# What wall thickness/tubing?



## Pete Gossett (Apr 1, 2008)

Hi, I recently decided to build my own frame(after not finding any that offered the geometry I wanted). I built a small jig, cut up a couple old mild steel frames, and got a rideable prototype finished up last weekend. So far, I'm really enjoying it & looking to build a *real* frame from 4130 chromoly.

I'm looking for input on what tubing and/or wall thickness to use, I want the frame to be as light as possible, but it needs to be strong enough for the type of riding I do as well. What I'm after is a bike that is rideable for XC(even if it's not ideal), has good geometry & light weight for Trials riding(including Urban), and is versatile enough for other riding types as well. I'm a smooth rider, reasonably light weight(145lbs), and have never broken a frame in ~30yrs of riding.

I'd like the finished frame to weigh in around 5lb - the mild steel prototype is closer to 8lb. I plan on using as large of diameter tubing as I can for the top/down/seat tubes for strength & stiffness.

What is the range of wall thickness and/or specific tubing you would recommend for the main tubes?

Would I be better off using a formed/shaped down- or top-tube?

I see Nova offers both a Standard & Light bottom bracket shell. Do you think I could get away with the light shell, or would I be better served going with the heavier shell?

Here's a pic of the prototype to give you an idea of what I'm after. Don't laugh too much at the welds or paint - I did this one quick with my flux-mig, I'll be using a friend's Tig for the final frame.


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## Live Wire (Aug 27, 2007)

Hi Pete,
Since this is such a "jack of all trades" type of frame and only your second one, I'd be sure to pick tubing that was plenty thick on the ends...at least .9. The Supertherm stuff from HJ is nice, strong, and judging by the size of the frame in the picture, it should be fairly easy to hit your 5lb goal.
Forget the Nova shells, get yours from Paragon- they are the best available.


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## pvd (Jan 4, 2006)

It sounds like you will end up with a fine frame for you and your needs no matter how light you go. Your only problem could be your skill in connecting the thin ends. Go for the challenge and practice on some .028" straight gauge for a little to get warmed up.

I prefer to work with extremes early in a process so that I can get a ballpark in which to work. If I were you, I would go as light as possible while keeping it cheap. That way you can push your limits in construction, learn how to dig yourself out of a hole, and still learn some honest bike design skills with regard to tube choice. If it's too light, then build another and give the light bike to your wife/girl/man.

Shop at Nova for some of the House brand tubes. Most of these tubes run less than $17 each, so you don't have to worry too much. Since you are so light, make sure to get the 8/5/8 or lighter butts.

Diameters: 1.375" DT, 1.125" TT, 1.125 ST, 16mm SS, the chainstay is usually a packaging issue if you don't have a bending set-up.


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## coconinocycles (Sep 23, 2006)

.035 4130 or the supertherm bmx tubing from henry james. get a stick of haedtube too, 37mm o.d. i'm with livewire on the bb shells, too. give the paragon site a good lookover while you are there, lots of good stuff on that site.........steve.


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## MichauxYeti (Nov 10, 2005)

Congrats on taking the initiative to build your first frame!

I think the others have pretty much nailed it for suggestions on the tubing choices. Here's another bike that's built for the type of riding you describe from EWR Bikes.


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## Walt (Jan 23, 2004)

*9/6/9 cromoly*

9/6/9 cromoly will easily build a <5 pound frame, especially given how small it's going to be. Heck, you might break 4# with a frame that tiny.

Do a 35mm DT, 32mm TT, 28.6 ST. Get cheap tubes from anywhere they've got the sizes you want (ie, Bringheli, Nova, HJ, whatever).

If you're going to do a lot of trials, I'd spend more time worrying about reinforcing the chainstays than the main triangle - slip off your bashguard funny and it's easy to smack your chainstay on a ledge pretty darn hard. I've seen a lot of trials bikes that broke, and almost all of them broke in the rear end, not the front. You might want to look into making some kind of yoke for short chainstays and good tire clearance, and using some kind of bash plate or gusset on the bottom of the stays.

Just throwing ideas out there. I never got beyond being able to (barely) pedal kick off a curb, so my trials input is pretty limited. Sounds like a great project, and kudos for building your first frame!

-Walt


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## shiggy (Dec 19, 1998)

Walt said:


> 9/6/9 cromoly will easily build a <5 pound frame, especially given how small it's going to be. Heck, you might break 4# with a frame that tiny.
> 
> Do a 35mm DT, 32mm TT, 28.6 ST. Get cheap tubes from anywhere they've got the sizes you want (ie, Bringheli, Nova, HJ, whatever).
> 
> ...


Walt, any ideas on how you would gusset the stays?


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## Pete Gossett (Apr 1, 2008)

Thanks for all the ideas & suggestions everyone!! 

I really appreciate the comment about reinforcing the chainstays - I had a hunch the rear triangle may be more important on this type of frame, thanks for confirming it. I'll look at my Monty & GT mods for some ideas of an integrated bash guard, it's something I was considering anyway & I have plenty of aluminum sheet stock to work with.

Oh, and that EWR looks sweet! I only recently discovered their work & I see they're building frames again.


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## dr.welby (Jan 6, 2004)

shiggy said:


> Walt, any ideas on how you would gusset the stays?


Here's how it's done on my Monty. The gusset runs up to the bottom bracket and the bashguard mount is welded to it. It looks like about 2mm thick steel. As you can see, it could probably go back a little further.


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