so I can weld up a new front triangle for my freeride frame. I want to make the geometry more DH oriented which means making it lower and slacker. I have the headtube material and I will be ordering a 73mm bottom bracket and a seattube.

    So my question is what thickness and diameter of straight gauge chromoly would work best? I'm not too concerned about weight, but I don't want the frame to weigh 50lbs either.

    Thanks in advance

    Also is there anywhere I can buy ISCG tabs in steel or buy a bottom bracket shell with ISCG tabs already attached?
    Buy a f-ing bike maybe you wouldn't be fat

  2. #2
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    More info needed

    So:
    1: If this is your first frame project, build a hardtail first so you can figure out what you're doing a tiny bit.
    2: In general, tube diameters and walls are going to depend on the rider size/riding style, but with FS bikes, you also have to make allowances for the mounting points for pivots and shocks. Those gotta be beefier, generally. So there's not an easy answer for you.
    3: For a new builder for XC, .9mm (.035") wall is a good starting point. For a DH bike, if you insist on starting on this, .049" would be better IMO.

    Paragon has all the BB shells and ISCG mounts you want.

    -Walt

    Quote Originally Posted by unknown-rider View Post
    I'm looking to purchase straight gauge chromoly tubing so I can weld up a new front triangle for my freeride frame. I want to make the geometry more DH oriented which means making it lower and slacker. I have the headtube material and I will be ordering a 73mm bottom bracket and a seattube.

    So my question is what thickness and diameter of straight gauge chromoly would work best? I'm not too concerned about weight, but I don't want the frame to weigh 50lbs either.

    Thanks in advance

    Also is there anywhere I can buy ISCG tabs in steel or buy a bottom bracket shell with ISCG tabs already attached?
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  3. #3
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    Walt thanks for the reply, this isn't my first bike frame project, although I haven't built a full frame yet. I will be enlisting my dad's help for this frame build. He has all the tools we will need to complete it. He has many years of tig and mig welding experience as well as fabrication and machining experience. He also has a frame (automotive) table we can use to mount the jig for the frame.

    We are only making the front half of the frame, I'm going to reuse the rear portion of the other frame. It is a single pivot frame so there will only be the main bearing mount, which we will machine up on the mill or lathe, and the front mount for the shock. Both of those mounting points will be on the downtube, so I'd imagine that tube should be thick and I could get away with a thinner toptube.

    From looking at a .035" wall piece of tube it looks rather thick, that wouldn't be thick enough for a downhill frame? I only weigh ~150lbs. We were thinking we could go thinner, using a 1.5" 4130 chromoly tubing... If this seems unreasonable let me know, I saw you made the front half of a full suspension frame, what wall thickness tubing did you use? also what tube diameter?

    Thanks
    Buy a f-ing bike maybe you wouldn't be fat

  4. #4
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    Don't go thinner

    .035" is absolutely as thin as you would ever want to go, even for an XC bike, if we're talking 4130 cromoly. Anything thinner is generally going to be too weak. If you get into nicer heat treated or air hardening tubing, you can go thinner.

    If this is your first real frame, you should forget about weight and concentrate on safety and easy mitering/welding for the tubes. You might look at some of the stuff that Kirk is selling at Bikelugs.com - he has some butted BMX tubing that might work really well.

    I do TONS of FS bikes, so I have used all kinds of tubes at various times (so I can't tell you unless you can refer me to the specific bike). IMO if you're using 4130:
    -1.5"x.049" downtube
    -1.25" or 1.375" x.035" toptube and seat tube. .049" would be good too.
    -44mm/taper head tube from Henry James or Paragon.

    -Walt

    Quote Originally Posted by unknown-rider View Post
    Walt thanks for the reply, this isn't my first bike frame project, although I haven't built a full frame yet. I will be enlisting my dad's help for this frame build. He has all the tools we will need to complete it. He has many years of tig and mig welding experience as well as fabrication and machining experience. He also has a frame (automotive) table we can use to mount the jig for the frame.

    We are only making the front half of the frame, I'm going to reuse the rear portion of the other frame. It is a single pivot frame so there will only be the main bearing mount, which we will machine up on the mill or lathe, and the front mount for the shock. Both of those mounting points will be on the downtube, so I'd imagine that tube should be thick and I could get away with a thinner toptube.

    From looking at a .035" wall piece of tube it looks rather thick, that wouldn't be thick enough for a downhill frame? I only weigh ~150lbs. We were thinking we could go thinner, using a 1.5" 4130 chromoly tubing... If this seems unreasonable let me know, I saw you made the front half of a full suspension frame, what wall thickness tubing did you use? also what tube diameter?

    Thanks
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  5. #5
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    Ok, I didn't realize that .035" was the thinnest you could go. Thanks for the info, I really appreciate it all. I am here to learn before I start this project. I have a stick of "standard" headtube material (I believe it's 37mm), the type that takes the external cupped headsets for 1 1/8" steerers, would that not be good for use on this frame build?
    Buy a f-ing bike maybe you wouldn't be fat

  6. #6
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    slightly off topic, but along the same lines.

    how would you go say running a 0.035" wall on 3" tubing? would that be of equal/more strength of 0.049x1.5?

    cheers.joe.

  7. #7
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    Does it exist?

    AFAIK, the largest diameter you'll ever find in thin (ie .035") wall is about 1.75".

    -Walt

    Quote Originally Posted by crazymofo View Post
    slightly off topic, but along the same lines.

    how would you go say running a 0.035" wall on 3" tubing? would that be of equal/more strength of 0.049x1.5?

    cheers.joe.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  8. #8
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    hey walt, i have found a local supplier for a 2" tube in 0.035" wall thickness, how do you think this would compare in strength/weight to 1.5x0.049 tubing?

    cheers.joe.

  9. #9
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    What do you mean by "strength"?

    Those tubes are basically the same weight (the 2" being a little heavier but not enough notice in any way). That big sucker will be WAY stiff - probably much stiffer than you want. Ultimate yield strength on either is pretty much irrelevant, you'd have to run into a parked car, assuming the joinery is good.

    Good luck fitting a 2" tube to most head tubes, bb shells, etc!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  10. #10
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    fully intended on utilizing 1.5" headset and an 83mm BB (it is a full blown 10" travel DH bike im aiming to build)

    i intended on flattening out the head tube tube ends to fit in better with the head tube the 83mm BB shell should have plenty nuff clearance

    2"x 0.035 DT, 1.5/8"x 0.035 TT, 3/4" box SS, CH.
    64* HA, 75* STA
    ive got my geometry and VPP linkages worked out to the point im ready to knock up a test mule out of mild steel tubing to see how it feels on a trail, but im still trying to workout a sliding drop out set up to alter geometry, and the use of a gearbox. however gearbox is the lower level of priority atm.

    first things first tho, need to get started on my jig

    thanks for the advice. i will share some progress stuff once i get started.

    cheers.joe.

  11. #11
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    Cool!

    Keep us apprised of your progress! I'm not sure I've seen a steel homebuild VPP - what software are you using to design the suspension? I've seen a couple of approaches there but I'm a single pivot guy in general so I can't recall much about them off the top of my head.

    FWIW, you do not need a 2" downtube for any reason unless you weigh 400 pounds. Yes, even for a DH bike. If you *want* to use one, by all means, go ahead. But it's not going to do anything for you.

    If you have some experience with machining and welding thin/hard tubing, it's hard to beat True Temper Supertherm for strength/weight/bling for this kind of bike. I have a 165mm travel 29er with a frame weight under 7.5# that is bombproof built from that stuff.

    The fitting for the BB shell is going to be annoying not because of the width, but because of the diameter of the shell. It's going to totally swallow it - but it's doable.

    -Walt

    Quote Originally Posted by crazymofo View Post
    fully intended on utilizing 1.5" headset and an 83mm BB (it is a full blown 10" travel DH bike im aiming to build)

    i intended on flattening out the head tube tube ends to fit in better with the head tube the 83mm BB shell should have plenty nuff clearance

    2"x 0.035 DT, 1.5/8"x 0.035 TT, 3/4" box SS, CH.
    64* HA, 75* STA
    ive got my geometry and VPP linkages worked out to the point im ready to knock up a test mule out of mild steel tubing to see how it feels on a trail, but im still trying to workout a sliding drop out set up to alter geometry, and the use of a gearbox. however gearbox is the lower level of priority atm.

    first things first tho, need to get started on my jig

    thanks for the advice. i will share some progress stuff once i get started.

    cheers.joe.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  12. #12
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    i'll be the first to agree with you about the fact the 2" tube isnt needed for strength, but i am doing it for an visual reasons, i love fat tubes, hence why i was questioning the strength of 1.5x 0.049 tube Vs 2x 0.035 tube. i'll gladly go the fat tube with thin wall if it looks better (shallow i know haha)
    my lower vpp linkage is right above the bottom bracket, so the larger down tube will give me will help me integrate a pivot point with more strength behind it.

    no design software, lots of nights with 2 threaded booker rods pinned down to a board in full scale, the booker rod being the linkage plate, tweaking their lengths and angles, and while im happy with the wheel path on the dummy rig, which travels back 0.5" and up 9.5" i really need to see how it rides, hence why i want to build a dummy bike out of a couple of $30 kmart bike frames cut up and some steel tubing. while it wont be a huck to flat machine, it will give me a basis and direction to go from.

    ive been designing this bike for the past 15 years in my head and on paper long before VPP bikes and gearboxes were popular, i finally just finished my apprenticship as a sheetmetal fabricator and have started to really play with chromoly welding, to the point where i feel i have the skill set to do something proper about it now. so now, its time to get busy!

    cheers.joe.

  13. #13
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    Let'r Rip, Joe.
    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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    Looking forward to seeing the prototype.

  15. #15
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    Quote Originally Posted by Live Wire View Post
    Looking forward to seeing the prototype.
    +1
    Buy a f-ing bike maybe you wouldn't be fat

  16. #16
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    Whoa.

    10" travel VPP bolted to a K-mart bike, eh?

    I think I'm done on this thread...

    -W

    Quote Originally Posted by crazymofo View Post
    hence why i want to build a dummy bike out of a couple of $30 kmart bike frames cut up and some steel tubing. while it wont be a huck to flat machine, it will give me a basis and direction to go from.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  17. #17
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    Quote Originally Posted by Walt View Post
    10" travel VPP bolted to a K-mart bike, eh?

    I think I'm done on this thread...

    -W
    I'm assuming this means there will be a dual crown fork on a K-mart bike as well... lol
    Buy a f-ing bike maybe you wouldn't be fat

  18. #18
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    Quote Originally Posted by Walt View Post
    10" travel VPP bolted to a K-mart bike, eh? I think I'm done on this thread...-W
    Think ya came unclipped there, Walt;

    I think he said he is building a test mule out of cut up Huffys just to try his suspension theories before committing to it with a bunch of expensive 4130. I think they call it prototyping. May not be the tack that everyone might take, but it doesn't sound that wack to me.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  19. #19
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    You are new here...

    If you hang around long enough, you will see dozens of guys like this. He is not going to build anything. Eventually you just start making fun of them because really, what can you do but laugh?

    If you search back you can find some really cool MSPaint designs with indignant designers insisting they were about to build them. Funny stuff.

    -Walt

    Quote Originally Posted by TrailMaker View Post
    Think ya came unclipped there, Walt;

    I think he said he is building a test mule out of cut up Huffys just to try his suspension theories before committing to it with a bunch of expensive 4130. I think they call it prototyping. May not be the tack that everyone might take, but it doesn't sound that wack to me.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  20. #20
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    Maybe so...

    On the odd chance that he may be for real, I guess I would have skipped the flip and evaporated quietly. Makes me wonder how many times - or perhaps why - you resisted hitting that send key on me?

    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  21. #21
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    Quote Originally Posted by Walt View Post
    If you hang around long enough, you will see dozens of guys like this. He is not going to build anything. Eventually you just start making fun of them because really, what can you do but laugh?

    If you search back you can find some really cool MSPaint designs with indignant designers insisting they were about to build them. Funny stuff.

    -Walt
    thanks for the vote of confidence!

    frame fixture suppliers arent exactly thick on the ground round here, so its all imported for me, chromoly tubing also only has a handfull of suppliers here aus as well!

    so im not going to go through with the expense and time delays of getting hold of materials, just for it to be not right.

    i want to do a full scale mock of out of **** steel to see how it pedals and bump sensitivity, i can buy some cheap steel frames for less then $10, so i dont see how its not a practical way to mock things up with.

    anyways, im not here to justify myself to you or anyone, im here to learn more about what it is i want to do.. build a frame. being a father of 3 (one of which has a DH addiction) i dont have a lot of spare cash, so im being carefull with what i do want to waste my money on.

    anyways, thanks for the tips. who knows? maybe i'll prove you wrong and a mock frame up :P

    cheers.joe.

  22. #22
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    Quote Originally Posted by TrailMaker View Post
    Maybe so...

    On the odd chance that he may be for real, I guess I would have skipped the flip and evaporated quietly. Makes me wonder how many times - or perhaps why - you resisted hitting that send key on me?

    You were very close to getting the "GONG".........but then you posted a pick of your jig with tubes in it, saved by the bell! It's a cool bike by the way!
    I'm hopen' not to get GONGED a Wally world bike showed at my house and it's gone
    Under the knife to become a 32er BMX.

    As far as DT tubing maybe 1.750 x .035 would work better..easier to fit to the BB
    And stronger (stiffer) by a little than 1.50 x .049
    PAYASO 36er.....Live the Circus

  23. #23
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    WALT

    We do things a little up-side down in this part of the world... we are special, 1 day always ahead of every one else...AND, it costs to experiment, so the cheap route is fine.

    Joe, post what you've got when its progressing...prove Walter wrong...
    Looking forward to the creativity.

    Eric
    If I don't make an attempt, how will I know if it will work?

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