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Tube recommendations for stiff touring/commuting bike

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Tube recommendations for stiff touring/commuting bike

Old 02-08-19, 08:36 AM
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audiisaac
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Tube recommendations for stiff touring/commuting bike

Hi All!,

Im looking for thoughts and recommendation on tube selection for my first (technically second) frame build. I am a fairly accomplished metal worker so am 100% confidant in my ability to fabricate the frame but dont have any experience designing frames. This frame will replace my current bike (1st gen Salsa Vaya Ti) as mostly a commuter bike. My main gripe with the Vaya is when loaded with 5+ pounds in a front rack bag and rear panniers with 10-15 pounds its WAY too flexy. Im about 195 pounds and 6'-2" and ride a 58-60cm frame so am on the larger size. The Vaya flexes has so much torsional flex that its jumps around when hammering out of the saddle and is a little uncontroable. If I am not careful it will shimmy when riding with no hands. I can get the bike to wiggle all over the road with a little shake of the bars. I would like this new frame to not flex in the same way so am thinking of building the frame with Nova's 38mm DT 8-5-8 29er tubeset. Is this a good choice? Should I jump up to the 42MM set or will 38mm be too much and I should go do down to 35mm DT? I have 38mm tires on the bike and will be using that to smooth out the ride. Any thoughts or recommendations on tubing choices would be greatly appreciated!
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Old 02-08-19, 10:54 AM
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Andrew R Stewart 
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It is trendy to focus far more on tubing diameter, I have done much the same at times too. But as a commuter and touring bike the wall thickness is a factor I would not diminish too much. One of the issues I have with current steel tube selections is that it's skewed towards the performance field. So as the diameter grows the availability of thick (.6 or .7 in the thin sections for main tubes) has gotten less. Dent resistance, wall strength WRT the braze ons locations are two factors that racing frames see little need for (the concept of a true racing frame being a life long item goes against what about every racer does with his equipment).

Will you build your own fork? IME the fork's stiffness (more the lateral then the more usually talked about vertical) says a lot about frame flex under loaded conditions. When I moved from a 1" steerer to a 1.125" steerer the improvement in the stability (WRT flexing) was dramatic. This might be a good situation for a tapered steerer with a 1.25 base. I would not suggest a wall thickness less them .6 if at all possible on the main frame for the greater durability that a working bike needs. I would increase the top tube diameter to equal the DT, with load the TT sees a lot of stress. I would not think a 42mm DT would be needed, I think the huge DT diameters are more about long travel suspension fork leverage being dealt with then increasing main frame stiffness under pedaling or for handling. Touring weight stays and blades will also be a good choice, perhaps those that are suggested for disk brakes?

What BB are you planning? The big tubes start to overlap a bunch with a traditional ENG threaded shell. But the serviceability and wide range of options that that threaded BB offers is hard to beat too. I wish that the T47 standard was more common.

You want a solid and stable bike that withstands the daily abuse that a commuter sees. You wand a stiff enough bike to handle well when loaded with a touring set up. This frame, in steel, will weight more then is trendy. I doubt you'll ever find out that the added weight held you back from the intended riding. But I do suspect that too light a frame will cause pause at some times. Andy
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Old 02-08-19, 11:56 AM
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Originally Posted by Andrew R Stewart View Post
It is trendy to focus far more on tubing diameter, I have done much the same at times too. But as a commuter and touring bike the wall thickness is a factor I would not diminish too much. One of the issues I have with current steel tube selections is that it's skewed towards the performance field. So as the diameter grows the availability of thick (.6 or .7 in the thin sections for main tubes) has gotten less. Dent resistance, wall strength WRT the braze ons locations are two factors that racing frames see little need for (the concept of a true racing frame being a life long item goes against what about every racer does with his equipment).

Will you build your own fork? IME the fork's stiffness (more the lateral then the more usually talked about vertical) says a lot about frame flex under loaded conditions. When I moved from a 1" steerer to a 1.125" steerer the improvement in the stability (WRT flexing) was dramatic. This might be a good situation for a tapered steerer with a 1.25 base. I would not suggest a wall thickness less them .6 if at all possible on the main frame for the greater durability that a working bike needs. I would increase the top tube diameter to equal the DT, with load the TT sees a lot of stress. I would not think a 42mm DT would be needed, I think the huge DT diameters are more about long travel suspension fork leverage being dealt with then increasing main frame stiffness under pedaling or for handling. Touring weight stays and blades will also be a good choice, perhaps those that are suggested for disk brakes?

What BB are you planning? The big tubes start to overlap a bunch with a traditional ENG threaded shell. But the serviceability and wide range of options that that threaded BB offers is hard to beat too. I wish that the T47 standard was more common.

You want a solid and stable bike that withstands the daily abuse that a commuter sees. You wand a stiff enough bike to handle well when loaded with a touring set up. This frame, in steel, will weight more then is trendy. I doubt you'll ever find out that the added weight held you back from the intended riding. But I do suspect that too light a frame will cause pause at some times. Andy

Thanks for the reply.

I was planning on using a standard 1.125 steerer and head tube mostly because of the ease of finding steel 1.125 QR disk forks. I plan on reusing my rack and QR dynamo wheels. I could put a tapered headtube on, but feel they look a little funny with smaller diameter steel forks whick I have yet to see for sale. I could make my own for too....

Im debating between a standard threaded BB and a T47, pluses for the standard one is I have a ton of crankset and the ease of getting the BB chased after welding, I dont know of anyone with T47 taps...

Would the standard 29er stay from nova be sufficient?Dia (mm)Wall(mm)Length(mm)DT380.9x0.6x0.9750
TT31.80.8x0.5x0.8680ST28.61.2x0.6x0.9520CS30-180.9x0.6440SS160.8600HT31.8, 36**1.1200
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Old 02-08-19, 12:44 PM
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Agreed that if you use an off the shelf fork your design options are controlled by others to a degree. I don't think the headtube has a big impact on the frame's stiffness as it's already typically the largest in diameter, has the thickest wall and is the shortest tube in the main frame. I agree in choosing a ENG threaded BB shell. Do know that there are thinner/lighter and thicker/heavier choices here. I tend to discount the stays contribution to frame stiffness as they are part of a triangulated structure. Still going somewhat bigger diameter isn't wrong as long as the components fit (like chain ring or tire clearances). Andy
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Old 02-08-19, 07:03 PM
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I think 1.25" (31.75mm) for the top and seat tubes and 1.375" (35mm) for the down tube will be sufficient. .8-.5 tubing should be fine. The matching head tube will be 36mm, or maybe 37mm for TIG, so going to a 38mm down tube won't fit unless you go with one of those super OS head tubes. Look for long butted tubes if you want to hedge your bet towards stiffness.
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Old 02-12-19, 12:23 PM
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stiffness can come from oversize tubing , and from increasing tube wall thicknss..

Specialized got a Japan company to make their Expedition bikes 1.125 top & seat, 1.25"down tubes... a little sway with every pedal stroke.


So, using a different design I built up with the shop help, one with 2 side by side .75" , .049" wall 4130 tubes * bent , so that were also the rear triangle ..
solid no wiggle down hill with 4 panniers .. or sway..

I used a few frame parts from the neighboring Burly tandem shop, in '90 , from & Alan who later went on to start the bike friday .green gear company
and cargo bike builder DBA 'Human Powered machines'...

I'd think a horizontally oval top tube and the same in a vertical orientation for the down tube would be another approach ..

* Side benefit , a frame fit pump lays in between them , so I can lift bike without knocking the pump off ..





FWIW, Ti Cycles made a new stiff steering mast, for my Bike Friday , to my design, its upper section a 1.125: steerer tube

It is butted ,

I have a bike with a short travel Suspension fork , It does not appear to be butted, as I look down its tube..








....

Last edited by fietsbob; 02-12-19 at 12:42 PM.
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