a frame building question about carbon & ti

[Climb01742]

every builder who has a carbon/ti frame has, it seems, decided which tubes should be ti and which should be carbon. and every rider who buys one of those frames gets that particular "pattern" shall we say of tubes. regardless of the rider and their individual characteristics.

this seems odd.

when a builder creates a custom frame, they match each tube to the desired characteristics. a number of steel builders, for instance, mix and match tubes from various manufacturers in a single frame to achieve a certain ride. there is no set "pattern" of tubing selection.

so why is there in carbon/ti frames? in an ottrott, for example, why -- for every rider -- should the TT necessarily be carbon? or the downtube? or the seattube be ti? conceptually, wouldn't it be better to match the "pattern" of tubing -- which tubes are carbon and which are ti -- to each rider? meaning, for some riders -- say riders who want maximum stiffness -- the downtube would be super stiff carbon. but for other riders -- say someone who wants super light weight and a bit of flex -- maybe the downtube would be lighter ti tubes.

i guess where i'm going is...should there really be a set legend frame -- all ti main triangle tubes -- and a set ottrott frame -- with carbon DT and TT, and ti ST? versus, say, simply a serotta frame that -- depending on the rider and their desired characteristics -- could be any combination of all ti tubes to all carbon tubes, or any combination of the two in between? (personally, i'd be curious about a legend with a carbon TT...or would that be an ottrott with a ti DT??????)

for a truly custom frame, to achieve an exact ride, shouldn't every tube be up for discussion? just a thought.

[zap]

I'm not a framebuilding expert but do have quite a bit of experience in manufacturing.

Serotta offers a lot of options and Ben has quite a bit of experience and probably knows more than most what combinations will work best. I have plenty of cycling experience and know what I'm looking for in handling and ride, but would defer to Ben & Team when it comes to tubing selection.

But more importantly, at some point manufacturers will have to say enough is enough, we can only offer so many options before the whole manufacturing process/costs becomes compromised.

Regarding costs, ti and carbon tubing will cost more than steel tubing. How much money does one want tied up in inventory?

[Matt Barkley]

I think these manufacturers of custom frames can claim that they will make a frame with your desired custom feel, etc. Whether these things are really happening or not is another question or opinion I won't get into.

Whether Serotta decides such and such a tube will be ti and this other tube will be carbon - they are doinght that from the design aspect of what they believe (including what their engineers believe) to be the best way of building their framesets. Mixing and matching tubes, if you know what you are doing, can yeild mostl or some of the desired affect - with different materials, or even the same materials.

[Climb01742]

zap, i certainly should have prefaced my comments just as you did--i sure am not a frame building expert by a LONG shot. and my thoughts weren't meant as a critcism of legends or ottrotts. i'm just curious about what seems to be a bit of a difference between philosophies for building steel frames and carbon/ti frames. i'm not sure tubing inventory is really an issue, because i'm not suggesting more tubing. it would be the same selection of legend and ottrott tubing, just the opportunity to use any tube for any part of the main triangle.

isn't it exactly the same thing as seatstays? you can spec carbon or ti seatstays for either an ottrott or a legend, yes? again, i may be asking a question that my knowledge isn't deep enough to answer. the folks who design frames for a living have more knowledge in their pinkies than i have. this whole question just struck me when i was riding my mx leader, with tubes of every possible shape, matched to every possible need. if it works for steel, maybe for carbon/ti too? but maybe it's a dumb question. :rolleyes:

[Matt Barkley]

Climb - to continue this thread - I really think these builders have well-thought-through their framesets - believing in a titanium rather than carbon, or carbon rather than titanium seat-tube. For whatever reasons... I have heard many reasons, as I am sure you have, as to why such and such tube is made of ti rather than carbon and vice versa.

It may go back to that thread on glue your bike together carbon jobs. If you want to pick and choose I am sure someone somewhere will build it for you.

I imagine and believe Serotta has their tubesets well researched and drawn to their specs for specific tube locations (ie. down tube, or seat tube) and few if any are interchangable. (I am making an educated guess here :) ) :beer: - Matt

[SPOKE]

building a bike frame is an effort in compromise no matter what material(s) are involved. much of the compromise results from the entire manufacturing process that each builder has developed over the years they have been practicing their craft. in many cases this process is handed down from one builder to an apprentice. also keep in mind that evolution can happen too due to improvements in tools used or better yet the builder decides to step outside "the box". examples of outside "the box" can include the first aluminum Vitus frames, heck throw Cannondale in there too. you also have the start of the titanium revolution with the Teledyne Titan and the Speedwell. these are all examples of outside "the box" innovations.
continuing along the compromise theme it's important to realize that Serotta, Merlin, Litespeed, and many other manufacturers have studied what stresses are applied to each tube in a bicycle frame. using CAD models then applying finite element analysis to these models manufacturers have determined exactly what tubes have the largest influence on the overall ride qualities. from this info they can select/make tubing to provide particular characteristics.
now all this info and test data gets tossed into the marketing blender. the finished product has to look good, meet performance requirements and be saleable. if you can't make and exceptable margin on the finished product then you have to try something different.
now here's the final question that many of us may want to know, why does Serotta choose to build the Ottrott with a carbon top and down tube? why does Seven build the Ondata with carbon seat tube, seat stays & top tube (i think)? there are several other examples of the hybrid frames that follow this same scheme, just pick one.
Climb, the simple answer to at least part of your question is that if each tube was specificly engineered to help the finished product meet your "exact" requirements i doubt that many of us could afford to buy it or at least cost justify it when compared to other readily available frames (off the rack as well as custom) you can easily pruchase that offer 90% + of all the qualities you desire.
at some level decisions have to be made by the manufacturer that allow them to consistantly build a top performing bike as well as manage the costs that go along with operational needs/goals.
simply, it's just COMPROMISE.

[jeffg]

At least when I talked to Tom Kellog he spoke of selecting which tubes were carbon or Ti based on desired ride characteristics, i.e. he would make suggestions of whether, ST, TT, DT should be carbon or Ti. I do not know if that is still up to date. I still think the Ottrott is the best riding of the hybrids I have tried, though that is somewhat unsurprising given my preference for the Legend as a Ti bike. For example, I did not like the odonata with carbon ST. It made the rear triangle feel lifeless to me. A Legend or an Axiom has more snap and feels better climbing on the smaller gears than the Odonata, IMHO. For that reason I would also steer away from the ST rear, but I know others feel differently about that.

Finally, I would like to urge folks not to discount the choices in tubing on something like the Ottrott. You can get different Ti tubes, chainstays, and even carbon tubes of varying stiffness. It does seem as if there is already a huge range of options available.

That is not to say that a hybrid is the best bike. I still have gone with one material at a time thus far and like it that way. ;)

[Climb01742]

At least when I talked to Tom Kellog he spoke of selecting which tubes were carbon or Ti based on desired ride characteristics, i.e. he would make suggestions of whether, ST, TT, DT should be carbon or Ti.

that's what i was thinking about. just to be clear, i'm not criticizing any particular design. and i'm sure not saying i know anywhere near what even the most neophyte builder knows. mine is just a philosophical question. summed up by the quote from TK above. i'll be quite now. :banana:

[Serotta_James]

We approached the carbon fiber placement of the Ottrott from a very pragmatic point of view. Which tubes of a bicycle are best suited for carbon fiber applications? In other words, where does carbon fiber do the most good, while presenting the least liability?

Carbon fiber is perfectly suited for the top and down tube applications. It resists the torsional loads placed on both of these tubes and makes for a stiffer drivetrain. At the same time it absorbs more high frequecy vibration than any other material available to us.

Chain stays and seat tubes, on the other hand, are not as well suited to carbon application. In a seat tube, there is a good amount of vertical pressure and elongation, which carbon fiber does not like. There is also a great amount of pressure applied by the front derailleur clamp; also not ideal for carbon fiber.
Chain stays experience flexing preasures that may tax carbon beyond its fatigue limit over time. Carbon chain stays can also be damaged severly if you drop your chain.
Titanium provides the perfect material for these locations, being increadibly strong and more resiliant than carbon fiber when exposed to these specific forces.

The Ottrott concept places each material where it does the most benefit to the overall ride of the bike, while maintaining maximum durability.
We can change ride characteristics by changing the type (stiffness) of carbon fiber or titanium used in each location, or by incorporating the ST stay or a classic rear triangle. There remains a great deal of individual variability and customization without compromising structural durability.

Hope this is what your question was aimed at originally.

[Climb01742]

serotta james,
wonderful, and wonderfully informative, answer. that's the first time i've heard it explained so clearly and logically. thank you very much.
a question: on my ottrott, i believe we isolated the over-stiffness issue to a too stiff DT. in subsequent frames from other builders, i've found that a less stiff DT (while keeping a stiff TT) creates a great balance between a stiffer top half of a frame, and a more flexible lower half. without giving away any secrets, what might the '05 ottrott offer in the way of lighter, less stiff carbon tube options, and reduced weight in general?
again, many many thanks for your informative and thoughtful answers. :D