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Old 11-23-07, 10:50 PM   #1
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6/4 vs. 3/2.5

Explain it to me please.

I am 5'9"/200lbs. I have been told different things by different people.

ie. With your size you can't ride 3/2.5 because it will fail. Or you can ride it but it has to have special geometry at the BB. Or 6/4 is the only thing that can handle your size.

So what the real truth? Give it to me straight.
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Old 11-24-07, 12:05 AM   #2
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None of those comments is true.

3/2.5 is not as strong as 6/4 but it's VERY unlikely you would experience any kind of tube failure (i.e. breaking). What you might want to do is look for a Ti frame that uses a large down tube (38mm or 1-1/2"), since the large tube will make for a stiffer frame.
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Old 11-24-07, 12:48 AM   #3
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How about the difference between the two regarding "drawn" seamless ti?
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Old 11-24-07, 10:03 AM   #4
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How about the difference between the two regarding "drawn" seamless ti?
There is nothing wrong with seamed tubing, contrary to what some people claim. In fact, controlling wall thickness is easier using seamed tubing which is why some companies, such as True Temper, roll all their tubing (including that used in golf club shafts where flex control and consistency between shafts is of paramount importance).

I know with steel tubing the entire tube is heat treated after rolling/welding to make the material homogeneous - erase the weld on the molecular level (or something near this). Not sure what the Ti guys do for 6/4. Litespeed rolls/forms 6/4 and they have a good track record.

Regarding 6/4 in general, most frames built using this stuff are designed to be killer light thus they really push the tube wall thickness down to the minimum. These thin tube walls are more of a failure risk than thicker 3/2.5 tubes in many cases. The thin tubes also tend to flex more which is contrary to what many people think - they think 6/4 frames are stiff as a rule. Bottom line is that the small details matter.
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Old 11-24-07, 10:27 AM   #5
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Ahhh okay. Controlling wall thickness. Thanks Nessism. Makes a lot of sense.

But as a tube that is rolled and seamed, it's not weaker compared to a drawn tube? Because it's not a SOLID piece of metal? Why can't 6/4 be drawn? Because it has to be so thin?

I'm honestly not trolling here. Just trying to learn.
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Old 11-24-07, 12:32 PM   #6
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But as a tube that is rolled and seamed, it's not weaker compared to a drawn tube? Because it's not a SOLID piece of metal? Why can't 6/4 be drawn? Because it has to be so thin?
The heat treatment operation after the seamed tubing is welded makes the tube more or less homogeneous - said another way, the welds effect on the metal is erased on the molecular level by the heat treatment.

6/4 seamless tubing is being sold by Reynolds. Not sure it's any better than the seamed 6/4 made by Litespeed though. There is no reason 6/4 has to be thin, that is a choice that manufacturers make. It's the same with steel; steel is available in thin and thick varieties. The thin varieties need to be made from stronger material or the tube may fail in use. Remember again, thin tubes flex more unless the diameter is increased. 6/4 metal is not stiffer than 3/2.5, only stronger.
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Old 11-24-07, 09:46 PM   #7
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Okay I see. So there IS seamless 6/4.

Now another question please? (sorry).

If 6/4 is stronger than why does 3/2.5 appear to be most common? Do you think it's because of the price difference? When I went to order my bike, I was told for what I was using the bike for (recreation) I didn't need to go for the 6/4. He tried to explain to me the difference but in the excitement of getting my first road bike I think it just flowed right through me. I just trusted him and said okay. *shrugs*

Oh and thanks for your time explaining all this to me! (Dang, this wasn't even my thread)
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Old 11-25-07, 04:32 AM   #8
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First, the difference in strength of 6/4 vs 3/2.5 is of the order of 3% as-rolled, drawn, heat treated and aged, in fact in any condition. Almost all of what you will hear from salesmen is B/S anyway, in all things, especially so with Ti alloys.

Right now it's almost certainly because of the market price of commodity titanium. It's unit price has shot up by a factor of at least three in recent years and aluminium and vanadium themselves (the two alloying elements added to both 6/4 and 3/2.5) do not decrease this value. A conscious decision has been made to reduce the content of both in the alloys produced to lower the total cost to manufacture...

If you look a round, you'll find some components that used to be manufactured from some of the more exotic titanium alloys - I'm thinking bottom bracket axles here especially - will also be being shifted to leaner alloys.
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Old 11-25-07, 05:14 AM   #9
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Originally Posted by Nessism View Post
The heat treatment operation after the seamed tubing is welded makes the tube more or less homogeneous - said another way, the welds effect on the metal is erased on the molecular level by the heat treatment.

6/4 seamless tubing is being sold by Reynolds. Not sure it's any better than the seamed 6/4 made by Litespeed though.
Reynolds seamless titanium tubing isn't made by them, just made for them. They preform the final draw and butting operations. It's made by an aerospace manufacturer, who've got years of experience in making seamless Ti alloys.

While the statement that heat treatment post weld undoes the damage that welding does to the alloy in Ti tubing (thanks to titanium's fairly unique thermal behaviour), it's a bit of an over simplification in aluminium alloys and steels. I'll save that for another day...
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Old 11-25-07, 11:40 AM   #10
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Wow!! (brain sizzling)

Thanks, Falanx and Nessism! I do, in fact, understand better now!
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Old 11-25-07, 12:58 PM   #11
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I ride a frame made with 6/4 ti, with at least two of the three main frame tubes seamed. Don't hate the seamed tubing; hate the seamy manufacturing process.

That said, I'd sure like a frame made with Reynolds 6/4 seamless tubing.

The whole seamed versus seamless comparison is valid to a point. It was an old sales pitch used to get customers on more expensive bikes under the generally valid pretense that seamed tubing was stronger, generally lighter, and provided a better ride. With time and improved manufacturing techniques, this argument has become less important but is still not completely invalid. Seamed tubing has its merits and there are those who might argue that True Temper's claim to get more consistent wall thickness with seamed construction is also a marketing ploy. Reynolds marketing and Reynolds proponents may take exception to that claim. Choose your weapons.
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