Framebuilders - questions about tubing thicknesses

who knows anything about tubing butts? how thick should i be looking at? 31.8 diameter, I know that much, but what is the major difference between .7/.4/.7 butting vs .8/.5/.8? (and don't come back and say that the former is lighter, while the latter is stiffer. I know that much. ) but what is the real world difference? does a lighter tube (thinner) make for a more or less harsh ride off road? while a thinner tube would be easier to dent, it would also (seems) to absorb more shock than a thicker tube, right? where is the tradeoff nuetral? anyone?

to clarify, this is for a cross bike. I want oversize tubes (going to be tigged), and I also want it light yet stiff, as this is going to be a race bike.

on a separate note, is there any way to ovalize a steel tube (OX Platinum) to make a more comfy top tube?

Thanks very much.

Well, a thinner tube will generally be dented more easily, unless it is super hard (apparently 953 does not dent much due to this property).

I am thinking of similar things. AFAIK, there are no ovalised top tubes a la Salsa etc. What you could do is take the oval section Deda tubes (forget which) and run them flat side down. That might work nicely.

Who is the builder?

that could work, but i'd rather go with a whole tubeset out of the same material. it's easier that way. not sure of the builder yet. just working out details to the best of my ability before it comes to that.

i guess what it boils down to, is do we think that a .7/.4/.7 tube would be too light for a cross bike? not so worried about denting, more concerned with ride quality.

Depends somewhat on rider size and weight. Assuming average racer weight and proportions, I say that no one alive can tell the difference in the ride qualities between two identically built bikes where the main tubes are the only difference and that difference is .1mm wall thickness-especially in 'cross racing conditions. I venture further to say that it would be easier to discern 5psi in tire pressure difference--maybe less. That's the way I unnerstand it today.

That said, note that top builders often select tubes individually and not by the "set". Also be sure to let your builder have a little input there.

wp

My opinion is to go for the thicker tubing; more dent resistant and margionally stiffer (assuming similar butted lengths).

One can also look up the data from Reynolds, TT, Columbus, etc. for specific tubing info, but it may lead to more confusion...trust your builder.

One can also look up the data from Reynolds, TT, Columbus, etc. for specific tubing info, but it may lead to more confusion...trust your builder.


This is a framebuilders forum where it's appropriate to discuss details about things like tubing instead of just sitting back and "trusting" someone to make the choice for you.

Agreed, but what builder wants a customer coming through the door with his mind made up about what tubes should be used in his frame?

No thing wrong with learning about the stuff. I'm all for that. carry on.

I saw an 08 Bianchi Volpe today. It had a flattended top tube (not much flattened though). So someone must be making that tube...

if we must know it isn't for a builder, per se. thinking about going the mass produced route. trying to iron out all of the specifics so i can go to the table knowing exactly what i want. that makes sense, right?

I'm no framebuilder, but I definitely know more than the average rider. I've had frames built for me, and have some framebuilder friends. furthermore, I find it very interesting and enjoy learning about it.

"to clarify, this is for a cross bike. I want oversize tubes (going to be tigged), and I also want it light yet stiff, as this is going to be a race bike."

Well obviously if you want fatter tubes they are very much stiffer, to the cube of the increase in diameter everything else being equal (means thicker walls, but even without that it will be noticeably stiffer). So you can afford, globally to go to thinner walls. So fat tubes with thin wall = stiff, more demanding to work with, and easier to dent. Thinner tubes with fatter walls equal more flexible, tougher relative to dents.

You can work out the weight differences by just comparing the circumference of one tube to the other x the thickness, you don't have to put an absolute number on it, but you can come up with the percent difference.

You can also calc the stiffness just by comparing the cube of the diameter so cube 32mm and 28 mm, that's 32768 to 21952. Those are just relative numbers. Want to know how the wall thickness affects it. just subtract the number for the air inside, so lets say the 32mm tube has a 1 mm wall and the 28 has a 1.5, by subtracting the cube of 30, and the cube of 25, respectively form the above numbers, that would be 5768 to 6327, the smaller tube is slightly stiffer because it has a 50% thicker wall. Those are just techniques for goofing around, but they allow you to get a feel for what the changes do.

By the way. When you get some tube, there are so many variable, of material and process, and butting, that you can set the tubes up in v blocks or something similar, and depress the tubes in mid span some constant amount, using a weight, and then read the differences with a dial indicator. That will give you some comparable number to go by. it's like when you are reading a map. It's great to have a theory about where you are, but periodically you should just raise your head from the map and look around to see if the Empire State building has come into view (or in our case the CN tower).

how. now my head will be spinning for days! that was a lot of information and numbers in there. i'll come back to that in a few hours when i'm awake.

and in this case, it's the difference of a .7/.4/.7 wall thicknesses or .8/.5/.8 wall. not much difference when it comes down to it. thinking thicker at this point.

thanks for all of the assistance (everyone), i really appreciate it.

Agreed, but what builder wants a customer coming through the door with his mind made up about what tubes should be used in his frame?

No thing wrong with learning about the stuff. I'm all for that. carry on.

If a builder will not openly discuss the differences in various tubesets with you, I suggest you find another builder. :( And the more informed one is regarding the differences, the more "intelligent" the conversation can be.

In my experience, some builders pay a lot of attention to "tuning the ride" so to speak by mixing and matching tubing to meet the customers desires, and other builders use the same tubeset for just about everyone. Builders in this later group say that in actual usage the differences are minor and thus, there is no benefit in fretting over the details. Again, a discussion with your builder is in order to get his feelings on the matter.

If a builder will not openly discuss the differences in various tubesets with you, I suggest you find another builder. :( And the more informed one is regarding the differences, the more "intelligent" the conversation can be.
agreed.

In my experience, some builders pay a lot of attention to "tuning the ride" so to speak by mixing and matching tubing to meet the customers desires, and other builders use the same tubeset for just about everyone. Builders in this later group say that in actual usage the differences are minor and thus, there is no benefit in fretting over the details. Again, a discussion with your builder is in order to get his feelings on the matter.
it's all in the details, we're talking about wall thickness and diamters in the abstract as we have no idea if the rider is 6'6" or 4'9". 240 or 120.

If OP is looking at off-the-peg stuff, I say throw a dart.